On some double Hyposulphites. 21 



alcohol and dried in vacuo. The second salt is difficult to 

 obtain pure by this method. In the second manner it may 

 be obtained by adding to a solution of the hyposulphite per- 

 fectly neutral nitrate of silver until the precipitate becomes 

 constant. The salt is at first flocculent, it afterwards becomes 

 crystalline, and must be washed out with water. 



First salt. — Has a sweet taste, is not changed by exposure 

 to light and air, but becomes coloured at a temperature below 

 100° C. Its aqueous solution is decomposed by long boiling, 

 sulphuret of silver is deposited; it is easily soluble in ammo- 

 nia, not perfectly insoluble in alcohol. Hydrochloric acid 

 affects it slowly; when boiled it produces a black precipitate, 

 from which ammonia extracts chloride of silver. Its formula 



is Ag S '+ 2 Na S -f 2 aq. 



The second salt is difficultly soluble in water, soluble in 

 ammonia and excess of hyposulphite of soda (forming the 

 above salt) ; it is a dirty white crystalline powder, which be- 

 comes black by boiling with water, and becomes gradually co- 

 loured in the air. Its formula is Ag S + Na S + aq. 



Plumbo-hyposulphite of Soda is best prepared by means of 

 acetate of lead, like the first argento-hyposulphite. It becomes 

 crystalline, is white, easily soluble in acetate of soda, little in 



water, difficultly in alcohol. Formula is Pb S + 2 Na S ; it 

 is therefore anhydrous. 



Cupro- hyposulphite of Soda. — On mixing a solution of the 

 hyposulphite of soda with an excess of sulphate of copper, a 

 yellow crystalline precipitate is formed ; this must be quickly 

 filtered and washed with very dilute acetic acid, and then 

 dried in vacuo^ for it easily becomes brown and is decomposed. 

 It is not at all soluble in alcohol, difficultly in water, easily in 

 hyposulphite of soda. Out of this solution alcohol precipi- 

 tates a salt easily soluble in water. It dissolves in ammonia 

 with a brownish vellow colour, which in the «air changes to 

 blue ; it is consequently a salt of the dinoxide. It is decom- 

 posed immediately by concentrated sulphuric acid, and by 

 dilute when boiled ; sulphurous acid is evolved and sulphuret 

 of copper precipitated, the solution contains oxide; when the 

 decomposition is effected by means of hydrochloric acid the 



solution contains dinoxide. Formula 3 Cu S + 2 Na S-f-5 aq. 

 By mixing solutions of the hyposulphite and of a neutral 

 salt of sesquioxide of iron, a deep black red liquid is obtained, 

 which speedily decolorizes and then contains protoxide. — 

 (Ann. der Chem. und Phar?n., vol. xl. p. 94-101.) 



