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Knight's Mechanical Encyclopedia (ed. Knight) 9 1 Browse Search
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to preparing a plate for the negative process — and dried in the dark. The sensitive surface so produced blackens on exposure to light, and will consequently give a picture under a photographic negative. An excess of free nitrate of silver is necessary to impart sensitiveness; an addition of citric acid and other organic substances is used to produce the desired tints. After exposure the picture is fixed and toned as usual. Col-lo′di-on-proc′ess. A process in photography invented by Archer. An iodized collodion is made by impregnating a solution of gun-cotton in ether, with a small quantity of iodide of potassium or cadmium. A film of the iodized collodion is spread on the glass, which is then immersed in a solution of nitrate of silver. The image is taken in the camera, developed by a weak solution of pyrogallic acid and acetic acid, or a solution of protosulphate of iron. Excess of iodide of silver is removed by hyposulphite of soda or cyanide of potassium. This gives<
ions which distinguish the history of photography, perhaps the most important in its effects was the introduction of collodion, which took place in 1850. To Mr. Scott Archer of London is due the credit of the negative-collodion process, which has made photography the most important art-industry of the world. In justice to M. le Gray, it should be added that he had previously suggested collodion as likely to be of service in photography. In the autumn of 1851, Mr. Archer published a full description of his process, which did not differ essentially from that now practiced. Collodion is a viscid solution of gun-cotton in a mixture of alcohol and ether. Subsequently the idea spread to almost all civilized nations. The perforating-machine, for partially dividing the postagestamps in the sheet, was invented by Mr. Archer of England, 1852, and he received £ 4,000 from Parliament for his invention. Rowland Hill's penny-postage scheme was adopted January 10, 1840. The number of
. 9, 1855. 13,961.Schwabe, Dec. 18, 1855. 18,244.Hannen, Sept. 22, 1857. 19,771.Hannen, Mar. 30, 1858. 20,731.Rowland, June 29, 1858. 22,036.Smith, Nov. 9, 1858. 22,679.Smith, Jan. 18, 1859. 23,815.Albert, May 3, 1859. 25,106.Erdmann, August 16, 1859. 29,665.Brumlen, Aug. 21, 1860. 30,521.Mayer, Oct. 23, 1860. 31,224.Brumlen, Jan. 29, 1861. 33,337.Cary, Sept. 24, 1861. 38,283.Cobley, Apr. 28, 1863. 42,407.Rowland, Apr. 19, 1864. 45,587.Coggeshall et al., Dec. 27, 1864. 46,706.Archer et al., March 7, 1865. 48,099.Rowland, June 6, 1865. 48,243.Baker, June 13, 1865. 51,018.Chadwick, Nov. 21, 1865. 52,144.Delafield, Jan. 23, 1866. 53,093.Spence, March 6, 1866. 53,583.Delafield, Apr. 3, 1866. 55,249.Delafield, June 5, 1866. 56,685.Fell et al., July 24, 1866. 59,135.Overmann, Oct. 23, 1866. 59,901.Fell Antedated. et al., Nov. 20, 1866. 59,902.Fell et al., Nov. 20, 1866. 62,097.Van Der Weyde, Antedated. Feb. 12, 1867. 62,130.Hannen, Feb. 19, 1867. 64,763.H