1814.] On the Cause of Chemical Proportions. 9i 



the analysis of the arseniates. I conceive, however, that more 

 confidence is due to the conclusion drawn from the analysis of the 

 arseniates than from that of arseuiciis acid. 



M. Laugier has published a set of excellent experiments on the 

 composition of some arseniates and arsenical sulphurets. He 

 obtained results very dilferent trom those which I ha\e just stated ; 

 and one would be disposed to say that a"n observation vviiich he has 

 made, namely, that in the arscniate of barytes the acid is to the 

 base inversely as it is in the arscniate of lime, is contrary to the laws 

 of chemical proportions, respecting which M. Laugier does not 

 seem to have any idea. We shall see, however, (hat the observa- 

 tion of Laugier is not without foundation. As we cannot suppose 

 that this skilful chemist could have analysed a neutral arseniate of 

 barytes so badly as to have obtained 33^ per cent, of barytes instead 

 of 42"f) per cent., I resolved to examine if tliere existed subar- 

 seniates of lead and barytes. I obtained such salts by digesting the 

 neutral arseniates in caustic ammonia, which extracted a portion of. 

 the acid and left the subarseniate undissolved : 100 parts of the 

 subarseniate of barytes thui, procured and heated to redness yielded 

 10r4 parts of sulphate of barytes; and 100 parts of subarseniate 

 of lead yielded 101*5 parts of sulphate of lead. Hence the com- 

 position of these subarseniates is as follows : — 



Arsenic acid 33-5 100 



Barytes 66-5 iyS-5y 



100-0 



Arsenic acid 2.5 •25 100 



Oxide of lead 7475 '29G-4 



100-00 



We find that the acid in these subsalts is neutralized by 1-i- as 

 much base as in the neutral arseniate, and of course the acid con- 

 tains twice as much oxygen as the base. I must observe that the 

 small aberration in the subarseniate of lead will be accounted for 

 by supposing an error of 0002 in the wcigiit of the subsalt 

 analysed. We see that Laugier analysed the sul)arseniate of barytes, 

 because he found that his arseniate wiicn converted into suljihate 

 did not alter its weight. If we admit, according to the above- 

 mentioned observation'of J\L Laugier, that the arscniate of liine is 

 coni|)osed of fjfj-o acid and ;}:5-5 of lime, it will follow that he" 

 analysed the neutral combination of that earth; for 33'5 parts of 

 lime (Tontain 7 43 of oxygen, whicli nuihiplied by 3 = 28-29; and 

 (>('>•') of acid contain '2J-'/'A parts of oxvgeu. 



'J'hc existence of these subsalis proves that arsenic acid must 

 foiitaiii either 3 or d volumes of oxvgcn ; but before di-^cussin<r 

 till- pomt, 1 must speak of my experiments on arsenious acid. 



J dissolved arsenious acid by boiling it in caustic ammonia, I 



