416 
MR. W. CROOKES OK THE VISCOSITY 
The marble is contained in the glass flask, a, to the upper part of which a thistle- 
shaped funnel, b, with a ground stopper, c, is attached. The bulb, b, is filled with 
hydrochloric acid, and by loosening the stopper some of the acid is allowed to run 
down on the marble. The carbonic anhydride passes along the tube, d, which is 
tightly packed with powdered bicarbonate of soda to stop hydrochloric acid, through 
the flexible spiral, e, to the tap, f On the other side of the flask the tube, g, dips into 
a tall glass containing mercury. The tap is connected with the viscosity apparatus, as 
shown in the general view in fig. 1. 
Before introducing carbonic anhydride into the apparatus the gas is freely generated, 
and allowed to bubble up for some time through the mercury in the upper reservoir of 
the tap, the ground tube in it being loosened for this purpose. When it is supposed 
that all air is driven out of the flask and tubes by the carbonic anhydride, the tube is 
tightly pressed into the tap so as to close it, and the gas then escapes through the 
tube, g, under considerable pressure of mercury. The viscosity apparatus on the other 
side of the tap being already well exhausted, the tap is slightly turned to allow a very 
slow stream of carbonic anhydride to pass into the apparatus, generation of gas being 
kept up by feeding in hydrochloric acid through the stopper, c b. When the apparatus 
is filled with carbonic anhydride the tap,/, is turned off, and exhaustion is proceeded 
with. These operations are repeated at least three times, several hours being allowed 
to elapse after filling the apparatus before pumping out the gas, so as to let it soak 
well into all parts, and displace any other gas which may cling to the surfaces. After 
the last filling, observations are commenced. Several series are taken, and if, as is 
sometimes the case, the earlier ones are not uniform with the others, they are 
rejected. 
In the following table I give the results of the observations with this gas :— 
