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Scientific American Supplement, No. 787, January 31, 1891
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SCIENTIFIC AMERICAN SUPPLEMENT NO. 787



NEW YORK, January 31, 1891

Scientific American Supplement. Vol. XXXI., No. 787.

Scientific American established 1845

Scientific American Supplement, $5 a year.

Scientific American and Supplement, $7 a year.

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TABLE OF CONTENTS.

I. BIOGRAPHY.—CHARLES GOODYEAR.—The life and discoveries of the inventor of vulcanized India rubber, with portrait.—1 illustration

II. BIOLOGY.—Can we Separate Animals from Plants?—By ANDREW WILSON.—A debated point well discussed.—The bases on which distinctions must be drawn

III. ELECTRICITY.—A New Electric Ballistic Target.—A target for investigations of the velocity of projectiles, now in use at the United States Military Academy, West Point, N.Y.—1 illustration.

Electric Erygmascope.—An electric lighting apparatus for examining earth strata in bore holes for geologists' and prospectors' use.—1 illustration

The Electro-Magnet.—By Prof. SILVANUS THOMPSON.—Continuation of this exhaustive treatise, giving further details on special points of construction.—1 illustrations

IV. ENTOMOLOGY.—Potash Salts.—The use of potash salts as insecticides, with accounts of experiments

The Outlook for Applied Entomology.—By Dr. C.V. RILEY, U.S. entomologist.—The conclusion of Prof. Riley's lecture, treating of the branch of entomology with which his name is so honorably associated

V. INSURANCE.—The Expense Margin in Life Insurance.—Elaborate review of the necessary expenses of conducting the insurance of lives, with tables and calculations

VI. MATHEMATICS.—The Trisection of Any Angle.—By FREDERIC R. HONEY, Ph.B.—A very ingenious demonstration of this problem, based on the properties of conjugate hyperbolas

VII. METEOROLOGY.—Note on the Mt. Blanc Meteorological Station

The Flood at Karlsbad.—Account of the recent flood and of its destructive effects.—1 illustration

VIII. MECHANICAL ENGINEERING.—Station for Testing Agricultural Machines.—A proposed establishment for applying dynamometer tests to agricultural machines.—1 illustration

Steam Engine Valves.—By THOMAS HAWLEY.—A review of modern slide valve practice, the lap, cut-off, and other points.—6 illustrations

IX. MISCELLANEOUS.—Science in the Theater.—Curious examples of stage effect in fictitious mesmerizing and hypnotizing.—4 illustrations

Theatrical Water Plays.—Recent episodes in real water plays at Hengler's Circus, London.—2 illustrations

X. NAVAL ENGINEERING.—The French Ironclad War Ship Colbert.—An armored wood and iron ship, with central battery.—1 illustration

XI. PHYSIOLOGY AND HYGIENE.—Newer Physiology and Pathology.—By Prof. SAMUEL BELL. M.D.—An excellent presentation of modern practice in the light of bacteriology

Test Card Hints.—How to test the eyes for selecting eyeglasses and spectacles

The Composition of Koch's Lymph.—What Prof. Koch says it is and what it can do.—The cabled account of the disclosure so long waited for

XII. TECHNOLOGY.—Firing Points of Various Explosives.—The leading explosives, with the temperature of their exploding points tabulated

The Recovery of Gold and Silver from Plating and Gilding Solutions—A paper of interest to silver and gold platers, as well as photographers

Water Softening and Purifying Apparatus.—An apparatus for treatment of sewage, etc., chemically and by deposition.—1 illustration

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THE FRENCH IRONCLAD WAR SHIP COLBERT.

The central battery ironclad Colbert is one of the ten ships of the French navy that constitute the group ranking next in importance to the squadron of great turret ships, of which the Formidable is the largest. The group consists of six types, as follows:

1. The Ocean type; three vessels; the Marengo, Ocean, and Suffren. 2. The Friedland type, of which no others are built. 3. The Richelieu type, of which no others are built. 4. The Colbert type, of which there are two; the Colbert and the Trident. 5. The Redoubtable type, of which no others are built. 6. The Devastation type, of which no others are built.



The Colbert was launched at Brest in 1875, and her sister ship, the Trident, in 1876. Both are of iron and wood, and the following are the principal dimensions of the Colbert, which apply very closely to the Trident: She is 321 ft. 6 in. long, 59 ft. 6 in. beam, and 29 ft. 6 in. draught aft. Her displacement is 8,457 tons, her indicated horse power is 4,652, and her speed 14.4 knots. She has coal carrying capacity for 700 tons, and her crew numbers 706. The thickness of her armor belt is 8.66 in., that protecting the central battery is 6.29 in. thick, which is also the thickness of the transverse armored bulkheads, while the deck is 0.43 in. in thickness. The armament of the Colbert consists of eight 10.63 in. guns, two 9.45 in., six 5.51 in., two quick firing guns, and fourteen revolving and machine guns.—Engineering.

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A compound locomotive, built by the Rhode Island Locomotive Works, has been tried on the Union Elevated Railroad, Brooklyn, N.Y. The engine can be run either single or compound. The economy in fuel was 37.7 per cent, and in water 23.8 per cent, over a simple engine which was tested at the same time. The smoothness of running and the stillness and comparative absence of cinders was fully demonstrated.

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STEAM ENGINE VALVES.

[Footnote: Lecture delivered at Wells Memorial Institute, Boston, in the Lowell Free Course for Engineers. From report in the Boston Journal of Commerce.]

By THOMAS HAWLEY.

RIDING CUT-OFF VALVES—PECULIARITIES AND MERITS OF THE DIFFERENT STYLES.

In considering the slide valve in its simple form with or without lap, we find there are certain limitations to its use as a valve that would give the best results. The limitation of most importance is that its construction will not allow of the proper cut off to obtain all the benefits of expansion without hindering the perfect action of the valve in other particulars. At this economical cut off the opening of the steam port is very little and very narrow, and although this is attempted to be overcome by exceedingly wide ports, sixteen inches in width in many cases in locomotive work, this great width adds largely to the unbalanced area of the valve. The exhausting functions of the valve are materially changed at the short cut off, and when much lap is added to overcome this defect, there usually takes place a choking of the exhaust port. You might inquire, why not make the port wider, but this would increase the minimum amount of load on the valve, and this must not be overlooked. Then the cut off is a fixed one, and we can govern only by throttling the pressure we have raised in the boiler or by using a cut off governor and the consequent wastes of an enormous clearance space. You will observe, therefore, that the plain slide valve engine gives the most general satisfaction at about two-thirds cut off and a very low economic result. The best of such engines will require forty-five to fifty pounds of steam per horse power per hour, and to generate this, assuming an evaporation of nine pounds of water to a pound of coal, would require between five and six pounds of coal per horse power per hour. And the only feature that the valve has specially to commend it is its extreme simplicity and the very little mechanism required to operate it.

Yet this is of considerable importance, and in consideration of some special features at its latest cut off, the attempt has been many times made to take advantage of these features. For instance, at 90 deg. advance, the valve opens very rapidly indeed and fully satisfies our requirements of a perfect valve. This is one good point, and in this position also the exhaust and compression can be regulated very closely and as desired without much lap, and as the opening of the exhaust port comes with the eccentric at its most rapid movement the release is very quick and as we would have it. This is only possible at the most uneconomic position of the valve as regards cut off.

The aim of many engineers has been to take advantage of these matters by using the valve with 90 deg. angular advance of eccentric ahead of crank, for the admission, release, and compression of the steam, and provide another means of cutting off, besides the one already referred to, viz., cutting off the supply of steam to the chest, and overcome the objection in this one of large clearance spaces. This is done by means of riding cut off valves, often called expansion valves, of which, perhaps, the most widely known types in this vicinity are the Kendall & Roberts engine and the Buckeye. The former is used in the simplest form of riding cut off, while the Buckeye has many peculiar features that engineers, I find, are too prone to overlook in a casual examination of the engine. In these uses of the slide valve, too, means are suggested and carried out of practically balancing the valve.

The origin of the riding cut off is most generally attributed to Gonzenbach. His arrangement had two steam chests, the lower one provided with the ordinary slide valve of late cut off, and steam was cut off from this steam chest by the expansion valve covering the ports connecting with the upper steam chest. This had the old disadvantage that all the steam in the lower chest expanded with that in the cylinder, at a consequent considerable loss. This was further improved by causing the riding cut off to be upon the top of the main valve, instead of its chest, and resulted in a considerable reduction of the clearance space.

