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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
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- http://digital.slub-dresden.de/id1780948042-18620000
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- Bandzählung
- No. 196, June 6, 1862
- Digitalisat
- SLUB Dresden
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- Wahlperiode
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Zeitschrift
The photographic news
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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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270 THE PHOTOGRAPHIC NEWS. [June 6,1862. health ; also, it is very unsightly to have the fingers in mourning while engaged in posing sitters, especially ladies, who are not always convinced by the assurance that “ it will not come off.” And yet developing is'the very part of the process that a photographer who really cares to excel cannot trust to an assistant; in witness of which it may be remarked, that all those gentlemen who most illustrate their profession by their photographic gems are in the habit of developing every picture they take with their own hands. It is evident, therefore, that any apparatus that could efficiently replace the hand for sustaining the plate during development, would be a great boon to all grades of photographers, both pro fessional and amateur. But, although several holders have been brought forward from time to time with this object, in the construction of which considerable ingenuity is evinced, they are not up to the mark sufficiently to induce their adoption in preference to the hand, for which not one of them is an effective substitute. One of the main objections to their use is, that—I think in all cases—the instrument is made to grasp the glass plate at several points by means of certain parts upon which it rests, and which are also kept pressed against its edges by means of springs or other appliances. These parts, which vary in form in different holders, may be generalized by fig. 27 ; the plass plate (a) Fig. 27. being held in pads of glass or gutta percha, or other neutral material (b). These pads being of a material not affecting silver solutions, are without any chemical influence during the process of development; but they act mischievously by serving as conductors to lead the liquid off the surface of the plate, which is soon left nearly dry, unless more than ordinary caution is used. This vice would be corrected if the shoulder of the pad pressing against the edge of the plate were made of less thickness than the thinnest plates used, but in such a case it would have only a very insecure hold upon the glass, and one evil would probably only be exchanged for another. Besides this common fault, most of the holders have other objectionable features peculiar to their several instances, which need not be noticed here. I have used considerably a very simple holder for deve loping plates up to whole-plate size, withing soiling the fingers, which, although much inferior to the unassisted hand, has proved, in my experience, more practical than several others which I have bought and tried. It has the advantage of cheapness and simplicity; anyone can make one for himself. It has not, necessarily, the disadvantage named above, as common to nearly all holders, but it has others, from which some are free. It consists simply of a piece of glass larger than the sized plate it is intended to Fig. 28. hold, with one of the corners cut off. Upon this glass plate are fixed with cement four very thin slips of glass, as shown in fig. 28, to serve as pads for the plate to rest against, ample space being provided, so that the glass cannot touch both sides or ends at one time. In use, the plate to k developed is laid on the glass between the pads, the holdet is held by the further end, and the developing liquid s poured off and on at the corner which projects over the cut off portion. It can he held safely at an angle of about 8O°to examine the progress, of development, which can be seen through the glass holder. It is needless to remark, that this holder, like every other, must be scrupulously washed after every plate that is developed upon it. The principal disadvantages of this holder are, that each one is only suited to one sized plate, consequently several are necessary for those operator's who work with different sizes. Also, sometimes a portion of the developing solution will get between the holder and the plate, and if it be dis coloured, or if any deposit be formed betwixt the glasses, i hinders to some extent the examination of the progress, the development. A little care will generally prevent this from occurring. (To be continued.) PHOTOGRAPHIC CHEMICALS: Theib. Manufacture, Adulterations, and AxALxsIs. Potash salts (continued).—Of all bases potash possesses the strongest affinity for the greatest number of acids, and neutralizes their effects in the most perfect manner. Its alkaline characters are so intense that when the acid is weak it is unable to mask the alkaline reaction of the base, unless several equivalents are taken. All potash salts are colourless except when the acid is coloured. In the absence of sod 1 they communicate a violet colour to the blow-pipe, or spirit flame, but this reaction cannot be observed, if the slightest trace of soda is present. All potash salts are soluble in water, except when they are united with a great excess of silicic, titanic, or other insoluble acid. Some of its salts ane however, sufficiently sparingly soluble to admit of their being employed as tests for the presence of this element when it is not in too small proportions; thus perchlorie acid, tartaric acid, carbazotic acid, sulphate of alumina hydro-fluosilicic acid, and chloride of polatinum, form preci pitates when a moderate quantity of potash is present, the precipitant being added in concentrated solution. Potash has a great tendency to form double salts, its combinations, of this class, with many metallic oxides, forming crystals ol extreme beauty and permanence. Potash is obtained com mercially almost solely by means of the vegetable kingdom, it is present in small quantity, as far as percentages are con cerned, but in enormous quantity, when the mass is con sidered, in felspar, granite, and many other rocks which, by the disintegrating action of the atmosphere and weather, con stitute the great bulk of earthy soils. Plants and vegetables growing in this debris of the primitive rocks have the pro- perty of absorbing and concentrating the potash from ft and it is from the ashes of these that potash is almost universally extracted on the large scale. Another source of potash is from tartar, this is a deposit consisting of the alkali combined with tartaric acid, and is deposited in enormous quantities from grape juice during the manufac ture of wine, the source of this being, of course, the same as in the preceding instance. From the crude ashes of inland plants the potash is obtained by soaking in tubs of water ; the alkaline solution thus obtained is boiled down in iron pans until it solidifies on cooling. It now forms a brown mass, which is placed in a reverberatory furnace, and the flame allowed to play over it with constant stirring with an iron rod, until the organio matter is entirely consumed ; in this state, it forms what 3 called burnt or calcined potash. To purify it, it is dissolved in two parts of boiling water and the solution after being filtered through white blotting paper, or bleached linen, 18 evaporated in an iron pot to the proper degree of concentra. tion : it is then, allowed to stand for some days, when the sulphate of potash crystallizes out, and may be strained ott Upon about lize o are la: then 1 or plai Wh one or in a a hot wa days i the cle of eitb observi rated c be perl silver three t for thnr from tl hecessa this op b con the nit Wha ein i Aver M; i parts oi then to it will for sub the pre: of the ducing Qecomp tories it the qua May all Mucin The: Ate ver eteetir notice t , Sulpi lydroel oawi ofpotas Phos, ofhydr Sarboni Amnmon Moccule Nitr Sxcess Snlphat (ced i Present Nitr Cyai Ehloric become (Positi »ell.) Bent, a
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