210 M. BerzeUus on the [March/ 



produces no trace of soluble double subarseniate ; but each por- 

 tion of arsenic acid that is added renders a certain quantity of 

 the peroxide soluble in ammonia. The subarseniate of peroxide 

 of iron which contains the sliohtest excess of base, and is inso- 

 luble in ammonia, is that which is formed by the oxidation of the 

 neutral arseniate of the protoxide. Consequently, if neutral 

 arseniate of protoxide be dissolved in nitromuriatic acid, and 

 ammonia in excess be added to the solution, all the arsenic acid 

 and all the peroxide of iron are precipitated. 



Caustic potash even, when in great excess, does not com- 

 pletely decompose arseniate of peroxide of iron. I twice 

 digested the same portion of this compound in strong solutions 

 of caustic potash, which left a substance perfectly similar to 

 peroxide of iron. When dried at the heat of boiling water, and 

 afterwards heated to redness, it lost 0-134 of its weight, which 

 was water ; the remaining 0*866 was dissolved in muriatic acid, 

 and precipitated by hydrosulphuret of ammonia. 



The sulphuret of iron, after being well washed, was dissolved 

 in nitric acid : precipitated by ammonia, it gave 0*796 of per- 

 oxide of iron. The arsenic acid, therefore, weighed 0*07. The 

 oxide of iron contained 24-4 parts of oxygen ; the water contained 

 12, and the arsenic acid 2*43 parts ; consequently these quanti- 

 ties are to each other as 1, 5, and 1(). This substance then, if it 

 be not a mixture, is composed of subarseniate, with water of 

 combination, and hydrate of peroxide of iron. When made 

 slowly red hot, it suffers more rapid combustion than most other 

 substances in which I have hitherto observed it. 



The arseniate and arsenite of protoxide of iron are also soluble 

 in ammonia, but less so than those of the peroxide : the solution 

 when exposed to the air assumes a greenish colour. 



The arseniate of nickel dissolves in ammonia in whatever pro- 

 portion the arsenic acid is combined ; but if in a solution of 

 arseniate of nickel there is any peroxide of iron, and if the 

 arsenic acid be not in sufficienl quantity to form neutral salts 

 with the two oxides; the ammonia precipitates not only some 

 subarseniate of iron, but also some subarseniate of nickel, in the 

 form of a double subsalt, which is of a green colour. If the 

 arsenic acid is not sufficient to form the double subsalt, it forms 

 a mixture of subarseniate of iron with the double salt, and in 

 this case, the precipitate has more or less the colour of oxide of 

 iron. 



If the arseniate of nickel does not contain any oxide of iroa 

 {protoxide or peroxide), it is totally decomposed by caustic 

 potash, especially if it be first dissolved in ammonia, and the 

 solution of potash be afterwards poured in. A compound of 

 nickel and potash precipitates, and the arsenic acid remains ia 

 solution combined with the alkalies. If, on the contrary, the., 

 liquid contains iron, the precipitate contains arsenic. 