This is the simplest form, and is shown in Fig. 1. The steam is supplied by a passage through the main valve which operates exactly as an ordinary slide valve would. That is, the inside edges of the steam passage are the same as the ordinary valve, the additional piece on each end, if I may so term it, being merely to provide a passage for the steam which can be closed, instead of allowing the steam to pass the edge. The eccentric of the main valve is fastened to the shaft to give the proper amount of lead, and the desired release and compression, and the expansion valve is operated by a separate eccentric fastened in line with or 180 deg. ahead of the crank. When the piston, therefore, commences to move from the crank end to open the port, D, the expansion valve is forced by its eccentric in the opposite direction, and is closing the steam port and would have closed it before the piston reached quarter stroke, thus allowing the steam then in the cylinder to do work by expansion. The eccentric operating this expansion valve may be set to close this steam port at any point in the stroke that is desired, the closing occurring when the expansion valve has covered the steam port. Continuing the movements of the valves, the two would move together until one or the other reached its dead center, when the movements would be in opposite directions.



There are three ways of effecting the cut off in such engines, the main valve meanwhile being undisturbed, its eccentric fastened securely so as not to disturb the points of lead, release, and compression. All that is required is to cause the edge of the expansion valve to cover the steam port earlier in the stroke, and this can be done, first, by increasing the angular advance of the cut off eccentric; second, by adding lap to the cut off valve; and third by changing the throw of the eccentric. In all these instances the riding valve is caused to reach the edge of the steam port earlier in the stroke. We will take first, as the simplest, those methods by which the lap of the cut off valve is increased.

It will be noted that there is but one edge of this valve that is required to do any work, and that is to close the valve. The eccentrics are so placed that the passage in the main valve is opened long before the main valve itself is ready to admit steam to the cylinder, so that only the outer edges are the ones to be considered, and it will be readily seen that the two valves traveling in opposite directions, any lap added to the working edge of the cut off valve will cause it to reach the edge and therefore close the port earlier than it would if there was less lap. And we might carry it to the extreme that we could add lap enough that the steam passage would not be opened at all.

In Fig. 2 is shown the method by which this is accomplished, in what is called Meyer's valve, and such as is used in the Kendall & Roberts engine. We have only one point to look after, the cut off, so we can add all the lap we wish without disturbing anything else. In this engine the lap is changed by hand by means of a little hand wheel on a stem that extends out of the rear of the steam chest. The valve is in two sections, and when it is desired to cut off earlier, the hand wheel is turned in such a direction that the right and left hand screws controlling the cut off valve move one valve portion back and the other forward, which would, if they were one valve and they should be so considered, have the effect of lengthening them, or adding lap to them. The result would be that the riding valve would reach the edge of the steam port earlier in the stroke, bringing about an earlier cut off. If the cut off is desired to be later, the hand wheel is so turned that the right and left hand screws will bring the valve sections nearer together, thus practically taking off lap. Now this may be done by hand or it may be done by the action of a governor.



In the latter case the governor at each change of load turns the right and left hand screws to add or take away lap, as the load demands an earlier or later cut off; in other cases the governor moves a rack in mesh with a gear by which the valve sections are brought closer together or are separated. The difficulty with the case where the hand wheel is turned by hand is that the cut off is fixed where you leave it, and governing can only be at the throttle. For this reason anywhere near full boiler pressure would not be obtained in the cylinder of the engine. If the load was a constant one, and the cut off could be fixed at about one-third, causing the throttle to open its widest, very good results would be obtained, but there is no margin left for governing.

If the load should increase at such a time the governor could not control it under these conditions, and it would lead to a decrease in speed unless the lap was again changed to give a later cut off. On this account the general practice soon becomes to leave the cut off at the later point and give range to the throttle, and we come back once more to the plain slide valve cutting off at half stroke, and the only gain there is, is in a quick port opening and quick cut off. But these matters are more than offset by the wire drawing between the steam pipe and chest, through the throttle, and the fact that there is added to the friction of the engine the friction of this additional slide valve and a considerable liability to have a leaky valve.

In the case where the governor changes the position of the cut off valve a greater decree of economy would result. In this engine, of which the Lambertville engine is a type, the main valve is a long D slide, with multiple ports at the ends through which the steam enters the cylinders. It is operated from an eccentric on the crank shaft in the usual manner. The cut off valve is also operated from the motion on an eccentric fixed upon the crank shaft. The rod or stem of the cut off valve passes through the main valve rod and slide. Upon the outer end of the cut off valve rod are tappets fastened to engage with tappets on the eccentric valve rod. Connection between the cut off eccentric, therefore, and the cut off valve is only by means of the engagement of these tappets. The eccentric rod is fastened to a rocker arm having motion swinging about a pin or bearing in the governor slide, which may be raised or lowered by a cam operated by the governor. The cut off slide is of cylindrical shape and incloses a spring and dash pot with disks attached by means of which the valve is closed. The motion for operating the valves is relatively in the same direction, the cut off eccentric having the greatest throw and greater angular advance to cause it to open earlier and quickly before the main valve is ready to admit steam. The cut off eccentric rod swinging the rocker arm, the tappets thereon engage with those upon the cut off valve rod and open the passages to the main valve, and in their movement compress the spring in the main valve. According as the speed of the engine, the rock arm will be raised or lowered so that the tappets upon the eccentric rod may keep in engagement a shorter or longer time before they disengage, thus allowing the spring that has been compressed by the movement of the cut off valve to close that valve quickly and the supply of steam to the engine, the cut off valve traveling with the main valve for the balance of the stroke. This device will give a remarkably quick opening and a quick cut off, but in view of the fact that the governor has so much to do, its delicacy is impaired and a quick response to the demands of the load changing not so likely to occur. The cut off cannot be as quick as in some other engines, because the valves are moving in opposite directions, and while this fact would help, so far as shortening the distance to be traveled before cut off, the resistance of the valves to travel in opposite directions, or rather the tendency of the valve to travel with the main valve, hinders its rapid action.



This is one great objection to the rack and gear operated by the governor, that two flat valves riding upon each other and sliding in opposite directions at times require a considerable amount of force to move them, and as only a slight change in load is required by the load, the governor cannot handle the work as delicately as it should. It is too much for the governor to do well. To overcome this difficulty the Ryder cut-off, shown in Fig. 3, was made by the Delamater people, of New York. The main slide valve is hollowed in the back and the ports cut diagonally across the valve to form almost a letter V. The expansion valve is V-shaped, and circular to fit its circular-seat. The valve rod of the expansion valve has a sector upon it and operated by a gear upon the governor stem, which rotates the valve rod, and the edge of the valve rod is brought farther over the steam port, thus practically adding lap to the valve. Little movement is found necessary to make the ordinary change in cut-off, and it is found to be much easier to move the riding valve across the valve than in a direction directly opposite. It would require considerable force to move the upper valve by the governor faster than the lower, or in a direction opposite to that in which it is moving, but very little force applied sideways at the same time it is moving forward will give it a sideways motion. In this device the governor has only to exert this side pressure and therefore has less to do than if it were called upon to move the upper valve directly against the movement of the lower.

Something similar is the valve of the Woodbury engine, of Rochester, N.Y. The cut-off valve is cylindrical, covering diagonal ports directly opposite, and is caused to be rotated by the action of the governor that operates a rack in mesh with a segment. Very little movement will effect a considerable change in the lappage of the valve, the valve turning about one-quarter a revolution for the extremes of cut off. The cut off valve rod works through a bracket and its end terminates in a ball in a socket on the end of the eccentric rod. In this case the governor has not as much to do as in other instances.



Still another method of effecting this change in cut off, but hardly by increasing the lap of the valve, is shown in the next drawing, Fig. 4. The cut off valve is held upon the main valve by the pressure of steam upon its back and rides with it until it comes in contact with the cut off wedge-shaped blocks, when its motion is arrested, and the main valve continuing its movement the steam port is closed by the main valve passing beneath the cut off valve. Thus the main valve travels and carries the cut off valve upon its back again until the cut off valve strikes the wedge on the other end and the cut off is effected. The relative positions of the blocks are determined by the governor, that will raise or lower them so that the cut off valve will engage with them earlier or later as desired. This device was designed specially as an inexpensive method of changing the common slide valve into an automatic cut off. The cut off would not be as quick as in other cases we have cited, depending here upon the movement of the lower valve alone, and that, too, is in its slowest movement; whereas in the other cases, the edges approaching each other, by the differing movement of the valves the cut off is very rapid, provided the distance to travel is not long. In this device considerable noise must result by the cut off valve striking the cut off blocks, and a considerable amount of leakage is likely to occur past this valve.

