Chapter VII: AGRICULTURE.--The Spectral Masdevallia.--Illustration (3)

The conditions upon which the working of a well conceived dynamo machine must depend were next alluded to, and it was demonstrated that when losses by unnecessary wire resistance, by Foucault currents, and by induced currents in the rotating armature were avoided, as much as 90 per cent., or even more, of the power communicated to the machine was realized in the form of electric energy, and that _vice versa_ the reconversion of electric into mechanical energy could be accomplished with similarly small loss. Thus, by means of two machines at a moderate distance apart, nearly 80 per cent, of the power imparted to one machine could be again yielded in the mechanical form by the second, leaving out of consideration frictional losses, which latter need not be great, considering that a dynamo machine had only one moving part well balanced, and was acted upon along its entire circumference by propelling force. Jacobi had proved, many years ago, that the maximum efficiency of a magneto-electric engine was obtained when

e / E = w / W = ½

which law had been frequently construed, by Verdet (Theorie Mecanique de la Chaleur) and others, to mean that one-half was the maximum theoretical efficiency obtainable in electric transmission of power, and that one half of the current must be necessarily wasted or turned into heat. The lecturer could never be reconciled to a law necessitating such a waste of energy, and had maintained, without disputing the accuracy of Jacobi's law, that it had reference really to the condition of maximum work accomplished with a given machine, whereas its efficiency must be governed by the equation:

e / E = w / W = nearly 1

From this it followed that the maximum yield was obtained when two dynamo machines (of similar construction) rotated nearly at the same speed, but that under these conditions the amount of force transmitted was a minimum. Practically the best condition of working consisted in giving to the primary machine such proportions as to produce a current of the same magnitude, but of 50 per cent, greater electromotive force than the secondary; by adopting such an arrangement, as much as 50 per cent, of the power imparted to the primary could be practically received from the secondary machine at a distance of several miles. Professor Silvanus Thompson, in his recent Cantor Lectures, had shown an ingenious graphical method of proving these important fundamental laws.

The possibility of transmitting power electrically was so obvious that suggestions to that effect had been frequently made since the days of Volta, by Ritchie, Jacobi, Henry, Page, Hjorth, and others; but it was only in recent years that such transmission had been rendered practically feasible.

Just six years ago, when delivering his presidential address to the Iron and Steel Institute, the lecturer had ventured to suggest that "time will probably reveal to us effectual means of carrying power to great distances, but I cannot refrain from alluding to one which is, in my opinion, worthy of consideration, namely, the electrical conductor. Suppose water power to be employed to give motion to a dynamo-electrical machine, a very powerful electrical current will be the result, which may be carried to a great distance, through a large metallic conductor, and then be made to impart motion to electromagnetic engines, to ignite the carbon points of electric lamps, or to effect the separation of metals from their combinations. A copper rod 3 in. in diameter would be capable of transmitting 1,000 horse power a distance of say thirty miles, an amount sufficient to supply one-quarter of a million candle power, which would suffice to illuminate a moderately-sized town." This suggestion had been much criticised at the time, when it was still thought that electricity was incapable of being massed so as to deal with many horse power of effect, and the size of conductor he had proposed was also considered wholly inadequate. It would be interesting to test this early calculation by recent experience. Mr. Marcel Deprez had, it was well known, lately succeeded in transmitting as much as three horse power to a distance of 40 kilometers (25 miles) through a pair of ordinary telegraph wires of 4 millimeters in diameter. The results so obtained had been carefully noted by Mr. Tresca, and had been communicated a fortnight ago to the French Academy of Sciences. Taking the relative conductivity of iron wire employed by Deprez, and the 3 in. rod proposed by the lecturer, the amount of power that could be transmitted through the latter would be about 4,000 horse power. But Deprez had employed a motor-dynamo of 2,000 volts, and was contented with a yield of 32 per cent. only of the energy imparted to the primary machine, whereas he had calculated at the time upon an electromotive force of 200 volts, and upon a return of at least 40 per cent. of the energy imparted. In March, 1878, when delivering one of the Science Lectures at Glasgow, he said that a 2 in. rod could be made to accomplish the object proposed, because he had by that time conceived the possibility of employing a current of at least 500 volts. Sir William Thomson had at once accepted these views, and with the conceptive ingenuity peculiar to himself, had gone far beyond him, in showing before the Parliamentary Electric Light Committee of 1879, that through a copper wire of only ½ in. diameter, 21,000 horse power might be conveyed to a distance of 300 miles with a current of an intensity of 80,000 volts. The time might come when such a current could be dealt with, having a striking distance of about 12 ft. in air, but then, probably, a very practical law enunciated by Sir William Thomson would be infringed. This was to the effect that electricity was conveyed at the cheapest rate through a conductor, the cost of which was such that the annual interest upon the money expended equaled the annual expenditure for lost effect in the conductor in producing the power to be conveyed. It appeared that Mr. Deprez had not followed this law in making his recent installations.

Sir William Armstrong was probably first to take practical, advantage of these suggestions in lighting his house at Cragside during night time, and working his lathe and saw bench during the day, by power transmitted through a wire from a waterfall nearly a mile distant from his mansion. The lecturer had also accomplished the several objects of pumping water, cutting wood, hay, and swedes, of lighting his house, and of carrying on experiments in electro-horticulture from a common center of steam power. The results had been most satisfactory; the whole of the management had been in the hands of a gardener and of laborers, who were without previous knowledge of electricity, and the only repairs that had been found necessary were one renewal of the commutators and an occasional change of metallic contact brushes.

