ARSENIC. 231 



It is evident, from this, that the rhomboidal crys- 

 tals contain two atoms of arsenic acid united to 

 1 atom of soda ; for &5-1&5 grains of them con- 

 tain just 4 grains of soda, which is equivalent to 

 an atom. 



It has been already explained, that nitrate of 

 lead is an anhydrous salt composed of 



1 atom nitric acid = 6-75 



1 atom protoxide of lead =14 



20-75 



Consequently, 41 *5 grains contain 28 grains of 

 protoxide of lead, which is equivalent to 2 

 atoms. 



19*5 grains of anhydrous binarseniate of soda, 

 and 41*5 grains of crystallized nitrate of lead, were 

 dissolved in separate portions of distilled water. 

 The solutions being mixed, a double decomposi- 

 tion took place ; the arsenic acid and protoxide 

 of lead united together, and precipitated in the 

 state of an insoluble arseniate. The clear trans- 

 parent colourless liquid remaining, after this salt 

 had subsided, reddened vegetable blues ; but it 

 was exactly neutralized by the addition of 18 

 grains of crystallized carbonate of soda. The 

 liquid thus neutralized was tested by sulphate of 

 soda, and likewise by nitrate of lead ; but the 

 solutions of neither of these salts produced any 

 sensible alteration ; showing the absence both 



of lead and arsenic acid. 



p 4 



