604 PERCOMPOUNDS OF TIN. 



formation. The existence of two varieties of the peroxide of 

 tin was observed by Berzelius so early as 181 1, and is the first 

 recorded instance of isomerism. 



Hydrochloric acid is capable of dissolving a great excess of 

 hydrated peroxide of tin, at least two or three equivalents. 

 The peroxide of tin is also soluble in alkalies ; and having in re- 

 gard to them the powers of a feeble acid, it is sometimes called 

 stannic acid. A very dilute solution of potash boiled with the 

 peroxide of tin, forms a solution in which 1 part of potash may 

 contain 16 parts of peroxide of tin. Peroxide of tin is employed 

 in the preparation of the white glass, known as enamel ; and the 

 ignited and finely levigated oxide forms jeweller's putty, which 

 is used in polishing hard objects. The hydrated oxide resem- 

 bles alumina in forming insoluble compounds with the organic 

 colouring matters, and hence its salts are much prized as mor- 

 dants. 



Bisulphuret of tin, Sn S 2 , is precipitated from persalts of 

 tin, of a dull yellow colour, by sulphuretted hydrogen gas. 

 Prepared in the dry way, by igniting a mixture of peroxide of 

 tin, sulphur and sal ammoniac in a covered crucible, it forms 

 the aurum musivum or mosaic gold of the alchemists. In this 

 operation the sal ammoniac is indispensable, although it seems 

 to serve no other purpose than to prevent the elevation of tem- 

 perature which results from the sulphuration. Mosaic gold, 

 when well prepared, has the yellow colour of gold, and consists 

 of brilliant translucent scales, which are soft to the touch. No 

 acid dissolves it, except aqua regia. It is decomposed by dry 

 chlorine, and the compound formed, SnCl 2 + SCl 2 (page 

 379). 



Bichloride of tin, Permuriate of tin, Sn C1 2 ; 1620.6 or 

 129.86. The anhydrous bichloride of tin, known as the fuming 

 liquor of Libavius, is procured by distilling, at a gentle heat, 

 a mixture of 4 parts of corrosive sublimate with 1 part of tin 

 in filings, or tin amalgamated with a little mercury and then 

 reduced to powder. A colourless, highly limpid liquid is 

 found in the condenser, which fumes strongly in humid air. 

 The bichloride boils at 248 ; the density of its vapour, observed 

 by Dumas, is 9.1997. It forms a solid saline mass with one 

 third of its weight of water, and dissolves in a larger quantity of 

 water. The same salt is obtained in solution, by conducting a 

 stream of chlorine gas into a strong solution of the protochlo- 