An interesting application of electric transmission to cranes, by Dr. Hopkinson, was shown in operation.

Among the numerous other applications of the electrical transmission of power, that to electrical railways, first exhibited by Dr. Werner Siemens, at the Berlin Exhibition of 1879, had created more than ordinary public attention. In it the current produced by the dynamo machine, fixed at a convenient station and driven by a steam engine or other motor, was conveyed to a dynamo placed upon the moving car, through a central rail supported upon insulating blocks of wood, the two working rails serving to convey the return current. The line was 900 yards long, of 2 ft gauge, and the moving car served its purpose of carrying twenty visitors through the exhibition each trip. The success of this experiment soon led to the laying of the Lichterfelde line, in which both rails were placed upon insulating sleepers, so that the one served for the conveyance of the current from the power station to the moving car, and the other for completing the return circuit. This line had a gauge of 3 ft. 3 in., was 2,500 yards in length, and was worked by two dynamo machines, developing an aggregate current of 9,000 watts, equal to 12 horse power. It had now been in constant operation since May 16, 1881, and had never failed in accomplishing its daily traffic. A line half a kilometer in length, but of 4 ft. 8½ in. gauge was established by the lecturer at Paris in connection with the Electric Exhibition of 1881. In this case, two suspended conductors in the form of hollow tubes with a longitudinal slit were adopted, the contact being made by metallic bolts drawn through these slit tubes, and connected with the dynamo machine on the moving car by copper ropes passing through the roof. On this line 95,000 passengers were conveyed within the short period of seven weeks.

An electric tramway, six miles in length, had just been completed, connecting Portrush with Bush Mills, in the north of Ireland, in the installation of which the lecturer was aided by Mr. Traill, as engineer of the company by Mr. Alexander Siemens, and by Dr. E. Hopkinson, representing his firm. In this instance the two rails, 3 ft. apart, were not insulated from the ground, but were joined electrically by means of copper staples and formed the return circuit, the current being conveyed to the car through a T iron placed upon short standards, and insulated by means of insulate caps. For the present the power was produced by a steam engine at Portrush, giving motion to a shunt-wound dynamo of 15,000 watts=20 horse power, but arrangements were in progress to utilize a waterfall of ample power near Bush Mills, by means of three turbines of 40 horse power each, now in course of erection. The working speed of this line was restricted by the Board of Trade to ten miles an hour, which was readily obtained, although the gradients of the line were decidedly unfavorable, including an incline of two miles in length at a gradient of 1 in 38. It was intended to extend the line six miles beyond Bush Mills, in order to join it at Dervock station with the north of Ireland narrow gauge railway system.

The electric system of propulsion was, in the lecturer's opinion, sufficiently advanced to assure practical success under suitable circumstances--such as for suburban tramways, elevated lines, and above all lines through tunnels; such as the Metropolitan and District Railways. The advantages were that the weight, of the engine, so destructive of power and of the plant itself in starting and stopping, would be saved, and that perfect immunity from products of combustion would be insured The experience at Lichterfelde, at Paris, and another electric line of 765 yards in length, and 2 ft. 2 in. gauge, worked in connection with the Zaukerode Colliery since October, 1882, were extremely favorable to this mode of propulsion. The lecturer however did not advocate its prospective application in competition with the locomotive engine for main lines of railway. For tramways within populous districts, the insulated conductor involved a serious difficulty. It would be more advantageous under these circumstances to resort to secondary batteries, forming a store of electrical energy carried under the seats of the car itself, and working a dynamo machine connected with the moving wheels by means of belts and chains.

The secondary battery was the only available means of propelling vessels by electrical power, and considering that these batteries might be made to serve the purpose of keel ballast, their weight, which was still considerable, would not be objectionable. The secondary battery was not an entirely new conception. The hydrogen gas battery suggested by Sir Wm. Grove in 1841, and which was shown in operation, realized in the most perfect manner the conception of storage, only that the power obtained from it was exceedingly slight. The lecturer, in working upon Sir Wm. Grove's conception, had twenty-five years ago constructed a battery of considerable power in substituting porous carbon for platinum, impregnating the same with a precipitate of lead peroxidized by a charging current. At that time little practical importance attached however to the object, and even when Plante, in 1860, produced his secondary battery, composed of lead plates peroxidized by a charging current, little more than scientific curiosity was excited. It was only since the dynamo machine had become an accomplished fact that the importance of this mode of storing energy had become of practical importance, and great credit was due to Faure, to Sellon, and to Volckmar for putting this valuable addition to practical science into available forms. A question of great interest in connection with the secondary battery had reference to its permanence. A fear had been expressed by many that local action would soon destroy the fabric of which it was composed, and that the active surfaces would become coated with sulphate of lead, preventing further action. It had, however, lately been proved in a paper read by Dr. Frankland before the Royal Society, corroborated by simultaneous investigations by Dr. Gladstone and Mr. Tribe, that the action of the secondary battery depended essentially upon the alternative composition and decomposition of sulphate of lead, which was therefore not an enemy, but the best friend to its continued action.

