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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
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- Englisch
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- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 183, March 7, 1862
- Digitalisat
- SLUB Dresden
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- Parlamentsperiode
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- Wahlperiode
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Zeitschrift
The photographic news
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Band
Band 6.1862
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- Ausgabe Ausgabe 73
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- Register Index 619
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Band
Band 6.1862
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62. it in ed are addi- meras hori- ect. nd by award , and t. It parts, ide of issing o this ne ad- screw amera 7 A y way to the conve- ments. bjects hance ways s s wort NARY e at s ' itself of the ■inches velop- Society of th® icrica’ 1 tulated Majot re waf olutid s in th® velope’ nes oid e plate t wate‘ led. Society- : J. AV er only, ieth of : set o’ aped if igth of March 7,1862.] THE PHOTOGRAPHIC NEWS. onate of time required in the camera depends on the heat of the water into which the plate is put before its development. The shorter the exposure the hotter the water must be. I have been using this process for about six months, having first tried it with marked effect on Dr. Hill Norris’s plates, when photographing the sun in my 13-feet reflector of 16-inches aperture. Several' of the members of the Society spoke of the great advantages that would accrue from the use of this method for portraits, &c., and said that although they had used hot developers, not noticed any such shortening action as in this instance, where the plate is hot and the developer cold. Protochloride of palladium, which I introduced as a strengthener some years ago, can be applied with great advantage to negatives produced by this method. Univertity of New York, February 13th, 1862. understood, that it readily unites with sulphur, forming a sulphide which is unacted upon by the ordinary acids, and PHOTOGRAPHIC CHEMICALS: Their MAXUPACTURE, Adulterations, and Analysis. Eydrosiilphwnc acid (continued).—The reactions of hydro sulphuric acid with the salts of different metals are very important, both to the chemist and photographer. In the chemical laboratory this substance, both in solution and in the gaseous state is of the utmost importance, inasmuch as the very definite nature of the compounds which it forms with metals, and their ready separation by this means into three classes, forms the basis of almost all systems of quali tative analysis. These classes are—1st, those metals which form insoluble sulphides when sulphuretted hydrogen is passed into their acid solutions; 2nd, those metals which are not precipitated in the insoluble form when sulphuretted hydrogen is passed into their acid solutions, but which come down as sulphides or oxides in solutions rendered alkaline by ammonia ; and 3rd, those metals which are not precipi tated by sulphuretted hydrogen either in an acid or alka line solution. The first group of metals consists of gold, silver, platinum, tin, arsenic, antimony, bismuth, lead, mercury, copper, and cadmium. The second consists of nickel, cobalt, manganese, iron, chromium, alumina, and zinc; while the third contains the alkalies and alkaline earths. It is not necessary for the photographer to enter very minutely into the analytical details, connected with these sulphides, but the broad facts just mentioned should, if possible, be remem bered for many reasons, some of which may now be mentioned, whilst others will appear subesquently. Owing to the decided colours and great permanency of several of the sulphides of the first group, they are largely used in painting, whilst on the other hand, several compounds of these metals with other bodies arc also used in painting. The above knowledge will enable anyone to know beforehand that a pigment consisting of a member of the first group with sulphur—sulphide of I cadmium for instance which is of a beautiful yellow colour— J will stand the attacks of sulphuretted hydrogen in the at- 1 mosphere, unchanged: whilst another pigment consisting I of a member of this group with some other body—chrome s yellow (chromate of lead) or white lead, (carbonate and ! oxide of lead) for instance—will, under the influence of lphuretted hydrogen lose its own colour and assume that 0 file sulphide of the metal which is present. Chrome butW and white lead are therefore not permanent colours, drosre liable to ^ arn ^ 1 in the presence of sulphuretted hy- mh8i the proper colour of sulphide of lead being black, is a AdYantage of zinc white over white lead in this respect , a PP ar ent from a knowledge of the chemistryof these i5 wh' Sulphide of lead being black whilst that of zinc ... 