ARSENIC. 229 



It will be shown in the next chapter, that the 

 specific gravity of most of the gases is obtained 

 by multiplying their atomic weights by 0*5555, 

 or half the specific gravity of oxygen gas. Now, 

 5-125 x 0-5555 = 2-8522, which must be the 

 specific gravity of selenietted hydrogen gas. 



SECT. VII. 



OF THE ATOMIC WEIGHT OF ARSENIC. 



ARSENIC has the property of combining with, at 

 least, two proportions of oxygen, and of forming 

 two well known and very poisonous compounds, 

 distinguished by the names of arsenious and ar- 

 senic acids. It unites, likewise, with hydrogen gas, 

 and forms a gaseous compound, the properties of 

 which have been but imperfectly investigated. 

 An examination of the acids of arsenic will en- 

 able us to determine the true atomic weight of 

 this substance. 



1. Arsenic acid is easily obtained, by dissolv- Atomic 



T . . . . . , 1 i weight of 



ing white arsenic in nitric acid, mixed with a arsenic 

 small quantity of muriatic acid, and evaporating ac 

 the solution to dryness. It is a white matter, 

 soluble in water ; and the aqueous solution has 

 a very sour taste. With most of the metallic 

 oxides it forms compounds, insoluble in water ; 

 but easily soluble in nitric acid ; with ammonia, 



P3 



