Analyfis of Earths and Stones. 169 

 are to be heated {lightly, to prevent their co- 

 hering and reiteratedly boiled in dephlogifti- 

 cated nitrous acid to drynefs, and finally dif- 

 folved in that acid, which will then take up 

 only the argill, which may be precipitated, 

 dried and weighed; though indeed this trou- 

 blefome operation may be unneceflary, as the- 

 weight of the martial part being known by 

 the experiment, with the Pruffian alkali ; that 

 of the argill is known of courfe, when only 

 the two remain. This is even better, as the 

 calx always increafes in weight by thefe ope- 

 rations. 



Befides this general method fotne others 

 may be ufed in particular cafes. 



Thus to difcover a fmall proportion of argill* 

 or magnefia^ inafolution of a large quantity of 

 calcareous Earth, cauftic volatile alkali may 

 be applied, which will precipitate the argill or 

 magnefia, if any be, but not the calcareous 

 Earth. Diftillcd vinegar applied to the pre- 

 cipitate,. will difcover whether it be argill or 

 magnefia. 



A minute portion of calcareous or pon- 

 derous Earthy inafolution of argill or magnefia* 

 may be difcqvered by the vitriolic acid, which 

 precipitates the calcareous and ponderous, 

 the folution ihould be dilute elfe the argili 



alfo 



