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Effect of Certain Dissolved Salts Upon the Cohesion of 



Water. 



By Edwin 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 

 can be demonstrated by bringing a clean, 

 horizontal disk of glass in contact with Flg - L 



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 Iowa 

 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 

 cm. 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 : 



