iy the Oxides of Lead and of Mavganese. 7 1 



The addition of carbonate of lime to a mixture of char- 

 coal and alkahnc sulphate, as was the practice in the first 

 .manufactory of soda, estabhshcd at St. Denys, near Paris, 

 uas not an expensive way of decomposing pretty speedily 

 the sulphuret of soda resulting from the decomposition of 

 tl'j« sulphate of soda by charcoal ; nevertheless the soda was 

 still contaminated with sulphuret and with sulphite of soda, 

 Avhich (nioht be detected by the smell and by the crystal- 

 lization. The substitution of iron for carbonate of lime, 

 or these two substances employed together, gave no better 

 result. The whole of the alkali could not be obtained pure 

 till after repeated washings, calcinations, and crysldiliza- 

 tions. 



Such is the state of our knowledge of the means of puri- 

 fying in the large way, and without incurring too great an 

 ■expense, the alkalies which may be prepared by the decom- 

 position of the alkaline sulphates. These difficulties, which 

 appear of little consequence in the operations of the labora- 

 tory, become very embarrassing in large manufactories, 

 \\here the results ought to be equally speedy and easy to be 

 obtained. 



Of all these processes the best is that empioyed in the 

 manufactory of St. Denys, near Paris, and which was pub- 

 lished at the time by order of government. This process 

 is still the most simple, and most easy to be executed in 

 the large way ; at least it has been judged so according to 

 ■experience. I believe that the result of mv researches upon 

 the decomposition of the sul[)hurets must add to its perfec- 

 tion, and afford some indication of which use may be made 

 in analogous operations. 



f shall not detail all the experiments vvhich have led me 

 to this improvement, but shall now s'.ate the means which 

 I employ for decomposing the alkaline sulpluirets, or freeing 

 the soda from the last portions of sulphuret and alkaline 

 sulphite which it contains. 



After having proceeded to the decomposition of the sul- 

 phate of soda, by the mixture of charcoal and carbonate of 

 lime, we lixiviate the crude soda, in order to extract the 

 alkali from it. This lixivium is commonly of a yellowish 

 colour, and exhahs the odour of sulphur: if we mix with 

 it some drops of diluted sulphuric acid, sulphur is precipi- 

 tated, and hydro-sulphurated gas and sulphurous acid are 

 rapidly disengaged. 



Were we to evaporate afterward^; and crystallize this lix- 

 ivium, we should obtain crystals of soda, from which di- 

 luted sulnhuric acid would disengage hydrosulphuref and 

 E 4 sulphurous 



