1820.] of different inorganic Bodies, 353 



which the mixture did not fill more than a fifth part. The con- 

 sequence was, that a portion of the sulphur was oxidized at the 

 expense of the air of the retort, and thus considerably increased 

 the loss of sulphur. 



Having found that the acids of phosphorus follow different 

 laws from all the other acids that I had occasion to examine, I 

 thought it likely that the acids of arsenic might follow the same 

 laws. This idea induced me to resume Ahe examination of these 

 acids. 



One hundred parts of arsenic were acidified by means of nitro- 

 muriatic acid, and the liquid was evaporated till the volatile acids 

 were driven off. The arsenic acid remaining was dissolved by 

 water acidulated with a little nitric acid, and 400 parts of oxide 

 of lead, just exposed to a red heat, were added to it. This mix- 

 ture was allowed to digest for some hours. It was then evapo- 

 rated to dryness, and exposed to a red heat till no more nitrous 

 vapours were exhaled. The oxide of lead had been added that 

 the presence of water in arsenic acid might not alter the result. 

 This experiment was several times repeated, and it gave results 

 which varied between 150 and 152 of arsenic acid produced from 

 100 of metal. This experiment, though not very precise in 

 itself, proves, however, very nearly the dose of oxygen absorbed. 



2-2715 grammes of pure arsenious acid were melted with an 

 equal weight of pure sulphur in a small apparatus made by a 

 glass blower. The bulb of this apparatus was entirely filled by 

 the pulverized mass. The sulphurous acid gas passed through a 

 long glass tube cui'ved into a spiral, and whose mouth was shut 

 by a piece of filtering paper to retain the flowers of sulphur, a 

 small quantity of which, without this precaution, might have 

 made its escape with the gas. began by heating the bottom 

 of the bulb by a very small oil lamp ; and by this means the 

 disengagement of the sulphi "ous acid began at the bottom, 

 before the surface had acquned the temperature necessary to 

 kindle the sulphur. Thus the sulphurous acid gas assumed the 

 place of the small quantity of air in the tubes before it was 

 decomposed. 1 then made use of a spirit of wine lamp, and the 

 experiment was continued as long as any gas continued to be 

 disengaged, which was from five to six hours. When the appa- 

 ratus was cold, and the sulphurous acid gas replaced by air, the 

 whole was weighed. It had lost 1-084 gramme. 



2-203 grammes of arsenious acid in a similar experiment gave 

 l-OCy of sulphurous acid. From these two experiments, the 

 laHt of which was made with peculiar care, arsenious acid con- 

 tains 24"176per cent, of oxygen. 



A gramme of arsenious acid dissolved by dilute muriatic acid 

 was precipitated by a current of sulphuretted hydrogen gas. 

 Care was taken to boil the liquid a quarter of an hour before 

 introducing the gas. The precipitate had a fine lemon-yellow 

 colour. It was collected on a filter and well washed. Dried at 



Vol. XV. N^ V. Z 



