EXPERIMENTS ON SULPHURIC ACID. 127 



of barytes into thofe warnings, when all the other fubftances 

 had been carefully feparated, and was thereby enabled to pre- 

 cipitate, in a ftate of purity, the fulphate of barytes, formed 

 by that earth, and by the portion of fulphur originally acidified, 

 in the tirft treatment of the ore by nitric acid. To come at 

 the knowledge of the proportion of fulphur, contained in a 

 given quantity of fulphate of barytes, I had recourfe, in the 

 firft inftance, to the quantity of fulphur, faid by Lavoifier to 

 be contained in fulphuric acid, and, in the next, to the pro- 

 portions of the latter, announced in the fynoptic tables of 

 Fourcroy, as entering into the compofition of fulphate of ba- 

 rytes. According to the former of thofe chymifts, 1 00 parts Deduction of the 

 of fulphuric acid contain 71 of fulphur and 29 of oxyg-en; and'^P hu b rf "™ thc 

 again, in adopting the proportions of the latter, we have 33 received propor- 

 per cent, of acid, in fulphate of barytes. But if 100 con- tions did " ot 

 tain 71 of fulphur, 33 muft contain 23.43. Confequently, for experiments. 

 every 100 parts of fulphate of barytes, I was to allow 23.43 

 of fulphur. But, by the refults of my analyfes, I had fuch 

 quantities of fulphate of barytes, as induced me to doubt the 

 accuracy of one or other of the ftatements, by which I efti- 

 mated the quantity of real fulphur contained in the ore. 



No perfon is better acquainted than our celebrated prefi- 

 dent, with the many difficulties that occur in the analyfis of 

 falts in general ; particularly with regard to the quantity of 

 real acid they may contain. It has been a work of trouble to 

 the ableft chymifts, and they have not always agreed in their 

 refults. The proportions, announced by Fourcroy, may there- 

 fore be doubted, in common with thofe of the other learned 

 operators, to whom I have alluded. 



The real quantity of acid, produced by the combuftion of The real quarr- 

 any acidifiable bafis, can be determined by one or other of the * lty of acid 

 following methods only : by direct combination, in fome fait, ing its radical, 

 the proportions of which are already known ; or by obtaining, determinable by 

 in a ftate perfectly free from water, the acid refulting from f°me known fak, 

 fuch combuftion. To the former method, the general objec- orelfeby obtain- 

 tions againft all analyfis of falts muft apply. The latter is j^?.** acid dry * 

 ftill more defective. It is by no means certain, that we have certain from 

 ever yet obtained any acid, in a ftate of perfect ficcity, unlefs complexity ; the 

 we except the phofphoric and the arfenic ; for even the cryftal- C afeT impTa°cli- 

 lized vegetable acids retain a portion of water in their cryftal- cable, 

 lization. It is not that I abfolutely deny our having obtained 



them 



