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January 4, 1867.] THE PHOTOGRAPHIC NEWS. 3 PAPIER LEPTOGRAPHIQUE. It appears to be now distinctly admitted that the lepto- graphic paper is coated with sensitive collodion, the two secrets maintained being the sensitive salts employed, and the material used for the preliminary sizing of the paper. Wo have no doubt now, and have not had from the first, that the collodio-chloride process is the base of the opera tions. The matt paper resembles paper prepared with collodio- chloride in all respects ;' and we have produced paper pre cisely similar to the “ enamelled ” leptographic paper by coating glazed or enamelled paper with collodio-chloride of silver. As we noted in a recent article, collodion applied to such a surface acquires the peculiar quality of being very difficult to dissolve by means of the ordinary solvents, our own prepared examples behaving exactly like the lepto- graphic paper in this respect. How far this paper will bo found a final success we cannot tell, as the accounts of experience arc very varied. Our own somewhat limited experiments have been favourable. Dr. Vogel’s, recorded on another page, are not so favourable. In any case, the price seems prohibitory. It is, we are informed, £40 per ream. We think that those concerned to try may produce similar results by means of our collodio- chloride process. It seems that at a recent meeting of the French Photo graphic Society considerable discussion took place as to the inherent qualities of this paper. M. Gaillard was of opinion that the material was not altogether satisfactory, what was gained in delicacy being lost, he thought, in durability; and the question at issue was, whether the film was liable to abrasion. M. Regnault gave a favourable account of the process, and described three distinct kinds ot paper, viz. :— 1. Unglazed (collodion on Saxe paper). 2. Enamelled on one side (coated with carbonate of baryta). 3. Enamelled on both sides. The experience of MM. Girard and Davanne was opposed to that of M. Regnault, and a great diversity of opinion existed among the members as to the value of the new material. The Leptographic Company is said to be anxious for an impartial trial of their paper. They state that it is three times as sensitive as ordinary albumenized paper, but the pictures should be somewhat over-printed, more especially when the unglazed quality is employed. The evidence does not bear out the statement of rapidity. NOTES ON PERMANGANATE OF SILVER. BY WILLlaN CROOKES, F.R.S. It has long appeared to me probable that the peculiar chemical constitution of permanganate of silver would render this salt of considerable value in the detection and removal of organic impurities from water required for use in photography. A series of experiments on this subject has been, for some time past, in progress in my laboratory, and the result shows that these anticipations were well founded. I propose to give, at the present time, an outline of the more useful results which have been obtained, but must defer a detailed account of the experiments until they are completed. I have already given an outline of the properties and composition of the metallic permanganates, and will there fore assume that their salient characters arc known to the readers of the PHOrOGRAPHTC News, and especially their energetic power of giving up oxygen to organic matter. 1 ho best known of these saltsis permanganate of potash, a beautifully crystallized salt, which is now, thanks to the labours of M r . Condy, an article of commerce. Permangan ate of silver is obtained by mixing warm and tolerably strong solutions of nitrate of silver and permanganate of potash in equivalent proportions. As the liquid cools, permangan ate of silver separates in large regular crystals. When quite cold, pour the supernatant liquid oft, and add about the same bulk of warm distilled water. Digest at 180° Fah., with repeated stirring for half-an-hour, or until the crystals have redissolved ; then filter the liquid, through a funnel loosely plugged with a tuft of gun-cotton, into a clean porce lain dish, and let the solution stand under cover in a cool place for twelve hours. At the end of that time, if the opera tion has been properly performed, the bottom of the dish will be covered with long crystals of permanganate of silver. Pour the solution off, and let the crystals drain on a funnel, preventing them from falling through by putting a glass rod in the neck. When dry, the crystals must be preserved in a wcll-stoppered bottle ; they will be quite permanent if kept from the light. Permanganate of silver thus formed is in the form of anhydrous crystals belonging to the oblique prismatic system. They dissolve in 109 times their weight of cold water, being, in fact, the least soluble of all the permanganates. Warm water dissolves them more abun dantly, but ebullition decomposes them. For experimental purposes, a cold saturated aqueous solution may be employed. This is of an intense red-purple colour, and appears to be quite stable. The solution affords a most delicate test for organic matter in water. If added to a liquid strongly charged with deleterious organic matter —such as putrefying albumen or carbolic acid—a volumin ous brown precipitate is instantly formed, and the purple liquid is decolourized. An examination of the precipitate shows that it contains both silver and manganese in com bination with oxygen, the exact composition not having been yet ascertained. The aqueous solution being free from both metals, add very gradually permanganate of silver solution to the liquid, and a point will eventually be reached at which no further precipitation takes place, and the super natant solution retains a pink tinge; add so much of the silver solution that the colour is still perceptible after standing for half-an-hour in a bright light at a temperature of 100° Fah., and then filter through fine filtering-paper. The solution will probably pass through with a pink tinge ; this may be removed by ebullition and passing through clean filtering-paper two or three times, when very soon a clear, colourless liquid is obtained, which contains neither manganese, silver, nor organic matter. Permanganate of silver has, therefore, the valuable property of entirely removing all photographically injurious matter from water, whilst each of its metallic constituents is at the same time rendered insoluble; and not only will it exert this action on organic matter, but, by virtue of the silver which it contains, it at the same time effectually removes all inorganic bodies which would be deleterioustrom a photographic point of view, such as chlorides, iodides, bromides, sulphides, carbonates, phosphates, cyanides, sulpho-cyanides, &c. Ammonia is likewise destroyed with evolution of nitrogen, and hyposulphites are at once con verted into sulphates. Experiments have been tried with the most complicated mixtures of liquids. Old hypo baths, cyanide solution, putrid albumen, and hydrochloric acid, have been mixed witl stagnant water from a pond ; when, with the greatest readiness, and with a very inconsiderable amount of trouble or care, the whole of the injurious matters have been separated, and a liquid produced, limpid, inodor ous, tasteless, and apparently better suited for the prepara tion of a nitrate bath than are many commercial samples of distilled water. As I mentioned at the beginning of this notice, the experiments have not yet been carried out with all the com pleteness and accuracy as to detail which is desirable. Further observations may show that this agent is not capable of such universal application as a theoretical study of its composition and properties would indicate. Enough has, however, been ascertained to show that it is likely to prove of considerable value in photographic operations, and
