PHYSICAL AND LITERARY. 399^ 



The earth, therefore, of this kind, which 

 is left in the filter after evaporation and 

 filtration, is owing to its diffolvent prin- 

 ciple being loft in that procefsj. And I 

 have reafon to believe, from experiments 

 which I have made, that, by repeated fo- 

 lutions, evaporations, and filtrations, the 

 pureft and moft genuine cryftals of vitri'- 

 olum Mart'u may be all reduced to an o- 

 kry, or bolar earth } efpecially if the folu« 

 tions be made in common water. 



7. The quantity of mineral principles 

 in this water varies, and is lefs after a 

 dry feafon, than a wet one (28); an un- 

 ufual circumllance, which probably pro- 

 ceeds from this caufe, that the water, in a 

 wet feafon, rifes higher in the veins which 

 contain the mineral principles, and con- 

 fequently diflblves and carries a greater 

 quantity of thefe principles along with it. 

 Whence it is likewife evident, that expe- 

 riments made on this water at different 

 times, will not always exadlly correfpond, . 

 but will vary more or lefs, in proportion 

 to the mineral contents of the water. 



8. The tenth experiment feems to be 



an 



