Read Ebook: Scientific American Supplement No. 401 September 8 1883 by Various

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Gold. 1 grain. Water. 5 ounces.

With this a very fine depth is soon attained, and a nice picture the result. Leave out the toning, and only a poor, sunken-looking picture will be the outcome; but directly the toning bath is employed richness at once comes to the fore. I have, however, known of instances where the picture needed no toning.

OPAL PRODUCTION IN PRACTICE.

Now, excellent pictures are to be made on opals by means of emulsion; but I propose first taking the transfer method as given above for pottery, since in practice it is found very ready, easy of manipulation, and safe. The details are much the same as above, and necessitate double transfer.

After the picture had been obtained on the plate , and after thoroughly fixing, washing, and toning, the picture then has to be loosened from its support, and this is done with a solution of sulphuric acid--one drachm to fifteen ounces of water--which is made to flow between the image and the glass, after which perfectly wash and mount. When the image is loosened a piece of tracing paper is put on the image, evened out, raised , and with the aid of the helper the picture is carefully centered, gently pressed out or down, and the transfer is so far effected. But what will happen, and does happen, in the case of vignettes, is impurity of the whites, when the picture becomes positively objectionable. Now the way to remedy this lies simply in the application, to the dirty-looking parts, of a solution of iodine dissolved in iodide of potassium to sherry color; after which, well wash and apply a weak solution of cyanide of potassium, and wash well again. This, by the way, is equally applicable to paper transfers; and it is to be remembered that the toning comes last of all. It is a rather difficult matter to clean a ground opal which has been used two or three times, and acid must then be had recourse to ; but by transferring from the support on the ground surface, all stains are at once avoided.

On the flushed glass, or on the pot metal , after well cleaning the surface it should be covered with a substratum of egg. Then the picture is taken direct, not transferred; that is, the plate is exposed direct in the camera, regularly proceeded with, and, when dried, varnished with a pale negative varnish, or with dead varnish if intended for chalk or water-color. This, when a good negative is used, gives a remarkably fine picture, not requiring a vestige of retouching, and having likewise the invaluable advantage of being perfectly durable if varnished with the negative varnish. Moreover, on that, effective pictures may be made in oil with simply tinting.

I hope I have left it clearly to be understood that the class of opal picture to which I have chiefly alluded is one that remains untouched after the transfer--that is, absolutely unpainted upon. It is pure photography in every sense of the word, and the resultant picture one hardly to be surpassed in any way. I have rather laid a stress on this point, well knowing how pictures are at times irretrievably ruined by the barbarous hand of would-be artists, who by far exceed the true artists in number; and the hint on retouching should not be lost sight of, either, at a period when the tendency is to stereotype every one in marble-like texture, or rather lack of texture, as if the face were devoid of all fleshiness and as hard and rigid as cast-iron. It might be wise to weigh this point carefully, and act upon it, before the enlightened public have raised a cry against the pernicious practice and made photographers smart for their want of applying timely remedial measures to a decided evil.

On reading the above again, fearing lest any misconception should arise in the mind of the reader, I deem it expedient, to clearly state that for terra-cotta recourse is had to double transfer; that is, the picture first taken is lifted from the support on tracing paper, put in the right position on terra-cotta, and pressed down while wet with blotting-paper, left to dry, and is then so far ready.

PAPER NEGATIVES.

The process of A.C.A. Thiebaut is as follows: the paper has the following advantages:

First. The sensitive coating is regular, and its thickness is uniform throughout the entire surface of each sheet.

Second. It can be exposed for a luminous impression in any kind of slide as usually constructed.

Third. It can be developed and fixed as easily as a negative on glass.

Fourth. The negative obtained dries quite flat on blotting paper.

Fifth. The film which constitutes the negative can be detached or peeled from its support or backing easily and readily by the hand, without the assistance of any dissolving or other agent. Thus this invention does away with all sensitive preparations on glass, which latter is both a brittle and relatively heavy material, thus diminishing the bulk and weight of amateur and scientific photographers' luggage when traveling; it produces photographic negatives as fine and as transparent as those on glass, in so much that the film does not contain any grain; and, lastly, it admits of printing from either face of the film, as regards the production of positives on paper or other material, as well as plates for phototypy and photo-engraving, which latter processes require a negative to be reversed.

For the manufacture of my sensitized film paper:

First. A gelatinized sheet of paper is properly damped with cold water, and when evenly saturated it is placed on a glass, to which it is attached by means of bands of paper pasted partially on the glass, and partially on the edges of the said sheet; in this state it is allowed to dry, whereby it is stretched quite flat.