But there is one great objection in the valve gears thus far cited, that the travel of the expansion valve upon the main valve is variable. I have in mind the case of a Kendall & Roberts engine, which had been run for a long time at no better economy than would be obtained from a plain slide valve engine, and when it was attempted to get an earlier cut off by separating the two cut off valves, they had worn so much in their old place on the valve that shoulders were found sufficient to cause a disagreeable noise and a leaky valve. This is very apt to occur, not only where the valve is run for a long time on one seat, but in cases of variation of the travel of the expansion valve. The result is that a change will bring about a leaky valve, something that every engineer abhors.

The construction of the Buckeye engine, which is also of this type, is such that the travel of the valve on the back of the main valve is always the same, no matter what the cut off may be. Then this engine makes use of our second proposition as a means of effecting the cut off, viz., by advancing the eccentric. You will readily observe that anything that will cause the cut off valve to reach a certain point earlier in the stroke will bring about an earlier cut off as it hastens everything all around. This is the plan pursued in the Buckeye, in which the governor, of the shaft type, turns the eccentric forward or back according as the load demands. Then, in addition, the valve is balanced partially, the attempt not being made to produce an absolutely balanced valve, on the ground that there should be friction enough to keep the surfaces bright and to prevent leakage. The most perfect valve will, of course, be entirely balanced under all conditions of pressure so as to move with perfect ease. With the riding cut off valve in connection with the plain slide valve, this is not accomplished, and it does not matter whether it is partially unbalanced to prevent leakage or not, the fact that it is not entirely balanced prevents it reaching the ideal valve.



This valve, Fig. 5, differs from the others also in this particular, that the exhaust takes place at the end of the valve instead of under the arch. Two eccentrics are used, the one for the main valve being fastened to the shaft and the other riding loosely upon it and connected to the fly wheel governor, by which it may be turned forward or back as the load requires. The three points of lead, or admission and exhaust and compression, are fixed and independent of the changes and cut off. The motion of the main eccentric is given to a rocker arm, the pivot of which is at the bottom, and from the upper end the valve rod transfers the motion to the valve without reversing the motion, as is done sometimes in the slide valve to overcome the effects of the angularity of the connecting rod. The action of the rocker arm, therefore, so far as the main valve in the Buckeye is concerned, is no different than that which would occur if no rocker arm intervened. The motion of the cut off eccentric, through its eccentric rod, is given to a rocker rocking in a bearing in the center of the main rocker arm (see Fig. 6). The motion of this eccentric is reversed, so far as the cut off valve is concerned, and when the cut off eccentric is moving forward, the cut off valve is being pushed back. The main valve rod is hollow, and the cut off valve rod passes through it.



The cut off eccentric can be placed in any position to cause it to cut off as desired, and by drawing the valve forward, by increasing the angular advance of the eccentric, the cut off valve is caused to reach and cover the steam passage in the main valve earlier in the stroke. Instead of being ahead of the crank, the main eccentric in this arrangement follows the crank, on account of the exhaust and steam edges being exactly opposite from those in the ordinary slide. What is the steam edge of the common slide is in this the exhaust edge, and what is the exhaust edge in the common valve is the steam edge in this one. The valve, therefore, must be moved in the opposite direction from what is ordinarily the case, the main eccentric being not 90 deg. behind the crank. It has a rapid and full opening just the same, for it is at this point behind the crank, or ahead of it, that the eccentric gives to the valve its quickest movement, or between the eccentric dead centers. The cut off eccentric is considerably ahead of the main eccentric, and about even with the crank. If it was not for the reversal of motion of the cut off valve through the rocker arm this eccentric would be about in line with the crank, but on the other end. The movement of the cut off valve, therefore, at the time of port opening is very little, being about on its dead center, passing which, it immediately commences to close.

The object of the peculiar construction of the rocker arm, and the pivot for the cut off rocker being placed thereon, is to provide equal travel on the back of the main valve, no matter what the cut off. I have already explained, in connection with the slide valve, that advancing the eccentric does not change the movement of the valve on its seat, but simply its relation to the movement of the piston. You will see that this is unchanged as using the main valve as a seat or any other seat. If the main valve was to remain stationary, and only the cut off valve to be operated by its eccentric, the movement of this cut off valve on a certain plane would be the same for all positions of the eccentric.

Moving the main slide does not affect the matter in any way, for it moves at the same time the pivot of the cut off, and while the cut off seat has assumed a different position with reference to the engine, it is still as though stationary so far as the cut off valve is concerned. This is the object of this peculiar construction, and not, as some engineers suppose, simply to make an odd way of doing things. And the object of it all is to give at all cut offs the same amount of travel, so that there might be no unequal wear to bring about a leak, to prevent which a perfect balancing has been sacrificed.

Referring to the valve and this engine as to how it will satisfy our requirements of a perfect valve gear, we find that the first requirement of a rapid and full opening is met, in that the opening occurs when the main eccentric is moving very rapidly, yet not its fastest, and while this opening will be very satisfactory, it is not so rapid an opening as is obtained in some other forms of valves and valve gears, but this could be overcome very readily by increasing the lead a trifle, and in my experience with these engines I find that the practice is very general by engineers and by builders themselves to give them a considerable amount of lead. As to the second requirement, the maintenance of initial pressure until cut off, giving a straight steam line, cards from this engine will not be found to show that the engine satisfies this requirement, and for this reason, that the cut-off valve commences to close the port immediately after the piston commences to move. The cut off eccentric you will remember is set to move with the crank or very nearly so, and the lighter the load, the greater will this fact appear. For the lightest loads the governor places the eccentric in advance of the crank, so that the cut off valve will commence to close the port before steam is admitted by the main valve to the engine. Now, the later the cut off, the less will this wire drawing appear at first, and the shorter the cut off, the amount of wire drawing increases sensibly. The operation of the valve, therefore, in this particular, cannot be considered as meeting our requirement that the port shall be held open full width until ready to be closed. Many men claim for this engine that the closing occurs when the cut off eccentric is moving its fastest. This is a fact, and if we consider the point of cut off only to be the point of absolute cut off, the cut off must be instantaneous, for there is an instantaneous point where the cut off is final only to be considered. The reasoning applied here would hold good also to a less extent on the slide valve, but is not the point of absolute cut off. We want to note how long it is from the time the valve commences to close at all until finally closed, and, as I have shown you, this is considerable in this engine.

Referring to the point of cut off finally, it is determined upon by a governor of the fly wheel type. The eccentric is loose about the shaft, and arms projecting therefrom are connected by other arms to the extremity of an arm upon which is mounted a weight, and which is attached to the spokes of the fly wheel, or special governor wheel in this case, and which is fastened to the crank shaft. As the speed increases through throwing off a portion of the load the governor weights fly out, and this movement is transferred through the lever connections to the eccentric, causing it to be turned ahead, and the manner hastening the movement of the cut off valve on its seat and causing it to reach and cover the edge of the steam port earlier in the stroke. This engine was the pioneer in governors of this character, the advantage being, in addition to its necessity for the work of turning the eccentric ahead or back, that the liability of the engine to run away, as very often happens from the breaking of the governor belt or a similar cause, was not possible.

The cut off valve has a travel considerably beyond the edge of the steam passage after the valve is closed, and this has one advantage, that the valve is less liable to leak, and to this must be added the loss from the friction of this moving valve, and moving too in opposition to the main valve. In our perfect valve, as we outlined it, the valve does not move after the port is closed. The exhausting functions of the valve are very good, giving a quick opening and a full opening, because this opening occurs when the eccentric is moving its fastest. The engine also possesses a distinct advantage in having remarkably small clearance spaces. The length of the steam passage is very small in comparison with any form of engine, and having but two ports instead of four, as in the Corliss and four valve type.

In these there must be included in the clearance, that to the exhaust port as well as the steam port, adding a considerable amount where the piston comes close to the head. As the engines leave the maker's hand the engines are provided with a considerable amount of lap to give plenty of compression, but are, of course, capable of having more added to increase compression, or some planed off to decrease it.

One of the peculiar things about this engine is the failure to realize anywhere near boiler pressure, noticeable in every case that has come under my notice. The considerable lead gives it for an instant, but it soon falls away, indicating the steam chest pressure only by a peak at the junction of the admission and steam lines. This is probably due to the fact that the cut off valve commences closing the steam passage so soon after steam is admitted, and in this particular does not satisfy the requirements of a perfect valve. There is this about the engine, that above all others of this type there has come under my notice fewer engines of this type with a maladjustment of valves from tampering by incompetent engineers.

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FIRING POINTS OF VARIOUS EXPLOSIVES.

