Method of avoiding observations of temperature. 377 
gas is, for example, nitrogen, the volume remaining the same, 
and that the gas to be measured is also nitrogen, we have 
w, Vii eV 8, Vie eS 
or simply Viol Wet te Ve (5) 
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the reduction of any gaseous mixture " I 
pressure and temperature. In absolute nitrogen determina- 
tions, however, proportion (5) gives the weight of the nitrogen 
measured at once, since the term w Vp is found by es 
the weight of 1 c.c of nitrogen at 0° and 760™™ by the reduc 
volume of air in the companion tube, and is a constant which 
for a ve long time. Even when filled with water I have 
1 last for some weeks. illiamson and Russell, in their 
for gas analysis, have employed a companion tube for 
ringing a gas to be measured to a constant pressure, but the 
application made above is, I believe, wholly new. 
