M. TECHNOLOGY. 551 



are first carefully washed, and immersed for a moment in a 

 saturated solution of gallic acid, and then in a solution of 

 twenty parts of nitrate of silver in 1000 parts of distilled 

 Avater. This double immersion is to be repeated until the 

 appearance of the fibre is of a fine silvery color. It is next 

 to be immediately placed in the mixture of the two first- 

 named solutions until it is perfectly silvered, and then in a 

 solution of carbonate of lime, washed, and allowed to dry. 



In the case of bones, leather, and other similar substances, 

 the solution may be applied with a brush, instead of im- 

 mersing the article in it. Earthenware, etc., must be coated 

 with stearine or varnish before the application of the silver 

 solution ; and when the articles are porous, even a coating 

 of soluble glass should be first applied. Ordinary glass or 

 porcelain is to be carefully cleaned with distilled water or 

 alcohol, and then treated with a mixture of the first-mention- 

 ed solution, which is to be kept in a dish of earthenware or 

 gutta-percha. The deposit of silver begins after a quarter 

 of an hour, and continues for several hours. The object is 

 then to be washed with distilled water, allowed to dry, and 

 covered with a protecting varnish. If the object be slightly 

 heated, it will accelerate the deposit of the silver. 



Metallic articles should be first cleaned with nitric acid, 

 and afterward rubbed with a mixture of cyanide of potassi- 

 um and silver powder, then washed with water, and immersed 

 in the above-mentioned solutions, Nos. 1 and 2, until they 

 are sufiiciently silvered. Iron, however, must previously be 

 immersed in a solution of sulphate of copper. 5 (7, 1872, xliii., 

 344, 



PEOCESS OF SILYEEING GLASS VESSELS. 



Dissolve 61f grains of nitrate of silver and 38^ grains of 

 aldehyde-ammonia in separate parts of If pints of distilled 

 water, mix the solutions, and filter. Cleanse the article to 

 be silvered from every trace of grease by washing with a solu' 

 tion of carbonate of potash, rinse with alcohol and with wa- 

 ter in succession, fill it w^ith the silvering solution as high as 

 it is to be silvered, and hang it in a water-bath. The latter 

 must be heated very gradually. When the temperature of 

 the water reaches 122Fahr., the silver begins to separate, 

 and little time is then required to complete the deposit. At 



A A 2 



