PUOTOCOMPOUNDS OF TIN. 601 



ride of gold produces a purple precipitate in a stannous salt, 

 consisting, it is believed, of the deutoxide of tin in combination 

 with protoxide of gold, a test by which the protoxide of tin may 

 always be distinguished. The same oxide is precipitated as a 

 black sulphuret, by sulphuretted hydrogen, even from acid solu- 

 tions. 



Protochloride of tin, Salt of tin; SnCl + 3HO; 1178 + 337.5 

 or 94.39 + 2/. This salt may be obtained in the anhydrous 

 state by raising the temperature of a mixture of equal weights of 

 calomel and tin in a gradual manner, and finally distilling the 

 protochloride by a strong red heat. The fused mass on cooling 

 is a grey solid, of considerable lustre, and having a vitreous 

 fracture. The hydrated chloride, known in commerce as salt 

 of tin, is procured by evaporating the solution of tin in concen- 

 trated hydrochloric acid to the point of crystallization. It is 

 thus obtained in needles or in larger four sided prismatic 

 crystals, which contain three atoms of water. The salt parts 

 with the greater portion., if not the whole of this water at 2 1 2, 

 but if distilled at a higher temperature, loses hydrochloric acid 

 also, and an oxichloride of tin remains. It dissolves completely 

 in a small quantity of water; but when treated with a large quan- 

 tity, the salt is partly decomposed, hydrochloric acid is dis- 

 solved, and a light milk-white powder separates, which is a 

 basic chloride, or oxichloride, Sn Cl + Sn O + 2HO. Both the 

 crystals and the solution absorb oxygen from the air, and then 

 a basic salt of the peroxide is formed which is also insoluble in 

 water. From both these causes, a complete and clear solution 

 of the salt of tin is rarely obtained, unless the water be previously 

 acidulated with hydrochloric acid. This salt is entirely soluble 

 in caustic alkali, but the solution is liable to an ulterior change 

 already mentioned. The protochloride of tin is not only used 

 in calico printing as a mordant, but also as a deoxidising agent, 

 particularly to deoxidise indigo, and to reduce to a lower state 

 of oxidation and discharge the peroxides of ircjn and manganese 

 fixed upon cloth. 



Protochloride of tin and potassium ; Sn Cl + K Cl, and 

 Sn Cl + K C1 + 3HO. The protochloride of tin forms a double 

 salt with chloride of potassium, and also with chloride of ammo- 

 nium, which crystallize in the anhydrous condition, and also 

 with three atoms of water. 



The anhydrous protochloride of tin fused in ammoniacal gas, 



