Chapter 2

Respecting the production of pictures by means of emulsion, ground opal being the best, the system I employ is as follows: After well cleaning the glass, coat it with emulsion (which had better not be too thick). When dry it is exposed and developed with the usual oxalate developer, to which a little bromide of potassium has been added. The remainder of the operations is as usual. Those varnished with dead varnish can be tinted and worked up with colored crayons or black lead pencil and make very pleasing pictures. It is needless to add that they are also to be finished in water-colors if thought preferable.--_G. W. Martyn, in Br. Jour. Photo_.

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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 (1½ per cent. gives very good results) and from 1½ to 2½ per cent. of castor oil (2 per cent. gives very good results); 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 (say) 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.

Fifthly. The film is peeled off the paper by hand, and can be immediately used for producing negatives _recto_ or _verso_ as above mentioned.

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.

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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 (such as citric) or a mineral acid (such as sulphuric), 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 (after fixing, but before washing) 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 (hydrate of alumina), 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.

The presence of traces of iron may be known by adding a few drops of hydrochloric acid to a small quantity of a saturated solution of alum in a test-tube, to which add strong liquid ammonia; should any iron be present, the mixture will have a reddish-brown tinge when examined over a sheet of white paper. Other alums exist, such as the double sulphate of alumina and sodium, and sodium or aluminum and ammonium; but hitherto their uses have been confined to the experimental portion of the community rather than the practical.--_Photo. News_.

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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.

The machine now illustrated is one we have recently seen in operation in a Salford finishing works. It is an improved form of another stretching machine which had been turned out in considerable numbers by Mr. Archibald Edmeston, engineer, of Salford, who makes a specialty of calico printers' and finishers' machinery. The improvements consist mainly of a simplification of the working parts and thoroughly substantial construction of the machine. The principle adopted is a well-known one. The selvages of the cloth, or more strictly the two edges of the cloth, of a width of about two inches, are caused to pass over and at the same time are held by the rims of two diverging pulleys. The rims are further apart where the cloth leaves them than where they seize it, hence the stretching is gradually, certainly, and uniformly performed. The cloth is gripped by the pressure of an endless belt acting against the lower half of each pulley, the edges being held between them. In the engraving these stretching pulleys are indicated by the letters AA; the endless leather band passes over the pulleys, CC, of which there are a set of four provided for each stretching pulley. The lower pair of pulleys in each case may be tightened up by a screw for the purpose of imparting the requisite tension to the bands. The stretching pulleys are mounted upon and driven by the same shaft, an ingenious but simple swiveling joint in their bosses enabling them to be set at any angle to the shaft and yet to revolve and be driven by it without throwing any undue strain upon the working parts. The piece, wound upon the ordinary batch shell, is placed upon the running-off center, D; it is led off over the rails, EE, and then downward to the nip of the bands and pulleys, AA. As explained, the selvages are here gripped between the bands and stretching pulleys, the rims of which are wider apart at the back than the front, and thus, in being conveyed underneath, the piece is suitably stretched. Leaving the grip at the back it passes over leading-off rollers, FF, and the scrimp or opening rail, G, and thence downward to the winding-on center, which cannot be seen. The winding-on center is driven by friction. As the batch fills it and tends to wind faster than the machine delivers the cloth, the driving slips. In addition to a capability of being set at an angle to the shaft, the stretching pulleys, AA, may be slided upon, so as to separate or bring them closer together, to allow for the treatment of different widths of cloths. This adjustment is provided for by mounting the stretching pulleys, AA, and the band pulleys, CC, etc., on frames, BB, the ends of which rest, as shown, upon rails, at the back and front of the machine. The adjustment either for width of piece or for the angularity (extent of stretching) is easily made by the hand-wheel, L. By the bevel wheels shown, two cross screws having nuts connected to the ends of frames, BB, are actuated in such a way that as desired the space between the back and front of the pulleys may be closed in or opened out, or the two wheels, maintaining the same angularity, may be separated or closed in, either adjustment being expeditiously made. The wheels, HHH, are called center stretching wheels, the use of which is sometimes advantageous. They act in conjunction with a set of stretching pulleys, of which one, K, may be seen in illustration. By a proper adjustment at the latter the piece is bent into a wavy form, where it passes between the whole of them, the effect of the corrugation being to loosen the center threads and to allow the piece to be more equally stretched with those near the selvages and more easily. This part of the machine may be used or not as required. The production, we observe, was about 120 yards per minute. The machine is solidly built and well fitted together, as was obvious to us from an inspection of some in course of construction at the maker's works. It is also claimed to be of considerable advantage to bleachers and finishers of white goods, on account of the uniformity of the stretching causing but small disturbance to the stiffening.--_Textile Manufacturer_.

