THEORY OF COHESION. 187 



of mortar is diminished by adding to it larger 

 proportions of water, in the same manner that 

 the cohesion of ice, metals, and other bodies, is 

 lessened by increasing their temperatures that 

 is, by altering the relative proportions of caloric 

 and ponderable matter. 



Innumerable liquids might be mentioned, the 

 atoms of which have no cohesion among them- 

 selves, which, nevertheless, operate as a bond of 

 union among the particles of various other solids 

 when in the state of powder. It is by virtue of 

 the affinity between wheat flour and water, that 

 they form a cohesive dough ; and so of a thou- 

 sand other bodies, the particles of which have little 

 attraction for each other, without the medium 

 of a liquid ; but if caloric be indispensable to 

 fluidity, it must be the ultimate and efficient 

 cause of attraction between fluids and solids. It 

 is the caloric of melted wax, glue, paste, gum, 

 melasses, &c. by which they are enabled to 

 combine with and hold together the particles of 

 solid bodies, for the same reason that the caloric 

 of melted metals, rocks, &c. enables them to 

 combine with solids, and to hold them together. 

 If sulphate of lime be reduced to the state of 

 powder, its particles have scarcely any cohesion 

 for each other ; but if converted into mortar by 

 the admixture of water, they cohere into a rocky 

 cement, the firmness of which is in proportion 

 to the force of attraction between the water and 

 the lime. 



