1894 - 95 .] 
Mr J. B. Hannay on Drops. 
445 
property of cohesion like solids, the pull required to rupture the 
neck would depend on the diameter of the neck, and would he inde- 
pendent of the medium in which the drop was formed. 
A similar conclusion was arrived at by Duclaux {cinn. Gh. Phys. 
[4] xxi.), who points out that it is only an extremely thin envelope 
of the drop which influences its size and shape. Summing up, he 
says: — “II n’est pas dificile de montrer que, non seulement 
Ihnfluence de cette couche est considerable mais qu’elle est pre- 
dominante, et que la cohesion du liquid ou en general toute force 
dependante des surfaces en contact n’a pas d’action sensible.” 
Duclaux shows that the weight of a drop is profoundly modified 
by the condition of the outer skin ; and by dropping water in a 
vessel whose walls were wet with alcohol, he showed that the dim- 
inution of the size of the drop was so great that it could only be 
accounted for by supposing that the alcohol formed a thin layer on 
the drop, which then acted as though its entire bulk were of the 
same composition as the outer skin. It appeared to me that this 
question might be more accurately examined by employing a liquid 
insoluble in water to form the film. An apparatus was fitted up as 
at fig. 4, where A is the measuring bulb and B the tube from 
which the drops fall. This tube was sealed into a wider tube C, 
which served to keep the dropping tube surrounded by water 
although passing through the rubber stoppers D and E. 
A lower vessel F, formed with a side well G, in which lay the 
liquid through whose vapour the drops were to fall, was fitted by a 
rubber stopper to the dropping tube B, having a lower bulb H, 
fitted with a stopcock I, sealed on after the stopper K was passed 
over the tube, so that the dropped liquid might be quickly removed 
for examination. 
A tube L with a stopcock gave free access to the air, so that the 
pressure throughout was that of the atmosphere, and it also served 
to introduce the liquid in whose vapour the drops were to be 
found. 
Two liquids were used, — Absolute Alcohol and Benzine. 
The temperature chosen was 37°, so that there might be a con- 
siderable quantity of the vapour present, and as the water was 
dropped at 20° there was a tendency for the vapour to quickly con- 
dense on the cooler drop. 
