210 — 
We may take an example illustrating the use of drop mea- 
surement in approximately measuring the proportion in a 
mixture of its two chemically and physically similar but not 
isomeric constituents. 
Suppose we had a liquid which we knew to consist wholly 
of a mixture of benzol and turpentol, and we wished to find 
the proportion in which these two ingredients were present. 
We could scarcely approach to an answer by any of the 
means hitherto employed. The specific gravities of the tivo 
liquids are so close (.864 — .863) that the density of the mix- 
ture would give us no substantial aid. Though there is a con- 
siderable difference (80 ° C.) in their boiling points, no one 
who is familiar with the difficulties of fractional distillation, 
would place any reliance upon a quantitative separation based 
upon volatility. Their refractive indices are nearly the same*. 
Their vapour densities 2.77 — 4.76, though comparatively dif- 
ferent are not absolutely very wide apart. They are active 
and passive towards most of the same chemical reagents, and 
interfere with one anothers reactions. If we have recourse to 
chemical analysis (C 12 He, C 20 IIig) a very small experimental 
error would point to a great difference in the proportion of 
the two. 
To find how far the stalagmometer Fig. VII is applicable 
in this case, it was filled with five liquids in succession, to wit : 
1st. With benzol = B 
2nd. With 2 parts benzol with 1 of turpentol = B 2 T 
The time growth being brought in each ease to 5”, the 
number of drops of water required to fill a given volume was 
counted : allowance being made for the meniscus. 
# The Refractive index of turpentol is 1.47G : that of benzol does not appear to 
have been measured ; but that it is almost identical with that of turpentol is seen 
on mixing the two. In those cases in which I propose to use stalagmometer 
chiefly, namely with isomeric bodies the method by refraction is useless because 
isomeric liquids seem always to have the same refractive indices. 
3rd. „ 1 „ 
4th. „ 1 ,, 
5 th. ,, turpentol 
1 
=BT 
= B T> 