An apparatus, devised by Horsley, was used, which consisted of an iron stand with a ring support holding a hemispherical iron vessel, in which paraffin or tin was put. Above this was another movable support, from which a thermometer was suspended and so adjusted that its bulb was immersed in molten material in the iron vessel. A thin copper cartridge case, 5/8 in. in diameter and 1-5/16 in. long, was suspended over the bath by means of a triangle, so that the end of the case was 1 in. below the surface of the liquid. On beginning the experiment the material in the bath was heated to just above the melting point, the thermometer was inserted in it, and a minute quantity of the explosive was placed in the bottom of the cartridge case. The temperature marked by the thermometer was noted as the initial temperature, the cartridge case containing the explosive was inserted in the bath, and the temperature quickly raised until the explosive flashed off or exploded, when the temperature marked by the thermometer was again noted as the firing point. The tables given show the results of about six experiments with each explosive. The initial temperatures range from 65 deg. to 280 deg. C. in some cases, but as the firing points remained fairly constant, only the extremes of the latter are quoted in the following table:

+ - Description of Explosive. Firing Point in deg. C. + - Compressed military gun-cotton. 186 - 201 Air-dried military gun-cotton. 179 - 186 " " " 186 - 189 " " " 137 - 139 " " " 154 - 161 Gun-cotton dried at 65 deg. C. 136 - 141 Air-dried collodion gun-cotton. 186 - 191 " " " 197 - 199 " " " 193 - 195 Air-dried gun-cotton. 192 - 197 " " 194 - 199 Hydro-nitrocellulose. 201 - 213 Nitroglycerin. 203 - 205 Kieselghur dynamite. No. 1. 197 - 200 Explosive gelatin. 203 - 209 Explosive gelatin, camphorated. 174 - 182 Mercury fulminate. 175 - 181 Gunpowder. 278 - 287 Hill's picric powder. 273 - 283 " " " 273 - 290 Forcite, No. 1. 184 - 200 Atlas powder, 75 per cent. 175 - 185 Emmensite, No. 1. 167 - 184 Emmensite, No. 2. 165 - 177 Emmensite, No. 5. 205 - 217 + - C.E. Munroe, J. Amer. Chem. Soc.

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STATION FOR TESTING AGRICULTURAL MACHINES.

The minister of agriculture has recently established a special laboratory for testing agricultural materiel. This establishment, which is as yet but little known, is destined to render the greatest services to manufacturers and cultivators.

In fact, agriculture now has recourse to physics and mechanics as well as to chemistry. Now, although there were agricultural laboratories whose mission it was to fix the choice of the cultivator upon such or such a seed or fertilizer, there was no official establishment designed to inform him as to the value of machines, the models of which are often very numerous. Chemical advice was to be had, but mechanical advice was wanting. It is such a want that has just been supplied. Upon the report presented by Mr. Tisserand, director of agriculture, a ministerial decree of the 24th of January, 1888, ordered the establishment of an experimental station. Mr. Ringelmann, professor of rural engineering at the school of Grignon, was put in charge of the installation of it, and was appointed its director. He immediately began to look around for a site, and on the 17th of December, 1888, the Municipal Council of Paris, taking into consideration the value of such an establishment to the city's industries, decided that a plot of ground of an area of 3,309 square meters, situated on Jenner Street, should be put at the disposal of the minister of agriculture for fifteen years for the establishment thereon of a trial station. This land, bordering on a very wide street and easy of access, opposite the municipal buildings, offers, through its area, its situation, and its neigborhood, indisputable advantages. A fence 70 meters in extent surrounds the station. An iron gate opens upon a paved path that ends at the station.

The year 1889 was devoted to the installation, and the station is now in full operation. The tests that can be made here are many, and concern all kinds of apparatus, even those connected with the electric lighting that the agriculturist may employ to facilitate his exploitation. However, the tests that are oftenest made are (1) of rotary apparatus, such as mills, thrashing machines, etc.; (2) of traction machines, such as wagons, carts, plows, etc.; and (3) of lifting apparatus. It is possible, also, to make experiments on the resistance of materials.

The experimental hall contains a 7 horse power gas motor, dynamometers with automatic registering apparatus, counters, balances, etc. A small machine shop contains a lathe, a forge, a drilling machine, etc. The main shaft is 12 meters in length and is 7 centimeters in diameter. It is supported at a distance of one meter from the floor by four pillow blocks, and is formed of three sections united by movable coupling boxes. Out of these 12 meters, 9 are in the hall and 3 extend beyond the hall to an annex, 14 meters in length and 4 in width, in which tests are made of machines whose operation creates dust. When the machines to be tested require more than the power of seven horses that the motor gives, the persons interested furnish a movable engine, which, placed under the annex, actuates the driving shaft. Alongside of the main building there is a ring for experimenting upon machines actuated by a horse whim. There will soon be erected in the center of the grounds an 18 meter tower for experiments on pumps. Platforms spaced 5 meters apart, a crane at the top, and some gauging apparatus will complete this hydraulic installation.

The equipment of the hall is very complete, and is fitted for all kinds of experiments.



The tests of rotary machines are made by means of a dynamometer (see figure). Two fast pulleys and one loose pulley are interposed between the machine to be tested and the motor. The pulley connected with the motor carries along the one connected with the machine, through the intermedium of spring plates, whose strength varies with the nature of the apparatus to be tested. The greater or less elongation of these plates gives the tangential stress exerted by the driving pulley to carry along the pulley that actuates the machine to be tested. This elongation is registered by means of a pencil connected with the spring plates, and which draws a diagram upon a sheet of paper. At the same time, a special totalizer gives the stress in kilogrammeters. Besides, the pulley shaft actuates a revolution counter, and a clock measures the time employed in the experiment. In order to obtain a simultaneous starting and stopping point for all these apparatus, they are connected electrically, and, through the maneuver of a commutator, are all controlled at once. The electric current is furnished by two series of bichromate batteries.

The tests of traction machines are effected by means of a three-wheeled vehicle carrying a dynamometer. The front wheel is capable of turning freely in the horizontal plane, and the dynamometer is mounted upon a frame provided with a screw that permits of regulating its position according to the slope of the ground. The method of suspension of the dynamometer allows it to take automatically the inclination of the line of traction without any torsion of the plates. There are two models of this vehicle, one designed to be drawn by a man, and the other by a horse.

The station is provided, in addition, with registering pressure gauges, a large double dynamometric indicator, a counter of electricity, balances of precision, etc.

An apparatus designed for measuring the rendering of presses is now in course of construction.

Although the station has been in operation only from the 1st of January, twenty-five machines have already been presented to be tested.—Extract from Le Genie Civil.

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WATER SOFTENING AND PURIFYING APPARATUS.

We have recently had brought under our notice a system of water and sewage purification which appears to possess several substantial advantages. Chief among these are simplicity in construction and operation, economy in first cost and working and efficiency in action. This system is the invention of Messrs. Slack & Brownlow, of Canning Works, Upper Medlock Street, Manchester, and the apparatus adopted in carrying it out is here illustrated. It consists of an iron cylindrical tank having inside a series of plates arranged in a spiral direction around a fixed center, and sloping downward at a considerable angle outward. The water to be purified and softened flows through the large inlet tube to the bottom, mixing on its way with the necessary chemicals, and entering the apparatus at the bottom, rises to the top, passing spirally round the whole circumference, and depositing on the plates all solids and impurities.

All that is needed in the way of attention, even when dealing with sewage, or the most polluted waters, is stated to be the mixing in the small tanks the necessary chemical reagents, at the commencement of the working day; and at the close of the day the opening of the mud cocks shown in our engraving, to remove the collected deposit upon the plates. For the past six months this system has been in operation at a dye works in Manchester, successfully purifying and softening the foul waters of the river Medlock. It is stated that 84,000 gallons per day can be easily purified by an apparatus 7 feet in diameter. The chemicals used are chiefly lime, soda, and alumina, and the cost of treatment is stated to vary from a farthing to twopence per 1,000 gallons, according to the degree of impurity of the water or sewage treated.

The results of working at Manchester show that all the visible filth is removed from the Medlock's inky waters, besides which the hardness of the water is reduced to about 6 deg. from a normal condition of about 30 deg.. The effluent is fit for all the varied uses of a dye works, and is stated to be perfectly capable of sustaining fish life. With results such as these the system should have a promising future before it in respect of sewage treatment, as well as the purification and softening of water generally for industrial and manufacturing purposes.—Iron.



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THE TRISECTION OF ANY ANGLE.

By FREDERIC R. HONEY, Ph.B., Yale University.

The following analysis shows that with the aid of an hyperbola any arc, and therefore any angle, may be trisected.

If the reader should not care to follow the analytical work, the construction is described in the last paragraph—referring to Fig. II.

Let a b c d (Fig. I.) be the arc subtending a given angle. Draw the chord a d and bisect it at o. Through o draw e f perpendicular to a d.

We wish to find the locus of a point c whose distance from a given straight line e f is one-half the distance from a given point d.

