356 Berzelius's Experiments to deferminetke Composition ('May, 



ammonia, prepared as above described, and care was taken not 

 to precipitate the whole of the oxide of lead. The precipitate, 

 well washed and dried, was fused in a glass retort. Ine vitreous 

 matter thus obtained was reduced to a fine powder.* Ten 

 grammes of this powder were dissolved in nitric acid, and then 

 precipitated by sulphate of ammonia. The liquid was then 

 neiiiralized by caustic ammonia. This occasioned a small addi- 

 tional precipitate, which was added to the former. The sulphate 

 of lead, washed and dried at a red heat, weighed 9*32 grammes, 

 equivalent to 6-87 grammes of oxide of lead; so that in this salt, 

 100 ofarsenious acid were combined with 219'5 of oxide of lead ; 

 but 111-17 X 2 = 222-34. Hence it follows, that neglecting 

 the inaccuracies of observation, the acid is combined in it Vv'ith 

 twice as nmch base as in the neutral salt. 



From these experiments, it appears to follow that the capacity 

 of saturation of arsenic acid is 13-886, and that in the subarse- 

 niates, the acid is combined with ll times as much base as in 

 the neutral arseniates. The capacity of saturation ofarsenious 

 acid is 7-972 ; and in the subarsenites, the acid is combined with 

 twice as much base as in the neutral arsenites. 



If arsenic acid, as we have stated above, is composed of 100 

 metal + 53-14 oxygen, it must contain 34-7 per cent, of that 

 substance ; but if we suppose the quantity of oxygen in the acid 

 to its capacity of saturation to be in the same ratio as we found 

 for phosphoric acid ; that is to say, that the acid contains 2-i- 

 times as much oxygen as the base which it neutralizes, it fol- 

 lows, that the quantity of oxygen in the arsenic acid is 13'8867 

 X 2^ = 34-717. Now this agrees perfectly well with expe- 

 riment. 



.In arsenious acid, we have found from 24-176 to 24-218 per 

 cent, of oxygen. Its capacity for saturation is 7-972, which, 

 multiplied by 3 = 23-916. The difference ought obviously to 

 be ascribed to inaccuracy of observation. In the subarsenite of 

 lead, the acid contains 1^ times as much oxygen as the base. 

 The same ratio holds in the neutral phosphites. 



If we admit that the analysis of arseniate of barytes gave an 

 exact result, and if we admit further that arsenic acid contains 

 2^ times as much oxygen as the base by which it is neutrahzed, 

 the result calculated for the composition ofarsenious acid agrees 

 perfectly with that found by the analytical experiments already 

 described. It follows then, that the acids ought to be composed 

 thus : 



Arsenic acid. Arsenious acid. 



Arsenic. .. 65-283 .... 100-000 75-81 .... 100-000 



Oxygen. .. 34-717 .... 53-179 24-19 .... 31-907 



* The two arsenites of lead, both before and after fusion, are so idio-electric 

 that it is difficult to pound them in a mortar, nithoiit a great part of the powder 

 Iwing driven out of the mortar by the electrii-al repulsion. 



