1389 
The pure gas') from a store cylinder is first let into a pipette P, 
in which it can be brought to a suitable pressure by means of 
mercury. By a high pressure regulating tap it is then conducted by 
a brass capillary to A, where the capillary forks. One branch leads 
to a mercury-water differential manometer, in which the level of the 
water is kept constant by the regulation of the tap C. At first we 
worked with oil manometers, which allow an easy adjustment at 
any pressure required. With these no constant values were found 
for the viscosity coefficient, which was perhaps in consequence of 
oil vapour solidifying on the capillary. On this account the oil 
manometers were replaced by mercury-water differential manometers. 
The other branch of the capillary at A leads the gas through a 
steel capillary EFG to the viscosity apparatus in the cryostat. 
Between D and # is a U tube of charcoal immersed in liquid 
air, by means of which the last possible traces of air would be 
kept back. 
A vertical glass tube carried the gas further. To this was soldered 
the spiral copper capillary of about 70 em. length, in which the 
above mentioned cooling of the gas took place, which had been 
shown to be indispensible. This terminated at A, from where the 
gas was carried to ZL. In L, which was a small reservoir, the tube 
divides into two branches viz. the capillary and the tube LJLN to 
the mercury manometer VU. Z and P could be directly connected 
by a tube in parallel with the capillary and provided with a stop- 
cock. This was necessary during the exhaustion. The transition from 
the capillary tube into Z, in which the gas may be considered as 
at rest, is very gradual. This is of importance for the correction of 
HaceNBacH, which can be omitted in these circumstances. From S a 
branch TO leads further to a second mercury manometer V, which 
registered the pressure p at the beginning of the capillary tube. 
Through the capillary tube, (about 65 cm. long, with a diameter of 
0.122 mm.) the gas flowed into P. As at L a tube PQR leads from 
here to the other end of the mercury manometer OQ. By means of 
this manometer we could thus read the difference p,—p,. Another 
tube WMYZ leads the gas from P to Z Z is connected on one 
side to the mercury-water differential manometer 5, and on the other 
side by « to c. At a there is a regulating tap, which enables us to 
keep the level of the manometer 4 at a constant height during the 
experiment. By doing this during the experiment we can keep p,—p, 
1) The gas was purified by passing over a spiral cooled’ by liquid hydrogen 
(Comm. N°. 83). A trace of air was afterwards found in the gas, this may have 
been absorbed during the compression in spite of the precautions taken. ~ 