In order to write the equation of this curve, refer it to the co-ordinate axes a d (axis of X) and e f (axis of Y), intersecting at the origin o.

Let g c = x

Therefore, from the definition c d = 2x

Let o d = D [Hence] h d = D-x

Let c h = y [Hence] (2x) squared = y squared + (D-x) squared or 4x squared = y squared + D squared-2Dx + x squared [Hence] y squared-3x squared + D squared-2Dx = o Ị

This is the equation of an hyperbola whose center is on the axis of abscisses. In order to determine the position of the center, eliminate the x term, and find the distance from the origin o to a new origin o'.

Let E = distance from o to o' [Hence] x = x' + E

Substituting this value of x in equation I.

y squared-3(x' + E) squared + D squared-2D(x' + E) = o or y squared-3x squared-6Ex'-3E squared + D squared-2Dx'-2DE = o [II.]

In this equation the x' terms should disappear.

[Hence] -6Ex' - 2Dx' = o [Hence] -E = - D/3

That is, the distance from the origin o to the new origin or the center of the hyperbola o' is equal to one-third of the distance from o to d; and the minus sign indicates that the measurement should be laid off to the left of the origin o. Substituting this value of E in equation II., and omitting accents—

We have

y squared - 3x squared + 2Dx - D squared/3 + D squared - 2Dx + 2D squared/3 = o [Hence] y squared - 3x squared = - 4D squared/3



This is the equation of an hyperbola referred to its center o' as the origin of co-ordinates. To write it in the ordinary form, that is in terms of the transverse and conjugate axes, multiply each term by C, i.e., _ Let /C = semi-transverse axis.

[TEX: sqrt{C} = ext{semi-transverse axis.}]

Thus Cy squared - 3Cx squared = - 4CD squared/3. [III.]

When in this form the product of the coefficients of the x squared and y squared terms should be equal to the remaining term.

That is

3C squared = - 4CD squared/3. [Hence] C = 4D squared/9.

And equation III. becomes:

4D squared 4D squared 16D^{4} ——- y squared - ——- x squared = - ————- 9 3 27

[TEX: frac{4D^2}{9} y^2 - frac{4D^2}{3} x^2 = -frac{16D^4}{27}] _ / 4D squared 2D The semi-transverse axis = / ——- = —— 9 3

[TEX: ext{The semi-transverse axis} = sqrt{frac{4D^2}{9}} = frac{2D}{3}] / 4D squared 2D The semi-conjugate axis = / ——- = ——- 3 / 3

[TEX: ext{The semi-conjugate axis} = sqrt{frac{4D^2}{3}} = frac{2D}{sqrt{3}}]

Since the distance from the center of the curve to either focus is equal to the square root of the sum of the squares of the semi-axes, the distance from o' to either focus

/4D squared 4D squared 4D = / /——- + ——- = —— / 9 3 3

[TEX: sqrt{frac{4D^2}{9} + frac{4D^2}{3}} = frac{4D}{3}]

We can therefore make the following construction (Fig. II.) Draw a d the chord of the arc a c d. Trisect a d at o' and k. Produce d a to l, making a l = a o' = o' k = k d. With a k as a transverse axis, and l and d as foci, construct the branch of the hyperbola k c c' c", which will intersect all arcs having the common chord a d at c, c', c", etc., making the arcs c d, c' d, c" d, etc., respectively, equal to one-third of the arcs a c d, a c' d, a c" d, etc.

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TEST CARD HINTS.

By Dr. F. OGDEN STOUT.

I know it is the custom with a great many if not the majority of opticians to fit a customer without knowing whether he has presbyopia, hypermetropia, or any of the other errors of refraction. Their method is first to try a convex, and if this does not improve, a concave, etc., until the proper one is found. This, of course, amounts to the same thing if the right glass is found. But in practice it will be found both time saving and more satisfactory to first decide with what error you have to deal. It is very simple, and, where you have no other means of diagnosing (such as the ophthalmoscope), it does away with the necessity of trying so many lenses before the proper one is found. You should have a distance test card placed at a distance of twenty feet from the person you are examining, and in a good light.

A distance test card consists of letters of various sizes which it has been found can be seen at certain distances by people with good vision. Thus the largest letter is marked with a cc, meaning that this should be seen at two hundred feet, and another line, XX, at twenty feet, which is the proper distance for testing vision for distance, for the reason that a normal eye is at rest when looking at any object twenty feet from it or beyond, and the rays coming from it are parallel and come to a focus on the retina. You must also have a near vision test card with lines that should be seen by a normal eye from ten to seventy-two inches, and a card of radiating lines for astigmatism. With this preparation you are ready to proceed. To illustrate, the first customer comes and tells you that up to six months ago he had very good vision, but he finds now that, especially at night, he has trouble in reading or writing, and that he finds he can see better a little farther away. His head aches and eyes smart. You will of course say that this is a very simple case. It must be old sight (presbyopia). Probably it is if he is old enough (45), but you must prove this for yourself, without asking his age, which is embarrassing in the case of a lady. If you direct him to the distance card twenty feet away, and find that he can see every one down to and including the one marked XX, his vision is up to the standard for distance, and you know that he can have no astigmatism worth correcting, nor any near sight, as both of these affect vision for distance, but he may have far sight or old sight or both combined. You must find which it is.

If, while he is still looking at the twenty-foot line, you place in front of the eyes a weak convex and he tells you he sees just as well with as without, it proves the existence of far-sight or hypermetropia, and the strongest convex that still leaves vision as good for distance as without any, corrects the manifest. But if the weak convex blurs it, it shows that there is some defect in focusing, if the near vision is below normal. You therefore know that you have a case of old sight or presbyopia, requiring the weakest convex to correct it, that will enable your customer to see the finest line on the near card at the required distance.

The next customer that comes to be fitted with glasses can only see the line marked XL on the distance card at 20 feet or about one-half of what he should see, which leads you to think that there is no far sight, for vision for distance is good except in very high degrees of this error. Nor can there be old-sight, for vision for distance is good in old-sight until after the fifty-fifth year, but it can be near sight (myopia) or astigmatism, or both. We next try the near card and find that even the finest line can be seen clearly if held sufficiently close to the eyes. We now know that this is a case of near sight, and we must fit them with glasses for distance. The weakest concave that will enable him to see the line that should be seen on the distance card at 20 feet is the proper one to give him for use.—The Optician.

* * * * *



CHARLES GOODYEAR.

CHARLES GOODYEAR was born in New Haven, December 29, 1800. He was the son of Amasa Goodyear, and the eldest among six children. His father was quite proud of being a descendant of Stephen Goodyear, one of the founders of the colony of New Haven in 1638.

Amasa Goodyear owned a little farm on the neck of land in New Haven which is now known as Oyster Point, and it was here that Charles spent the earliest years of his life. When, however, he was quite young, his father secured an interest in a patent for the manufacture of ivory buttons, and looking for a convenient location for a small mill, settled at Naugatuck, Conn., where he made use of the valuable water power that is there. Aside from his manufacturing, the elder Goodyear ran a farm, and between the two lines of industry kept young Charles pretty busy.

In 1816, Charles left his home and went to Philadelphia to learn the hardware business. He worked at this very industriously until he was twenty-one years old, and then, returning to Connecticut, entered into partnership with his father at the old stand in Naugatuck, where they manufactured not only ivory and metal buttons, but a variety of agricultural implements, which were just beginning to be appreciated by the farmers. In August of 1824 he was united in marriage with Clarissa Beecher, a woman of remarkable strength of character and kindness of disposition, and one who in after years was of the greatest assistance to the impulsive inventor. Two years later he removed again to Philadelphia, and there opened a hardware store. His specialties were the valuable agricultural implements that his firm had been manufacturing, and after the first distrust of home made goods had worn away—for all agricultural implements were imported from England at that time—he found himself established at the head of a successful business.

This continued to increase until it seemed but a question of a few years until he would be a very wealthy man. Between 1829 and 1830 he suddenly broke down in health, being troubled with dyspepsia. At the same time came the failure of a number of business houses that seriously embarrassed his firm. They struggled on, however, for some time, but were finally obliged to fail. The ten years that followed this were full of the bitterest struggles and trials to Goodyear. Under the law that then existed he was imprisoned time after time for debts, even while he was trying to perfect inventions that should pay off his indebtedness.

Between the years 1831 and 1832 he began to hear about gum elastic and very carefully examined every article that appeared in the newspapers relative to this new material. The Roxbury Rubber Company, of Boston, had been for some time experimenting with the gum, and believing that they had found means for manufacturing goods from it, had a large plant and were sending their goods all over the country. It was some of their goods that first attracted his attention. Soon after this Goodyear visited New York, and went at once to the store of the Roxbury Rubber Company. While there, he examined with considerable care some of their life preservers, and it struck him that the tube used for inflation was not very perfect. He, therefore, on his return to Philadelphia, made some tubes and brought them down to New York and showed them to the manager of the Roxbury Rubber Company.