In conclusion, the lecturer referred to electric nomenclature, and to the means for measuring and recording the passage of electric energy. When he addressed the British Association at Southampton, he had ventured to suggest two electrical units additional to those established at the Electrical Congress in 1881, viz.: the watt and the joule, in order to complete the chain of units connecting electrical with mechanical energy and with the unit quantity of heat. He was glad to find that this suggestion had met with a favorable reception, especially that of the watt, which was convenient for expressing in an intelligible manner the effective power of a dynamo machine, and for giving a precise idea of the number of lights or effective power to be realized by its current, as well as of the engine power necessary to drive it; 746 watts represented 1 horse-power.

Finally, the watt meter, an instrument recently developed by his firm, was shown in operation. This consisted simply of a coil of thick conductor suspended by a torsion wire, and opposed laterally to a fixed coil of wire of high resistance. The current to be measured flowed through both coils in parallel circuit, the one representing its quantity expressible in amperes, and the other its potential expressible in volts. Their joint attractive action expressed therefore volt-amperes or watts, which were read off upon a scale of equal divisions.

The lecture was illustrated by experiments, and by numerous diagrams and tables of results. Measuring instruments by Professors Ayrton and Perry, by Mr. Edison and by Mr. Boys, were also exhibited.

* * * * *

ON THE PREPARATION OF GELATINE PLATES.

[Footnote: Being an abstract of the introductory lecture to a course on photography at the Polytechnic Institute, November 11.]

By E. HOWARD FARMER, F.C.S.

Since the first announcement of these lectures, our Secretary has asked me to give a free introductory lecture, so that all who are interested in the subject may come and gather a better idea as to them than they can possibly do by simply leading a prospectus. This evening, therefore, I propose to give first a typical lecture of the course, and secondly, at its conclusion, to say a few words as to our principal object. As the subject for this evening's lecture I have chosen, "The Preparation of Gelatine Plates," as it is probably one of very general interest to photographers.

Before preparing our emulsion, we must first decide upon the particular materials we are going to use, and of these the first requisite is nitrate of silver. Nitrate of silver is supplied by chemists in three principal conditions:

1. The ordinary crystallized salt, prepared by dissolving silver in nitric acid, and evaporating the solution until the salt crystallizes out. This sample usually presents the appearance of imperfect crystals, having a faint yellowish tinge, and a strong odor of nitrous fumes, and contains, as might be expected, a considerable amount of free acid.

2. Fused nitrate, or "lunar caustic," prepared by fusing the crystallized salt and casting it into sticks. Lunar caustic is usually alkaline to test paper.

3. Recrystallized silver nitrate, prepared by redissolving the ordinary salt in distilled water, and again evaporating to the crystallizing point. By this means the impurities and free acid are removed.

I have a specimen of this on the table, and it consists, as you observe, of fine crystals which are perfectly colorless and transparent; it is also perfectly neutral to test paper. No doubt either of these samples can be used with success in preparing emulsions, but to those who are inexperienced, I recommend that the recrystallized salt be employed. We make, then, a solution of recrystallized silver nitrate in distilled water, containing in every 12 ounces of solution 1¼ ounces of the salt.

The next material we require is a soluble bromide. I have here specimens of various bromides which can be employed, such as ammonium, potassium, barium, and zinc bromides; as a rule, however, either the ammonium or potassium salt is used, and I should like to say a few words respecting the relative efficiency of these two salts.

1. As to ammonium bromide. This substance is a highly unstable salt. A sample of ammonium bromide which is perfectly neutral when first prepared will, on keeping, be found to become decidedly acid in character. Moreover, during this decomposition, the percentage of bromine does not remain constant; as a rule, it will be found to contain more than the theoretical amount of bromine. Finally, all ammonium salts have a most destructive action on gelatine; if gelatine, which has been boiled for a short time with either ammonium bromide or ammonium nitrate, be added to an emulsion, it will be found to produce pink fog--and probably frilling--on plates prepared with the emulsion. For these reasons, I venture to say that ammonium bromide, which figures so largely in formulæ for gelatine emulsions, is one of the worst bromides that can be employed for that purpose, and is, indeed, a frequent source of pink fog and frilling.

2. As to potassium bromide. This is a perfectly stable substance, can be readily obtained pure, and is constant in composition; neither has it (nor the nitrate) any appreciable destructive action on gelatine. We prepare, then, a solution of potassium bromide in water containing in every 12 ounces of solution 1 ounce of the salt. On testing it with litmus paper, the solution may be either slightly alkaline or neutral; in either case, it should be faintly acidified with hydrochloric acid.

The last material we require is the gelatine, one of the most important, and at the same time the most difficult substance to obtain of good quality. I have various samples here--notably Nelson's No. 1 and "X opaque;" Coignet's gold medal; Heinrich's; the Autotype Company's; and Russian isinglass.

The only method I know of securing a uniform quality of gelatine is to purchase several small samples, make a trial emulsion with each, and buy a stock of the sample which gives the best results. To those who do not care to go to this trouble, equal quantities of Nelson's No. 1 and X opaque, as recommended by Captain Abney, can be employed. Having selected the gelatine, 1¼ ounces should be allowed to soak in water, and then melted, when it will be found to have a bulk of about 6 ounces.

In order to prepare our emulsion, I take equal bulks of the silver nitrate and potassium bromide solutions in beakers, and place them in the water bath to get hot. I also take an equal bulk of hot water in a large beaker, and add to it one-half an ounce of the gelatine solution to every 12 ounces of water. Having raised all these to about 180° F., I add (as you observe) to the large beaker containing the dilute gelatine a little of the bromide, then, through a funnel having a fine orifice, a little of the silver, swirling the liquid round during the operation; then again some bromide and silver, and so on until all is added.

