155 



light into their apartments ; but Agricola considered what 

 was then used as a plaister-stone*, (Sulphate of Lime, 

 tab. 67.) saying that although it was not affected by the 

 heat of summer or cold of winter, yet wet wasted it con- 

 siderably. These characters confirm his opinion ; for we 

 know that Sulphate of Lime is found in France in crystal- 

 lized masses sufficiently large to form, when split and cut, 

 squares of many inches diameter. The name Talc has 

 been applied to any laminated substance. 



Mica analysed by Vauquelin was found to contains 



Silica 50'0 



Argilla 35.0 



Oxide of Iron . . . 7"0 



Magnesia .. .. 1*35 



Lime 1*33 



94-68 

 Loss 5*32 



100-00 



* It seems to have been used in Agricola's time to shelter plants ; in which 

 case it would be much exposed to weather. 



