BETWEEN” THE VISCOSITY OF LIQUIDS AND THEIR CHEMICAL NATURE. 409 
a capillary tube of known size, tlie temperature being known and kept uniform 
during the interval. 
The liquid under observation is contained in a vessel fitted with a capillary tube. 
This instrument, on the suggestion of Principal Bodington, we propose to term a 
glischrometer. It is immersed in a bath of water or glycerin, the temperature of which 
can be altered as desired. The definite volume of liquid which is forced through the 
capillary tube is measured by suitable marks etched upon the instrument. A head 
of water serves to set up the pressure, which is ascertained by a water manometer, 
and the time of flow is noted by means of a stop-watch. 
In deciding upon the form of the glischrometer several conditions had to be 
observed. In most of the instruments used by previous observers, the liquid after 
passing through the capillary was allowed to escape, and hence the apparatus had to 
be re-charged before another observation could be made. In the form adopted by us 
the time spent in re-charging was saved, by arrarjging that in all the observations on 
any one liquid the same sample could be used repeatedly; and further economy in 
time was obtained by arranging that observations could be taken while the liquid 
was flowing in either direction through the capillary tube, and that wdiile an 
observation was in progress, and liquid was leaving one portion of the instrument, it 
was entering another portion and getting into position for a fresh observation. It 
was also desirable to avoid the use of corks or caoutchouc, at least in such parts 
as would be in contact with the liquid ; it w-as therefore necessary that tlie instru¬ 
ment should be made entirely of glass. This condition presented the first serious 
difficulty in construction. To obtain absolute values of the coefficient of viscosity 
the exact dimensions of the capillary tube had to be known, and the problem to be 
solved was, how to seal the capillary tube to the other parts of the instrument in 
such a way that the direction and size of its bore should not be altered. 
The form of apparatus designed to meet these requirements is shown in fig. 1. 
It consists of two upright limbs, L, and R, (left and right), connected near their 
lower ends by a cross-piece. Within the cross-piece is the capillaiy tube, C, P, 
the bore of which is about '008 centim. radius, and the thickness of the wmll 
about 2 millims., the internal radius of the cross-piece being a millimeter or so 
greater than the external radius of the capillary. At the zone, B, B', the walls of 
the cross-piece are constricted and made continuous with those of the capillary, the 
latter is thus gripped at its middle portion and held axially within the cross-piece. 
The use of the cross-piece will now be obvious, for by its means the risk of altering 
the bore of the capillary tube was lessened, as only one sealing operation wms 
necessary in order to make the capillary tube the sole means of communication from 
the one limb to the other. 
To ascertain that this was really the case and that the capillary was quite continuous 
with the cross-piece all the way round, two simple tests were applied. A deeply- 
coloured liquid was introduced into the instrument, when it was observed that the 
MDCCCXCIV.—A 3 G 
