CARBON DIOXIDE AT DIFFERENT TEMPERATURES. 



217 



following, which is a modification of REGNAULT'S method of measuring the rate of 

 flow, by measuring the fall in pressure in a certain time in a reservoir which supplies 

 the gas. Since the time to be measured was, in the large flow, as small as 90 seconds, 

 it was necessary to devise an automatic method of recording it. 



A strong iron vessel of about 50 litres capacity was obtained ; it was made thoroughly 

 air-tight, and tested by blowing up a pressure under water. In this way a leak, 

 corresponding to an error of 1 part in 10,000 in the main experiments, could easily 

 have been detected ; tests were also made during the main experiments. The mouth 

 of the vessel was closed by a screw cap and washer. From the cap three outlets 

 projected : one, T, for connection to a mercury pressure gauge, one for pumping in the 

 gas, and one for the exit of the gas to the bell of the pressure regulator. The last- 

 named tube was provided with two glass taps, T x and T 2 (fig. 6) ; tap T 3 lead to the 



Reservoir. 



Stirrer 



Contact BreiKer. 



Fig. 6. 



bellows. By means of clamps the reservoir was held immersed in a large vessel 

 containing water which was kept stirred. To the steel tape supporting the bell, a 

 metal piece, S, was fixed (fig. 6). When the bell descended, S struck a lever and 

 broke an electrical connection, causing a pen to record a mark on a chronograph. The 

 contact breaker is shown in the figure, c is the lever resting in a V groove in the 

 brass support B. W is a weight which keeps the bent end of the lever pressed against 

 the top of the ebonite pillar A, the surfaces of contact being capped with platinum. 

 A piece of platinum wire, P, was soldered to the lever, and caused to dip deeply into a 

 mercury cup in a block of ebonite, M, so that good electrical contact existed between 

 the lever and the mercury cup. 



The method of performing an experiment was as follows : The reservoir was first 

 freed from moist air by exhausting it two or three times, and allowing air to enter 

 through the drying apparatus ; then, by means of a combined suction and compression 

 pump, air was sucked through the drying apparatus and forced into the reservoir 

 until the excess pressure over that of the atmosphere was about 80 cm. of mercury. 



VOL. OCX. A. 2 F 



