■4-BUS.] 
VISCOSITY OF GASES. 
243 
In Fig. 43 the apparatus for pro- 
ducing the pressure in question is 
fully given. The scaffolding consists 
of four vertical tubes of gas pipe, ab y 
ab, ab, ab, about 15 cm apart and 200 cin 
high. They are screwed below to a 
suitable base and coupled together 
above, forming together a long rect- 
angular column of square section. 
The tops of each tube end in vertical 
and lateral screws a, a, a, a, to which 
similar pipe may be attached, either 
vertically or horizon tally, thus greatly 
increasing the efficiency of the stand- 
ard either for the present purposes 
or for use in supporting the manome- 
ter tubes of an air thermometer (cf., / 
pp. 168, 209). The two vessels for mer- 
cury are shown at A and B, of which 
B is stationary, while A can be raised 
to any necessary height by the cord 
F G R passing over the pulley G and 
fastened by a flat-headed thumb- 
screw, H. The vessel A is practically 
a Mariotte flask, provided with a 
stop-cock at G. B has a similar stop- 
cock at D, and the connecting rubber 
hose is shown at G E D. These con- 
nections, in addition to the stoj)-cocks 
G audi), should be of wide bore, so 
as to insure a nearly frictionless flow 
of mercury. 
The head of the vessel B commu- 
nicates with the capillary tube J, 
carries the open mercury manometer 
E for the measurement of pressures, 
and is in connection with a stop-cock 
(not shown in figure), by means of 
which atmospheric air or any other 
gas may be introduced into B through 
a desicating tube. As this will be 
more clearly shown in the diagram 
below, I need only say that the cap- 
illary tubes are shut off by a faucet, 
K. Finally, a wide lateral tube, 
P Q, in communication with the 
(897) 
Fig. 43. General disposition of apparatus 
for viscosity measurement. Scale T V 
