Cf Chfification. 47 duce confufion, I think they may be referved for a feparate work of that nature; but when they do not clafh vvith other natural divifions, £ would not hefitate to place them in the fame rank; and in eff’edi thefe fame mineralogiüs allow potters earth, fullers earth, tripoli, &c. a place in what they effeem the natural fyftcm. Hence i". The generic earths, combined with an acid, are fpecifically different from thole that are not. 2 0 . The fame generic earth, combined with different acids, forms different fpecies. 3'’. The fame generic earth, combined with a notable proportion of one or more of the other earths, forms a different fpecies from the fame generic earth, either uncombined or combined with a lefs important proportion of other earths. I call a Proportion notable or important when it introduces a confiderable alteration in the external or inter nal charadters of the compound. Thus fuch a proportion as induces a confiderable change in the fpecific gravity, or in the fufibility of any fubftance, is notable or important; fo in the cal- careous genus fuch a proportion of foreign earth, or earths as would prevent it from burn- ing to lime, is certainly of importance, and the diflindtion grounded in nature: fo propor- tions that alter the fufibility of fubffances, with refpedt to the degree at which they are fufible, are certainly notable, and a good foundation for fpecific diftindtions. But varieties of proportion, or even of ingre- dients, that produce no notable change, either in the internal or external properties of a com pound, make no alteration in the fpecies ; and in faft there are fcarcely any earths or flones that have,