Photography, Artistic and Scientific

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Downey and Company, 1895 - Photography - 257 pages
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Page 192 - At the commencement the solution has a pure green colour, by continued digestion it turns yellowish-green, and finally greenish-brown. When this moment has arrived, the remaining ferric hydrate should be filtered off, and the solution be submitted to a quantitative chemical analysis. Although the determination of the amount of iron and oxalic acid contained in the solution is one of the simplest of analytical operations, we tried at first to dispense with it. Closer investigation, however, proved...
Page 191 - The precipitate is then washed with hot water by decantation, until the wash water is no longer alkaline. It is next placed in a cloth, and by pressure freed from the greater part of the water. With the ferric hydrate thus obtained, which ought to have a syrupy consistency, there should be mixed about 200...
Page 192 - ... of determining the composition of the solution by analysis and then diluting it to the required degree. Further it should be noted that any quantity of the solution may be prepared at once, and then kept in stock. From the analysis we ascertain the quantity of ferric oxalate contained in 100 c.cm.
Page 193 - To the normal ferric oxalate solution is added in the dark room, and keeping the dish rocking, as much of neutral ammonium or sodium oxalate as will just dissolve at the ordinary temperature. For this purpose will be required of the above named salts : To normal ferric oxalate solution 100 cc.
Page 257 - BEGINNERS, because always ready for use, free from mechanical complic n lions, and extremely easy to work, USED BY THE LEADING EXPERTS, because they take any Lens, work with any Plates ur Films, and provide every adjustment required in Photography.
Page 48 - As the area of a circle is proportional to the square of its diameter, it follows that the resistances of round conductors are inversely proportional to the squares of their diameters.
Page 192 - ... of the solution, as well as any slight excess of oxalic acid which happens to be present. The liquid is then diluted with so much distilled water that every ounce of it may contain 100 grains of ferric oxalate, Fe2(C2O4)3.
Page 195 - Directly this has taken place, the sensitised surface should be dried before a fire or stove, or over a gas-burner. It is of the utmost importance that the paper be perfectly dried. The drying point is indicated by the change in colour of the surface, which changes from lemon to orange yellow, and by the crackling sound of the paper. Great care should be taken not to scorch the surface. A scorched sensitive surface gives grey, fogged prints. It is important to allow a sufficient, but not too long,...
Page 191 - ... of the exposure as accurately as with silver. Besides this, the development of the paper is entirely omitted. A simple, short washing of the prints, first in acidulated, then in ordinary water, is sufficient for finishing the pictures.

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