When this is completed, a little of the emulsion is poured on a glass plate, and examined by transmitted light; if the mixing be efficient, the light will appear--as it does here--of an orange or orange red color.

It will be observed that we keep the bromide in excess while mixing. I must not forget to mention that to those experienced in mixing, by far the best method is that described by Captain Abney in his Cantor lectures, of keeping the silver in excess.

The emulsion, being properly mixed, has now to be placed in the water bath, and kept at the boiling point for forty-five minutes. As, obviously, I cannot keep you waiting while this is done, I propose to divide our emulsion into two portions, allowing one portion to stew, and to proceed with the next operation with the remainder.

Supposing, then, this emulsion has been boiled, it is placed in cold water to cool. While it is cooling, let us consider for a moment what takes place during the boiling. It is found that during this time the emulsion undergoes two remarkable changes:

1. The molecules of silver bromide gradually aggregate together, forming larger and larger particles.

2. The emulsion increases rapidly in sensitiveness. Now what is the cause, in the first place, of this aggregation of molecules: and, in the second place, of the increase of sensitiveness? We know that the two invariably go together, so that we are right in concluding that the same cause produces both.

It might be thought that heat is the cause, but the same changes take place more slowly in the cold, so we can only say that heat accelerates the action, and hence must conclude that the prime cause is one of the materials in the emulsion itself.

Now, besides the silver bromide, we have in the emulsion water, gelatine, potassium nitrate, and a small excess of potassium bromide; and in order to find which of these is the cause, we must make different emulsions, omitting in succession each of these materials. Suppose we take an emulsion which has just been mixed, and, instead of boiling it, we precipitate the gelatine and silver bromide with alcohol; on redissolving the pellicle in the same quantity of water, we have an emulsion the same as previously, with the exception that the niter and excess of potassium bromide are absent. If such an emulsion be boiled, we shall find the remarkable fact that, however long it be boiled, the silver bromide undergoes no change, neither does the emulsion become any more sensitive. We therefore conclude, that either the niter or the small excess of potassium bromide, or both together, produce the change.

Now take portions of a similarly washed emulsion, and add to one portion some niter, and to another some potassium bromide; on boiling these we find that the one containing niter does not change, while that containing the potassium bromide rapidly undergoes the changes mentioned.

Here, then, by a direct appeal to experiment, we prove that to all appearance comparatively useless excess of potassium bromide is really one of the most important constituents of the emulsion.

The following table gives some interesting results respecting this action of potassium bromide:

__________________________________________________________
Excess of potash bromide. | Time to acquire maximum |
| sensitiveness. |
--------------------------+------------------------------+
0.2 grain per ounce | no increase after six hours. |
2.0 " " | about one-half an hour. |
20.0 " " | seven minutes. |
--------------------------+------------------------------+

I must here leave the _rationale_ of the process for the present, and proceed with the next operation.

Our emulsion being cold, I add to it, for every 6 ounces of mixed emulsion, 1 ounce of a saturated cold solution of potassium bichromate; then, gently swirling the mixture round, a few drops of a dilute (1 to 8) solution of hydrochloric acid, and place it on one side for a minute or two.

When hydrochloric acid is added to bichromate of potash, chromic acid is liberated. Now, chromic acid has the property of precipitating gelatine, so that what I hope to have done is to have precipitated the gelatine in this emulsion, and which will carry down the silver bromide as well. You see here I can pour off the supernatant liquid clear, leaving our silver and gelatine as a clot at the bottom of the vessel.

Another action of chromic acid is, that it destroys the action of light on silver bromide, so that up to this point operations can be carried on in broad daylight.

The precipitated emulsion is now taken into the dark room and washed until the wash water shows no trace of color; if there be a large quantity, this is best done on a fine muslin filter; if a small quantity, by decantation.

Having been thoroughly washed, I dissolve the pellicle in water by immersing the beaker containing it in the water bath. I then add the remaining gelatine, and make up the whole with 3 ounces of alcohol and water to 30 ounces for the quantities given. I pass the emulsion through a funnel containing a pellet of cotton wool in order to filter it, and it is ready for coating the plates.

To coat a plate, I place it on this small block of leveled wood, and pour on down a glass rod a small quantity of the emulsion, and by means of the rod held horizontally, spread it over the plate. I then transfer the plate to this leveled slab of plate glass, in order that the emulsion on it may set. As soon as set, it is placed in the drying box.

This process, as here described, does not give plates of the highest degree of sensitiveness, to attain which a further operation is necessary; they are, however, of exceedingly good quality, and very suitable for landscape work.--_Photo. News_.

* * * * *

PICTURES ON GLASS.

The invention of M. E. Godard, of Paris, has for its object the reproduction of images and drawings, by means of vitrifiable colors on glass, wood, stone, on canvas or paper prepared for oil-painting and on other substances having polished surfaces, e. g., earthenware, copper, etc. The original drawings or images should be well executed, and drawn on white, or preferably bluish paper, similar to paper used for ordinary drawings. In the patterns for glass painting, by this process, the place to be occupied is marked by the lead, before cutting the glass to suit the various shades which compose the color of a panel, as is usually done in this kind of work; the operation changes only when the glass cutter hands these sheets over to the man who undertakes the painting. The sheets of glass are cut according to the lines of the drawing, and after being well cleaned, they are placed on the paper on the places for which they have been cut out. If the window to be stained is of large size and consists of several panels, only one panel is proceeded with at a time. The glass is laid on the reverse side of the paper (the side opposite to the drawing), the latter having been made transparent by saturating it with petroleum. This operation also serves to fix the outlines of the drawing more distinctly, and to give more vigor to the dark tone of the paper. When the paper is thus prepared, and the sheets of glass each in its place, they are coated by means of a brush with a sensitizing solution on the side which comes into contact with the paper. This coating should be as thin and as uniform as possible on the surface of the glass. For more perfectly equalizing the coating, a second brush is used.

