234 ACIDIFIABLE COMBUSTIBLES. 



12 parts nitric acid of the specific gravity 1-25, 

 and 1 part of muriatic acid of the specific gra- 

 vity 1'2. The retort being exposed to a moder- 

 ate heat, the arsenious acid was soon dissolved 

 with effervescerfce ; but the heat was continued 

 till all the liquid portion was distilled over into 

 the receiver, and till the interior surface of the 

 retort had become quite dry. The best way of 

 drying the retort is to put it on the sand batib 

 and to cover the whole of it except the extremity 

 of the beak, with sand of a temperature between 

 500 and 600, and keep it in this situation for 

 several hours. By this process the arsenious 

 acid was converted into arsenic acid, and its 

 weight was found to be exactly 7*75 grains. 



From this experiment it is evident, that arse- 

 nious acid contains one atom of oxygen less than 

 arsenic acid. Consequently, its atomic weight 

 is 6'J5 ; and it is a compound of one atom ar- 

 senic, and two atoms oxygen. 



From the preceding investigation it is obvious, 

 that an atom of arsenic weighs 4*75, and that 

 the constitution and atomic weights of the acids 

 of arsenic are as follows : 



ARSENIC. OXYGEN. ATOMIC WEIGHT. 



Arsenious acid of 1 atom + 2 atoms 6-75 



Arsenic acid - - 1 +3 7-75 



So that the constitution of these acids is the 

 same as that of sulphurous and sulphuric acids. 

 4. It is exceedingly probable that there exists 



