ARSENIC. 233 



efferverscence. As soon as the solution was com- 

 pleted, a receiver was attached to the retort, 

 the whole nitric acid was not only distilled off, 

 but the heat was continued till the inside of the 

 retort had become quite dry. By this process, 

 the arsenic had been converted into arsenic acid, 

 and its weight was exactly 7*7^ grains. 



From this experiment it is obvious, that ar- 

 senic acid is a compound of 



Arsenic 4'75 



Oxygen 3 



7-75 

 From this it appears, that the atomic weight of Atomic 



weight of 



arsenic is 4 '75, and that arsenic acid is a com- arsenic, 

 pound of 1 atom arsenic and 3 atoms oxygen. 



3. Let us now investigate the atomic weight Atomic 

 of arsenious acid. This is the substance known, arsen 

 in common language, by the name of white ar- 

 senic. It reddens vegetable blues, dissolves in 

 water, and unites to bases ; though it does not 

 seem capable of neutralizing them. But the 

 atomic weight, and the composition of this 

 acid, is rendered evident by the following sim- 

 ple and easy experiment. 



6*75 grains of pure arsenious acid were put 

 into a small retort, the weight of which had 

 been previously determined ; and there was 

 poured over it, about an ounce of a mixture of 