The sensitizing solution which serves to produce the verifiable image is prepared as follows: Bichromate of ammonia is dissolved in water till the latter is saturated; five grammes of powdered dextrin or glucose are then dissolved in 100 grammes of water; to either of these solutions is added 10 per cent. of the solution of bichromate, and the mixture filtered.

The coating of the glass takes place immediately afterward in a dark room; the coated sheets are then subjected to a heat of 50° or 60° C. (120° to 140° Fahr.) in a small hot chamber, where they are laid one after the other on a wire grating situated 35 centimeters above the bottom. Care should be taken not to introduce the glass under treatment into the hot chamber before the required degree of heat has been obtained. A few seconds are sufficient to dry each sheet, and the wire grating should be large enough to allow of the dried glass being laid in rows, on one side where the heat is less intense. For the reproduction of the pictures or images a photographic copying frame of the size of the original is used. A stained glass window being for greater security generally divided into different panels, the size of one panel is seldom more than one square meter. If the picture to be reproduced should be larger in size than any available copying frame, the prepared glass sheets are laid between two large sheets of plate-glass, and part after part is proceeded with, by sliding the original between the two sheets. A photographic copying frame, however, is always preferable, as it presses the glass sheets better against the original. The original drawing is laid fiat on the glass of the frame. The lines where the lead is to connect the respective sheets of glass are marked on the drawing with blue or red pencil. The prepared sheets of glass are then placed one after the other on the original in their respective places, so that the coated side comes in contact with the original. The frame is then closed. It should be borne in mind that the latter operations must be performed in the dark room. The closed frame is now exposed to light. If the operations are performed outdoors, the frame is laid flat, so that the light falls directly on it; if indoors, the frame is placed inclined behind a window, so that it may receive the light in front. The time necessary for exposing the frame depends upon the light and the temperature; for instance, if the weather is fine and cloudless and the temperature from 16° to 18° C. (60° to 64° Fahr.), it will require from 12 to 15 minutes.

It will be observed that the time of exposure also depends on the thickness of the paper used for the original. If, however, the weather is dark, it requires from 30 to 50 minutes for the exposure. It will be observed that if the temperature is above 25° C. (about 80° Fahr.), the sheets of glass should be kept very cool and be less dried; otherwise, when exposed the sheets are instantly metallized, and the reproduction cannot take place. The same inconvenience takes place if the temperature is beneath 5° C. (41° Fahr.). In this case the sheets should be kept warm, and care should be taken not to expose the frame to the open air, but always behind a glass window at a temperature of from 14° to 18° C. (about 60° Fahr.). The time necessary for the exposure can be ascertained by taking out one of the many pieces of glass, applying to the sensitive surface a vitrifiable color, and observing whether the color adheres well. If the color adheres but slightly to the dark, shady portions of the image, the exposure has been too long, and the process must be recommenced; if, on the contrary, the color adheres too well, the exposure has not been sufficient, the frames must be closed again, and the exposure continued. When the frame has been sufficiently exposed, it is taken into the dark room, the sensitized pieces of glass laid on a plate of glass or marble with the sensitive surface turned upward, and the previously prepared vitrifiable color strewed over it by means of a few light strokes of a brush. This powder does not adhere to the parts of the picture fully exposed to light, but adheres only to the more or less shady portions of the picture. This operation develops on the glass the image as it is on the paper. Thirty to 40 grammes of nitric acid are added to 1,000 grammes of wood-spirit, such as is generally used in photography, and the prepared pieces of glass are dipped into the bath, leaving them afterward to dry. If the bath becomes of a yellowish color, it must be renewed. This bath has for its object to remove the coating of bichromate, so as to allow the color to adhere to the glass, from which it has been separated by the layer of glucose and bichromate, which would prevent the vitrification. The bath has also for its object to render the light parts of the picture perfectly pure and capable of being easily retouched or painted by hand. The application of variously colored enamels and the heating are then effected as in ordinary glass painting. The same process may be applied to marble, wood, stone, lava, canvas prepared for oil painting, earthenware, pure or enameled iron. The result is the same in all cases, and the process is the same as with glass, with the difference only that the above named materials are not dipped into the bath, but the liquid is poured over the objects after the latter have been placed in an inclined position.

* * * * *

PREPARATION OF HYDROGEN SULPHIDE FROM COAL-GAS.

By I. TAYLOR, B.A., Science Master at Christ College, Brecon.

Hydrogen sulphide may be prepared very easily, and sufficiently pure for ordinary analytical purposes, by passing coal-gas through boiling sulphur. Coal-gas contains 40 to 50 per cent, of hydrogen, nearly the whole of which may, by means of a suitable arrangement, be converted into sulphureted hydrogen. The other constituents of coal-gas--methane, carbon monoxide, olefines, etc.--are not affected by passing through boiling sulphur, and for ordinary laboratory work their removal is quite unnecessary, as they do not in any way interfere with the precipitation of metallic sulphides.

