Chapter 8

Engine oil used to brighten smoke stacks, no matter with what painted, will cause blistering. Tallow and "japan drop black" mixed, and apply while stack is hot, with an occasional rubbing over with the same, will remain bright a long time.

Rust always contains dampness, and will feed on itself, extending underneath and destroying solidly painted surfaces. It is, therefore, necessary, in order to secure good results, that the rust should be killed before priming, or that the priming be so mixed that it will assimilate with the rust and prevent spreading.

Steel tanks will not rust as rapidly as iron, but the scale is more apt to flake off by the expansion and contraction of the metal, taking the paint with it.

Heated oil, or heated oil priming, will dry faster and be more penetrating than cold. I consider heated "boiled oil" and red lead the best primer for iron.

In regard to ornamentation, my _taste_ is governed by the fact that I work "by contract," and get no more for a highly ornate locomotive than I do for a plain one, therefore I like the _plain ones best_, and I hope that our "good brother Burch's" prophecy, that "the days of 'fancy locomotives' will return," will never be fulfilled until after I go out of the business. There is a happy medium between a hearse and a circus wagon, and the locomotive painter, when not tied down by "specifications," can produce a neat and handsomely painted engine without the "spread eagle" or "star spangled banner." My own ideas are in the direction of simple lines of striping, following the lines of the surfaces upon which they are drawn.

Finally, take all the time you can get, the more the better, and use _oil_ accordingly.

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"CRACKLE" GLASS.

An ingenious process of producing glass with an iced or crackled surface, suitable for many decorative purposes, has been invented in France by Bay. The product appears in the form of sheets or panes, one side of which is smooth or glossy, like common window glass, while the other is rough and filled with innumerable crevices, giving it the frozen or crackled appearance so much admired for many decorative purposes. This peculiar cracked surface is obtained by covering the surface of the sheet on the table with a thick coating of some coarse-grained flux mixed to form a paste, or with a coating of some more easily fusible glass, and then subjecting it to the action of a strong fire, either open or in a muffle. As soon as the coating is fused, and the table is red-hot, it is withdrawn and rapidly cooled. The superficial layer of flux separates itself in this operation from the underlying glass surface, and leaves behind the evidence of its attachment to the same in the form of numberless irregularities, scales, irregular crystal forms, etc., giving the glass surface the peculiar appearance to which the above name has been given. The rapid cooling of the glass may be facilitated with the aid of a stream of cold air, or by continuously projecting a spray of cold water upon it. By protecting certain portions of the glass surface from contact with the flux, with the use of a template of any ornamental or other desired form, these portions will retain their ordinary appearance, and will show the form of the design very strongly outlined beside the crackled surface. In this manner, letters, arabesque, and other patterns in white or colored glass can be produced with great ease and with fine effect.

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HOW MARBLES ARE MADE.

Marbles are named from the Latin word "_marmor_," by which similar playthings were known to the boys of Rome, 2,000 years ago. Some marbles are made of potter's clay and baked in an oven just as earthenware is baked, but most of them are made of a hard kind of a stone found in Saxony, Germany. Marbles are manufactured there in great numbers and sent to all parts of the world, even to China, for the use of the Chinese children.

The stone is broken up with a hammer into pieces, which are then ground round in a mill. The mill has a fixed slab of stone, with its surface full of little grooves or furrows. Above this a flat block of oak wood of the same size as the stone is made to turn round rapidly, and, while turning, little streams of water run in the grooves and keep the mill from getting too hot. About 100 pieces of the square pieces of stone are put in the grooves at once, and in a few minutes are made round and polished by the wooden block.

China and white marbles are also used to make the round rollers which have delighted the hearts of the boys of all nations for hundred of years. Marbles thus made are known to the boys as "chinas," or "alleys." Real china ones are made of porcelain clay, and baked like chinaware or other pottery. Some of them have a pearly glaze, and some are painted in various colors, which will not rub off, because they are baked in, just as the pictures are on the plates and other tableware.

Glass marbles are known as "agates." They are made of both clear and colored glass. The former are made by taking up a little melted glass on the end of an iron rod and making it round by dropping it into a round mould, which shapes it, or by whirling it around the head until the glass is made into a little ball.

Sometimes the figure of a dog or squirrel or a kitten or some other object is put on the end of the rod, and when it is dipped into the melted glass the glass runs all around it, and when the marble is done the animal can be seen shut up in it. Colored glass marbles are made by holding a bunch of glass rods in the fire until they melt; then the workmen twist them round into a ball or press them into a mould, so that when done the marble is marked with bands or ribbons of color. Real agates, which are the nicest of all marbles, are made in Germany, out of the stone called agate. The workmen chip the pieces of agate nearly round with hammers and then grind them round and smooth on grindstones.--_Philadelphia Times_.

