421 
of bubbles and drops by Quincke, Magie and Wilbkreorce, (3) deter- 
mination by nieans of ripples (Lord Rayleigh Phil. Mag. XXX 
p. 386), v 4) Lenard’s (Wied. Ann. XXX p. 209) method of determ- 
ination by oscillalions of a spherical drop of liquid, (5) determination 
by the size of drops (Rayleigh Phil. Mog. 48, p. 321) (6) Wilhelmy’s 
method of measuring the downward pull exerted by a liquid on a 
thin plate of glass or metal partly immersed in the liquid, (7) Jaeger’s 
method of measuring the least pressure whicli will force bubbles 
of air from the uarrovv oritice of a capillary tube dipping into the 
liquid, (8) by measuring the pull required to drag a plate of known 
area away from the surface of a liquid etc. 
Besides (i/) the surface tension, another constant is sometimes 
employed ; it is called specific cohesion, and is usually denoted by 
a 2 . The relation betvveen a 2 and (y) is expressed as follows : 
2u 
<f = — ■ == specific cohesion, where a — density of the liquid, whence 
d 
since (y) = 1 / 2 rhd (where r — radius of the capillary tube, h‘— 
= rise in the tube), it is seen that the specific cohesion is measured 
by the height to wliicli a liquid rises in a capillary tube of unit 
radius. 
Walden [Zeit. Phys. Chern. 65, 129, 257 (1908;] has recently 
found that specific cohesion may be applied in another way to esti- 
mate the degree of association of both liquids and solids. A com- 
parison of the experimental data showed the relationship 
T 7 
- — = constant — 17.9 
where T, is the latent heat of vaporisation at a boiling point and 
a 2 „ the specific cohesion at the same temperature. Combining this 
expression with Trouton’s rule, we see that the molecular cohesion 
of a liquid at its boiling point is proportional to the boiling temper- 
ature expressed on the absolute scale. This relation liolds only for 
non-associated liquids. 
Moreover Walden points out that if substances are in corresponding 
States at their melting points, there would be a similar relation 
between the latent heat of fusion and the specific cohesion at the 
melting point. 
The specific cohesion of fused metals and salts has been investi- 
gated by Quincke in a very thorough marnier. The measurements 
were obtained from the weight of falling drops of a liquid, or from 
the curvature of flat drops of the solidified material. 
It was found (Pogg. Ann. 135, 643, 1868) that all salts and 
metals and some organic substances near their melting points have 
