The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Silver
M. Tranchant has written a book entitled "La Linotypie" (Paris, 1896: Gauthier-Villars), in which he describes many processes for photographing on textiles.
Silver (Ger., Silber; Fr., Argent; Ital., Argento). Ag= 108. This metal occurs either alone or in combination with various metals and elements. There are three principle methods of extraction of the metal from its ores : (a) alloying with lead, and subsequent cupellation, (b) amalgamation with mercury, and recovery of mercury by distillation, (c) hydrometallurgic process, in which the silver is converted into a soluble salt, and pre-cipitated with copper. Silver may be obtained, chemically pure, by decomposing the chloride AgCl with hydrochloric acid and zinc; the metal separates in a spongy form, and may be fused under carbonate of soda to prevent access of air, and obtain a button of silver ; or by adding hydrochloric acid to silver nitrate solution, collecting the chloride and reducing this to the metallic state. When pure, silver will absorb twenty-two times its volume of oxygen if exposed to the air in a melted state, but on cooling the oxygen is given off. It is the best conductor of heat and electricity of all the metals, and it is extremely malleable and ductile. When examined by transmitted light, as the thinnest leaf, it is of a distinct emerald green colour. It can be drawn into wire, 400 ft. of which only weigh 1 gr., and its tenacity is so great that a silver wire £ of an inch in diameter will support a weight of 187 lbs. It melts at about 1,832o F. Molten caustic alkalies, or alkaline nitrates, have no effect upon it; it is unaffected by the air, but oxidised by ozone; sulphurous vapours, however, immediately act upon it, forming sulphides. Many silver salts are acted upon by light, with partial reduction to the metallic state.
The relative sensitiveness of various silver salts, as given in the following tables, should prove of very great value to the experi-menter ; but it must not be forgotten that special circumstances may considerably influence the question - a matter obvious enough when we mention that chloride of silver by itself (that is to say, in an absolutely dry state) appears to be quite insensitive to light, and doubtless the same holds good for the other haloid salts of silver. Speaking generally, the tables are as accurate as possible, in relation to usual methods of working.
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