34 ACCOUNT of a MINERAL 



To make a fmall addition to the hiftory of barytes, and to 

 correft a miflake that has prevailed refpedling the native com- 

 bination with carbonic acid, I beg leave to add a few words. 



1. All the chemifts who have made native carbonate of ba- 

 rytes the fubjedl of their experiments, concur in afTerting, that 

 the carbonic acid cannot be difengaged from it by heat alone ; 

 and upon this fuppofed fadl, a theory of pretty extenfive applica- 

 tion has been founded. Dr Withering, in his admirable paper, 

 Phil. Tranf. vol. Ixxiv. p. 298. fays, " It is very remarkable, that 

 " the terra ponderofa fpar in its native ftate will not burn to lime. 

 *' When urged with a ftronger fire, it melts and unites to the cru- 

 *' cible, but does not become cauflic." " May we not conjec- 

 " ture then, that as cauflic lime cannot unite to fixed air with- 

 out the intervention of moifture, and as this fpar feems to 

 contain no water in its compofition, that it is the want of 

 water which prevents the fixed air alfuming its elaftic aerial 



*' ftate." This fuppofition becomes, in his opinion, flill more 

 probable from the circumflance, that the artificial aerated terra 

 ponderofa, which contains water, lofes its fixed air by the ac- 

 tion of heat. 



2. Dr Priestley adopted this notion, and adds his teflimony 

 to the fadl upon which it refls. In the Phil. Tranf. vol. Ixxviii. 

 p. 152. we have the following words : " Terra ponderofa aerata 

 " gives no fixed air by mere heat. But I find, that when 

 " fleam is fent over it in a red heat in an earthea tube, fixed 

 " air is produced with the greatefl rapidity, and in the fame 

 *' quantity, as when it is diflolved in fpirit of fait, and making 

 *^ the experiment with the greatefl care, I find that fixed air 



" confifls 



