iS2 ESSAYS AND OBSERVATIONS 



means of a fixed alkali, and carefully wafh- 

 ed away the whole of the fait. 



The chalk when dryed was not found to 

 have fuffered any alteration ; for it efFervef- 

 ced with the vitriolic acid, but did not diflblve 

 in it; and when expofed to a violent fire, 

 was converted into a quick-lime, in all re- 

 fpedls fimilar to that obtained from common 

 chalk. 



In another experiment of the fame kind, 

 I ufed the vitriolic acid with the fame event. 



Any calcarious matter reduced to a fine 

 powder, and thrown into a warm folution of 

 alum, immediately raifes a brifk effervefcence. 

 But the powder is not diflblved ; it is rather 

 increafed in bulk : and if the addition be re- 

 peated until it is no longer accompanied with 

 effervefcence, the liquor lofes all tafte of the 

 alum, and yields only a very light cloud upon 

 the admixture of an alkali. 



From this experiment we learn, that acids 

 attract the calcarious earths more ftrongly 

 than they do the earth of alum ; and as the 

 acid in this fait is exactly the fame with the 

 vitriolic, it compofes with the calcarious 

 earth a neutral fubflance, which is very diffi- 

 cultly foluble in water, and therefore falls 



down 