A convenient apparatus for the preparation of hydrogen sulphide from coal-gas, such as we have at present in use in the Christ College laboratory, consists of a retort, R, in which sulphur is placed. Through the tubulure of the retort there passes a bent glass-tube, T E, perforated near the closed end, F, with a number of small holes. (The perforations are easily made by piercing the partially softened glass with a white-hot steel needle; an ordinary crotchet needle, the hook having been removed and the end sharpened, answers the purpose very well.) The end, T, of the glass tube is connected by caoutchouc tubing with the coal-gas supply, the perforated end dipping into the sulphur. The neck of the retort, inclined slightly upward to allow the condensed sulpur, as it remelts, to flow back, is connected with awash bottle, B, to which is attached the flask, F, containing the solution through which it is required to pass the hydrogen sulphide; F is connected with an aspirator, A.

About one pound of sulphur having been introduced into the retort and heated to the boiling-point, the tap of the aspirator is turned on and a current of coal-gas drawn through the boiling sulphur; the hydrogen sulphide formed is washed by the water contained in B, passes on into F, and finally into the aspirator. The speed of the current may be regulated by the tap, and as the aspirator itself acts as a receptacle for excess of gas, very little as a rule escapes into the room, and consequently unpleasant smells are avoided.

This method of preparing sulphureted hydrogen will, I think, be found useful in the laboratory. It is cleanly, much cheaper than the ordinary method, and very convenient. During laboratory work, a burner is placed under the retort and the sulphur kept hot, so that its temperature may be quickly raised to the boiling-point when the gas is required. From time to time it is necessary to replenish the retort with sulphur and to remove the condensed portions from the neck.--_Chem. News_.

* * * * *

"SETTING" OF GYPSUM.--This setting is the result of two distinct, though simultaneous, phenomena. On the one hand, portions of anhydrous calcium sulphate, when moistened with water, dissolve as they are hydrated, forming a supersaturated solution. On the other hand, this same solution deposits crystals of the hydrated sulphate, gradually augment in bulk, and unite together.--_H. Le Chatellier_.

* * * * *

[Continued from SUPPLEMENT No. 383, page 6118.]

MALARIA.

By JAMES H. SALISBURY, A.M., M.D.

PRIZE ESSAY OF THE ALBANY MEDICAL COLLEGE ALUMNI ASSOCIATION, FEB., 1882.

VII.

I have made careful microscopic examinations of the blood in several cases of Panama fever I have treated, and find in all severe cases many of the colorless corpuscles filled more or less with spores of ague vegetation and the serum quite full of the same spores (see Fig. N, Plate VIII.).

Mr. John Thomas. Panama fever. Vegetation in blood and colorless corpuscles. (Fig N, Plate VIII.) Vegetation, spores of, in the colorless corpuscles of the blood. Spores in serum of blood adhering to fibrin filaments.

Mr. Thomas has charge of the bridge building on the Tehuantepec Railroad. Went there about one year ago. Was taken down with the fever last October. Returned home in February last, all broken down. Put him under treatment March 15, 1882. Gained rapidly (after washing him out with hot water, and getting his urine clear and bowels open every day) on two grains of quinia every day, two hours, till sixteen doses were taken. After an interval of seven days, repeated the quinia, and so on. This fever prevails on all the low lands, as soon as the fresh soil is exposed to the drying rays of the sun. The vegetation grows on the drying soil, and the spores rise in the night air, and fall after sunrise. All who are exposed to the night air, which is loaded with the spores, suffer with the disease. The natives of the country suffer about as badly as foreigners. Nearly half of the workmen die of the disease. The fever is a congestive intermittent of a severe type.

Henry Thoman. Leucocythæmia. Spleen 11 inches in diameter, two white globules to one red. German. Thirty-six years of age. Weight, 180 pounds. Colorless corpuscles very large and varying much in size, as seen at N. Corpuscles filled--many of them--with the spores of ague vegetation. Also spores swimming in serum.

This man has been a gardener back of Hoboken on ague lands, and has had ague for two years preceding this disease.

I will now introduce a communication made to me by a medical gentleman who has followed somewhat my researches for many years, and has taken great pains of time and expense to see if my researches are correct.

REPORT ON THE CAUSE OF AGUE.--BY DR. EPHRAIM CUTTER, TO THE WRITER

At your request I give the evidence on which I base my opinion that your plan in relation to ague is true.

From my very start into the medical profession, I had a natural intense interest in the causes of disease, which was also fostered by my father, the late Dr. Cutter, who honored his profession nearly forty years. Hence, I read your paper on ague with enthusiasm, and wrote to you for some of the plants of which you spoke. You sent me six boxes containing soil, which you said was full of the gemiasmas. You gave some drawings, so that I should know the plants when I saw them, and directed me to moisten the soil with water and expose to air and sunlight. In the course of a few days I was to proceed to collect. I faithfully followed the instructions, but without any success. I could detect no plants whatever,

This result would have settled the case ordinarily, and I would have said that you were mistaken, as the material submitted by yourself failed as evidence. But I thought that there was too much internal evidence of the truth of your story, and having been for many years an observer in natural history, I had learned that it is often very difficult for one to acquire the art of properly making examinations, even though the procedures are of the simplest description. So I distrusted, not you, but myself, and hence, you may remember, I forsook all and fled many hundred miles to you from my home with the boxes you had sent me. In three minutes after my arrival you showed me how to collect the plants in abundance from the very soil in the boxes that had traveled so far backward and forward, from the very specimens on which I had failed to do so.