Secondly. I coat the dry sheet with a solution of ordinary collodion, containing from one to two per cent. cubic measure of azotic cotton and from 1 1/2 to 2 1/2 per cent. of castor oil ; this coating is allowed to dry; and,

Thirdly. The glass, with the prepared paper upward, is leveled, and then it is coated, in a room from which all rays but red rays of light are excluded, with a tepid emulsion of bromide of silver to the extent of about one millimeter thick, and after leaving it in this position until the gelatine has set about five minutes, with the film paper still attached, it is placed upright in a drying-room, where it should remain about twelve hours exposed to a temperature of from 62 to 66 degrees Fahrenheit; and,

Fourthly. The film paper is detached from the glass ready for exposure, development, and fixing in the usual manner. For the purpose of developing, oxalate of iron or pyrogallic acid answers equally well; for the purpose of fixing, I have found that a mixture by weight, water, 1,000, hyposulphite of soda 150, and powdered alum 60, produces excellent results, after being allowed to dry.

I claim as my invention:

First. The preparation or formation of gelatino-bromide film paper for photographic negatives, in the manner and for the purposes above described; and,

Secondly. The use for this purpose of castor oil, or any other analogous oil, more especially with the view of peeling off the film from the paper backing as above described.

SOME OF THE USES OF COMMON ALUM.

A substance very much used by photographers of late years--in fact, so much used that no well-appointed laboratory could be considered complete without it--is the substance known is common alum, or potash alum, being a double sulphate of alumina and potash; but it is interesting to note that much of the commercial alum met with at the present time is ammonia alum, or the double sulphate of alum and ammonia. It is quite a matter of indifference to the photographer whether he uses potash alum or ammonia alum.

Besides its great value to the autotype, Woodburytype, and mechanical printers as an agent for hardening the gelatine films, it has been recommended for all sorts of ailments photographic. The silver printer adds a small portion to his sensitizing bath to keep it in working order, and to prevent blistering of the albumen; then, again, silver prints are soaked in a dilute solution of alum, having for its object the thorough elimination of the last traces of the fixing salt. A very good proportion to use for this latter purpose is four fluid ounces of a saturated solution, diluted with one gallon of water, the prints being well agitated during an immersion of ten minutes.

Of all the uses to which alum is put, perhaps not in any single instance can so much satisfaction be derived as when it is used to arrest frilling of gelatine plates. This it has the power to do instantaneously, and many of the most careful workers, both amateur and professional, or at least those who do net care to run any unnecessary risks with negatives which have cost them a good deal of anxiety and trouble to secure, but prefer to make assurance doubly sure--such individuals may be numbered by the hundred--make it a point in every-day practice to immerse all their plates in a solution of alum, either before fixing, or immediately afterward. In fact, some operators have two alum baths in use, one a normal bath, as above mentioned, for immersing the plates in when of the ordinary printing intensity; and the other a saturated solution strongly acidified by means of a vegetable acid or a mineral acid , for use when there is too much printing density, since it has been found in practice that an acid solution of alum in contact with sodium thio-sulphate on the gelatine image not only removes the color or stain caused by the alkaline or pyrogallol, but perceptibly reduces the strength of the image. Moreover, the color does not again reappear after washing, as it does sometimes when the fixing salt has been partially washed away. In cases where there is great tendency to frill--such, for instance, as when a soft sample of gelatine has been employed, or old decomposed emulsion worked in with the fresh emulsion--it will in such cases be safer to put the plates in the normal-bath for a few minutes previous to immersing them in the acid bath.

Potash alum is obtained tolerably pure in commerce in colorless transparent crystalline masses, having an acid, sweetish, astringent taste. It is soluble in 18 parts of water at 60? F., and in its own weight of water at 212? F.; but the excess crystallizes out upon cooling. The solution reddens litmus paper, and, when impure, usually contains traces of oxide of iron. Upon the addition of either caustic soda or potash, a white gelatinous precipitate is formed , which is soluble in excess of the reagent employed. The precipitate thus obtained has much of the character of the opalescent film sometimes observed on gelatine plates, when dry, which have been soaked in alum, and not well washed afterward.

Alkaline carbonates--such as washing soda, for instance--precipitate hydrate of alumina, which does not dissolve in an excess of the reagents, and carbon dioxide is evolved.

Ammonia hydrate produces a precipitate in a much finer state of divison, which does not dissolve in excess when examined in a test-tube, it somewhat resembles thin starch paste.

CLOTH STRETCHING MACHINE.

As is well known, in the process of bleaching and dyeing, cotton cloths become considerably contracted in the width, in consequence of carrying on the operations when the cloth is in the form of a rope. The effect is that, together with the tension, although slight, and the drying, the weft partly shrinks and partly curls up, the latter, however, being scarcely observable to the naked eye. It may almost be said that as regards the width the shrinkage is due to a number of minute crumples because the cloth is easily streatched again by the fingers almost to its gray width. The main use of a stretching machine, therefore, is not so much to make the cloth more than it is as to bring it again to its normal or woven width after operations that tend to shrinkage have been performed upon it. The stretching operation, therefore, is especially useful to calico printers, as it enables them to obtain when desired a white margin of even width, the irregularities due to bleaching being corrected before printing.

