[ 3^5 ] 



upon the fubject -> which is very convenient when 

 there is no opportunity, nor time, of ufing this in- 

 flrument. 



SECT. LVIIL 



The Gypfa, which confift of lime and the vitri- 

 olic acid, ( Sect, xviii. 12.) are not in the leaft at- 

 tacked by the acid of nitre, if they contain a fuffi- 

 cient quantity of their own acid, becaufe the vi- 

 triolic acid has a ftronger attraction to the lime, 

 than the acid of nitre : but if the calcareous fub- 

 flance is not perfectly faturated with the acid of 

 vitriol, then an efFervefcence arifes with the acid 

 of nitre, more or lefs in proportion to the want of 

 the vitriolic acid. Thefe circumftances are often 

 very effential in diftinguifhing the calcarei and 

 gypfa from one another. 



SECT. LIX. 



The acid of nitre is likewife neceffary in tryincr 

 the zeolites, of which fome fpecies have the. fin- 

 gular effect to diffolve with efFervefcence in the 

 abovementioned acid ; and v/ithin a quarter of an 

 hour, or even fometimes not until feveral hours 

 after, to change the whole folution into a clear 

 jelly, of fo firm a confidence, that the glafs, wherein 

 it is contained, may be reverfed, without its falling 

 out. 



SECT. LX. 



If any mineral body is tried in this menftruum, 

 and only a fmall quantity is iufpected to bedifiblved, 

 though it was impoflible to piftihguifh it wi'th the 



eye during the folution, it can be eafily difcovered 



by 



