MINERALOGY. 9 



and fome can be decompounded ; neverthe- 

 lefs, in a melting heat they can again be re- 

 covered, or brought to their former Hate, 

 by adding to them the phlogifton they loft 

 during their decompofition*. 



SECT. III. 



The FIRST CLASS. 



Earths, Terr<e, are thofe mineral bodies, 

 not ductile, for the moft part not diflbluble in 

 water or oils, and that preferve their conititution 

 in a ftrong heat. 



S E C T. IV. 



Thefe earths (Seel:. III.) are here arranged ac- 

 cording to their conftituent parts, as far as hi* 

 therto difcovered, and are divided into nine or- 

 ders. 



* Here occurs the fame difficulty in regard to the defini- 

 tions, as was before (Seel. I.) obferved, becaufe thefe enume- 

 rated clarfes are likewife blended one with another ; anci there- 

 fore fome exceptions muft be allowed in every one of them : 

 for inftance, in the firlt clafs, the calcareous e^rth is in fome 

 meafure diflbluble in water, and pipe clay with fome others 

 diminifh fomewhat in their bulk, when kept for a long time 

 in a calcining heat. In the third clafs, the calx of arfenic 

 has nearly the fame properties as falts; and there is no pof- 

 fible definition of fait, that can exclude the arfenic, though, 

 2t the lame time, it is impofiible to arrange it elfewhere than 

 among the femi-merals. In the fourth clafs it is to be ob- 

 ferved, that the metals and femi-metals, perfect or imperfeel, 

 have r.ot the fame qualities common to them all; becaufe 

 fome of them may be calcined, or deprived of their phio- 

 gifton, in the fame degree of fire, in which others are not in 

 the leaft charged, unlefs particular artifices or procefies are 

 made ufe of: fome of them alfo may be made malleable, 

 when others are by no means to be rendered fo. That the 



convex 



