The photographic news

• Bandzählung: 11.1867
• Erscheinungsdatum: 1867
• 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-id1780948042-186700008
• PURL: http://digital.slub-dresden.de/id1780948042-18670000
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• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

4 THE PHOTOGRAPHIC NEWS. [January 4, 1867. it is therefore hoped that experimentalists in this branch of science will take the matter up, and will investigate its special photographic bearings in that complete manner which is only possible to those who are in the daily habit of working at experimental photography. A VERY SENSITIVE TEST FOR HYPOSULPHITE OF SODA IN WASHING WATERS. BY DR. n. VOGEL. Nothing is more important to a conscientious photographer, and especially to one who works on a large scale, than the certainty of his print being perfectly washed. This point will always be uncertain as long as we shall be obliged to trust to the care of other people, for generally this part of the work is performed by very subordinate individuals. There fore, a convenient and sure means of controlling the washing process (that is to say, of examining the water for a trace of hypo) is of the greatest importance. Several methods of testing have already been proposed for this purpose. One of these proofs depends upon the application of pure zinc and diluted pure sulphuric acid. If both of these work together, they develop hydrogen ; the smallest quantity of hypo then being present, sulphuret of hydrogen is formed, and may be easily recognized by its blackening lead-paper. As M. Reissig remarked, there is a fault in this process, viz., zinc and sulphuric acid, not being always pure in trade, develop sulphuretted hydrogen, without any other sub stance being present. According to Dr. Reissig, hypo in a dilution of 1'250,000 is still to be recognized by this proof. By the second method, adding nitrate of silver or a salt of mercury to the washing water, no results of sufficient certainty are obtained. Reissig, therefore, recommends an electrolytical proof. When the silver pole of a galvanic element is put into the water to be proved, the silver plate at the positive pole instantly grows brownish, if the least quantity of hypo be present in the water. This method of trying, however, requires a galvanic pile, which is difficult to be kept in a good condition, but by which hypo in a dilution of 11,000,000 may still be perceived. The same exactness is secured by the following proof, which, as I believe, is to be preferred to others on account of its simplicity and surety, and which rests on the well-known reaction of hyposulphite of soda on iodized starch :— When hyposulphite of soda is added to a solution of blue iodized starch, the latter is decolourized instantly. The more the solution of iodized starch is concentrated, the greater a quantity of hyposulphite is necessary for decolour izing it; and if, therefore, a much diluted solution of hypo (viz., washing water) is to be examined, a much weakened solution of blue starch must be employed. I prepare this solution as follows:—One part of arrow root is mixed with a few drops of cold water; about 100 parts of boiling water are then added, and thus is obtained a colourless solution of starch, which keeps in a good con dition for six weeks and more. The mixture being cooled, about one-fifth of a gold-coloured solution of iodine and iodide of potash (a small grain of iodine in a solution of iodide of potash gives in 1'20 this colouration in some seconds) is added to it, and a transparent blue solution of iodized starch results. When to a small quantity of this solution the water to be proved be poured, the iodized starch naturally is more diluted, and looks therefore more pale, if even the water be without chemical contents. In order to avoid confounding this paleness with a decolouration, trying is to be performed in the following way :—Into two cleansed testing tubes of equal diameter, about one cubic centimetre of blue iodized starch is poured. To one of the tubes clear fresh water (as it is employed for washing), and to the other as much of the washing water to be proved, is added. Then both the tubes, having been shaken, are placed before a sheet of paper, or white cloth, and compared to each other. By the very lamp light, lividness in one of the tubes appears in a most striking manner, if any hypo be present in the water; especially you may perceive it in looking down into the tube from above its mouth. The exactest cleanness, both of glasses and of hands, is necessary, the slightest traces of hyposulphite of soda else being instantly perceived. For examining the proofs exactness, I procured a solution of one part of hypo in a million parts of water. This solution changed the vapour of iodized starch in a perfectly perceptible degree. PHOTOGRAPHIC GLEANINGS FROM THE CONTINENT. M. Ommeganck, writing in the Bulletin Beige de la Photo- graphie, comments on the large number of new formula!, innovations, and results which are communicated from time to time to photographic journals, and remarks that the publication of so many fresh methods often mystify rather than encourage photographers, many of whom, having met with but little success in the employment of some strongly- recommended preparation, are thenceforth disposed to disregard all novel suggestions. It states, that while we ought to feel indebted to investigators for making known their experience to other’s, who, from want of time or means, are themselves unable to pursue similar experiments, we are glad to have confirmatory evidence of the success of a pro cess or preparation before adopting it. For the purpose, therefore, of giving its readers an opinion on certain novel ties, the Bulletin proceeds to criticise some of the processes recently published in its columns. Pinholes in Negatives.—The formation of pinholes, he re marks, is not due so much to the presence of a minute quantity of sulphate in the silver bath, but rather to the production of acetate of silver or other analogous bodies by the oxidation of ether or alcohol introduced into the bath with the collo dion. The collodion often contains a small quantity of pure iodine, and this, being converted into iodide of silver, liberates the oxygen. After a bath has been in use for some time, iodoform and iodide of carbon arc both present, and these bodies have a tendency to diminish the solubility of the iodide of silver contained in the bath, which is already saturated with that compound. Minute crystals of iodide of silver are there fore deposited on the plate and on the sides of the bath, the same effect being produced by the introduction with the collodion of a large excess of ether and alcohol. The best remedy is to add distilled water, then to filter, and afterwards boil the solution, adding a requisite amount of nitrate of silver. If the bath is much worked, it will be found advantageous to pursue this treatment every day. Pinholes are likewise caused by nitrate of lead con tained in nitrate of silver when made from cupelled silver; there is no efficacious method of remedying defects arising from this cause, as they are constantlv recurring, and the presence of the lead is very difficult to discover. On the method of Recovering Gold Residues, as proposed by Mr. England in our pages, he says, from long experience he thinks that this process is not altogether satisfactory. The sulphate of iron precipitates all the gold, but fails to do the same with the silver salts. It is better to treat the old gold baths with a mixture of sulphate of iron and common salt, to which a few drops of hydrochloric acid have been added; by these means the precious metals are com pletely precipitated, the gold being in a metallic state, and the silver in the form of chloride. The mass is washed, first with water slightly acidulated with hydrochloric acid, then in pure water, and finally treated with aqua regia, which dissolves out the gold. The chloride of silver is worked up with the residues obtained from the washings of prints. Residues should not be reduced in small quantities. Fumigation of Sensitized Paper.—According to experi ments recently made on this subject, he finds it best to