72 On the Decomposition of Alkaline Sulphurets 



sulphurous acid. The rest of the liquor would give soda 

 less pure than the first crystallization. 



To purifv this lixiviuiu, and free the alkali from the suU 

 phur which it contains in solution, and cause the sulphite 

 to disappear, I add to the ley, while it is in ebullition, a 

 sufficient quantity of well pulverized senii-vitrcous oxide of 

 lead. Tliis oxide separates the sulphur from the alkali, and 

 forms by its combination an in^^oluble sulphuret of lead : 

 the sulphite disappears, and is converted into sulphate. The 

 eemi-vitreous oxide of lead loses its red colour, and assumes 

 a deep chestnut or blackish hue, by reason of the quantity 

 of sulphur which the alkali contains. The liquor or lixi- 

 vium becomes as clear as pure water; dilute sulpliuric acid 

 disengages from it only carbonic acid gas, and forms no pre- 

 cipitate: in a word, this lixivium precipitates the nitrate of 

 lead in a white state, and the sulphate of copper is a beau- 

 tiful green ; whilst, previous to the addition of the semir 

 vitreous oxide of lead, the same lixiviuui precipitated these 

 two metals of a very dark chestnut colour, that is to say, 

 in the state of sulphuret. Thus the semi-vitrcous oxide of 

 lead, iu the humid wav, carries off the sulphur from the 

 alkali of the soda, and may serve for purifying in the larga 

 way, and in a very easy manner, the soda proceeding froiTj 

 the decomposition of the sulphate of soda. 



After these experiments, and a calculation of the expense 

 of the semi-vitreous oxide of lead, I substituted for it, with 

 equal success, oxide of manganese well pulverized. 'I'liis 

 oxide, which is cheaper than the former, presents another 

 advantage: it may be employed several tinjes for the same 

 operation, freeing it first from the sulphur by simple cal- 

 cination. 



The facility with which sulphur is thus separated from 

 soda in the humid way, without engaging it in a \M:t\v com- 

 bination, that is to say, leaving it isolated and dissolved 

 in the liquid, induced me to try the saiTie means for de- 

 composing sulphuret of barytes ; and my attempt was at- 

 tended with success. 



Decomposition of Sulphuret of Barytes. 

 In order to obtain barytes in a caustic state, sulphate of 

 barytes is comOiOnly dccomposetl with charcoal, from wiiich 

 first operation results a sulphuret of barytes solubJe in water: 

 this sulphuret is decomposed with nitric acid : distillation 

 separates the nitric acid from the barytes, and this alkali 

 remains pure, and fixed at the bottom of the retort. This 

 process is extremely expensive^ on account of the large 



(quantity 



