Permanent Colours of Opake Bodies. 197 



and, in like manner, reftores it to its (late of mild 

 calcareous earth. 



The experiments and obfervations, on which 

 Dr. Black has eftablifhed his comprehenfive and 

 confident theory, clearly prove, that lime is pre- 

 cipitated from lime water, by fixed air: but his 

 views were not extended to an inveftigation of 

 the particular matter, or quality, whereby fixed 

 air operates that efFed. 



Lime which has been precipitated from lime 

 water, and reftored to the (late of a mild calca- 

 reous earth, is again foluble by the addition of a 

 larger proportion of fixed air. This folution is at- 

 tributed to the acid quality of fixed air; and it 

 has been confidered as a (Irangc and extraordinary 

 circumftance, that accordingly as different pro- 

 portions of it are applied, it (hould act as a pre- 

 cipitant, and a folvent, of the fame fubftance. 



The fimplicity, which nature obferves in all 

 her operations, will not permit us to fuppofe, 

 that fix^d air is po(re(red of two different or oppo- 

 fite qualities, by one of which it precipitates, and 

 by the other of which, it difi!blves. 



The precipitation of lime from lime water, and 

 its refolution, are effefted by an equable uniform 

 adlion, exercifed by one and the fame fimple 

 principle, which is a conflituent and e(rential 

 part of fixed air. And, fuch a precipitation, and 

 refolution, are not extraordinary or complex phie- 

 nomena, as they have been efteemed, but are 



O 3 analogous 



