tyi Purification of Alkalis, 



therefore, a fmall quantity of the barytlc prufliatc, and applied a gentle heat for a few 

 minutes. The folution, when filtered, no longer precipitated muriate of barytes (except 

 after fome time in the manner I have pointed out, p. 32.) The purer the alcali, em- 

 ployed in making the pruffiate of pot-afli, the lefs, it is obvious, will be the proportion of 

 prufliated barytes required. 



I have lately contrived a method of preparing pure and carbonated alkalis, which has 

 many advantages over the common ones. Indeed the formation of a carbonated alcali, 

 perfectly free from fulphate of pot-afh, is a problem of confiderable difficulty, except by 

 very expenfive procefles. Cryflalization is incompetent to feparate the whole of the ful- 

 phate. The lixivium of the aflies of tartar, and the alcali prepared from nitre, I have 

 never found free from fulphate of pot-afh. By faturating the alcali with acetous acid, and 

 then adding acetite of barytes, a pure acetite of alcali may be obtained, which, when de- 

 compofed by heat, affords a pure carbonate. But this mode is troublefome and coftly. I 

 recommend the following, as a cheap and eafy procefs : 



Render the alcali, whether vegetable, mineral, or volatile, perfe£i;ly cauftic by quick- 

 lime ; and to the clear folution add, by degrees, a warm folution of pure barytic earth, till 

 the precipitation ceafes. The barytes feizes the fulphuric acid ; and leaves the alcali pure, 

 which may, if required, be afterwards faturated with carbonic acid, in any of the common 

 modes. During its reftoration to a mild ftate, any barytes, that may remain in excefs, is 

 alfo precipitated. If the carbonic acid, employed for faturation, be obtained from carbo- 

 nate of lime by fulphuric acid, the gas fhould be previoufly paffed through a folution of 

 carbonate of pot-afh, in order to feparate any fulphuric acid, that may happen to be at- 

 tached to it. A carbonate of alcali thus prepared, when faturated with acetous acid, gives 

 no Cgns of fulphuric acid, on adding acetite of barytes. 



Cauftic alcali, however, purified in the above mode, flill retains a fmall portion of lime j 

 . for, on examining the precipitate very attentively, I found no lime in its compofition, 

 which might perhaps have been expefted in it, from fome late experiments of M. M. 

 Guyton, Kirwan, and Hatchett, on the affinity of earths in the humid way. If a cauftic 

 alcali be required, perfeiStly free from lime, as may fometimes happen in nice experiments, 

 the alcali may be deprived of its carbonic acid, entirely from the beginning, by pure 

 barytes. 



I am, Sir, 



Your obedient humble Servant, 



WILLIAM HENRY. 



■OllM 



