VISCOSITY OF GASES 179 



and on integration, since from (1) piVi-\-p2V2 = c, a constant, 



pl—p2 2fXViV2 



where yl is a constant of integration. If p'l, p'2 be the initial pressures 

 pi=p\; p2 = p'2 'when t=0. Thus, 



AiJLViV2 J {pi-'rp2) {p'l— p'2) 

 KC ' ""^ ipi-p2) (P'i+P'2) ' 



The value of the last expression may be calculated for each experiment. 

 It varies with the atmospheric pressure, but the variation is small. 

 If the pressure differences are small we have, very approximately, for 

 the time T, in which the pressure difference decreases to half its initial 

 value, 



T= — ^ . z^iy2 . log 2. 

 KC 



The apparatus employed consisted of two glass tubes placed side 

 by side in an oil bath. They were connected by a capillary tube which 

 was immersed in the oil. Small tubes, 1 mm. in internal diameter, led 

 to the manometer, and two others served to lead in the gas. 



The oil in the bath was well stirred, explorations with a ther- 

 mometer showing no appreciable variation in temperature. Two 

 regulators were employed, one a toluol tube, with copper turnings to 

 reduce the lag, otherwise quite appreciable, which was used for most 

 of the observations, the other an electrical arrangement which was 

 more sensitive. These regulators shunted the resistance coils which 

 heated the oil. When the current was adjusted so that the tempera- 

 ture varied at the rate of half a degree per hour, the shunt was opened 

 and closed again about once in every 3 minutes. The temperature 

 was taken as the mean of the indications of two mercurial thermo- 

 meters. Their fixed points were determined and the proper correc- 

 tions applied. 



Pressure differences were read on a manometer tube of U-shape, 

 mounted in front of an engraved scale and read through a telescope. 

 As only one meniscus could be observed, the manometer was cali- 

 brated, and a correction applied for the amount of liquid adhering 

 to the walls. Certain divisions on the scale were selected, and the 

 time of transit of the meniscus across them was recorded on a chrono- 

 graph. 



The gases whose viscosities have been determined at different 

 temperatures between 0° C. and 110° C. are carbon dioxide, hydrogen 



