1820. J of different inorganic Bodies. ■ 357 



The analogous manner in which the acids of phosphorus and 

 arsenic deviate from the general law of the combmations of 

 oxidized bodies is a very remarkable circumstance ; and so much 

 the more so, as these acids have a great deal of analogy in other 

 respects. Phosphoric and arsenic acids form with the alkalies 

 crystalhzable salts, which, though proportional to the other 

 neutral arseniates and phosphates, have an alkaline reaction ; 

 and if we saturate their solutions exactly by adding acid, and 

 then concentrate the liquid by evaporation, the salt which crys- 

 tallizes reacts as an alkali ; while an acid and less crystallizable 

 salt remains in solution. Both arsenic and phosphorus give with 

 hydrogen combinations which have not acid characters, and 

 which in their chemical properties differ completely from the 

 combinations of hydrogen with sulphur, selenium, and tellurium. 

 Both give degrees of acidification, between which the ratio of 

 the oxygen is as 3 to 5, and in both, the greater number of the 

 anomalies would disappear, if what we consider as the simple 

 radical contained a portion of oxygen, amounting to one-fifth of 

 what it absorbs in order to become an acid in ic. But I have 

 already, in speaking of phosphorus, shown, that at present we 

 have no probable reason for believing that it contains oxygen ; 

 and the probability is still smaller for arsenic, which possesses 

 most of the characters of metals. 



In the great number of the combinations of oxidized bodies 

 which I have examined, the law of the multiples of the oxygen 

 of the two oxides combined is always followed, except in the 

 compounds formed by the acids of arsenic, phosphorus, and 

 azote, when we consider this last as a simple substance. 



In the acids formed by these radicals, the ratio of the oxygen 

 of the acid in ous is to that of the acid in ic as 3 to 5. In the 

 neutral arseniates and phosphates, the acid contains 2^ times as 

 much oxygen as the base, and this ratio exists likewise in some 

 subnitrates. In all the arseniates, phosphates, and nitrates, the 

 oxygen of the base is a certain submultiple by 5, or, more rarely, 

 by 10, of the oxygen of the acid (with the exception of some 

 phosphates of lime). This may give rise to the following ques- 

 tions : Does the law of multiples of oxygen in the two oxides 

 combined (that is to say, that the oxygen of the one is a multiple 

 by a whole number of the oxygen of the other) hold in all cases, 

 except those in which the radical has two degrees of acidificii- 

 tion, the oxygen of which is in the ratio of 3 to 5 ? What is the 

 reason that m the compounds formed by these acids, it happeixs 

 so rarely that the oxygen of the acid is a multiple by a whole 

 number of the oxygen of the base ? It is evident that a satisfac- 

 tory answer to these questions would be of the greatest import- 

 ance to the theory of chemistry. It api)ears clear likewise that 

 if we prove hereafter that azote is an oxide, which is probable, 

 and which will be determined when the phenomena of tne reduc- 

 tion of ammonia by the electric pile have been better studied and 



