400 ESSAYS ANH OBSERVATION^ 



an indication, that this water contains si 

 vitriolum Martis nativum j no other mineral 

 water, that I know of, turns green with 

 oh tart, p» d. : But, when this oil is dropC 

 into a folution of vitriolum Martis^ it be- 

 comes green. And, though there is no 

 vifible effervefcence in this experiment 

 (lo.), yet the many air-bubbles genera- 

 ted, feem to be the effedl of the alkali's 

 uniting itfelf to the acid, which kept the 

 chalybeate principle dilTolved, and which 

 chalybeate principle, being now by the oh 

 tart- difengaged from its difTolvent, ap" 

 pears in the form of green or yellow clouds; 

 and at laft is found, at the bottom of the 

 glafs, under the form of a fubtile okry, 

 or bolar earth. 



It may perhaps befaid,that,fmee there 

 is probably alum in this water, the air- 

 bubbles are generated by the alkali's uni- 

 ting itfelf to the acid of the alum. To 

 deftroy this fuppofition, I diflblved alum 

 in water, and that in a greater proportion 

 than it can be in this fpaw, and then 

 dropt into it oL tart. p. d. ; there enfued 

 no effervefcence, er fenfible change upon 



the 