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DRAWING-ROOM PHOTOGRAPHY.

Among the examples we have received are some which would certainly do credit to any professional artist, alike for the posing, lighting, and general treatment; indeed, we may say that some of the poses are of a high artistic order, and quite a relief from the conventional positions and accessories so frequently seen in professional work. The expressions secured are also, as a rule, unusually pleasing and natural. This is, no doubt, in a great measure due to the sitter feeling more at ease in the amateur friend's drawing room than in a stranger's studio. Particularly is this the case in some excellent work--full-length pictures--sent from the other side of the Atlantic, and taken in a room of very modest dimensions, and with only one window. Among the failures (if such they may be called) the chief fault lies in the lighting, and from either under or over exposure--the former chiefly arising when a landscape lens was used, and the latter when a portrait combination was employed. Some correspondents also complain of the long exposure that, in their case, had been imperative; but, curiously enough, with all the successful pictures a very brief exposure has always been mentioned, and generally with an exceedingly small window.

With a view to the further assistance of those who have met with difficulties, we recur again to the subject of the lighting, for upon this must entirely depend the success or failure in producing satisfactory results; and, as we explained in previous articles, unless proper _chiaroscuro_ is secured on the model, it will be impossible to obtain it in the picture. The chief defect in this respect has been either that the light has been too abrupt, and consequently the high lights are very white and the shadows heavy, giving the pictures an under-exposed appearance, or the face is devoid of shadow, one side being as light as the other; hence it lacks the roundness necessary to constitute a good picture. In most instances the former defect has arisen from the reflecting screen not being properly placed so as to reflect back the light in the right direction, or it has been too far from the model; hence it has lost the greater part of its value. It should be borne in mind that the nearer the sitter is to the source of light the nearer the reflector must be to him, and also that at whatever angle the light falls upon the reflector it is always thrown off at a corresponding one.

Now, supposing that the light falls upon the model at an angle of, say, 40°: we shall have to place our reflecting screen at somewhat the same angle, and the nearer it is approached the greater will be the effect produced. If the sitter be placed very close to the window and the reflector a long way off, or if it project the light in a wrong direction, it is manifest that in the resulting pictures the shadows will, of necessity, be heavy, and the negative will have an under-exposed appearance, however long may have been given, simply because there was no harmony in the lighting of the model. In the case where the picture has been flat it has arisen from the sitter being placed too far back from the window, so that the direct light falling upon him has been too feeble to produce any strong lights, and the reflector arranged so that it received a stronger illumination than the model, then reflecting it on to the latter, quite overpowering the dominant lights. The remedy for this is simply to bring the sitter more forward, so as to obtain a stronger dominant light.

With regard to the time of exposure: we must again impress upon the student the necessity for placing the sitter as close to the window as can be conveniently done, for then he will receive the strongest illumination; and, no matter how strong the shadows which may be produced, they can always be modified sufficiently by the judicious use of the reflector. Of course, in practice there is a limit as to the closeness the sitter can be placed, inasmuch as if too near there will not be room enough for the background. As we have before said, the effective light falling upon the sitter is governed by the amount of direct skylight to which he is exposed. For experiment, let any one seat himself, say, one foot from the window and sideways to it, and note the amount of sky that can be seen from this position, then take a seat six feet within the room, and note it from thence. The difference will be very marked indeed, and it will fully account for the long exposure that some have found imperative.

In our previous articles we directed special attention to the advantage accruing from arranging the sitter in such a position that he received as much direct light as possible, so that it practically helps to soften the shadows; hence the sitter should be placed so that he is turned as little away from the source of light as will enable the desired view of the face being obtained. That this may the more advantageously be done the camera should always be placed as close as possible to the side wall in which the window is situated. As an experiment illustrating the advantage of this: let a camera be placed close to the wall, then the sitter arranged so that from that point of view a three-quarter face is obtained, and it will be noticed that there is very little need of the reflector at all. Let a negative now be taken, and the camera brought, say, five feet into the room, and the sitter, without changing his seat, turned round until a similar view of the face is obtained from that point. It will now be seen that the shadows are very much deeper than before, and the reflector will have to be brought pretty close in order to overcome them; nevertheless they may be obtained quite as soft and harmonious as in the former case. Let a second negative now be taken, giving the same exposure as before, and it will be found that if the first one were correctly timed the second will be considerably under-exposed. Yet the sitter was at the same distance from the window in each case.

