1^21.] Strontian, Lime, Magnesia, Phosphoric Acid, S^c, 15 



There is reason to conclude from the experiments made by- 

 different chemists on arsenic and arsenious acid, that the weight 

 of an atom of arsenic is 4-75. It may be seen by consulting my 

 System of Chemistry (either fifth or sixth edition) that Berzelius's 

 experiments lead to the conclusion that arsenious acid is a com- 

 pound of 4-75 arsenic 4- 1*5 oxygen. The preceding experiment 

 leaves no doubt that arsenic acid is a compound of 4*75 arsenic 

 ^ 3 oxygen. Thus we have these two acids composed as 

 follows : 



Arsenious acid of. .. 4*75 arsenic + 1-5 oxygen 

 Arsenic acid of. .... 4*75 + 3*0 



We see that the oxygen in these two acids has not the ratio 

 of 3 to 5, as BerzeUus supposed, but of 1 to 2. The anomaly 

 of li atom of oxygen combined with 1 atom of arsenic in arse- 

 nious acid still continues. I have not yet hit upon a method of 

 putting the atomic weight of an atom of arsenious acid to the 

 test of an unequivocal experiment ; but I have little doubt that 

 the true weight of oxygen in arsenious acid combined with 4*75 

 arsenic is 2 ; and that the oxygen in arsenious and arsenic acids 

 have to each other the ratio of 2 to 3 ; as is the case in sulphu- 

 rous and sulphuric acids. I conceive the atomic weights of 

 arsenic, arsenious, and arsenic acids, to be as follows : 



Weight of atom. 



Arsenic 4*75 



Arsenious acid 6*75 



Arsenic acid 7*75 



The two acids are composed as follows : 



Arsenious acid 1 atom arsenic + 2 atoms oxygen 

 Arsenic acid . . 1 +3 



I do not despair of being able to decide this very important 

 point hereafter by satisfactory experiments. In the mean time 

 we may conclude that the ratio of 2 to 5, which Berzelius has 

 endeavoured to establish in the oxygen combining with phos- 

 phorus and with arsenic, does not exist. This is a simphfication 

 of the atomic theory of some importance. I am thoroughly per- 

 suaded that as we proceed in our investigations, the simplicity 

 of the atomic theory will become more and more apparent. The 

 complex numbers of Berzelius will all disappear ; and the appli- 

 cation of mathematical reasoning will by and by enable us to 

 advance with unexpected rapidity in the chemical investigatioa 

 of the vegetable and animal kingdoms. 



Uio« 