The trouble was with me--that I went too deep with my needle. You showed me it was simply necessary to remove the slightest possible amount on the point of a cambric needle; deposit this in a drop of clean water on a slide cover with, a covering glass and put it under your elegant 1/5 inch objective, and there were the gemiasmas just as you had described.

I have always felt humbled by this teaching, and I at the time rejoiced that instead of denouncing you as a cheat and fraud (as some did at that time), I did not do anything as to the formation of an opinion until I had known more and more accurately about the subject.

I found all the varieties of the palmellæ you described in the boxes, and I kept them for several years and demonstrated them as I had opportunity. You also showed me on this visit the following experiments that I regarded as crucial:

1st. I saw you scrape from the skin of an ague patient sweat and epithelium with the spores and the full grown plants of the Gemiasma verdans.

2d. I saw you take the sputa of a ague patient and demonstrate the spores and sporangia of the Gemiasma verdans.

3d. I saw you take the urine of a female patient suffering from ague (though from motives of delicacy I did not see the urine voided--still I believe that she did pass the urine, as I did not think it necessary to insult the patient), and you demonstrated to me beautiful specimens of Gemiasma rubra. You said it was not common to find the full development in the urine of such cases, but only in the urine of the old severe cases. This was a mild case.

4th. I saw you take the blood from the forearm of an ague patient, and under the microscope I saw you demonstrate the gemiasma, white and bleached in the blood. You said that the coloring matter did not develop in the blood, that it was a difficult task to demonstrate the plants in the blood, that it required usually a long and careful search of hours sometimes, and at other times the plants would be obtained at once.

When I had fully comprehended the significance of the experiments I was filled with joy, and like the converts in apostolic times I desired to go about and promulgate the news to the profession. I did so in many places, notably in New York city, where I satisfactorily demonstrated the plants to many eminent physicians at my room at the Fifth Avenue Hotel; also before a medical society where more than one hundred persons were present. I did all that I could, but such was the preoccupation of the medical gentlemen that a respectful hearing was all I got. This is not to be wondered at, as it was a subject, now, after the lapse of nearly a decade and a half, quite unstudied and unknown. After this I studied the plants as I had opportunity, and in 1877 made a special journey to Long Island, N.Y., for the purpose of studying the plants in their natural habitat, when they were in a state of maturity. I have also examined moist soils in localities where ague is occasionally known, with other localities where it prevails during the warm months.

Below I give the results, which from convenience I divide into two parts: 1st. Studies of the ague plants in their natural habitat. 2d. Studies of the ague plants in their unnatural habitat (parasitic). I think one should know the first before attempting the second.

_First_--Studies to find in their natural habitat the palmellæ described as the Gemiasma rubra, Gemiasma verdans, Gemiasma plumba, Gemiasma alba, Protuberans lamella.

_Second_--_Outfit_.--Glass slides, covers, needles, toothpicks, bottle of water, white paper and handkerchief, portable microscope with a good Tolles one inch eyepiece, and one-quarter inch objective.

Wherever there was found on low, marshy soil a white incrustation like dried salt, a very minute portion was removed by needle or toothpick, deposited on a slide, moistened with a drop of water, rubbed up with a needle or toothpick into a uniformly diffused cloud in and through the water. The cover was put on, and the excess of water removed by touching with a handkerchief the edge of the cover. Then the capillary attraction held the cover in place, as is well known. The handkerchief or white paper was spread on the ground at my feet, and the observation conducted at once after the collection and on the very habitat. It is possible thus to conduct observations with the microscope besides in boats on ponds or sea, and adding a good kerosene light in bed or bunk or on lounge.

August 11, 1877.--Excursion to College Point, Flushing, Long Island:

Observation 1. 1:50 P.M. Sun excessively hot. Gathered some of the white incrustation on sand in a marsh west of Long Island Railroad depot. Found some Gemiasma verdans, G. rubra; the latter were dry and not good specimens, but the field swarmed with the automobile spores. The full developed plant is termed sporangia, and seeds are called spores.

Observation 2. Another specimen from same locality, not good; that is, forms were seen but they were not decisive and characteristic.

Observation 3. Earth from Wallabout, near Naval Hospital, Brooklyn, Rich in spores (A) with automobile protoplasmic motions, (B) Gemiasma rubra, (C) G. verdans, very beautiful indeed. Plants very abundant.

Observation 4. Walking up the track east of L. I. R.R. depot, I took an incrustation near creek; not much found but dirt and moving spores.

Observation 5. Seated on long marsh grass I scraped carefully from the stalks near the roots of the grass where the plants were protected from the action of the sunlight and wind. Found a great abundance of mature Gemiasma verdans very beautiful in appearance.

_Notes_.--The time of my visit was most unfavorable. The best time is when the morning has just dawned and the dew is on the grass. One then can find an abundance, while after the sun is up and the air is hot the plants disappear; probably burst and scatter the spores in billions, which, as night comes on and passes, develop into the mature plants, when they may be found in vast numbers. It would seem from this that the life epoch of a gemiasma is one day under such circumstances, but I have known them to be present for weeks under a cover on a slide, when the slide was surrounded with a bandage wet with water, or kept in a culture box. The plants may be cultivated any time in a glass with a water joint. A, Goblet inverted over a saucer; B, filled with water; C, D, specimen of earth with ague plants.

