249 
Errect oF Certarx DissoLvep Sauts Upon tHE COHESION OF 
WATER. 
By Epwin Morrison. 
Cohesion is defined as “that force which holds molecules of the same 
kind together.” This force is very manifest in all solids, giving rise to 
such properties as hardness, brittleness, malleability, ductility, tensile 
strength, etc. Although not so apparent, 
all liquids manifest the same kind of an 
attractive force between molecules. Sur- 
face tension and the phenomenon of capil- 
larity are due in a measure to cohesion 
of the molecules. That molecules of water 
are held together by means of cohesion 
‘an be demonstrated by bringing a clean, 
horizontal disk of glass in contact with Pig. 1. 
the surface of water and then adding sufficient force to pull the disk away 
from the water. In case the surface of the disk is wet when it comes 
away from the water we know that the force applied has separated two 
films of water, each equal in area to that of the disk. 
Probably Gay-Lussac first experimented upon this force and estab- 
lished the commonly accepted data of 526.875 dynes per square cm. Gay- 
Lussac used a glass disk supported by three guy cords as shown in Fig. 1. 
The author designed and constructed a piece of apparatus for measur- 
ing cohesion of water and other liquids and reported the same to the Lowa 
Academy of Science in 1904. This apparatus consists of a round glass disk 
10.6898 cm. in diameter mounted upon an accurately constructed cone 10.5 
em. high. with an eyelet in the apex for suspending the cone from the hook 
of a specific gravity balance. A cut of this apparatus is shown in Fig. 2. 
In 1905 the author carefully worked out and reported to the Iowa 
Academy of Science the value of the cohesion of water as follows: 
