143 



--winch anci you see bubbles of air through the body of 



-the water. First, they are thick, but small; then they 



, grow. large, and rise to the top of the water. And as 



long as the pump works, so long the air rises, but more 



aloirly, and in. larger bubbles* In wine the air-bubbles 



.-rush violently to the top and burst; nay, and the liquor 



perfectly boils like water on the fire. Yea, and hot 



water may be made to boil by -the air-pump as v?ell ;is 



by lire. Hence it appears, that boiling is nothing but 



the motion produced from the -.-/expansion of the air, 



whether by tire, or by the warmth and pump conjointly, 



By another experiment it appears, that any piece of 



-wood is pervious to tiie air, and that its air-vessels run 



through the whole length or substance uf the tree.- 



Nay, quicksilver may be made to pass through a piece 



of wood, and descend in the form of a shower of rain. 



By the air-pump we likewise measure the weight, and 



.find that a pint of it weighs 8 grains. Consequently a 



: ;;v! I on weighs a little more than a drachm: therefore a 



bushel weighs an ounce and huSf^a drachm. 



Another experiment proves what one would not sus- 

 pect. Bodies moving in a fluid meet so much the more 

 resistance, as tlieir bulk is larger in equal weight. So a 

 cork, of equal weight with a guinea, meets with so much 

 the moro resistance from the air. But in an exhausted 

 receiver, the largest bulk of cork, .which was before the 

 most resisted, now proves the heavier body, and accord- 

 ingly falls more swiftly than the gold. 



Again. Strike a flint against the steel invacuo, and 

 it will occasion no sparks, So necessary is air to the 

 'very appearance of fire. 



Air is generated likewise from minerals by fermen- - 

 tation. By other fermenting mixtures it is absorbed- 

 .again, and by others generated and absorbed alternately. 

 A quarter of an inch of jilings of iron; and an inch of 

 compound aquafortis, in four days absorbed 27 inches 

 of air. When hot water was poured upon it, it gt?ne- 

 r.aied three or four inches, which after some da\s it ab- 

 sorbed again. A quarter of an inch of iron filings, with 

 an inch of powdered brimstone, absorbed nineteen inches 