Observation 6. Some Gemiasma verdaus; good specimens, but scanty. Innumerable mobile spores. Dried.

Observation 7. Red dust on gray soil. Innumerable mobile spores. Dried red sporangia of G. rubra.

Observation 8. White incrustation. Innumerable mobile spores. No plants.

Observation 9. White incrustation. Many minute algæ, but two sporangia of a pale pink color; another variety of color of gemiasma. Innumerable mobile spores.

Observation 10. Gemiasma verdans and G. rubra in small quantities. Innumerable mobile spores.

Observation 11. Specimen taken from under the shade of short marsh grass. Gemiasma exceedingly rich and beautiful. Innumerable mobile spores.

Observation 12. Good specimens of Gemiasma rubra. Innumerable spores present in all specimens.

Observation 13. Very good specimens of Protuberans lamella.

Observation 14. The same.

Observation 15. Dead Gemiasma verdans and rubra.

Observation 16. Collection very unpromising by macroscopy, but by microscopy showed many spores, mature specimens of Gemiasma rubra and verdans. One empty specimen with double walls.

Observation 17. Dry land by the side of railroad. Protuberans not abundant.

Observation 18. From side of ditch. Filled with mature Geraiasma verdans.

Observation 19. Moist earth near a rejected timber of the railroad bridge. Abundance of Gemiasma verdans, Sphærotheca Diatoms.

Observation 20. Scrapings on earth under high grass. Large mature specimens of Gemiasma rubra and verdans. Many small.

Observation 21. Same locality. Gemiasma rubra and verdans; good specimens.

Observation 22. A dry stem of a last year's annual plant lay in the ditch not submerged, that appeared as if painted red with iron rust. This redness evidently made up of Gemiasma rubra dried.

Observation 23. A twig submerged in a ditch was scraped. Gemiasma verdans found abundantly with many other things, which if rehearsed would cloud this story.

Observation 24. Scrapings from the dirty end of the stick (23) gave specimens of the beautiful double wall palmellæ and some empty G. verdans.

Observation 25. Stirred up the littoral margins of the ditch with stick found in the path, and the drip showed Gemiasma rubra and verdans mixed in with dirt, debris, other algae, fungi, infusoria, especially diatoms.

Observation 26. I was myself seized with sneezing and discharge running from nostrils during these examinations. Some of the contents of the right nostril were blown on a slide, covered, and examined morphologically. Several oval bodies, round algae, were found with the characteristics of G. verdans and rubra. Also some colorless sporangia, and spores abundantly present. These were in addition to the normal morphological elements found in the excretions.

Observation 27. Dried clay on margin of the river showed dry G. verdans.

Observation 28. Saline dust on earth that had been thrown out during the setting of a new post in the railroad bridge showed some Gemiasma alba.

Observation 29. The dry white incrustation found on fresh earth near railroad track entirely away from water, where it appeared as if white sugar or sand had been sprinkled over in a fine dust, showed an abundance of automobile spores and dry sporangia of G. rubra and verdans. It was not made up of salts from evaporation.

Observation 30. Some very thick, long, green, matted marsh grass was carefully separated apart like the parting of thick hair on the head. A little earth was taken from the crack, and the Protuberans lamella, the Gemiasma rubra and verdans found were beautiful and well developed.

Observation 31. Brooklyn Naval Hospital, August 12, 1877, 4 A.M. Called up by the Quartermaster. With Surgeon C. W. White, U.S.N., took (A) one five inch glass beaker, bottomless, (B) three clean glass slides, (C) chloride of calcium solution, [symbol: dra(ch)m] i to [symbol: ounce] i water. We went, as near as I could judge in the darkness, to about that portion of the wall that lies west of the hospital, southeast corner (now all filled up), where on the 10th of August previously I had found some actively growing specimens of the Gemiasma verdans, rubra, and protuberans. The chloride of calcium solution was poured into a glass tumbler, then rubbed over the inside and outside of the beaker. It was then placed on the ground, the rim of the mouth coming on the soil and the bottom elevated on an old tin pan, so that the beaker stood inclined at an angle of about forty-five degrees with the horizon. The slides were moistened, one was laid on a stone, one on a clod, and a third on the grass. Returned to bed, not having been gone over ten minutes.

At 6 A.M. collected and examined for specimens the drops of dew deposited. Results: In every one of the five instances collected the automobile spores, and the sporangia of the gemiasmas and the protuberans on both sides of slides and beaker. There were also spores and mycelial filaments of fungi, dirt, and zoospores. The drops of dew were collected with capillary tubes such as were used in Edinburgh for vaccine virus. The fluid was then preserved and examined in the naval laboratory. In a few hours the spores disappeared.

Observation 32. Some of the earth near the site of the exposure referred to in Observation 31, was examined and found to contain abundantly the Gemiasma verdans, rubra, Protuberans lamella, confirmed by three more observations.

Observation 33. In company with Surgeon F. M. Dearborne, U.S.N., in charge of Naval Hospital, the same day later explored the wall about marsh west of hospital. Found the area abundantly supplied with palmellæ, Gemiasma rubra, verdans, and Protuberans lamella, even where there was no incrustation or green mould. Made very many examinations, always finding the plants and spores, giving up only when both of us were overcome with the heat.