1814.] On the Cause of Chemical Proportions. 103 



Chromic acid 40-15 100-000 



Bar^tes 59-S5 149-066* 



100-00 



Now 149-066 of barytes contain 15-6 of oxygen, which differs a 

 little from what we found by the synthesis of chromate of lead ; 

 but this is owing to the property which sulphate of barytes has to 

 precipitate along with it a portion of the oxide of chromium : and 

 this happens in almost all the metalline solutions from wliich it is 

 precipitated ; as, for example, those of kon and copper. The 

 solution of green muriate of chromium, from which the sulphate 

 of barytes was precipitated, was now evaporated to dryness in a 

 platinum crucible, and exposed to a red heat. It left 3-043 of 

 green oxide of chromium. Thus the chromate of barytes, besides 

 the 59-85 parts of barytes, has given 30-43 of green oxide of chro- 

 mium and 9-72 of loss, which ought to be the oxygen of the 

 decomposed acid ; but 59 -8S of barytes contain 6-284 of oxygen, 

 which multiplied by 1^ = 9-426. We see, then, that abstracting 

 from the imperfection of the experiment, the acid has lost, in be- 

 coming green oxide, l-^ times as much oxygen as the barytes contains. 



This seems to prove that chromic acid contains twice as much 

 oxygen as the green oxide, and 3 times as much as the base by 

 which it is neutralized ; for if the green oxide contained twice as 

 much oxygen as it required to become acid, the oxygen of the acid 

 could not be a multiple by a whole numlier of the oxygen in the 

 base by which it is neutralized : and, on the other hand, if the 

 green oxide contained S times as much oxygen as would be neces- 

 sary to convert it into acid, the quantity of oxygen in that oxide 

 would surpass the bounds of credibility. The green oxide, then, 

 can only contain a quantity of oxygen equal to that necessary for 

 converting it into the acid, or half that quantity. In the first case 

 the acid contains 3 times as much oxygen as the base by which it is 

 neutralized ; and in the second case, twice as much. 



To determine between these two probabilities, I prepared a green 

 muriate of chromium, which I evaporated to dryness to get rid of 

 the excess of acid. A solution of this salt was precipitated by a 

 great excess of ammonia, and the solution being filtered and 

 neutralized by nitric acid, I precipitated it by nitrate of silver. I 

 obtained 30-5 parts of green oxide of chromium and 156-1 of 

 muriate of silver, equivalent to 29-73 of muriatic acid. Now 

 29-73 : 30-5 :: 100 : 102-4 ; but in these 102-4 of green oxide the 

 muriatic acid supposes 29*454 of oxygen : therefore 100 parts of 

 green oxide must contain 28-7 parts of oxygen : but if, as we hare 

 determined above, the oxide of cluromium contains a quantity of 



• III two other experiments I obtnincd for 100 of rhromic aciJ 149-2 t«i 149-1 

 •f barytes. I atcribc thU circumitHiice to the sulphate of barytes being alwayi a 

 liltic coloured by chromic acid, notwithstanding tht; exc«bS vf acid } but thil wat 

 icarccly perceptible ia the experinent utated i« the tezt. 



