BETWEEN THE VISCOSITY OF LIQUIDS AND THEIR CHEMICAL NATURE. 431 
scale, 1 millimeter broad, was g;ummed along the entire length of each limb of the 
glischrometer, A quantity of water was then introduced into the instrument, which 
was transferred to the bath, and after a constant state of temperature (that of the 
atmosphere) had been obtained, the working volume of liquid was adjusted. The 
position occupied by the mark M® was ascertained by a cathetometer, the level 
of liquid in the right limb brought just into contact with the mark M®, and the 
position of the level in the left limb read ofl'. As the level fell in the right limb to 
the mark M^, readings were taken on the cathetometer and paper scales, of the 
levels in both limbs, when that in any one limb was leaving a narrow portion of the 
limb to enter a wide portion, or vice versd. Finally the cathetometer reading of the 
mark was observed, the level brought into contact with it, and the position of 
the corresponding level in the left limb noted. The positions of corresponding levels 
are numbered alike, and are roughly indicated in fig. 1, p. 410. The temperature 
remaining unaltered, the time was next observed, by fixing the cross hair of the 
observing telescope on the corresponding reading of the paper scale, which the 
liquid took to pass from ] to 2, 2 to 3, &c., under a constant pressure. It was then 
possible to plot out a curve having as abscissae the times, and as ordinates the heads 
of liquid, — 1l, 2^ — 2l, &c., representing the variation in the head of liquid with 
the time throughout the entire flow, the curve between any two consecutive, ordinates 
being assumed to be straight. The curve consisted, of course, of two portions, one 
above, the other below the axis of abscissae. On dividing the difference in the area 
enclosed between the upper part of the curve and the axis of abscissae, and that 
enclosed between the lower part of the curve and the axis of abscissae, by the total 
time of flow, the mean head of water of density corresponding to the temperature of 
the experiment which influences the flow is obtained. In the case of the left limb 
this was found to be — T3.9 centim. at 19°T5 ; in the case of Alie right limb it was 
— '253 centim. It is obvious that with the same liquid this height will be subject to 
a correction for expansion of the glass of the glischrometer, but as the height is 
small compared with the cotal pressure, 130 centims. or so, the correction may 
be neglected. Thus, for any liquid for any temperature — T39 centim. represents 
the mean head of liquid opposing the flow from the left limb. In order to put this 
head into the form of a correction to be applied to the reduced reading of the water 
manometer, account has to be taken of the densities of the different liquids, and of 
the variation in density of each liquid with change of temperature. A table has 
been constructed for each limb of the glischrometer, from which, knowing p, the 
density of the liquid at 0°, and s, the volume which 1 cub. centim. at 0° occupies at 
the temperature of experiment, it is possible to obtain by inspection the value, in 
centims., of water at 4°, corresponding to the mean effective pressure head of any 
liquid at any temperature. The tables include densities from 07 to 3'0, and volumes 
from 1 at 0°, to 1'2 at the highest point of observation. 
Determination of Time .—Two stop watches supplied by Dent were used. The 