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WOOLEN FABRICS PURIFIED BY HYDROCHLORIC ACID GAS.

All known methods for chemically purifying woolen stuffs from vegetable fibers depend on the action of acids or substances of acid reaction. The excessive temperature, hitherto unavoidable in the operation, acts injuriously on the woolen fibers, especially during the formation of hydrochloric acid, with which process especially the development of an injuriously high temperature has been hitherto unavoidable. The best method of absorbing the heat developed is in the evaporation of the moisture naturally present in the wool. The patentees find agitation of the fabric and the use of an exhauster during the process of material assistance. The operation maybe successfully performed in two ways--either by acting on the fabric at the ordinary pressure with constant agitation, or by saturation without agitation in a vacuum. For the first method the patentees employ a wooden cylinder with an aperture at one end for inserting and removing the cloth, and having apertures all round to allow free access of air. This cylinder rests on a hollow axle, closed at one end and perforated with holes, through which the acid gas is passed. By the rotation of the cylinder the gas is drawn through the material and the latter exposed to the atmosphere, whereby it gives up a quantity of aqueous vapor. An average temperature of 30° Cent. is best suited to the operation, and it can be regulated according to the supply of gas by opening or shutting a three-way cock between the gas generator and the revolving cylinder. This process is assisted by the use of an exhauster of the usual construction. When fully saturated, the fabric is allowed to remain until the vegetable fibers are sufficiently friable. The treatment _in vacuo_ is as follows:

The hydrochloric acid gas passes into a vessel of suitable material provided with a perforated false bottom. From under this false bottom a pipe connects with a second similar vessel connected itself with a vacuum pump having a let-off pipe. As soon as the maximum vacuum is attained, the gas is turned on through a three-way cock at a pressure of 40 mm. mercury. The gas fills the first vessel and saturates the cloth. The warmth set free (about 500 calories per kilo, gas) is taken up by the combined water in the wool, as, owing to the low pressure, a quantity of vapor is formed sufficient to take up the heat. This vapor streams through the second vessel at a temperature of 35° Cent., penetrates the material, and passes out through the pump. After saturating the contents of the first vessel the gas passes into the second. AS soon as this is one-quarter or one-third saturated the first vessel is taken out and replaced by a third, which receives the overplus from No. 2 in like manner, and so on. This plan of working prevents gas passing through and damaging the pump. Instead of working under reduced pressure, the desired low temperature can be maintained by passing alternately with the gas currents of air which absorb heat in evaporating the moisture of the material. The cloth, after saturation by these processes, is left from six to twelve hours in the vessels, after which it is freely exposed to the air until the vegetable particles are friable. As soon as this occurs, the fabrics are washed. It is advantageous to add to the wash water powdered carbonate of baryta, strontia, magnesia, or preferably lime, and subsequently to rinse in pure water. Phosphate of lime containing carbonate may also be employed for neutralizing the acid, and the residue recovered and separated from the organic residues mixed with it.--"_H. J.," Journal of the Society of Chemical Industry._

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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.

In the latter case the metal is brought to the state of oxide in presence of the water that is necessary for the reaction. But the results obtained in practicing this method are deceiving, as far as bleaching is concerned, and it is evidently more rational and economical to endeavor to compound the hypochlorite directly by borrowing all its elements from the metallic chloride itself, and from the water by means of which such transformation is to be effected. This is a reversal of the problem, and, _à propos_ thereof, we would call the attention of the reader to an apparatus invented by Messrs. Naudin & Schneider for effecting such synthesis in a simple and practical manner.

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:

2NaCl + 2 H_{2}O = NaCl + NaO, ClO + 4H.

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 (this being ascertained by chlorometric tests), 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 (as a natural consequence of the elevation of the level of the liquid in A brought about by the entrance of a new supply of chloride), 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.