230 ACIDIFIABLE COMBUSTIBLES. 



potash, and soda, it unites in two proportions, 

 and forms soluble compounds with each. Bi- 

 narseniates of potash and soda crystallize readily 

 the former in four sided prisms the latter 

 in rhomboids. Binarseniate of soda contains 

 rather more than 20 per cent, of water, being 

 composed of 



2 atoms arsenic acid = 15-5 

 1 atom soda . = 4-0 

 5 atoms water . = 5*625 



25-125 



as I ascertained by a careful analysis.* When 

 this salt is heated to about 500, it loses the 

 whole of its water of crystallization, melting at 

 first into a liquid, and then falling down in the 

 state of a white powder. At a red heat this 

 powder melts into a transparent liquid, which is 

 quite anhydrous. 



If we add 18 grains of crystallized carbonate 

 of soda to a solution of 25-125 grains of crystals 

 of binarseniate of soda, and agitate the mixture 

 till the whole soda be dissolved, and till the car- 

 bonic acid has made its escape, the liquid will be 

 found incapable of reddening vegetable blues. 

 Now, 18 grains of carbonate of' soda contain just 

 4 grains of soda, which is equivalent to an atom. 



* Or rather synthesis. The experiment, which is of importance, because 

 it proves the inaccuracy of Berzelius's opinions respecting the composition 

 of this acid, will be given at large in chapter XVIII. of this work. 



