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604 THE PHOTOGRAPHIC NEWS. [August 28, 1891 of ether by frequent agitation. Then the following three solutions are prepared :— Solution No. I. Crystallised eosin ... ... ... 4 grammes Distilled water 50 c.c. Alcohol (96 per cent.) 450 „ Solution No, II. Silver nitrate ... ... ... ... 3'4 grammes Distilled water ... ... ... 50 c.c. Alcohol (96 per cent.)... ... ... 150 „ Ammonia, concentrated solution, until the first formed precipitate is again dissolved. Solution No. III. Picric acid 3 grammes Distilled water ... ... ... 10 c.c. Ammonia to neutralise the solution Alcohol (96 per cent.) up to 300 c.c. Just before use, mix— Solution No. I. ... ... ... 75 c.c. SolutionNo.il. ... ... ... 30 „ Solution No. III. ... ... ... 30 ,, Glycerine, chem. pure... ... ... 20 „ Alcohol (96 per cent.) 45,, This eoside of silver solution is allowed to stand for one or two days and filtered, and 20 c.c. of it are mixed with each 100 c.c. of the raw emulsion. This dyed emulsion requires only about one-third of the exposure of wet collodion, but it keeps only one or two days. The glass plates, before being coated with the emulsion, are provided with the following substratum: 5 grammes of white gela tine are dissolved in 500 c.c. of distilled water, and to this solution are added 15 c.c. of acetic acid and 10 c.c. of alcohol. The solution is filtered at a temperature of 100° to 110° F., and, whilst still warm, poured twice upon the plate. After being coated with emulsion, the plates are placed directly, without washing, into the dark slide, and can be at once exposed; they will, however, keep damp for thirty to forty minutes in not too hot a room. When exposed, the plates are washed by dark red light until all greasiness has disappeared, and allowed to drain in an upright position for some time. This draining must continue the longer the larger the plates are ; if they are not sufficiently drained, streaks will be produced on the film during development. Development takes place by copiously pouring the developer over the plate, as in the case of the wet collodion process. The following concen trated hydroquinone developer is recommended as the best for this purpose :— Solution Distilled water A. , 500 C.C. Sodium sulphite ... , 200 grammes Potash . 200 »3 Solution Hydroquinone B. 25 grammes Alcohol (96 per cent.) ... .. 100 C.C. Solution Bromide of ammonium ... c. 25 grammes Distilled water , 100 C.C. The concentrated developing solution consists of— Solution A ... 100 c.c. Solution B 5 „ Solution C ... ... ... ... 7 ,, In the case of hard negatives, solution B is increased to from 6 to 7 c.c. The actual developer is prepared by mixing— Concentrated developer 150 c.c. Water ... ... ... ... 1,000 „ The plates can be intensified with pyrogallic acid and silver by preparing the following two solutions :— Solution A. Pyrogallic acid 7 grammes Citric acid ... ... ... ... 7 » Distilled water ... ... ... 1,500 c.c. When dissolved, add— Acetic acid ... ... ... ... 25 drops Solution B. Nitrate of silver 10 grammes Distilled water 100 c.c. Just before use, 100 c.c. of solution A are mixed with 5 c.c. of solution B. If it is desired to intensify the plates after fixing, the same pyro and silver intensifier may be used, but the hydroquinone and silver intensifier also answers very well. For reducing the negatives, the hypo and ferricyanide of potassium reducer, as used for gelatine plates, may be used. Increasing the Sensitiveness of Asphaltum.—E. Valenta has found that the sensitiveness of asphaltum may be materi ally increased if it is incorporated with sulphur. He dis solves from 7 to 10 grammes of sulphur in a sufficient quantity of bi-sulphuret of carbon, and adds 100 grammes of Syrian asphaltum. The solution is then freed from the bi-sulpuret of carbon, and for about one hour heated up to 100° C. ; it is then transferred to an air-bath, and gradually heated up to about 180° C., until sulphuretted hydrogen is escaping. At this temperature it is kept for about five hours. The asphaltum forms, after this treat ment, a black and shining mass, which does not dissolve in alcohol, and only to a small degree in ether, whilst it dissolves perfectly in turpentine, benzole, chloroform, and bi-sulphide of carbon. Four parts of this prepara tion are then dissolved in 100 parts of benzole, and the solution is applied in the usual manner to a polished zinc plate. It forms a light yellow, thin film of comparatively high sensitiveness to light, and gives, therefore, beneath a negative of good density clear and sharp impressions after the development with turpentine, even with com paratively short exposures. THE DECOMPOSITION OF SILVER CHLORIDE BY LIGHT* BY A. RICHARDSON, PH.D. It is known that the presence of hydrochloric acid exer- cisesa retarding influence on the decomposition of chlorine- water by light, and a series of experiments have been made (B. A. Report, 1888) in order to determine the influence of different quantities of acid on its stability. The results given in Table II. show that even minute quantities of the acid exercise a very decided influence on the rate at which free chlorine is converted into hydrochloric acid under the influence of sunlight (exposure seven days, August 17—24). Table II. In the case of silver chloride in water, the chlorine evolved during exposure to light is at first speedily con- Parts of Cl per 100 HaO. Parts of IIC1 per 100 Ha0 added. Per cent, free Cl found. Per cent, combined Cl found—HCl added. 0-284 0-029 2-34 97-66 0-270 0-289 12-61 87-38 0-260 0-400 28-57 71-42 0-290 0-587 39-25 60-95 0-290 0-724 58-71 41-29 0-282 1-158 87-82 12-18 0-291 1-447 95-47 4-53 * Continued from page 59".