'J'2 IMPURITY AND MANUFACTURE OF SODA. 



the decomposition of the sulphate of soda by charcoal ; and 

 that this was the cause of the formation of the hidrosuiphuret. 

 This was probably the case, and no doubt tho-oc manufac- 

 turers avaihd themselves of the discovery of Mr. Vauquelin. 

 Butitexiits in The following' observations however show, that the hidro-« 

 * sulphuret exists also in the soda obtained in the combustion 

 of the plants, that furnish this alkali. 

 Sulphuretted On saturating a lixivium of Alicant soda with the tartar- 

 evolvedln ^"^ oxidule, in order 'to prepare the' tartrite of soda and 

 preparing: potash, during the effervescence I perceived a very evident 

 Roehelle salt, sfpeji of sulphuretted hidrogen gas. Reflecting on this, I 

 imagined the evolution of this gas must be owing to the de- 

 composition of some hidrosuiphuret, contained in the al- 

 kaline lixivium ; and I determined to make some experiments 

 for the purpose of satisfying myself on this head, 

 A lixivium of Taking a certain quantity of the lixivium, I evaporated 

 soda set to jj. g^ j,g ^^ separate the greater part of the carbonate of soda 



CrVStlUi/.?. I,- • i r- • 1 1 1 ■ r 1 1 



by crystuliization. Alter it bad etood at rest a tew days, I 

 decanted the liquor, and put about two quarts into a glass 

 Two sorts of vessel, which I placed on a shelf in my laboratory. After 9. 

 crystals from month I examined it, and found the bottom of the vessel 

 wotci"" strewed with crj^stals of a colourless transparent salt, in 



rectangular tetraedral prisms, terminated by quadrilateral 

 pyramids. I likewise observed oclaedral crystals with 

 rhombic bases. The supernatant liquor, being decanted 

 and evaporated, furnished a fresh quantity of the same salt, 

 differing only in being colourtd, and in the octaedral crystals 

 being less abundant. The geometrical figures of these crys-» 

 tals led me to presume, that they were a mixture of hidro- 

 suiphuret and carbonate of soda, the latter being the smaller 

 One hidrosiil quantity. The prismatic crystals, being separated from the 

 phuretofspda others, exhibited the chemical characters of hidrosuiphuret 

 of soda. They had an acid and caustic taste, followed by- 

 considerable bitterness. They diffused ^ slight smell of 

 sulphuretted hidrogen gas; and acids poured into a solution 

 of them expelled this gas in some quantity. Not fused, 

 they gave a green cplour to blotting paper. With the solu- 

 tions of sulphate of iron and of copper they threw down a 

 black precipitate, as well as with those of acetate of lead and 

 nitrate of silver. On pouring an acid on the saline crystals 



