562 ANNUAL EECOED OF SCIENCE AND INDUSTEY. 



first, while thin, the film appears dark, but increases in brill- 

 iancy until a beautiful silvered surface is produced, when the 

 object must be removed, emptied, and washed with distilled 

 water, or its brilliancy may be impaired. The aldehyde-am- 

 monia may be prepared by passing dry ammonia gas through 

 aldehyde. 1 C, 1872, xxi., 336. 



METHOD OF GILDING GLASS. 



The following simplification of Wernicke's process for gild- 

 ing glass has been suggested by Professor Bottger, as exceed- 

 ingly rapid, besides being economical, and adapted to ordi- 

 nary temperatures. Dissolve the chloride of gold, obtained 

 by solution of 1 gramme of pure gold in aqua regia, as nearly 

 neutral as possible, in 120 cubic centimeters of pure water, and 

 6 grammes of caustic soda in 100 cubic centimeters of water. 

 Prepare, as needed, a reducing solution of 2 grammes of glu- 

 cose, 24 cubic centimeters of water, 24 cubic centimeters of 80 

 per cent, alcohol, and 24 cubic centimeters of commercial alde- 

 liyde (specific gravity, 0.870). To cover the interior of a tum- 

 bler, for example, w^ith a brilliant film of gold, put into a sepa- 

 rate glass four volumes of gold solution, add one volume of 

 soda solution, and then one-sixteenth volume of reducing so- 

 lution, and pour quickly into the tumbler to be gilded enough 

 of the mixture to half fill it. Keep it in motion for several 

 minutes, so that every part may be continually moistened. 

 5 (7, 1872, xxxYL, 286. 



COATING COPPER WITH IRON. 



Professor Bottger states that ammonia-sulphate of iron, 

 with suitable batteries, gives beautiful results in the electric- 

 al deposition of iron into thin films or thick plates, accord- 

 ing to the process with double salts of iron described by him 

 about twenty-six years ago. This has proved of great prac- 

 tical value in the preservation of engraved copper-yjlates 

 from wear in printing, by covering them with a thin film of 

 this peculiarly hard, steel-like iron. 15 C, 1872, xyiil, 274. 



TEMPERING STEEL GRAVERS, DRILLS, ETC. 



According to Schiitzleder, of Gosling, watch-makers temper 

 the points of drills, etc., so that "they can be used upon steel 

 tempered in the ordinary way, by heating them to a white 



