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XVI. On Silvering Glass. By Justus yon Liebig*. 



THE following are the proportions which a long series of 

 experiments has led me to adopt as the best for preparing 

 silver looking-glasses. 



Solution of Silver. — One part of fused nitrate of silver is dis- 

 solved in ten parts of distilled water. 



Solution of Ammonia. — (a) Commercial nitric acid free from 

 chlorine is neutralized with sesquicarbonate of ammonia and the 

 solution diluted to the specific gravity 1*115. For 37 parts of 

 nitric acid of 1*29, 14 parts of sesquicarbonate are wanted ; yet, 

 as the sesquicarbonate does not always contain the same amount 

 of ammonia, the proportion is not quite definite. 



Nitrate of ammonia may be advantageously replaced by sul- 

 phate of ammonia. 



(b) 242 grammes of sulphate of ammonia are dissolved in 

 water, and the volume made up to 1200 cubic centims. ; the 

 specific gravity of this solutionis 1*105 to 1*106. 



Caustic Soda. — This must be prepared from carbonate of soda 

 free from chlorine, and have a specific gravity of 1*05; 3 vol- 

 umes of a lye of 1*035 specific gravity, such as is obtained in the 

 manufacture, when evaporated to 2 volumes yield a lye of 1*05. 



A. Silvering -Mixture. 

 100 volumes of solution of ammonia. 

 140 „ „ silver. 



750 „ soda-lye. 



990 



If sulphate of ammonia be used, the solution of sulphate of 

 ammonia must be poured into the solution of silver, and then 

 the soda-lye added in small portions ; after mixing, the liquor is 

 turbid, and must stand at least three days before being used. 

 The clear solution is drawn off with a siphon. 



Reducing -Liquid. — (a) 50 grammes of white sugarcandy are 

 dissolved in water to a thin syrup, 3*1 grms. of tartaric acid 

 are then added and kept boiling for an hour ; the liquid is then- 

 diluted with water to the volume of 500 cubic centims. 



(b) Water is poured on 2*857 grammes of tartrate of copper, 

 and soda-lye added by drops until the blue powder is dissolved. 

 The solution is diluted to the volume of 500 cubic centims. 



B. Reducing -Mixture. — 1 volume of the solution of sugar (a) is 

 mixed with 1 of the solution of copper (b), and 8 volumes of 

 water added, so as to make the whole 10 volumes. 



C. Silvering -Liquid. 

 50 volumes of the silvering-mixture (A). 

 10 „ „ reducing „ (B). 



250 to 300 „ of water. 



* Translated from Liebig's Annalen (Supplement), vol. v. p. 259. 



