CHEMICAL SCIENCE. 207 



and three of spirit, are carefully mixed together and allowed to stand 

 for three or four hours, after which the mixture is filtered. To each 

 ounce of the liquid is then added an ounce of saccharine matter (grape- 

 sugar being preferred), dissolved in equal portions of spirit and water, 

 say about half a pint of each. This liquid may be used for depositing 

 silver either upon horizontal or vertical surfaces, provided it is kept in 

 contact with the glass, which must be kept heated to about 160 Fahr., 

 until the deposit has been obtained. As soon as the silver on the 

 glass is dry, it may be varnished with common mastic varnish to pre- 

 serve it from injury. This invention may be employed for depositing 

 silver upon looking-glasses and all other descriptions of glass. The 

 process is not unhealthy, and there is not at any time a disagreeable 

 smell. The coating of silver is very durable, and is capable of with- 

 standing heat as well as damp. London Journal of Arts, July, 1849. 



APPLICATION OF GUN-COTTON TO THE SILVERING OF MIRRORS. 



MR. H. VOHL, a member of the Paris Academy of Sciences, has 

 discovered that a solution of gun-cotton in a caustic alkaline lye pos- 

 sesses in a high degree the property of precipitating silver from its 

 solutions in the metallic forms. If gun-cotton be placed in contact 

 with a caustic alkaline lye of sufficient strength, the cotton dissolves, 

 disengaging considerable heat and also ammonia, and furnishing a 

 deep brown liquor, which, on the addition of an acid, gives rise to a 

 brisk effervescence, with a disengagement of carbonic and nitrous acids. 

 The manner in which the gun-cotton comports itself shows that it is 

 not dissolved as such, but undergoes a decomposition, in which the 

 atoms of the oxygen in the nitric acid combine with an atom of the 

 carbon of the cotton, and give rise to the carbonic acid, which, as well 

 as the nitrous acid, combines with a portion of the potash. A new 

 decomposition of the nitrous salt by the potash, in presence of sub- 

 stances containing hydrogen, furnishes the ammonia. The following 

 is the most remarkable property of this alkaline solution. If a few 

 drops of nitrate of silver be added to the solution, with enough ammonia 

 to redissolve the oxide of silver which is formed, and if heat be applied 

 gently by means of a water-bath, a moment arrives when the liquid as- 

 sumes a dark brown color, showing an effervescence, and then all the 

 silver is precipitated on the sides of the wood containing the solution, 

 as a polished mirror. This mirror surpasses in brilliancy that ob- 

 tained by ethereal oils or ammoniacal aldehyde. It is found also that 

 cane-sugar, milk-sugar, mannite, gums, and other substances which 

 become explosive when treated with nitric acid, act in the same man- 

 ner. Picroazotic acid, under the same circumstances, produces a 

 bright metallic surface. It would seem that this reaction takes place 

 with all bodies which do not furnish the products of oxidation when 

 treated with nitric acid. 



PHOSPHORUS IN IRON. 



AT the meeting of the British Scientific Association at Birming- 

 ham, Mr. Rinman stated that phosphorus had been discovered in 



