BETWEEN THE VISCOSITY OF LIQUIDS AND THEIR CHEMICAL NATURE. 419 
trolled. The rate of stirring was altered by regulating the water supply and the 
length of stroke adjusted by attending to the cut-ofiP. 
By rapid stirring the temperature soon falls, and becomes steady at 0°'3 or 0°’5, the 
exact temperature depending on the temperature of the laboratory. As a general 
rule, observations at as nearly as possible the same temperature were taken in both 
limbs of tlie glischrometer; for this purpose, as will be evident from what follows, tlie 
first observation at a given temperature had to be taken in the right limb. 
When the liquid in the glischrometer had acquired the constant temperature of the 
hath, the first point to be attended to was the adjustment of the working volume of 
liquid. During the time that the glischrometer had been standing after being filled, 
the liquid was slowly flowing through the capillary, and the level, which after filling 
was much higher in the right limb, had been falling and approaching that in the left 
limb. The cock Z was now turned so as to put the right limb of the glischrometer 
to air. The pressure of the air reservoir, which was acting upon the liquid in the left 
limb, caused the level in this limb to fall, and as soon as the meniscus, as seen by a 
lens through the glass wall of the bath, touched the mark fig. 1, the pressure on 
both limbs was equalized. The slight excess of liquid over the volume which was 
introduced in filling the glischrometer, escaped into the trap Tb This process was 
carried out before observing the time of flow at any temperature, and in this way at 
the beginning of any experiment, the head of liquid in the limb, subject to a small 
correction for expansion of the glass of the glischrometer, was constant. As will be 
shown later, by this means a pressure correction for the effect of the varying head of 
liquid in the limbs of the glischrometer during the time of flow can be evaluated. 
The head of liquid having been adjusted, the left limb was now put to air. Under 
the pressure of the air reservoir the level in the right limb, which meanwhile had 
been slowly filling, descended more rapidly. 
The telescope on the right-hand outer rod was now clamped against the upper stop, 
when the mark was in the field. As soon as the meniscus was seen through the 
telescope to touch this mark the stud of the stop-watch was pressed and the hands 
started. Readings of the thermometer T through the telescope, of the water levels 
in the manometer, and of the manometer thermometer through a lens, were imme¬ 
diately taken. The telescope on the right hand rod was undamped and allowed to 
slide down to the lower stop, the mark being then in view. During the experiment, 
attention was directed to keeping the temperature of the bath as uniform as possible. 
This temperature was noted at regular intervals during the flow, and if the latter 
were long, the manometer readings were also repeated. When the meniscus was seen 
through the telescope to touch the mark the hands of the watch were arrested and 
readings of the thermometer and manometer noted immediately as before. The time 
indicated by the watch was next taken, and the hands brought back to zero. If it 
was judged that these final readings could be taken and noted before the level in the 
limb fell to U the disposition of the cocks Z, Z' was left unaltered ; if the level, 
3 H 2 
