hj means of Soda, ^9 



laboratory the barytes we require. For this purpose we 

 strongly calcine^ in close vessels, 100 parts of sulphate of 

 barytes well mixed with 20 parts of charcoal in powder. 

 After an hour's calcination the crucible is allowed to cool ; 

 the residue is separated from it ; it is then diluted in water, 

 and a sufficient quantity of rutrie acid, muriatic acid, or 

 acetous acid, is added to it : the mixture is then slightly 

 heated, which liberates a great quantity of sulphuretted hy- 

 drogen and carbonic acid, of which we must be upon our 

 guard. When the effervescence ceases, and the reagent 

 paper announces in the liquor a slight excess of acid, we filter 

 and evaporate it, in order to decompose the sulphuretted hy- 

 drogen, and to precipitate the sulphur which was held in 

 solution*. The residue is re-dissolved in the least possible 

 quantity of water, and we add to this solution a saturated so- 

 lution of caustic potash. There is precipitated, even at the 

 moment of mixture, a great quantity of crystals of barytes ; 

 the whole is then allowed to settle at the lowest possible tem- 

 perature for an hour or two : the mother water is then de- 

 canted, the crystals are washed with a little distilled water, and 

 dried by pressing them between several sheets of blotting pa- 

 per, and they are dissolved in the necessary quantity of boiling 

 v^^ater : the filtered liquor deposits the barytes upon cooling, 

 which by this process is far purer and cheaper than that ob- 

 tained by decomposing the nitrate of barytes, by exposing it 

 alone to a high temperature. 



It must be observed, that we ought to prefer the employ- 

 ment of the muriatic or acetous acid to that of the nitric 

 acid ; in the first place, because the first two acids form 

 with barytes, salts more soluble than the nitrate, and the 

 washing is easier in this case : secondly, because in the so* 

 lution, the nitric acid, on being decomposed, oxygenates a 

 part of the sulphuret of barytes, and there is then a portion 

 of acid lost, and a part of the barytes absorbed by the sul- 

 phuric acid which is formed. 



As to the caustic potash required in this operation, it is 



# 



* We may more easily obtain thd same end by pouring into the liquor 

 some drops of nitrate of copper or lead, by allowing the metallic sulphuret 

 to subside, and by filtering over again, &c. 



C 4 essential 



