[ 221 ] 



Wenzel was fet aftray by his 2d experiment; for having 

 calcined 240 grains of his ftiells for 4 hours he concluded they 

 were wholly converted into lime and he found their weight 133,5, 

 .but here lay the miflake, he had no proof that 3 or 4 grains did not 

 remain uncalcined, and the prcfence of phofphorated lime he did not 

 fufpcd. In a third experiment he came' very near the truth for he 

 concluded the quantity of lime to be 125 grains, but the difference 

 between this and 133,5 ^^ attributed to the caujiicum. 



Seliwn 7. 



Of Magnesia and Epsom. 



This earth may be obtained in three ftates, either/^//)' aerated 

 and cryftallized, and then from its great folubility in water it may 

 be called a fait ; or imperfeaiy aerated, fuch as common magnefia ; or 

 perfeElly deaerated and freed from water by a white heat. 



The proportion of ingredients even in cryftallized magnefia 

 are differently ftated, probably from having undergone fome un- 

 perceived efflorefence ; according to Fourcroy who feems to have 

 beftowed moft attention ^o this objed, 100 parts cryftallized 

 magnefia contain 50 fixed air 



25 magnefia 



25 water 



100 



hence 



