[ 3oo ] 



Air extracted from fpars cannot 

 be examined, nor even obtained, 

 but by making ufe of mercury 

 inilead of water : for this lingular 

 air, which corrodes glafs, is im- 

 mediately reduced into {tone by 

 the firft contact with water. 



This trough coniifts of two dif- 

 ferent ftrong wooden boxes. a a 

 is the box containing the mercury; 

 it is in the infide \\\ Paris inches 

 long, 4 inches and i lines deep, 

 and 4 inches and i lines wide. 

 The board c is placed at one inch 

 and 2 lines diftance from the brim, 

 and is 7 lines thick. The orifice dot 

 the funnel hollowed out of the un- 

 der-iide of this board is two lines 

 above the furface of the board. 

 This box is placed within another 

 larger box equally ftrong, b b b b^ 



which 



