i/2 On the Oxides of Arsenic. [Sept. 



in the Journal de Physique, the white oxide of arsenic is com- 

 posed of 



Arsenic „ 100 



Oxygen 32979 



And arsenic acid of 



Arsenic 100 



Oxygen 52505 



These experiments were afterwards repeated by Rose, whose 

 accuracy is well known, and he obtained precisely the same results. 

 Bucholz also made experiments on the subject, and came nearly to 

 the same conclusions. 



Thenard, in his paper on nickel, published in the 50th volume 

 ■of the Annales de Chimie, gives us a set of experiments which he 

 made to determine the constitution of arsenic acid, in order to 

 enable him by means of it to ascertain the quantity of arsenic 

 which existed in certain ores that he was analysing. He informs 

 lis that he acidified 100 grains of arsenic by means of nitric acid, 

 and that he found 100 parts of arsenic acid to be composed of 64 

 arsenic -+- 34 oxygen. According to this statement, arsenic acid is 

 composed of 



Arsenic 100 



Oxygen 56*25 



He informs us farther, that 100 parts of white oxide of arsenic 

 -when converted into arsenic acid become 116 parts, and of course 

 combine with 16 parts of oxygen. According to this statement, 

 white oxide of arsenic is composed of 



Arsenic 100 



Oxygen 34*694 



Still more lately Berzelius made a set of experiments on the 

 same subject, assisted by his peculiar ideas respecting the ratio 

 ■existing between the oxygen of the acid and the base of salts. 

 These experiments were published in the 80th volume of the 

 Annales de Chimie. He converted 100 parts of arsenic into acid 

 by means of nitric acid, evaporated the liquid to dryness to get rid 

 of the nitric acid, re-dissolved it in water, and put the solution 

 into a platinum crucible together with a solution of a determinate 

 quantity of oxide of lead dissolved in nitiic acid. This mixture was 

 evaporated to dryness, and then heated to redness. Different 

 experiments made in this way gave him arsenic acid composed of 

 100 arsenic combined with 48*3, 49*5, and 53 of oxygen. These 

 experiments, though they do not coincide exactly with each other, 

 yet agree sufficiently with those of preceding chemists to confirm 

 their results, and to satisfy us that arsenic acid must be a compound 



