MINERALOGY. ioj 



principal ingredient in the making of crucibles, 

 retorts, &c. 



The boles have almoft loft their value* as me- 

 dicines, and are employed to make bricks, pot- 

 ters-ware, and pig-iron. 



The tripoli is an indifpenfible article for the 

 polifhing of metals, and fome forts of ftones j it 

 is likewiie on certain occafions preferred for 

 making- moulds to call metals in. 



The common clay is of the greateft benefit in 

 agriculture, except however the white clay and 

 the fermenting clay, both of Seel:, xc. which 

 varieties we know not yet how to apply to 

 any ufe. By virtue of its coherency, this clay 

 retains humidity, on which perhaps its chief be- 

 nefit to vegetables depends, its other effects being 

 occasional, owing either to nature or art; unlefs 

 the clay has formerly been a mould or humus 

 ater, in which cafe it is juft, that part of it mould 

 enter a°;ain into the formation of the new veg-eta- 

 bles. The clay ufed in the refining of fugar, 

 wants no other quality than that it may not dry 

 too foon. But that fpecies which is to be em- 

 ployed in fulling, muft, if we Were to judge a 

 priori, befides the finenefs of its particles, be of 

 a dry nature, or fuch as attracts oils ; though this 

 quality may perhaps not be found in all thofe 

 clays which are now employed in that bufi- 

 nefs. 



SECT. XCIII. 



The FiFy h Or d jzr," 



The Micaceous Kind, Mcacea. The Glimmer* 

 Daze, or Gfift. 



H a Thefe 