WOOLEN FABRICS PURIFIED BY HYDROCHLORIC ACID GAS.

APPLICATION OF ELECTRICITY TO THE BLEACHING OF VEGETABLE TEXTILE MATERIALS.

It is a recognized fact that chemical bodies in a nascent state are characterized by peculiarly energetic affinities, and the results of numerous experiments permit us to affirm that animal and vegetable fibers are rapidly bleached when they are placed in contact with oxides and chlorides which, when submitted to electrolysis, permit oxygen and chlorine to disengage themselves in the nascent state.

The coloring matter that impregnates the majority of vegetable textile substances, such as cotton, flax, and hemp, to cite only those most generally known, is in fact completely destroyed only by the combined action of oxygen and chlorine, which always act in the same manner, whether the fibers be in a raw or woven state.

In the application of electrolysis to the bleaching of textile materials, it is only necessary to have the electrodes of any sufficiently powerful generator of electricity end in a vessel containing in aqueous solution such decolorizing agents as the hypochlorites in general, and chlorides, bromides, and iodides that are capable of disengaging chlorine, and iodine or an iodide in a nascent state. These gases perform the role of oxidizing or decolorizing agents.

The fibers that are immersed in the solution during the passage of the electric current must necessarily remain therein for a greater or less length of time, according to the nature of the material to be bleached, and must, after this first operation, be washed, rinsed, and dried.

The use of an electric current for decomposing the metallic chlorides and disengaging their elements is not new, and there have been specially utilized for this purpose, up to the present time, the alkaline hypochlorites that are obtained by well known processes.

If a solution of chloride of sodium or kitchen salt, NaCl, be submitted to electrolysis in a hermetically closed vessel containing the material to be bleached, a formation of hypochlorite of soda is produced in the following way:

In operating in this manner we shall have the advantage that results from the nascent body through the electrical double decomposition of the chloride of sodium and water, which puts the chlorine, the metal, the hydrogen, and the oxygen simultaneously in presence. The chlorine and oxygen will combine their action to decolorize the textile material.

While starting from this idea, it will nevertheless be preferable to adopt Naudin & Schneider's arrangement.

The apparatus consists of a hermetically closed electrolyzer, A, into the lower part of which enters the electrodes, E and F, of any electrical machine whatever. The receptacle, A, is provided with a safety-tube, T, that issues from its upper part and communicates with a reservoir, B. A second tube, D, forms a communication between the electrolyzer and the vessel, C. The liquid contained in this latter is sucked up by a pump, P, and forced to the lower part of the vessel, A, by means of the tubes, G and H.

The apparatus operates as follows:

The closed vessel, C, in which the material to be bleached is put, is filled, as is also the electrolyzer, with a solution of chloride of sodium. This solution is then submitted to the action of an electric current, when, as a consequence of the chemical decomposition of the chloride and the water, the elements in a nascent state form hypochlorite of soda. When the partial or total conversion of the liquid has been effected , the pump, P, is set rapidly in operation, and, as a consequence, draws up the chloride of sodium from the bottom of the vessel, C, to the lower part of the electrolyzer, A. The hypochlorite that has formed passes through the tube, D , and distributes itself throughout the vessel, C, where it acts upon the textile material.

The safety-tube, T, which is attached to the electrolyzer, permits of the escape of the hydrogen which is produced during the chemical reaction, and fixes, through an alkaline solution contained in the reservoir, B, the chloride whose escape might discommode the operator.

As may be conceived, the slow transfer of the saline solution from the receptacle, C, to the electrolyzer, and its rapid conversion into decolorizing chloride, as well as its prompt application upon the materials to be bleached, presents important advantages.

While, in the present state of the industries that make use of bleaching chlorides, the chloride of sodium is converted into hydrochloric acid, which, in order to disengage chlorine, must in its turn react upon binoxide of manganese, we shall be able, with this new method, to utilize the chloride of sodium, which is derived from ordinary salt works, and extract from it the constituent elements of the hypochlorite by a simple displacement of molecules produced under the influence of an electric current.

Another and very serious advantage of electric bleaching is that of having constantly at hand a fresh solution of hypochlorite possessing a uniform decolorizing power, which may be regulated by the always known intensity of the current.

IMPROVED SPRING TRACTION ENGINE.

TABLE SHOWING THE RELATIVE DIMENSIONS, LENGTHS, RESISTANCES, AND WEIGHTS OF PURE COPPER WIRE.

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