This gentlemen was so pleased with the ingenuity that Goodyear had shown in manufacturing these tubes, that he talked very freely with him and confessed to him that the business was on the verge of ruin, that the goods had to be tested for a year before they could tell whether they were perfect or not, and to their surprise, thousands of dollars worth of goods that they had supposed were all right were coming back to them, the gum having rotted and made them so offensive that it was necessary to bury them in the ground to get them out of the way.

Goodyear at once made up his mind to experiment on this gum and see if he could not overcome its stickiness.

He, therefore, returned to Philadelphia, and, as usual, met a creditor, who had him arrested and thrown into prison. While there, he tried his first experiments with India rubber. The gum was very cheap then, and by heating it and working it in his hands, he managed to incorporate in it a certain amount of magnesia which produced a beautiful white compound and appeared to take away the stickiness.

He therefore thought he had discovered the secret, and through the kindness of friends was put in the way of further perfecting his invention at a little place in New Haven. The first thing that he made here was shoes, and he used his own house for grinding room, calender room, and vulcanizing department, and his wife and children helped to make up the goods. His compound at this time was India rubber, lampblack, and magnesia, the whole dissolved in turpentine and spread upon the flannel cloth which served as the lining for the shoes. It was not long, however, before he discovered that the gum, even treated this way, became sticky, and then those who had supplied the money for the furtherance of these experiments, completely discouraged, made up their minds that they could go no further, and so told the inventor.



He, however, had no mind to stop here in his experiments, but, selling his furniture and placing his family in a quiet boarding place, he went to New York, and there, in an attic, helped by a friendly druggist, continued his experiments. His next step in this line was to compound the rubber with magnesia and then boil it in quicklime and water. This appeared to really solve the problem, and he made some beautiful goods. At once it was noised abroad that India rubber had been so treated that it lost its stickiness, and he received medals and testimonials and seemed on the high road to success, till one day he noticed that a drop of weak acid, falling on the cloth, neutralized the alkali, and immediately the rubber was soft again. To see this, with his knowledge of what rubber should do, proved to him at once that his process was not a successful one. He therefore continued experimenting, and after preparing his mixtures in his attic in New York, would walk three miles to the mill of a Mr. Pike, at Greenwich village, and there try various experiments.

In the line of these, he discovered that rubber, dipped in nitric acid, formed a surface cure, and he made a great many goods with this acid cure which were spoken of, and which even received a letter of commendation from Andrew Jackson.

The constant and varied experiments that Goodyear went through with affected his health more or less, and at one time he came very near being suffocated by gas generated in his laboratory. That he did not die then everybody knows, but he was thrown then into a fever by the accident and came very near losing his life.

It was there that he formed an acquaintance with Dr. Bradshaw, who was very much pleased with the samples of rubber goods that he saw in Goodyear's room, and when the doctor went to Europe he took them with him, where they attracted a great deal of attention, but beyond that nothing was done about them. Now that he appeared to have success, he found no difficulty in obtaining a partner, and together the two gentlemen fitted up a factory and began to make clothing, life preservers, rubber shoes, and a great variety of rubber goods. They also had a large factory, with special machinery, built at Staten Island, where he removed his family and again had a home of his own. Just about this time, when everything looked bright, the great panic of 1836-1837 came, and swept away the entire fortune of his associate and left Goodyear without a cent, and no means of earning one.

His next move was to go to Boston, where he became acquainted with J. Haskins, of the Roxbury Rubber Company, and found in him a firm friend, who loaned him money and stood by him when no one would have anything to do with the visionary inventor. Mr. Chaffee was also exceedingly kind and ever ready to lend a listening ear to his plans, and to also assist him in a pecuniary way. It was about this time that it occurred to Mr. Chaffee that much of the trouble that they had experienced in working India rubber might come from the solvent that was used. He therefore invented a huge machine for doing the mixing by mechanical means. The goods that were made in this way were beautiful to look at, and it appeared, as it had before, that all difficulties were overcome.

Goodyear discovered a new method for making rubber shoes and got a patent on it, which he sold to the Providence Company, in Rhode Island.

The secret of making the rubber so that it would stand heat and cold and acids, however, had not been discovered, and the goods were constantly growing sticky and decomposing and being returned.

In 1838 he, for the first time, met Nathaniel Hayward, who was then running a factory in Woburn. Some time after this Goodyear himself moved to Woburn, all the time continuing his experiments. He was very much interested in Hayward's sulphur experiments for drying rubber, but it appears that neither of them at that time appreciated the fact that it needed heat to make the sulphur combine with the rubber and to vulcanize it.

The circumstances attending the discovery of his celebrated process is thus described by Mr. Goodyear himself in his book, "Gum Elastic." It will be observed that he makes use of the third person in all references to himself:

"In the summer of 1838 he became acquainted with Mr. Nathaniel Hayward, of Woburn, Mass., who had been employed as the foreman of the Eagle Company at Woburn, where he had made use of sulphur by impregnating the solvent with it. It was through him that the writer (Charles Goodyear, who makes use all through his book of the third person) received the first knowledge of the use of sulphur as a drier of gum elastic.

"Mr. Hayward was left in possession of the factory which was abandoned by the Eagle Company. Soon after this it was occupied by the writer, who employed him for the purpose of manufacturing life preservers and other articles by the acid gas process. At this period he made many novel and useful applications of this substance. Among other fancy articles he had newspapers printed on the gum elastic drapery, and the improvement began to be highly appreciated. He therefore now entered, as he thought, upon a successful career for the future. A far different result awaited him.

"It was supposed by others as well as himself that a change was wrought through the mass of the goods acted upon by the acid gas, and that the whole body of the article was made better than the native gum. The surface of the goods really was so, but owing to the eventual decomposition of the goods beneath the surface, the process was pronounced by the public a complete failure. Thus instead of realizing the large fortune which by all acquainted with his prospects was considered certain, his whole invention would not bring him a week's living.

"He was obliged for the want of means to discontinue manufacturing, and Mr. Hayward left his employment. The inventor now applied himself alone, with unabated ardor and diligence, to detect the cause of his misfortune and if possible to retrieve the lost reputation of his invention. On one occasion he made some experiments to ascertain the effect of heat upon the same compound that had decomposed in the articles previously manufactured, and was surprised to find that the specimen, being carelessly brought in contact with a hot stove, charred like leather. He endeavored to call the attention of his brother as well as some other individuals who were present, and who were acquainted with the manufacture of gum elastic, to this effect as remarkable and unlike any before known, since gum elastic always melted when exposed to a high degree of heat. The occurrence did not at the time appear to them to be worthy of notice. It was considered as one of the frequent appeals that he was in the habit of making in behalf of some new experiment. He, however, directly inferred that if the process of charring could be stopped at the right point, it might divest the gum of its native adhesiveness throughout, which would make it better than the native gum.

"He made another trial of heating a similar fabric, before an open fire. The same effect, that of charring the gum, followed, but there were further and very satisfactory indications of ultimate success in producing the desired result, as upon the edge of the charred portions of the fabric there appeared a line, or border, that was not charred, but perfectly cured.

"These facts have been stated precisely as they occurred in reference to the acid gas, as well as the vulcanizing process.

"The incidents attending the discovery of both have a strong resemblance, so much so they may be considered parallel cases. It being now known that the results of the vulcanizing process are produced by means and in a manner which would not have been anticipated from any reasoning on the subject, and that they have not yet been satisfactorily accounted for, it has been sometimes asked, how the inventor came to make the discovery? The answer has already been given. It may be added that he was many years seeking to accomplish this object, and that he allowed nothing to escape his notice that related to the subject. Like the falling of an apple, it was suggestive of an important fact to one whose mind was previously prepared to draw an inference from any occurrence which might favor the object of his research. While the inventor admits that these discoveries were not the results of scientific chemical investigations, he is not willing to admit that they were the result of what is commonly termed accident; he claims them to be the result of the closest application and observation.

"The discoloring and charring of the specimens proved nothing and discovered nothing of value, but quite the contrary, for in the first instance, as stated in the acid gas improvement, the specimen acted upon was thrown away as worthless and left for some time; in the latter instance, the specimen that was charred was in like manner disregarded by others.

"It may, therefore, be considered as one of those cases where the leading of the Creator providentially aids his creatures, by what are termed 'accidents,' to attain those things which are not attainable by the powers of reasoning he has conferred on them."

