BETWEEN THE VISCOSITY OF LIQUIDS AND THEIR CHEMICAL NATURE. -121 
During its flow the liquid in one limb of the glischrometer was at atmospheric 
pressure, an observation could therefore not be taken at a temperature above the 
ordinary boiling-point of the liquid. The highest temperature at which an obsei’’ 
vation was taken depended on the appearance of bubbles of vapour in the liquid. It 
invariably happened that bubbles began to form in the left limb, never near the 
capillary, but in the region of the mark m®. The temperature was raised till bubbles 
appeared in the left limb. A right limb observation was then taken, a few bubbles 
forming in the left limb while the flow was in progress, these bubbles affecting but 
slightly, if at all, the validity of the observation. A left hmb observation was then 
taken at the same temperature, and could always be carried on without the appearance 
of hubbies. The fact that the results of these two observations are concordant proves 
that the effect of bubbles during the right limb observation is inappreciable. 
As a general rule, duplicate observations—one in each limb—were taken at the 
same temperature in the case of each liquid, and these observations were made at 
twelve temperatures, occurring at approximately regular intervals between 0° and the 
hoiling-point of the liquid. It was found, however, that the variation of the coefii- 
cient of viscosity with the temperature was of such a kind that it was needless for 
the purpose of the research to take observations at temperatures separated by intervals 
smaller than 5°. When, therefore, the range of temperature between 0° and the 
hoiling-point of the liquid was but short, fewer than twelve pairs of observations 
were made, the number being regulated by the 5° interval. 
In all cases the time of flow decreases as the temperature rises. In the case of 
relatively viscous liquids, at low temperatures, single observations only were taken, 
alternately from the right and left limbs. When, however, by rise in the tem¬ 
perature the time of flow was reduced to a convenient amount, duplicate observations 
were again taken. 
If during a series of observations on any liquid the latter had to stand overnight in 
the glischrometer, the cocks Z, Z' were turned so as to prevent all passage from the 
limhs of the glischrometer, and the apparatus was then disposed as when not in use. 
When the cocks Z, Z' were placed as described above, the bottle M was in communi¬ 
cation with the atmosphere, and, therefore, to prevent access of moisture, the exits of 
the cocks were joined by a piece of rubber tubing. If the temperature of tl)e bath 
was below that of the air, it was advisable to make the levels of the liquid in the two 
limbs about the same before turning the cocks, otherwise, on the temperature rising 
during the night to that of the atmosphere, the expansion of the air in the limb 
containing the smaller quantity of liquid might force the liquid from the other limb 
into the trap, and thus affect the working volume. 
