25 8 Dr. ingenhousz on Air . 
other which contains common air. I found it a difficult 
matter to force always juft the fame quantity of nitrous 
air into the veftel; hecaufe I could never be lure that the 
nitrous air had diftodged all the common air out of it, or 
had diftodged always the fame quantity of common air. 
If this quantity is not always juft the fame, fome variety 
muft happen in every experiment; and thus an exadt 
valuation of the quantity of air ablorbed cannot well be 
made. % To obviate in fome meafure this difficulty, 
and to abridge the experiment by mixing luddenly the 
two airs together, I contrived the inftrument of which I 
fend you here a drawing. It is a ftrong glafs veftel, 
nearly two inches and a half in diameter, and about as 
much in height : a conical figure would perhaps be bet- 
ter. A brafs cover, which embraces the glafs about 
half an inch downwards, is cemented to it, and has 
a hole in its middle, correfponding with the hole in the 
glafs veftel. This hole of the brafs cover has a female 
fcrew fitted to receive the male fcrew of a brafs tube, 
about feven inches long and about an inch in diameter, 
terminating at one end in a male fcrew (adapted to 
the abovementioned copper plate) and at the other, in. 
a neck adapted to enter the mouth of an elaftic gum 
bottle, otherwife called boradchio or cciout-chouc , to be 
tied to it tvith a ftrong ribbon. This brafs tube has 
towards each extremity an air-tight cock, by which the 
communication between one extremity and the other 
may be opened or fhut. Between tliefe two cocks, about 
the middle of the tube, is a fhort lateral tube, commu- 
nicating' 