This shows the advisability of utilizing all the direct light it is possible to do, and thereby leaving as little as we can to be accomplished by the reflector. When the sitter is arranged to the best advantage at a window of ordinary size, fully exposed pictures can generally be obtained with a portrait lens (full opening) in fairly good light, on moderately sensitive plates, with one or two seconds' (or even less) exposure. If a longer exposure than this be necessary, it may fairly be assumed that the lighting has not been properly managed.--_British Journal of Photography_.

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A NEW METHOD OF PREPARING PHOTOGRAPHIC GELATINE EMULSION BY PRECIPITATION OF THE BROMIDE OF SILVER.

By FRANZ STOLZE, Ph.D.

I consider the method of precipitation described below as far superior to any other hitherto employed, particularly on account of its infallible certainty. I began at first with a thirtieth of the whole quantity of gelatine, and increased that quantity to a tenth without the precipitate forming with greater difficulty. The salts were dissolved in the usual quantity of water, the bromide of potassium was added to the separately-dissolved gelatine, and both solutions cooled in iced water. I soon found that even this was not necessary. I accelerated the solution of the salts by vigorous agitation, so that the temperature became so much lowered that, even after the addition of the warm gelatine, it still remained low enough to give the precipitate when mixed. The mixing took place gradually, all the usual precautionary measures being observed; such as pouring the silver solution into No. 2 in small quantities at a time, and constantly stirring, and the separation from the mother lye was complete.

The formula according to which I worked latterly was as follows:

SOLUTION I. Nitrate of silver...................... 463 grains. Water................................... 16¾ ounces.

SOLUTION II. Bromide of potassium................... 355 grains. Iodide of potassium..................... 15 grains. Gelatine................................ 46 grains. Water................................... 16¾ ounces.

After the mixing is completed the perfect separation of the precipitate takes place in four minutes at most. The clear fluid may be decanted off almost to the last drop, after which the precipitate is washed three times with water. In order to dissolve the precipitate pour over it a solution of 1.5 part of bromide of potassium in 100 parts of water, agitate, and then add a solution formed of 8 parts of ammonia of the usual strength in 600 parts of water. The emulsification will begin at once without any further heating. When now heated on the water bath--already at from 95° F to 104° F--the whole precipitate will be suspended, and thin films of the emulsion, when looked through, will have a grayish tint, but when dry they will appear partially red. Digestion at 104° F is continued--from half an hour to an hour is usually long enough--until the film, even when dry, remains violet through and through. The remaining gelatine, 450 grains dissolved in 16 ounces of warm water, is then added, filtered, and plates coated with the resultant emulsion. But if it be desired to prepare emulsion for storage, wash the precipitate finally with alcohol, and store it either under alcohol or dry it as usual. To use it dissolve in the manner described above and mix with gelatine.

The great advantages of this process are evident. Not only is the troublesome washing saved, but, what is more important, the great mass of the gelatine is added to the emulsion in a condition which secures to the film a hitherto unattainable firmness. Also, it enables one to prepare a keeping emulsion with a minimum of alcohol, and, since the quantity of gelatine in the original emulsion is so small, it dries, when it is not desired to keep it under alcohol, so much more rapidly, and thereby also furnishes a more constant preparation.

I am convinced that this process is as yet but in its infancy, and that it is susceptible of great improvement. From the purely theoretical standpoint, the property possessed by gelatine, of combining in sufficiently cold solutions with bromide of silver in the nascent state, and falling to the bottom in a flaky condition, is exceedingly interesting. Evidently this property plays a part in the preparation of emulsion which has not until now been recognized. I do not doubt that it may be possible to effect, by a sufficiently low temperature, precipitation even from solutions rich in gelatine, if experiments in that direction were set on foot. What influence variations in temperature may have upon the subsequent sensitiveness of the emulsion, and whether the action of the ammonia and the bromide of potassium is more energetic, in the absence of the elsewhere-present nitric salts, are questions which can only be answered after thorough examination; and the parts played by the various additions of iodide or chloride of silver in this method of emulsification must likewise also be ascertained by experiment. The object of this article is to point out this rich province for research, and to induce experimenters to turn their attention to it; for it is only after the behavior of emulsion under all these conditions has been thoroughly examined that we can hope to reap the best results from the new process.--_Wochenblatt_.

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TAYLOR'S FREEZING MICROTOME.

