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660 THE PHOTOGRAPHIC NEWS. ^October 16, 1885. be accomplished by chemical means, or the use of baths, but by rubbing with a piece of linen moistened by strong alcohol. This method was first communicated to me by Herr Lenhard, in Vienna. I saw many good results thus obtained, and succeeded perfectly myself with the method, which I can, therefore, thoroughly recommend. A piece of fine linen is dipped in alcohol, and rubbed with considerable pressure on the too-intense portions of the dried plate until they are sufficiently clear. The linen becomes black, and the intense portions thinner, without loss of detail. Small places can be cleared with a little stick of pliant wood that has been dipped in alcohol. I saw at the atelier of Herr Burger difficult retouching accomplished in this manner. 4.—Citrate of Iron Developer for Warm BROWN Tones upon Chloride of Silver Gelatine Films. A very favourite developer for transparencies upon chloride of silver gelatine plates, and also suitable for paper, is the citrate of iron. It is prepared by mixing an acid solution of citrate of ammonia with sulphate of iron. I have now simplified the preparation of the ammonia citrate solution, and my formula is as follows :— 700 cub. cents, of distilled water are poured upon 150 grammes of citric acid, and 160 cub. cents, of ammonia (sp. gr. 0-910) are added, and stirred. In a short time the citric acid dissolves in the solution, which, at the same time, rises in temperature. The solution is then tested with litmus paper to see whether it is neutral or slightly alkaline; if strongly acid, more ammonia is added ; if strongly alkaline, a few crystals of citric acid are thrown in. When the solution shows a neutral or slightly alkaline reaction, 100 grammes more of crystals of citric acid are added, and, when dissolved, the whole is filtered. To develop chloride of silver pictures, take— 15 volumes of ammonium citrate solution. 5 ,, sulphate of iron solution (1: 3). 1 ,, chloride of sodium solution (1: 30). This developer can, as is known, be used repeatedly. 5.—Acid Chloride of Silver Gelatine Emulsion. Chloride of silver separates in a flocculent precipitate more readily than bromide, and therefore it is well to add a good quantity of gelatine to the solution of chloride of sodium, as well as to that of nitrate of silver. This pro ceeding has already been described, and after many experi ments I have settled upon the following formula. Three solutions are prepared in flasks. A.—Chlor, of sod. (or 13 gram, chlor, of amm ) 14 gram.* Gelatine 25 ,, Water 200 c.c. B.—Nitrate of silver 30 gram. Water 50 c.c. G.—Gelatine... ... ... ... ... 25 gram. Water 250 c.c. The gelatine is dissolved in flasks, A and C, by immers ing them in warm water ; the gelatine solution C is then poured into the silver solution B, and shaken, then (by yellow light) the chloride solution A is added. The tem perature may be at from 408 to 50° Cent. The emulsion is left standing for a few minutes until the froth disappears, when it is poured out to set; afterwards it is divided, and washed as usual. Chloride of silver is mcstly employed without further • It is much the same thing whether the one or the other chloride be em ployed. Chloride of ammonium gives somewhat softer pictures than chloride of sodium. The sal ammoniac of commerce (chloride of ammonium), when in the form of crystalline powder, contains much moisture, which must be driven off by heat (100’ Cent.) before being weighed. Sublimed sal-ammoniac, occurring in large quantities, is, on the other hand, seldom moist, and does not require hot drying. For chloride of sodium we recom mend the pure salt, which may be weighed without previous drying. ripening, because then it gives clear reddish-brown images. The emulsion in thin films appears by transmitted light reddish-yellow, and very transparent. Nevertheless, it gives powerful pictures. After cooking for half an-hour, or digesting for a longer time at 40 per cent., the colour of the emulsion becomes grey by transmitted light, and the sensitiveness is in- creasedfrom twotofourtimes. The transparencies or paper pictures obtained with such an emulsion have a colder and more neutral tone than is given by the uncooked. The addition of one drop of hydrochloric acid to the emulsion keeps the pictures clear. Citric acid, from 10 to 20 grammes to the foregoing quantity, produced light coloured (yellowish or reddish-brown) pictures. PHOTOGRAPHY AND MEDICAL JURIS PRUDENCE. BY WILLIAM MATHEWS. The Birth of Photographic Composites : A Review of Events. “ Out of this nettle, danger, we pluck this flower, safely.” —Hotspur [reading a letter}. The method of admeasurement of photographs by an adapted geometric process was first promulgated iu 1873-4, and the thesis was maintained that determinate identifica tion by means of photography was certainly within the scope and province of scientific solution. The employ ment of a datum line, taking its origin from th j centres, respectively, of the pupils of the eye, was an inherent feature of the new analysis, and was an entirely new departure. There were involved some anterior questions relating to the actual permanence or otherwise of certain leading details of the included area. These were dealt with, and the results placed before the world — first in a quarto leaflet, subsequently in an illustrated pamphlet. In the year 1875 the British Association held its annual session in the city of Bristol. Opportunity was taken to forward a leaflet through post to all, or nearly all, those in attendance. The brochure assumed the form of a challenge to the scientific gentlemen assembled to test for themselves the accuracy of the principles advanced, and especially in their application to the case of the Tichborne Claimant, then recently im prisoned. The formulary of procedure was fully set foith, and all necessary information conveyed. Among those to whom the leaflet was addressed was Professor Francis Galton, to whom belongs the merit of having subsequently introduced the now well-known “ Galton Composites.” Shortly after the issue of the pamphlet, the apparatus known as the “ identiscope ” was matured ; and a little later, operating upon the identiscopic lines, the combina tion was successfully effected of the Tichborne portraits; that is to say, of the Chilian Daguerreotype of young Roger Tichborne and of Messrs. Maull’s portrait of the Tichborne Claimant. This was the first-recorded instance of even an attempt to superimpose two separately- produced photographs. Some twelve months later, mention was made in the pages of the Photographic News of the curious composite portraiture then first brought into notice by Professor Galton at a soiree of the Society of Arts. The Professor seems at the outset to have tried his ’prentice hand ex clusively upon the photographs of criminals, and the sur mise is a natural one, that his first efforts had been bestowed with a view to ascertain whether or not a game of abracadabra had been pursued in effecting the asserted unison of the Tichborne photographs. For certainly it is of the very essence of the Galton process that the por trait of one individual is confederated into apparent alliance with that of another individual totally distinct But the professor’s experiments shortly expanded them-