Now that Goodyear was sure that he had the key to the intricate puzzle that he had worked over for so many years, he began at once to tell his friends about it and to try to secure capital, but they had listened to their sorrow so many times that his efforts were futile. For a number of years be struggled and experimented and worked along in a small way, his family suffering with himself the pangs of the extremest poverty. At last he went to New York and showed some of his samples to William Ryder, who, with his brother Emory, at once appreciated the value of the discovery and started in to manufacturing. Even here Goodyear's bad luck seemed to follow him, for the Ryder Bros. failed and it was impossible to continue the business.

He had, however, started a small factory at Springfield, Mass., and his brother-in-law, Mr. De Forest, who was a wealthy woolen manufacturer, took Ryder's place, and the work of making the invention practical was continued. In 1844 it was so far perfected that Goodyear felt it safe to take out a patent. The factory at Springfield was run by his brothers, Nelson and Henry.

In 1843 Henry started one in Naugatuck, and in 1844 introduced mechanical mixing in place of the mixture by the use of solvents.

In the year 1852 Goodyear went to Europe, a trip that he had long planned, and saw Hancock, then in the employ of Charles Macintosh & Co. Hancock admitted in evidence that the first piece of vulcanized rubber he ever saw came from America, but claimed to have reinvented vulcanization and secured patents in Great Britain, but it is a remarkable fact that Charles Goodyear's French patent was the first publication in Europe of this discovery.

In 1852 a French company were licensed by Mr. Goodyear to make shoes, and a great deal of interest was felt in the new business. In 1855 the French emperor gave to Charles Goodyear the grand medal of honor and decorated him with the cross of the legion of honor in recognition of his services as a public benefactor, but the French courts subsequently set aside his French patents on the ground of the importation of vulcanized goods from America by licenses under the United States patents. He died July 1, 1860, at the Fifth Avenue Hotel, New York City.—India Rubber World.

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[Continued from SUPPLEMENT, No. 786, page 12558.]



THE ELECTROMAGNET.

[Footnote: Lectures delivered before the Society of Arts, London, 1890. From the Journal of the Society.]

BY PROFESSOR SILVANUS P. THOMPSON, D. SC., B.A., M.I.E.E.

III.

RESEARCHES OF PROFESSOR HUGHES.



His object was to find out the best form of electromagnet, the best distance between the poles, and the best form of armature for the rapid work required in Hughes' printing telegraphs. One word about Hughes' magnets. This diagram (Fig. 51) shows the form of the well known Hughes' electromagnet. I feel almost ashamed to say those words "well known," because on the Continent everybody knows what you mean by a Hughes' electromagnet. In England scarcely anyone knows what you mean. Englishmen do not even know that Professor Hughes has invented a special form of electromagnet. Hughes' special form is this: A permanent steel magnet, generally a compound one, having soft iron pole pieces, and a couple of coils on the pole pieces only. As I have to speak of Hughes' special contrivance among the mechanisms that will occupy our attention later on, I only now refer to this magnet in one particular. If you wish a magnet to work rapidly, you will secure the most rapid action, not when the coils are distributed all along, but when they are heaped up near, not necessarily entirely on, the poles. Hughes made a number of researches to find out what the right length and thickness of these pole pieces should be. It was found an advantage not to use too thin pole pieces, otherwise the magnetism from the permanent magnet did not pass through the iron without considerable reluctance, being choked by insufficiency of section: also not to use too thick pieces, otherwise they presented too much surface for leakage across from one to the other. Eventually a particular length was settled upon, in proportion about six times the diameter, or rather longer. In the further researches that Hughes made he used a magnet of shorter form, not shown here, more like those employed in relays, and with an armature from 2 to 3 millimeters thick, 1 centimeter wide and 5 centimeters long. The poles were turned over at the top toward one another. Hughes tried whether there was any advantage in making those poles approach one another, and whether there was any advantage in having as long an armature as 5 centimeters. He tried all the different kinds, and plotted out the results of observations in curves, which could be compared and studied. His object was to ascertain the conditions which would give the strongest pull, not with a steady current, but with such currents as were required for operating his printing telegraph instruments; currents which lasted but one to twenty hundredths of a second. He found it was decidedly an advantage to shorten the length of the armature, so that it did not protrude far over the poles. In fact, he got a sufficient magnetic circuit to secure all the attractive power that he needed, without allowing as much chance of leakage as there would have been had the armature extended a longer distance over the poles. He also tried various forms of armature having very various cross sections.

POSITION AND FORM OF ARMATURE.

In one of Du Moncel's papers on electromagnets[1] you will also find a discussion on armatures, and the best forms for working in different positions. Among other things in Du Moncel you will find this paradox: that whereas using a horseshoe magnet with fat poles, and a flat piece of soft iron for armature, it sticks on far tighter when put on edgeways; on the other hand, if you are going to work at a distance, across air, the attraction is far greater when it is set flatways. I explained the advantage of narrowing the surfaces of contact by the law of traction, B squared, coming in. Why should we have for action at a distance the greater advantage from placing the armature flatway to the poles? It is simply that you thereby reduce the reluctance offered by the air gap to the flow of the magnetic lines. Du Moncel also tried the difference between round armatures and flat ones, and found that a cylindrical armature was only attracted about half as strongly as a prismatic armature having the same surface when at the same distance. Let us examine this fact in the light of the magnetic circuit. The poles are flat. You have at a certain distance away a round armature; there is a certain distance between its nearest side and the polar surfaces. If you have at the same distance away a flat armature having the same surface, and, therefore, about the same tendency to leak, why do you get a greater pull in this case than in that? I think it is clear that if they are at the same distance away, giving the same range of motion, there is a greater magnetic reluctance in the case of the round armature, although there is the same periphery, because, though the nearest part of the surface is at the prescribed distance, the rest of the under surface is farther away; so that the gain found in substituting an armature with a flat surface is a gain resulting from the diminution in the resistance offered by the air gap.

[Footnote 1: "La Lumiere Electrique," vol. ii.]

POLE PIECES ON HORSESHOE MAGNETS.

Another of Du Moncel's researches[2] relates to the effect of polar projections or shoes—movable pole pieces, if you like—upon a horseshoe electromagnet. The core of this magnet was of round iron 4 centimeters in diameter, and the parallel limbs were 10 centimeters long and 6 centimeters apart. The shoes consisted of two flat pieces of iron slotted out at one end, so that they could be slid along over the poles and brought nearer together. The attraction exerted on a flat armature across air gaps 2 millimeters thick was measured by counterpoising. Exciting this electromagnet with a certain battery, it was found that the attraction was greatest when the shoes were pushed to about 15 millimeters, or about one-quarter of the interpolar distance, apart. The numbers were as follows:

Distance between shoes. Attraction, Millimeters. in grammes.

2 900 10 1,012 15 1,025 25 965 40 890 60 550

[Footnote 2: "La Lumiere Electrique," vol. iv., p. 129.]

With a stronger battery the magnet without shoes had an attraction of 885 grammes, but with the shoes 15 millimeters apart, 1,195 grammes. When one pole only was employed, the attraction, which was 88 grammes without a shoe, was diminished by adding a shoe to 39 grammes!

CONTRAST BETWEEN ELECTROMAGNETS AND PERMANENT MAGNETS.

Now I want particularly to ask you to guard against the idea that all these results obtained from electromagnets are equally applicable to permanent magnets of steel; they are not, for this simple reason. With an electromagnet, when you put the armature near, and make the magnetic circuit better, you not only get more magnetic lines going through that armature, but you get more magnetic lines going through the whole of the iron. You get more magnetic lines round the bend when you put an armature on to the poles, because you have a magnetic circuit of less reluctance with the same external magnetizing power in the coils acting around it. Therefore, in that case, you will have a greater magnetic flux all the way round. The data obtained with the electromagnet (Fig. 42), with the exploring coil, C, on the bend of the core, where the armature was in contact, and when it was removed are most significant. When the armature was present it multiplied the total magnetic flow tenfold for weak currents and nearly threefold for strong currents. But with a steel horseshoe, magnetized once for all, the magnetic lines that flow around the bend of the steel are a fixed quantity, and, however much you diminish the reluctance of the magnetic circuit, you do not create or evoke any more. When the armature is away the magnetic lines arch across, not at the ends of the horseshoe only, but from its flanks; the whole of the magnetic lines leaking somehow across the space. Where you have put the armature on, these lines, instead of arching out into space as freely as they did, pass for the most part along the steel limbs and through the iron armature. You may still have a considerable amount of leakage, but you have not made one line more go through the bent part. You have absolutely the same number going through the bend with the armature off as with the armature on. You do not add to the total number by reducing the magnetic reluctance, because you are not working under the influence of a constantly impressed magnetizing force. By putting the armature on to a steel horseshoe magnet you only collect the magnetic lines, you do not multiply them. This is not a matter of conjecture. A group of my students have been making experiments in the following way: They took this large steel horseshoe magnet (Fig. 52), the length of which, from end to end, through the steel, is 421/2 inches. A light, narrow frame was constructed so that it could be slipped on over the magnet, and on it were wound 30 turns of fine wire, to serve as an exploring coil. The ends of this coil were carried to a distant part of the laboratory, and connected to a sensitive ballistic galvanometer. The mode of experimenting is as follows:

The coil is slipped on over the magnet (or over its armature) to any desired position. The armature of the magnet is placed gently upon the poles, and time enough is allowed to elapse for the galvanometer needle to settle to zero. The armature is then suddenly detached. The first swing measures the change, due to removing the armature, in the number of magnetic lines that pass through the coil in the particular position.



