PREFACE. xiii 



being \hzfubftratum of all vegetable, animal 

 and mineral fubftance^, difcriminated only by 

 particular forms, which in the two former 

 were held to be fubftantial, and in the latter 

 purely accidental. From this ungrounded 

 opinion (to which however fome of the 

 greateft men in the laft century were much 

 attached) that of the tranfmutability of me- 

 tals into each other naturally arofe ; and to 

 this notion, and fome other equally f alfe, the 

 progrefs of Mineralogy, and every branch of 

 Chymiftry, is undoubtedly owing. To ac- 

 complifh their favourite purpofe experiments 

 were multiplied without end, and by means 

 of thefe the arts of dying, pottery, glafs- 

 making and metallurgy were infenfibly im- 

 proved. 



The two laft named arts neceflarily re- 

 quired fome knowledge of the chymical pro- 

 perties of ftones and earths. Accordingly 

 we find that all thofe that were ufeful in the 

 former were called vitrifiable -> thofe that were 

 capable of burning to lime calcareous, and 

 thofe on which fire could produce neither ef- 

 fecT:, apyrous. For a long time thefe three 

 divifions were thoyght to comprehend all 

 fpecies of earths and ftones. The fame nar- 

 row fpirit of referring every thing to what is 

 already known, induced Mineralogifts toclafs 

 all metallic fubftances under fome of the fpe- 



