354 Berzelius's Experiments to determine the Composition [M a y , 



a temperature a little above 212°, it weighed 1-245. From the 

 quantity of oxygen absorbed by the hydrog-en of the sulphuretted 

 hydrogen gas, arsenious acid should contain 24-218 per cent, of 

 oxygen. According to these experiments, 100 arsenic combine 

 with 31-884 oxygen, and not with 334-, ^^ ^'^^ been hitherto 

 believed. And as experiment proves that 100 arsenic absorb 

 more than 50 to become arsenic acid, it follows that the ratio of 

 the oxygen in the two acids of arsenic cannot be that of 2 to 3. 

 It remains, therefore, to try, whether the ratio between the 

 oxygen of phosphorous and phosphoric acids ; that is to say, 

 3 to 6, does not hold likewise in the corresponding acids of 

 arsenic. In this case 3:5:: 31-884 : 53-14. If this is the case, 

 we have reason to expect that the acids of -arsenic will deviate 

 from the laws of the combinations of oxided bodies in the same 

 way as the acids of phosphorus. Let us then examine the capa- 

 city of saturation of arsenic and arsenious acids. 



Arseniate of Lend. — A solution of nitrate of lead was mixed 

 with a solution of arseniate of soda, with the precaution of not 

 precipitating all the arsenic acid. The precipitate was washed, 

 dried, and heated, to redness : 1 grammes of arseniate of lead 

 decomposed by sulphuric acid produced 8-953 grammes of sul- 

 phate of lead. According to this experiment, arseniate of lead 

 is composed of 



Arsenic acid 34-14 100-00 



Protoxide of lead .... 6586 192-91 



Now 192-91 parts of oxide of lead contain 13-834 of oxygen. 



One part of arseniate of lead which had not been dried was 

 digested with caustic ammonia, and then washed and dried at 

 a red heat: 100 parts of subarseniate of lead thus obtained, 

 decomposed by sulphuric acid, produced 101-6 parts of sulphate 

 of lead. Hence this subsalt is composed of 



Arsenic acid 25-25 100-00 



Oxide of lead 74-75 296-04 



But 192-91 X li = 299-3.* Hence it is evident that abstract- 

 ing the errors of the analytical experiments, arsenic acid combines 

 in the subsalt with one and a half times as much base as in the 

 neutral arseniate. 



Arseniate of Bari/tes. — It was prepared by pouring nitrate of 

 barytes into a solution of crystaUized arseniate of soda, to which 

 a little arsenic acid was added ; so that the alkaline reaction was 

 removed as exactly as possible. No precipitate appeared at first ; 

 but after an interval of a few moments, the arseniate of barytes 

 precipitated in the form of small crystalline scales, which were 

 washed and dried at a red heat. Ten grammes of this arseniate 



* 192-91 X H = 289-36.— T. 



