gB CHEMICAL AN A LTS I S, i^c. 



may be united to carbonic acid, cryflallizes, and alfo any neu- 

 tral fak that may remain ; and the fokition being decanted a 

 fecond time, is obtained perfedlly pure, colourlefs, and tranfjpa- 

 rent. 



Im the lad boiling it is fomewhat diiEcult to obferve the ex- 

 acfl degree of concentration at which all the alkaline carbonate will 

 cryltallize ; and if the evaporation is carried too far, the cauflic 

 alkali, if potafli, cryftallizes itfelf: fo that feveral evaporations 

 are fometimes requifite. 



When no more water remains in the folution than is juft 

 fufEcient to hold the cauftic alkali diffolved, it contains nearly 

 half its weight of alkali ; but the exa£l quantity is eafily known, 

 by evaporating a portion to drynefs in a filver crucible. Before 

 uling fuch a folution for analyfes, I afcertain its purity in the 

 following manner : Son^e of it being fuperfaturated with per- 

 fedtly pure nitric acid, is examined with nitrate of barytes and 

 of filver; with neither of which, if properly made, it will give 

 the fmalleft cloud ; confequently it can contain no fulphuric or 

 muriatic acid. 



Another portion being faturated exadlly with a pure acid, 

 the whole is evaporated to drynefs, and the fait left is rediflbl- 

 ved in a little water. If any earth were contained in the cauftic 

 alkali, it would remain thus undiflblved ; but when made as 

 above defcribed, I have never, in this examination, obferved the 

 fmalleft fediment. 



After the alkali is purified from neutral falts, and from the 

 part united to carbonic acid, it may itfelf be cryftallized by far- 

 ther evaporation, as Mr Lowitz has fhown. But this procefs 

 feems of no ufe in chemical analyfis, as the alkali is previoufly 

 obtained altogether pure. 



V. 



