CHEMISTRY. 25 



COHESION. 



Cohesion is the force by which the particles of a homogene- 

 ous body are held together and resist separation. Caloric is 

 the opposing or antagonizing force of cohesion. " The three 

 different forms which matter assumes, viz. solid, liquid and 

 gaseous, are determined by the degree of the cohesive force 

 existing among the elementary particles." This force is great- 

 est in solids, less in fluids, and least in gases. In gases this 

 force is negative or absent, the particles having a tendency to 

 repel each other. The globular form of the drops of liquids 

 depends upon this force. 



It is easy to conceive that if cohesion were to be suspended, 

 all solids as well as fluids would assume the gaseous form ; 

 the repulsive tendency beingt henu ncontrolled. This can be 

 effected to a certain extent by means of heat : heat overcomes 

 the cohesive power of solids and changes them to liquids : but 

 when the heat is removed, they are again changed to solids by 

 cohesion, as in the case of melted iron : bodies naturally 

 liquid, as water and mercury, are volatilized by heat, and as- 

 sume the gaseous form. The cohesive force acts at insensible 

 distances. 



DIVISIBILITY. 



Matter is capable of being divided into inconceivably small 

 particles. We have, however, no means of determining the 

 question of its infinite divisibility. We can easily imagine that 

 the minutest particle which can be produced by mechanical 

 means, must still have extension, form and weight, and would 

 be divisible, (had we instruments sufficiently delicate,) into 

 other particles, and these again into others, and so on until 

 they totally disappeared from the limit of our conceptions. 

 But we cannot by any process whatever annihilate or destroy 

 the least particle of matter. 



The particles of hydrogen gas, which is itself fourteen times 

 lighter than common air, would, individually present an idea 



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