Dr. ingenhousz on Air. 261 
all the while exactly flint. The two airs being thoroughly 
mixed, I put one extremity into a veffel filled with quick- 
filver, and withdrawing the finger from the opening, the 
quickfilver rifes immediately within the tube, and fhews 
by its height the exaft quantity of air diminifhed. The 
other method is this : I tve to the end of the fame tube the 
neck of a l'mall elaific gum-bottle, the bottom of which is 
cut away : having put fome iron filings into a little phial, 
filled with aqua for tis, I put the end of the tube within the 
mouth of the phial, clapping my hand faff to the orifice 
of the phial, the loofe part of the elaflic bottle, fo that 
the nitrous air, riling from the phial, muff take its courfe 
through the tube. When the whole tube is filled with red 
fumes, I take it out, and fhut the two extremities with my 
two fore-fingers. Then I put one end of the tube in a 
veffel with quickfilver, and withdraw both fingers for an 
inflant, to make the column of quickfilver rife within the 
tube. I apply immediately both fingers ; and holding the 
tube nearly in a horizontal direction, fothat the extremity 
where the quickfilver is may be rather the higheft, I open 
and flint at the fame time both extremities, fo that the co- 
lumn of quickfilver gradually advances towards the mid- 
dle. The quickfilver advancing towards the middle, as 
much common air follows the quickfilver as it forces out 
nitrous air from the other extremity. As loon as the co- 
lumn of quickfilver is in the middle, I keep both extre- 
mities well flint with my fingers, and moving the tube in 
various ways, I force the two airs to come into mutual 
contact, and to mix intimately together. Then I put one 
extremitv 
