The photographic news

• Bandzählung: 6.1862
• Erscheinungsdatum: 1862
• 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-id1780948042-186200003
• PURL: http://digital.slub-dresden.de/id1780948042-18620000
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• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
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• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

Feb. 21, 1862.] THE PHOTOGRAPHIC NEWS. solution, striking on the glass plate, being broken up on reaching the side of the bath. The result is an inequality of action upon the iodide; the inequalities are reproduced upon the film by reason of the promptitude with which the latter is decomposed under the influence of the nitrate of silver. From this we may readily conceive that this effect may be diminished by the employment of a vertical bath, especially by allowing the plate to descend gradually and gently into the solution : this is verified by experience. The same kind of spots are produced also when the col lodion contains a notable quantity of free iodine. Lastly, the same accident occurs when the collodion con tains too large a proportion of iodides, especially if the sensitizing silver solution is new and strong. Moreover, these various phenomena depend upon the relative quan tities of pyroxyline, ether, and alcohol, contained in the collodion. The three iodides we have examined are nearly all that are employed in the preparation of wet collodion. Some times, however, iodide of iron and iodide of zinc are intro duced* Iodide of iron appears to me of no advantage in collodion. Much has been said in praise of its rapidity ; as for myself, I have never observed anything remarkable in it in this respect; at least when this salt is produced, as recommended by M. Eugene Sahler, in the collodion itself, my various experiments lead me to suppose that the same result would take place with other iodides in the same condition. I shall say only a few words upon iodide of zinc. Its properties are nearly the same as those of iodide of cadmium. It does not appear to me advantageous when employed alone; but I have obtained a very good collodion in em ploying it concurrently with other iodides. Before speaking of the different bromides, it remains to examine the action of iodine, when free in the collodion. A well-established fact is the preservative action of iodine against fogged negatives. A pale collodion, that is, one containing no free iodine, sensitized in a neutral silver solu tion, almost always gives fogged negatives. 'To make the fogging disappear, the silver solution must be acidified, or what indirectly produces the same result, free iodine must be added to the collodion. To this end, we may also make use of chloride of iodine, which, at the moment of sensitizing, is transformed into chloride and iodide of silver, and set a certain quantity of nitric acid in the film at liberty. (To be continued.) • * I shall not in this,, oonic bases, nor of th i enter upon the examination of the iodides with introduced. 5 iodides of the metals of the first section, recently PHOTOGRAPHIC CHEMICALS: Their Manufacture, Adulterations, and Analysis. Ilydrosulphuric Acid.—Frequent mention has been made in these articles of hydrosulphuric acid, or sulphuretted hydrogen, as it is just as frequently called, and in most works on photography it is referred to. It is essential, therefore, that the photographer who desires to acquire a knowledge of the chemistry of photography, should be ac quainted with the history and properties of this body. Hydrosulphuric acid is prepared by acting on a metallic zulphide with an acid, in a gas generating apparatus. As Ins apparatus is of very general use, we think it advisable o give a brief account of the readiest method of construct ing one. A large, wide-mouthed bottle, containing about a pin is fitted with a good cork. Through this is pierced .''ll 1018, to admit of moderately stout glass tubing, techni- f a IY.2no n.as " quill tubing.” One piece is long enough ° re shto 1e bottom of the bottle, and to project about C1 ”/l ■ .8 above the cork, being surmounted at its upper end bysafupnel blown on to it (^ch “funnel tubes” can be vurchased tor a f... 1 x- Mo EE “ 1ew pence at an operative chemists); through the other hole in the cork a piece of glass tube about six inches long is fitted; this tube is bent at right angles; one arm just passes through the cork, and the other projects horizontally outwards. Another bottle is now selected of a smaller capacity to the former, and fitted in like manner with a cork having two holes in it. Through one hole a glass tube passes, one end of which reaches half way down the interior of the bottle, and the other end, being bent, at about three inches from its extremity, ar right angles, rises up to and just meets the bent tube of the larger bottle. In the second hole of the cork of the smaller bottle 'another right angled tube is fitted, one end of which just passes through the cork, and the other end of which projects outwards horizontally. Finally., a fifth piece of glass tube is bent at right angles about two inches from one extremity, and the other end cut off to such a length that when the bent end is on a level with the bent tube of the second bottle, the straight end is within an inch of the table. The tubes connecting the two bottles are then joined together by fine vulcanised india-rubber tube; the loose tube is in a similar way connected with the smaller bottle, and the apparatus is complete. The first large bottle is called the generating bottle, and the other the washing bottle. The latter is to be filled with water until it rises to about half an inch above the extremity of the tube, which we have explained is to project half-way into it, and the large bottle is to have about a dozen lumps (about the size of marbles) of fused sulphide of iron placed in it, which are then to be covered with water. The apparatus is then to be tested for leakage in the following manner:—moisten the surface of the corks, the necks of the bottles where the corks fit, and the india- rubber tubes, with plenty of water, then apply the lips to the loose tube hanging down, and blow air in gently ; the liquid will be forced up each long tube in the bottles, and, upon stopping the end of the loose tube with the tongue, should remain at the same level quite stationary. If, how ever, the apparatus leaks, the column of liquid in the tubes will rapidly descend, and the condensed air will escape at the leaky places with a hissing noise, where also it may sometimes be seen bubbling through the water used to wet the corks, &c. If the leakage occurs round the neck of the bottle it may frequently be prevented by giving the cork a tighter squeeze into the neck. If the leakage be at the india-rubber joints, the best plan is to wet them and then bind them round with fine copper wire; but if it be at the holes in the corks, or through flaws in their substance, the remedy will not be so simple. A paste must be made of linseed and almond meal, and, having well wetted the corks, they must be well smeared over with this until all leakage has been found to have ceased upon being tested for; the linseed coating may be smoothed over with the fingers, having wetted them with a little water. As soon as the apparatus is tight it is ready for use. A good stoppered bottle is nearly filled with distilled water, which has been recently boiled and allowed to cool (to deprive it of air), and then placed near the washing bottle, so that the loose glass tube dips into the distilled water and goes nearly to the bottom. Dilute sulphuric acid (one part of oil of vitriol to four of water) is now to be poured into the generating bottle through the funnel tube when the hydrosulphuric acid gas will be immediately seen to rise from the sulphide of iron through the liquid in the form of minute bubbles. The reaction is expressed in the following equation FeS+HO.SO=FeO.S04+HS. FeS being the sulphide of iron and HS being the hydro sulphuric acid, a compound of equal atoms of hydrogen and sulphur; the other product of the reaction being sulphate of iron FeO.SO 3 . The gas accumulating in the upper part of the bottle drives the air before it, and bubbles first through the washing bottle, where it is deprived of its impurities, mechanically carried over, and then through the bottle of distilled water, where it is absorbed. It is necessary either to perform this operation in the open air, or under a chimney where there is a good draught, in consequence of the dele-