}(50 On the Cause of Chemical Proportions. [Feb. 



hours it was converted into an amalgam, in which pieces of metallic 

 arsenic floated. The liquor contained muriate and arsenite of 

 potash. Ammonia, the alkaline carbonates, and in general all 

 substances which combined with muriatic acid, decomposed it in 

 tl)e same manner, though less rapidly. 



It follows that the brown sublimate is a triple muriate with a 

 mercurial base, and that the arsenic has a lower degree of oxidation 

 than arsenious acid, because when it forms arsenious acid by the 

 action of an alkali, not only a part of itself is reduced to the me- 

 tallic state, but likewise the whole quantity of oxide of mercury 

 present. 



All my attempts to convert this triple muriate into pure muriate 

 of areenic have been ineffectual. It follows from these experi- 

 ments that arsenic, among other properties which it has in commori 

 with sulphur, has this also, of producing a salifiable oxide with 

 muriatic acid, but which, like the oxides of sulphur, has no exist- 

 ence in a separate state, but the instant it is separated from muriatic 

 3cid is decomposed into metallic arsenic and arsenious acid. Though 

 I have not yet made analytical experiments on this muriate, there 

 can be no doubt that it is proportional to the sulphuret at a mini- 

 mum, that is to say, that it raust contain half as much oxygen as the 

 acid. 



If we add the existence of this oxide to the composition of 

 realgar, it appears to follow clearly that arsenic acid contains & 

 volumes of oxygen. Hence a volume of arsenic will weigh 83i>'9, 

 or at a maximum 852-2. 



The known degrees of oxidation of arsenic are, 1. The suboxide 

 or black powder which forms upon metallic arsenic. In my former 

 experiments I found that in it 100 parts of arsenic were united to 

 8'5 of oxygen. This is certainly either too much or too little, 

 because this suboxide must either be 2 As + O or As + O. I 

 shall make experiments on it hereafter. 2. The salifiable oxide 

 As + 3 C). 3. Arsenious acid, As + 4 O. 4. Arsenic acid. 

 As 4- 6 O. Is there an oxide As + 2 O ? 



2. Molijhdemtm (Mo). — The degrees of oxidation of this metal 

 have been carefully examined by M. Bucholz. He found that 100 

 parts of native sulphuret of molybdenum gave from 28S to 290 parts 

 of sulphate of barytes, and that it contains about 1 per cent, of 

 foreign matters. According to this determination, 100 of molyb- 

 denum combine with 66-5 of sulphur. M. Bucholz found, like- 

 wise, that 100 parts of the sulphuret of this metal gave 90 parts of 

 molybdic acid, in other experiments in which he oxidized metallic 

 molybdenum, he found that 100 of the metal combined with from 

 49 to 50 of oxygen to form molybdic acid. These experiments 

 accord well with each other : but the composition of the sulphuret 

 is not proportional to that of the acid, which according to Bucholz 

 was the only oxide of the metal known. But that eminent chemist 

 discovered that molybdenum forms likewise an acid in ous, and a 

 suboxide of a very dark purple colour. It seems to follow from the 



