Synopsis
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1864 Excerpt: ... by the action This is the second artiole of a series. The first, on The History of Photography, appeared in No. 27, April, 1864. The third and concluding paper will be given at an early date. of light in the camera, are then removed by a strong solution of common salt, or a weak solution of hyposulphite of soda, which takes away the golden tint; and finally, the plate is washed with hot distilled water. If the exposure in the camera is allowed to exceed a certain limit, the mercurial vapour will bring out a negative, instead of a positive picture; since a certain amount of actinic action gives to the iodide, etc., of silver a power of condensing the mercury, while a greater amount takes that power away. Process with Paper. A very simple process consists in soaking paper of a suitable texture in a solution of common salt, drying it in blotting-paper, and then brushing it with a solution of nitrate of silver. If the paper is required to be very sensitive, iodide of potassium is substituted for the common salt; and if extremely sensitive, bromide of potassium is used instead of either. The relative amounts of the salts employed is of great importance. After exposure in the camera, the picture is fixed with hyposulphite of soda. The Galotype. The paper is washed with nitrate of silver, and then dipped in a solution of iodide of potassium: in this state it is unaffected by light, but it is rendered highly sensitive by washing with a solution of nitrate of silver, to which acetic acid and gallic acid have been added. When removed from the camera, the picture will gradually develop itself in the dark; but it is brought out at once, by gallo-nitrate of silver and heating at the fire. It is fixed with hyposulphite. Pictures obtained by this and similar processes ar...
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