!b 



.1814.] On the Cause of Chemical Proportions. 95 



Article III. 



Essay on the Cause of Chemical Proportions, and on some Cir- 

 cumstances relating to them: together uith a short and easy 

 Method of expressing them. By Jacob Berzelius, M.D. 

 F.R.S. Professor of Chemistry at Stockholm. 



{Continued from p. 62.) 



C. — The Metals. 



1. Arsenictnn, arsenic (As). — The experiments of Thenard, 

 Proust, and Bucholz, as well as those which I have published, on 

 the capacity of saturation of arsenic acid, seem to prove that arsenic 

 combines with -i- of its weight of oxygen to become the acid in oii.<>y 

 and with i its weight to become acid in ic. In my experiments on 

 the arseniate of lead 1 found that arsenic acid ought to contain 

 twice as much oxygen as the oxide by which it is neutralized : but 

 as, on the other hand, the relation between the quantities of 

 oxygen found in the two acids shows that arsenic acid must contain 

 at least 3 volumes of oxygen, it appeared to me that the neutral 

 arseniates offered an exception to the general relation between the 

 volumes of oxygen in the acid and those in the base, an exception 

 which deserved to be examined with care. I determined, then, to 

 repeat my experiments on the arseniates, in such a manner as to be 

 certain that I operated upon perfectly neutral arseniates, and free 

 from all mixture of ai'senious acid. 



On examining a portion of the arseniate of soda which I had 

 employed in my former experiments for preparing a;-seniate of lead, 

 1 found, to my great surprise, that this salt, which had been care- 

 fully crystallized, gave unequivocal signs of containing an excess of 

 alkali. It had effloresced a little ; and when I neutralized it with 

 arsenic acid, I found it no longer capable of crystallizing. 



I prepared a portion of aisciiiate of soda, and to be quite certain 

 that it contained no arsenious acid I fused it with nitrate of soda. 

 The fused mass was dissolved in water, and rendered neutral by the 

 addition of a few drops of nitric acid. W ith this solution I preci- 

 pitated neutral solutions of nitrate of lead and muriate of barytcs. 



ylrscniale of Lead. — I dissolved 10 parts of arseniate of lend in 

 nitric acid, and then prccipiiatcd the solution l)y means of sulphate 

 of ammonia. The sulphate of lead thus obtained being washed, 

 dried, and heated to redness, weiglied 8-805 parts. The acid 

 solution from which this precipitate fell being neutralized l)y ani- 

 monu yielded a precipitate, wliicli was arseniate of lead. 'JVeated 

 anew with sul|)hiiric acid I obtained 0*088 part of sulphate of lead ; 

 so that 100 parts of arseniate of lead yielded h9-.'):J parts of sulphate 

 of lead, equivalent to dG parts of o.\ide of lead. Hence arseniate 

 of laid is composed of 



