chemical change by measurement of the gases evolved. 583 
the rotating shaft and the guiding tube. It was found that the 
apparatus was airtight under a pressure of 30 cm. of water when 
the paddle was rotating at full speed. 
In those cases where it was necessary to mix the solutions 
in an inert atmos23here, the apparatus IFS was employed. By 
pressing the rubber bulb I, the liquid in F was squirted through 
the stopcock S — which was then turned off — into the reaction 
vessel R, the time occupied being less than 2 seconds. To fill 
with the inert atmosphere, the whole apparatus was exhausted 
by an air-pump, and the gas in question was allowed to enter, the 
process being repeated three times. In all such cases the gas 
used was the same as that which was evolved in the course of 
the reaction. 
Fig. 2 represents a general view of the apparatus. The part 
above described is immersed at R in the water bath A, the delivery 
tube being connected by means of a three-way cock C with the 
burette B. The liquid in the burette in most cases was the same as 
the solvent employed for the reaction, and in all cases was saturated 
with the gas evolved in the course of the reaction. The levelling 
tube L was arranged to slide on vertical guides and was raised, 
lowered or maintained at any point by means of the windlass W. 
