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
• OAI: oai:de:slub-dresden:db:id-1780948042-18620000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Seite 1-72 fehlen in der Vorlage. Vorlagebedingter Textverlust.
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

, 1862. ie ar, ig it ini tir field® epartm. rance w the g rtificati tograpb) epartm® vengeap’ he part' f the P lepartu? link at • ish pho’ iavebel’ d day 1 away: A mel imissio” he soli the wall the Br iouncet2 ght rea re a pri% nent. 3 door"l altered steps;M rat he i, as a d it. pb f art," in I s vere 10 u »le. I to one', have” ve enq, re jou^ iced in. main 83 ave, if 7 ill,evd time y 'the be, the Bo" a the" so, wa® c con® Contip. IS acce" I a plaPy , then, cd the F ; no* papery hicpof> the " ■ the i #0 42 produd r ind4 itter r I May 9, 1862 J THE PHOTOGRAPHIC NEWS. 219 DECOMPOSITION IN COLLODION. BY AUG. TESTELIX. PHOTOGRAPHIC collodion is a mixture of many substances which readily react upon each other, giving rise to sponta neous decompositions which effect great changes in the com position of this valuable photographic agent. The principal elements of collodion are ether and alcohol; the former, especially, constituting the greater portion of it. Ether being a very unstable compound, it is easily decom posed by the action of the air, hence it follows that collodion is also altered under similar circumstances. On the other hand, prepared photographic collodion con tains salts, with bases’almost always alkaline, whose presence singularly hastens this alteration ; moreover, these bases are combined with a metalloid (iodine), which also exercises, in another direction, and under the influence of light, a decom posing action upon ether and alcohol. Lastly, the products resulting from these successive decompositions act injuri ously upon the pyroxyline, which forms the most delicate part of collodion. It is this series of complex reactions which are the primary causes of the variability of photo- graphic processes, where the solution of the pyroxyline serves as a basis, and as the medium of the sensitive agent, that we propose to study in this present article. We now proceed to carefully analyse the changes that take place through the contact of air with these various sub stances, and the reactions which these latter exercise upon each other. 1. The presence of air in the bottles in which ether is kept, changes it partly into water and acetic acid; this latter combines slowly with another portion of the ether, not yet decomposed, and forms acetic ether, but under the influence of light the action is much more vivid and com plex. When the ether is in contact with an oxydisable metal, such as zinc, cadmium, lead, iron, &c., the alteration is more profound, the absorption of the oxygen proceeds more rapidly, and in this case a metallic acetate is produced, and then the reaction is always accompanied by the producton of formyle, which immediately produces a formiate of oxide of ethyl, and a metallic formiate. ,2 - The anhydrous salts with alkaline bases arc for a time without action upon pure ether at ordinary temperature; but when moist air has access, the ether appears reddish brown by transmitted light, and after the lapse of a certain time, acetates and formiates of the same bases are found. . When the alkaline salts are not anhydrous, as is the case 111 Collodion, this reaction always takes place, and in a much aDore evident manner when the ether is in presence of Iohol, which furnishes water in a state quite favourable 0 the reactions, either by decomposition, if it is anhydrous, tr in ceding its water of hydration if it be less concen- The brown tint which the ether then assumes is not re- marked in the collodion, the iodides of which have alkaline “Mes, because it is concealed by other simultaneous reactions, which also give rise to a more intense colouring. Besides this brown tint, due to the decomposition of aldehyde, evolved in these several cases, cannot be very apparent in collodion where, the alkaline substances exist only in very small quantities. 3. When the ether contains an iodide or a bromide in solution, and it is in this condition that we must always regard the ether of the collodion, the spontaneous changes developed are always more numerous; and if a slight decomposition has already commenced by the absorption of oxygen, the reactions proceed rapidly, although they take place nevertheless with an ether at first very pure. besides most of the iodides and bromides, as well as ome c on es, by dissolving in ether, are partially decom posed, disengaging according to the nature of the salt, iqdiner,bromine, or chlorine, the contact of which, with , j. determines the decomposition of this latter, by producing corresponding acids, which themselves act upon the ether to form other products (acetic acid, formic acid, for nitrate of oxide of ethyl, aldehydic acid. &c.). Under the influence of light the iodine and bromine of the iodides and bromides dissolve, the contact of hydro genous organic substances (ether and alcohol) paitially de composed these matters by removing their hydrogen, with which the iodine and bromine have a great tendency to combine, there is formed on the one hand an oxide of the base as first united to these metalloids, and this oxide com bines with the acetic acid, which, in the first place, existed in the ether, and which is also produced in a quantity pro portionate to the oxygen disengaged during this reaction, there results then an acetate, while, on the other hand, the iodine or bromine, removing the hydrogen from it, produce hydriodic or hydrobromic acid, which, in the nascent state, is in its turn decomposed by the ether, forming water and hydriodic and hydrobromic ether. Iodine or bromine, added directly to the ether, produce hydriodic and hydrobromic ether (corresponding, we might say, with formic acid), iodized or bromodized compounds, formyle, a body resembling heavy chloric ether, and lastly, a product analogous to chloral. In distilling the liquid by a gentle and gradual heat, we obtain all these products in succession, with the exception of the periodide of formyle, and liquids analogous to chloral, which remain in the retort, mixed with a variable quantity of heavy bromic ether. 4. Iodine dissolves in alcohol, absolute or diluted with water, and colours it of a very deep red; but it does not appear to cause any very evident reaction ; nevertheless, if we add to this liquid some hydrate of potassa, or of soda, the colour completely disappears when the liquid is warmed, and quicker in proportion as the solutions are more concen trated. Here is, then, produced some iodide of potassium or of sodium, according to the base added, some formic acid, formiates of the same bases, and periodide of formyle, if the potassa or soda does not remain in excess. This reaction is produced in the same manner, and almost as quickly, with the oxides of most other metals. Fragments of zinc, cadmium, iron, lead, &c., produce the same effect, and in every case where we deprive an alcoholic solution of iodine of its colour, by introducing slips of metal, there is formed, among other products, a certain quantity of iodide of formyle. The greater part of this iodide is deposited, on straining, in an extremely light granular form, which dis engages a very pungent odour when isolated from the mixture. Upon gently evaporating the liquid, in proportion as the alcohol becomes volatilized, crystals of iodide of formyle are deposited, which a slight washing with pure water sepa rates from the metallic iodide and the formiates which have appeared during the reaction. 5. When we leave to itself a mixture of alcohol, ether, iodine, and monohydrated nitric acid, in a bottle that is not quite full, or slightly corked, beside the formation of all the bodies we have instanced, we remark, at the expiration of a certain time, a deposit of yellowish white needle- shaped crystals. Sometimes it happens that this deposit consists of a heavy oily liquid, but the latter is produced when the mixture is prepared with bromine instead of iodine. The composition of this substance is unknown to us ; its instability, even when kept under water, only admits of our ascertaining that the influence of light colours it brown, and appears to decompose it into iodine and a gaseous substance, the odour of which is similar to that of chloral. If wc mention these facts, which, perhaps, may appear foreign to the question, it is, on the contrary, because we find their application in all the reactions which take place during the different phases of the alteration which photo graphic collodion undergoes. For, in studying, for example, the reactions to which a mixture of iodine, alcohol, ether, and nitric acid give rise