362 Berzelius's Expenmentstodetermiuethe Composition [Ma y. 



Article IX. 



Experiments to determine the Composition of different inorganic 

 Bodies which serve as a Basis to the Cakniations relative to tfte 

 Theory of Chemical Proportions. By J. Berzelius. 



{Continued from p. 2»3.) 



Composition of the Acids of Arsenic ; their Capacity of Satura- 

 tion ; Oxide and Snlphurets of Arsenic. 



The experiments of the greater number of chemists agree in 

 general thatarsenic absorbs about athird of its weight of ox'ygen to 

 become arsenious acid, and half its weight to become arsenic 

 acid. Such also was the result of some experiments which I 

 made on the subject long ago. I conceived that I ascertained at 

 the same time that the capacity of saturation of arsenic acid was 

 16'66, and that consequently this acid contained twice as much 

 oxygen as the base with which it was combined. But tlie same 

 observations which induced me to make a new examination of 

 the acids of phosphorus led me to undertake experiments on the 

 acids of arsenic. These first experiments gave me inaccurate 

 results. I found that the capacity of saturation of arsenic acid, 

 in its neutral combinations, was 13-8, a number which was not 

 a submultiple of the oxygen of the acid as I had found in the 

 other acids. Hence I concluded that the analyses had given 

 inaccurate results; and the more so as M. Laugier had found 

 that lOU arsenic combine with 71-8 sulphur; a quantity which 

 does not ascree in any manner with the ordinary ratio between 

 sulphur and oxygen ii; the other metals. I, therefore, had 

 recourse to the analytical method, as synthesis had hitherto been 

 employed to determine the composition of these acids. I mixed 

 arsenious acid with sulphur, and I heated the mixture in a retort 

 till the acid was completely converted into sulphuret. One hun- 

 dred parts of arsenious acid lost in sulphur and in oxygen 61 

 parts, of which 30^ must have been oxygen. Making use of 

 this analysis as the basis of my calculations, and admitting that 

 arsenic forms arsenic acid with one and a half times as much 

 oxygen, it follows that in the neutral arseniotes the acid contains 

 three times the oxygen of the base, and in the subarseniates 

 twice that quantity. The analysis of sulphuret of arsenic by M. 

 Laugier agreed perfectly with the composition of an oxide of 

 arsenic, in which the radical is combined with half the oxygen 

 contained in the acid, and it induced me to consider the exist- 

 ence of such an oxide probable. This ahnost perfect coinci- 

 dence suiprised me so agreeably that I thought it unnecessary 

 to repeat the analytical experiment. The result of this experi- 

 ment, however, was inaccurate, owing to a cause to which 1 did 

 not at the time attend. The experiment was made in a retort, of 



