66 
SILVERING GLASS BY GUN-COTTON. 
The action of the gun-cotton in this instance shows that 
it is not simply dissolved, but undergoes decomposition, by 
which the atoms of oxygen in the nitric acid enter into 
combination with the atoms of carbon in the cotton, thus 
producing carbonic acid, which, as well as the nitrous acid 
produced by the nitric acid, combines with one part of pot- 
ash. A fresh decomposition of nitrous salt by the potash, 
in the presence of hydrogenated substances, furnishes 
ammonia. 
The most remarkable property of this alkaline solution 
is the following: On pouring into it a few drops of a solu- 
tion of nitrate of silver, and adding ammonia until the 
oxide of silver formed is re-dissolved (the mixture being 
slowly heated in a water-bath,) the liquid will at a certain 
period assume a deep-brown color and effervesce, the whole 
of the silver being precipitated on the sides of the vessel. 
The mirror thus produced is much superior in brilliancy to 
those produced by means of ethereal oils or ammoniacal alde- 
hyde ; and the facility with which it is produced will doubt- 
less render it of practical importance. 
This property is not exclusively possessed by gun-cotton ; 
it is found also in cane-sugar, sugar of milk, manna, gums, 
and other substances which may be rendered explosive by 
treating them with nitric acid. Nitropicric acid produces 
under the same circumstances a reflecting metallic surface ; 
and it appears that this reaction takes place with all bodies 
which, when treated with nitric acid, do not furnish pro- 
ducts of oxidation, but another series of bodies, which 
admit of carbonic acid forming one of their constituent 
parts. — Pharmaceutical Journal, from Technologiste, and 
Newton's Journal. 