I will roughly repeat the experiment before you: The spot of light on the screen is reflected from my galvanometer at the far end of the table. I place the exploring coil just over the pole, and slide on the armature; then close the galvanometer circuit. Now I detach the armature, and you observe the large swing. I shift the exploring coil, right up to the bend; replace the armature; wait until the spot of light is brought to rest at the zero of the scale. Now, on detaching the armature, the movement of the spot of light is quite imperceptible. In our careful laboratory experiments, the effect was noticed inch by inch all along the magnet. The effect when the exploring coil was over the bend was not as great as 1-3000th part of the effect when the coil was hard up to the pole. We are, therefore, justified in saying that the number of magnetic lines in a permanently magnetized steel horseshoe magnet is not altered by the presence or absence of the armature.

You will have noticed that I always put on the armature gently. It does not do to slam on the armature; every time you do so, you knock some of the so-called permanent magnetism out of it. But you may pull off the armature as suddenly as you like. It does the magnet good rather than harm. There is a popular superstition that you ought never to pull off the keeper of a magnet suddenly. On investigation, it is found that the facts are just the other way. You may pull off the keeper as suddenly as you like, but you should never slam it on.

From these experimental results I pass to the special design of electromagnets for special purposes.

ELECTROMAGNETS FOR MAXIMUM TRACTION.

These have already been dealt with in the preceding lecture; the characteristic feature of all the forms suitable for traction being the compact magnetic circuit.

Several times it has been proposed to increase the power of electromagnets by constructing them with intermediate masses of iron between the central core and the outside, between the layers of windings. All these constructions are founded on fallacies. Such iron is far better placed either right inside the coils or right outside them, so that it may properly constitute a part of the magnetic circuit. The constructions known as Camacho's and Cance's, and one patented by Mr. S.A. Varley, in 1877, belonging to this delusive order of ideas, are now entirely obsolete.

Another construction which is periodically brought forward as a novelty is the use of iron windings of wire or strip in place of copper winding. The lower electric conductivity of iron, as compared with copper, makes such a construction wasteful of exciting power. To apply equal magnetizing power by means of an iron coil implies the expenditure of about six times as many watts as need be expended if the coil is of copper.

ELECTROMAGNETS FOR MAXIMUM RANGE OF ATTRACTION.

We have already laid down the principle which will enable us to design electromagnets to act at a distance. We want our magnet to project, as it were, its force across the greatest length of air gap. Clearly, then, such a magnet must have a very large magnetizing power, with many ampere turns upon it, to be able to make the required number of magnetic lines pass across the air resistance. Also it is clear that the poles must not be too close together for its work, otherwise the magnetic lines at one pole will be likely to curl round and take short cuts to the other pole. There must be a wider width between the poles than is desirable in electromagnets for traction.

ELECTROMAGNETS OF MINIMUM WEIGHT.

In designing an apparatus to put on board a boat or a balloon, where weight is a consideration of primary importance, there is again a difference. There are three things that come into play—iron, copper, and electric current. The current weighs nothing, therefore, if you are going to sacrifice everything else to weight, you may have comparatively little iron, but you must have enough copper to be able to carry the electric current; and under such circumstances you must not mind heating your wires nearly red hot to pass the biggest possible current. Provide as little copper as you conveniently can, sacrificing economy in that case to the attainment of your object; but, of course, you must use fireproof material, such as asbestos, for insulating, instead of cotton or silk.

A USEFUL GUIDING PRINCIPLE.

In all cases of design there is one leading principle which will be found of great assistance, namely, that a magnet always tends so to act as though it tried to diminish the length of its magnetic circuit. It tries to grow more compact. This is the reverse of that which holds good with an electric current. The electric circuit always tries to enlarge itself, so as to inclose as much space as possible, but the magnetic circuit always tries to make itself as compact as possible. Armatures are drawn in as near as can be, to close up the magnetic circuit. Many two-pole electromagnets show a tendency to bend together when the current is turned on. One form in particular, which was devised by Ruhmkorff for the purpose of repeating Faraday's celebrated experiment on the magnetic rotation of polarized light, is liable to this defect. Indeed, this form of electromagnet is often designed very badly, the yoke being too thin, both mechanically and magnetically, for the purpose which it has to fulfill.

Here is a small electric bell, constructed by Wagener, of Wiesbaden, the construction of which illustrates this principle. The electromagnet, a horseshoe, lies horizontally; its poles are provided with protruding curved pins of brass. Through the armature are drilled two holes, so that it can be hung upon the two brass pins; and when so hung up it touches the ends of the iron cores just at one edge, being held from more perfect contact by a spring. There is no complete gap, therefore, in the magnetic circuit. When the current comes and applies a magnetizing power, it finds the magnetic circuit already complete in the sense that there are no absolute gaps. But the circuit can be bettered by tilting the armature to bring it flat against the polar ends, that being indeed the mode of motion. This is a most reliable and sensitive pattern of bell.



Electromagnetic Pop-gun.—Here is another curious illustration of the tendency to complete the magnetic circuit. Here is a tubular electromagnet (Fig. 53), consisting of a small bobbin, the core of which is an iron tube about two inches long. There is nothing very unusual about it; it will stick on, as you see, to pieces of iron when the current is turned on. It clearly is an ordinary electromagnet in that respect. Now suppose I take a little round rod of iron, about an inch long, and put it into the end of the tube, what will happen when I turn on my current? In this apparatus as it stands, the magnetic circuit consists of a short length of iron, and then all the rest is air. The magnetic circuit will try to complete itself, not by shortening the iron, but by lengthening it; by pushing the piece of iron out so as to afford more surface for leakage. That is exactly what happens; for, as you see, when I turn on the current, the little piece of iron shoots out and drops down. You see that little piece of iron shoot out with considerable force. It becomes a sort of magnetic popgun. This is an experiment which has been twice discovered. I found it first described by Count Du Moncel, in the pages of La Lumiere Electrique, under the name of the "pistolet electromagnetique;" and Mr. Shelford Bidwell invented it independently. I am indebted to him for the use of this apparatus. He gave an account of it to the Physical Society, in 1885, but the reporter missed it, I suppose, as there is no record in the society's proceedings.

ELECTROMAGNETS FOR USE WITH ALTERNATING CURRENTS.

When you are designing electromagnets for use with alternating currents, it is necessary to make a change in one respect, namely, you must so laminate the iron that internal eddy currents shall not occur; indeed, for all rapid-acting electromagnetic apparatus it is a good rule that the iron must not be solid. It is not usual with telegraphic instruments to laminate them by making up the core of bundles of iron plates or wires, but they are often made with tubular cores, that is to say, the cylindrical iron core is drilled with a hole down the middle, and the tube so formed is slit with a saw cut to prevent the circulation of currents in the substance of the tube. Now when electromagnets are to be employed with rapidly alternating currents, such as are used for electric lighting, the frequency of the alternations being usually about 100 periods per second, slitting the cores is insufficient to guard against eddy currents; nothing short of completely laminating the cores is a satisfactory remedy. I have here, thanks to the Brush Electric Engineering Company, an electromagnet of the special form that is used in the Brush arc lamp when required for the purpose of working in an alternating current circuit. It has two bobbins that are screwed up against the top of an iron box at the head of the lamp. The iron slab serves as a kind of yoke to carry the magnetism across the top. There are no fixed cores In the bobbins, which are entered by the ends of a pair of yoked plungers. Now in the ordinary Brush lamp for use with a steady current, the plungers are simply two round pieces of iron tapped into a common yoke; but for alternate current working this construction must not be used, and instead a U-shaped double plunger is used, made up of laminated iron, riveted together. Of course it is no novelty to use a laminated core; that device, first used by Joule, and then by Cowper, has been repatented rather too often during the past fifty years to be considered as a recent invention.

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