This microtome presents all the advantages of any plan heretofore employed in hardening animal or vegetable tissues for section cutting, while it has many advantages over all other devices employed for the same purpose.

Microscopists who are interested in the study of histology and pathology have long felt the necessity for a better method of freezing animal and vegetable tissue than has been heretofore at their command.

In hardening tissues by chemical agents, the tissues are more or less distorted by the solutions used, and the process is very slow. Ether and rhigolene have been employed with some degree of success, but both are expensive, and they cannot be used in the presence of artificial light, because of danger of explosion. Another disadvantage is that two persons are required to attend to the manipulations, one to force the vapor into the freezing box, while the other uses the section-cutting knife.

The moment the pumping of the ether or rhigolene ceases, the tissue operated on ceases to be frozen, so ephemeral is the degree of the cold obtained by these means.

The principal advantages to be obtained by the use of this microtome are, first, great economy in the method of freezing, and, second, celerity and certainty of freezing. With an expenditure of twenty-five cents, the tissues to be operated on can be kept frozen for several hours at a time.

Small objects immersed in gum solutions are frozen and in condition for cutting in less than one minute.

The method of using this microtome can be understood by reference to the illustration. A represents a revolving plane, by which the thickness of the section is regulated, in the center of which an insulated chamber is secured for freezing the tissue. It resembles a pill-box constructed of metal. A brass tube enters it on each side. The larger one is the supply tube, and communicates with the pail, a, situated on bracket, s, by means of the upper tube, t. To the smaller brass tube is attached the rubber tube, t b, which discharges the cold salt water into a pail placed under it. (See b.) The salt and water as it passes from pail, a, to pail, b, is at a temperature of about zero. The water should not be allowed to waste. It should be returned to the first pail for continual use, or as long as it has freezing properties. As a matter of further economy, it is necessary to limit the rate of exit of the freezing water. This is regulated by nipping the discharge-tube with the spring clothes pin supplied for the purpose. Should the cold within the chamber be too intense, the edge of the knife is liable to be turned and the cutting will be imperfect. When this occurs the flow of water through the chamber is stopped by using the spring clothes-pin as a clip on the upper tube. In order to regulate the thickness of the tissue to be cut a scale is engraved on the edge of the revolving plate, A, which, in conjunction with the pointer, e, indicates the thickness of the section.--_Microscopical Journal_.

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THE ST. GOTHARD TUNNEL.--It appears that the traffic through the St. Gothard Tunnel has increased, since the inauguration of through international services, to such an extent that the Company have already obtained sanction for laying the second pair of rails in the tunnel. The Great Eastern Railway Company has increased its steamer traffic, and built additional station accommodation at Harwich.

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VINCENT'S CHLORIDE OF METHYL ICE MACHINE.

Chloride of methyl was discovered in 1840 by Messrs. Dumas and Peligot, who obtained it by treating methylic alcohol with a mixture of sea salt and sulphuric acid. It is a gaseous product at ordinary temperature, but when compressed and cooled, easily liquefies and produces a colorless, neutral liquid which enters into ebullition at 237.7° above zero and under a pressure of 0.76 m.

Up to recent times, chloride of methyl in a free state had received scarcely any industrial application, by reason of the difficulty of preparing it in a state of purity at a low price. Mr. C. Vincent, however, has made known a process which permits of this product being obtained abundantly and cheaply. It consists in submitting to the action of heat the hydrochlorate of trimethylamine, which is obtained as a by-product in the manufacture of potash of beets. The hydrochlorate is thus decomposed into free trimethylamine, ammonia, and chloride of methyl. A washing with hydrochloric acid takes away all traces of alkali, and the gas, which is gathered under a receiver full of water, may afterward be dried by means of sulphuric acid, and be liquefied by pressure.

Pure liquid chloride of methyl is now an abundant product. There are two uses to which it is applied: first, for producing cold, and second, for manufacturing coal tar colors.

At present we shall occupy ourselves with the first of such applications--the production of cold.

The apparatus serving for the production of cold by this material are three in number: (1) the _freezer_ (Figs. 1, 2, and 3), in which is produced the lowering of temperature that converts into ice the water placed in carafes or any other receptacles; (2) the _pump_ (Figs. 4, 5, and 6), which sucks the chloride of methyl in a gaseous state up into the freezer and forces it into the liquefier; and (3) the _liquefier_, which is nothing else than a spiral condenser in which the chloride of methyl condenses, and from thence returns to the freezer to serve anew for the production of cold.