160 Elements of Mineralogy. 



tain 33 of aerial acid, and 67 of phlogifton j 

 for 100 grains of nitre contain about 33 of 

 real nitrous acid. This is decompofed when 

 it receives as much acid as is neceflary to 

 convert it into nitrous air, or a little more- 

 Now 33 grains of nitrous acid are converted 

 into nitrous air by about 6,7 grains of phlo- 

 gifton : then 1000 grains of nitre require for 

 their decompofition 67 of phlogifton : and 

 fince 100 grains of plumbago decompofe 

 1000 of nitre, they muft contain 67 of phlo- 

 gifton. 



APPENDIX IF. 



Of the general Examination and Analyjis of 

 Earths and Stones. 



SECTION I. 

 Of the Examination of Earths. 



When Earths are well dried and feparated 

 from every vifible heterogeneity, a portion of 

 them mould be weighed and diftilled in a glafs 

 retort, until the bottom begins to grow red hot. 

 In fome cafes it may be proper to receive the 

 air that arifes, in a pneumatic apparatus ; in 

 ail it will be proper to examine what diftills 

 over, or fublimes, whether it be acid or al- 

 kaline, with" paper tinged blue by litmus, and 

 partly reddened by diftilled vinegar : if the 



blue 



