] 74 On the Oxides of Arsenic. [Sept. 



sufficiently well with each other ; hut whether we multiply them by 

 two or bv three, they will not give us a quantity of oxygen cor- 

 responding with the constitution of arsenic acid as previously deter- 

 mined by experiment. Therefore if that previous determination be 

 accurate, it follows that the law of Berzelius respecting the quan- 

 tity of oxvgen in the acid being a simple multiple of the oxygen in 

 the base, does not hold with the arseniates. 



Tin's deviation from the law induced him to consider the previous 

 determination of chemists as erroneous. To decide the point expe- 

 rimentally, he mixed five parts of arsenious acid with 20 parts of 

 sulphur in a small retort By the application of heat, the sulphur 

 absoi bed the oxygen from the acid, and made its escape in the form 

 of sulpburous acid. The loss of weight was 305 parts, which 

 Berxelius considered as sulphurous acid. Now 3-05 of sulphurous 

 acid contain, according to Berzelius' estimate, 15185 of oxygen. 

 This therefore must have been the quantity of oxygen contained in 

 five of arsenious acid. Hence 100 parts of arsenious acid contain 

 at least 30-37 P arts of oxygen ; so that it is composed of 



Arsenic 100-000 



Oxygen 43-616 



This result he considers as fully confirming the suspicion deduced 

 from the analysis of the arseniates, that both arsenious and arsenic 

 acids contain a greater proportion of oxygen than has been hitherto 

 supposed. Arsenic acid, he conceives, must contain thrice the 

 quantity of oxygen in the base with which it combines. But we 

 have seen that arsenic acid combines with a quantity of yellow 

 oxide of lead which contains 13*878 oxygen. Now 13-878 x 3 

 = 41-634. Therefore 100 arsenic acid must contain 41-631 

 oxygen. It is therefore composed of 



Arsenic 1 00 



Oxygen 71'333 



By more exact experiments than those published in the Annales 

 de Chimie, above referred to, he found that arsenite of lead is 

 composed of 



Arsenious acid 100 



Yellow oxide of lead 111-17 



Now 11117 yellow oxide of lead contain J'95 oxygen, and 

 7'95 x 4 = 31*8. This nearly coincides with the analysis of 

 arsenious acid, and shows that in the atsenites the acid contains 

 four times the quantity of oxygen that exists in the base. 



Berzelius likewise made a set of experiments to discover, if pos- 

 sible, the existence of an oxide of arsenic containing less oxygen 

 than arsenious acid. He distilled a mixture of pounded arsenic and 

 calomel in a retort, and obtained a brown mass bordering upon 

 yellow, which he considered as a triple muriate, composed of 



