* Tußbility. 49 Section v. f Experiments on the fuftble and infußble Proportions of Simple Eartbs. f As the fufibility öf fimple earths when mixed together in certain proportions, while thofe earths fingly taken are infufible, forms one of the nioft furprifing phtenomena in natural philofophy, and one of the moft important grounds of fpecific diftindtion aniong earths and flones in mineralogy, I have taken the pains of afcertaining, with more accuracy than has already been pradtifed, the proportions and degrees of heat at which it takes place (rnany of which had never before been tried), and, allo the fufibility of mixtures in which an earth is introduced that never before had been effayed. Thefe experi- ments are alfo produktive of two capital advan- tages: 1. They lead to the knowledge of the compofition of fotne minerals, ot whofe analyfis vve are as yet ignorant; and, 2,dly, they ferve as a teft of the analyfis already made; for it is plain, that analyfes that afiign a Jufible proportion of in- gredients to an infufible ftone or earth, or an infußble proportion to one that is fufible, muft be erroneous. To promote thefe purpofcs as far as poffible, it is nectirary to introduce and fet forth not only my own experiments, but all thofe of my prede- E ceffors