The photographic news

• Bandzählung: 12.1868
• Erscheinungsdatum: 1868
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-186800009
• PURL: http://digital.slub-dresden.de/id1780948042-18680000
• OAI: oai:de:slub-dresden:db:id-1780948042-18680000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

26 THE PHOTOGRAPHIC NEWS. [January 17, 1868. enabled to eliminate all but a very minute trace of the silver always left in the whites of the print after fixing with hypo sulphite of soda; and expresses a conviction that if the ammonia salt can be introduced cheaply into commerce it will prove a great boon to photographers. Mr. Spiller proposes to prepare the hyposulphite of am monia, by double decomposition, from hyposulphite of baryta and carbonate or sulphate of ammonia, the hyposulphite ot baryta being formed by mixing, in nearly equal parts by weight, chloride of barium with hyposulphite of soda, in concentrated aqueous solutions. The product is a pure salt of hyposulphurous acid and barium : a sample before us, pre pared by Mr. Spiller, is in very fine, minute, and beautifully lustrous crystals something like pyrogallic acid in appear ance, and something of the saponaceous feeling of steatite to the touch. From its insolubility it is, however, useless to the photographer, and is chiefly interesting from its fitness for the use for which Mr. Spiller proposes it. The practical extent to which hyposulphite of ammonia will prove a per fect fixing agent can, of course, be only determined practi cally. Theoretically it should promise a solvent power much more complete than that of other hyposulphites from the behaviour of the -base ammonia as well as the hypo- chlorous acid towards salts of silver. Our object now, however, is to mention that in the spring of last year we received from an esteemed correspondent, Mr. F. H. Redin, Governor of Carlisle Gaol, and a skilful amateur photographer, some excellent prints which had been fixed with hyposulphite of ammonia. Tested with sulphide of ammonium the existence of silver in the whites appeared much less than is common ; but still it was manifestly pre sent. Mr. Spiller has used it as a second bath to eliminate, if possible, the silver from the whites of a fixed, albuminized print. If the use of a second bath be conducive to this end, notwithstanding the extra trouble, many a conscientious pho tographer will not hesitate to use it. When the old mixed toning and fixing bath was in vogue, Mr. Lake Price used to employ, and recommended in his useful book, a second bath of a strong, fresh solution of hyposulphite of soda to secure perfect fixation, applied when the print had acquired a proper colour in the first bath. At the time we received the prints to which we have referred from Mr. Redin, he informed us that the hyposul phite of ammonia was prepared by a new process, by Mr. Lush, one of the visiting justices of the gaol, and that he was prepared to introduce it into commerce. We hoped to have heard more of the matter, but it has not again come under our notice. Now is the time, however, to bring it under the attention of photographers in a commercial way. There is another question of importance introduced in Mr. Spiller’s paper. One sample of hyposulphite of soda he examined contained not less than sixteen percent, of im purity. The impurity was not necessarily injurious to the photographs subjected to its action, but the fixing bath would be weaker in just the proportion in which the impu rity was present. To all large consumers of hyposulphite of soda this suggests the importance of testing each stock when first purchased by the simple method indicated in the paper. To smaller consumers, or those unable or unwilling to under take such tests, it suggests the importance of a liberal use of the fixing salt, so as always to be on the safe side. The use of excess of hypo is only a little waste of a cheap salt; the use of too little is risking the permanence of valuable pictures, and the waste of reputation. ANOTHER SENSITIVE SALT FOR PHOTO GRAPHERS—FLUORIDE OF SILVER. Wusr all the haloid salts of silver have been for years known as sensitive to light, the chloride, iodide, and bromide only have been available to photographers. The fluoride of silver, although extremely sensitive, possessed a peculiarity which disqualified it for the uses for which its congeners were employed—it was soluble in water. The consequence was, that when a fluoride was employed in collodion by Archer and others, the fluoride of silver, formed in the film by double decomposition in the bath of nitrate of silver, being itself soluble, was dissolved by the aqueous solution, and lost from the film as fast as it was formed. The insolubility in water of iodide, bromide, and chloride of silver is the quality which has made them especially suitable for manipu lative convenience, whilst the solubility in water of the fluoride has prevented its utilization in photography. In the course of some recent experiments by M. Prat, another form of fluoride of silver has been discovered, which differs essentially from the soluble salt which has hitherto been known by chemists. The new salt is stated to be more sensitive to light than chloride of silver, and, being in soluble in water, it is available for the operations of the photographer in the same degree as the other haloid salts. M. Prat’s paper, Fluorine and its Compounds, was recently communicated to the French Academy, but will not be pub lished at length until the chemical referees of the Academy have reported thereon. Our excellent contemporary, the Chemical News, has, however, a full abstract of the paper, which, as it will possess much interest for many of our readers, we subjoin:— “ M. Prat considers that chemists have hitherto been mis taken as to the composition of fluorides and the theory of fluorine. He regards the fluorides as in reality oxyfluorides, and the equivalent of fluorine as consequently much higher than is usually 7 supposed. He represents fluoride of calcium by— 2 equivalents of calcium ... ... 40 0 1 equivalent of oxygen 8'0 1 „ the new fluorine ... 29-6 77-6 This accords with the known analysis of fluor spar, since it contains 515 per cent, of calcium. “ By doubling the old equivalent of fluorine (19), we get 38; that is to say, nearly the sum of the equivalents of oxygen (8), and of the new fluorine (29 6) = 37'6. “ According to M. Prat, in order to obtain true fluorine, it suffices to heat fluoride of calcium with chlorate, or, rather, with perchlorate of potash, since it is only after the forma tion of this latter salt that the reaction takes place. Oxygen is disengaged, and also a product which silver absorbs. The compound so formed is fluoride of silver, insoluble in water, soluble in ammonia, from which it is precipitated by nitric acid, and more rapidly altered in the light than chloride of silver. Neither chlorine nor oxygen attack it even at the fusing point of the fluoride. It is, however, decomposed by potash at a dull red heat, and this reaction permits its ana lysis ; it contains— Silver 0-785 1080 = 1 equivalent Fluorine 0-215 290 „ „ Fluoride of silver 1-000 137'6 “ This fluoride of silver, insoluble and very stable, and having great analogy with the chloride and the other com pounds of this family, differs essentially from the soluble fluoride of silver of chemists, which, according to M. Prat, is a compound of— AgFl, AgO, HO, in the hydrated state; AgFI, AgO, in the anhydrous state. “ Fluorine combines with chlorine. To obtain this com pound it is sufficient to pour a weak solution of the hydro fluoric acid of the chemists into a solution of hypochlorous acid: there form Fill, IIO + CIO = 2HO + F1C1. “ Fluoride of chorine is gaseous, of a more intense colour than chlorine. It converts silver into a mixture of chloride, and fluoride.