19, the latter can stand, undimmed, an atmosphere Wn .Would instantly darken white lead. Further details on iis subject must be deferred till we speak of the prin- cpaLstallic sulphides seriatim. We cannot warn photo- grap Uf 8 / 00 strongly against the danger of allowing sul- 1 Phure ed hydrogen to escape from the bottle into a room Where any photographic operation is going on. Themetai silver is in the first group above named, and hence it will be which, indeed, is formed in their presence. We will now pass on to the most important sulphides. Sulphide of potassium. These two elements are capable of uniting in various proportions. The only compound which is of interest to the photographer is the one called Heer of sulphide or hepar sulphuris. This consists of tersulphide, pentasulphide, and intermediate sulphides of potassium, mixed with sulphate, and frequently with carb. potash, varying according to the proportion of sulphur used in its manufacture. The common receipt is to take two parts of carbonate of potash and one part of sulphur and heat them together in a covered earthen or cast-iron crucible. When the mass is melted, it is allowed to fuse quietly for some time, and afterwards poured out on to an iron or stone slab. As soon as it is cold it must be broken up, and pre served for future use in a well stoppered wide-mouthed bottle. The above proportion of sulphur to carbonate is too small. The smallest quantity that ought to be used is, for 27G'8 parts (four atoms) of carbonate of potash 160 parts of sulphur, which forms one atom of sulphate of potash and three atoms of tersulphide of potassium. The largest quantity of sulphur which can be used with 276’8 parts of carbonate of potash is 256 parts of sulphur, which when heated together forms sulphate of potash and pentasulphide of potassium, any excess of sulphur beyond this volatilises without enter ing into combination. Liver of sulphur forms a dark grey or brown mass, soluble in water, alcohol also dissolves the poly-sulphides,of potassium which may be present, and leaves the impurities of sulphur, sulphate, carbonate, and hyposul phite of potash undissolved. When the solid mass is kept in badly closed vessels it gradually oxidises and formsamixture of hyposulphite of potash and sulphur. When the aqueous solu tion is added to a liquid, silver, containing gold, platinum, or in fact any of the metals of the first or second group, they are precipitated as sulphides, an excess of sulphur coming down at the same time. On this account, and by reason of its cheapness, liver of sulphur is recommended for precipi tating the valuable metals from the photographer’s old solu tions. This it does in a very perfect manner if care be taken not to employ an excess, but it is liable to the objection of throwing down considerable quantities of sulphur as well unless the operation be conducted by an experienced chemist, who would know exactly when to stop. On this account we do not like liver of sulphur for this purpose so well as sulphide of ammonium, and even this is not so good a means of separating the silver, &c., as the passage of sulphuretted hydrogen through the clear liquids. Sulphide of Ammonium is a very extensively used salt. It is prepared by dividing a quantity of solution of ammonia into two equal parts, and then saturating one with hydro sulphuric acid gas. When no more is absorbed, the other portion of the ammonia is added to the liquid, and the whole shaken together, and preserved in a well stoppered bottle. When freshly prepared, this solution is colourless, and smells strongly of both ingredients; after some time, especially if free access of air can be obtained, it becomes yellow, in consequence of the absorption of oxygen and separation of sulphur, which latter is dissolved by the ex cess of the sulphide of ammonium. The formula of sulphide of ammonium being NH 4 S, and that of ammonia NH,O, the reaction expressing this decomposition will be 2NH,S+0=NH,SHNH,O. This bisulphide of ammonium (NH,S,) is not injurious when in small quantity, and it is even advantageous in some precipitations. Its presence, therefore, may be disre garded. When sulphide of ammonium is fresh, it will precipitate the pure metallic sulphide from solutions con taining silver or gold, without the admixture of any free sulphur. When it has stood for some time, and has acquired a yellow tinge, free sulphur of a white colour is precipitated along with the metallic sulphide. A white precipitate of pure sulphur is obtained when hydrochloric acid is mixed
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