OF CfiEMISTRY. 129 



Stituent parts. If, on the contrary, we divide a body by cut- 

 ting it to pieces, or even by grinding it to the finest powder, 

 each of these small particles will consist of a portion of the 

 several constituent parts of the whole body : these are called 

 the integrant parts. Compound bodies are formed by the 

 combination of two or more simple substances with each 

 other. 



Attraction is that unknown force which causes bodies to 

 approach each other. Its most obvious instances are, the 

 gravitation of bodies to the earth ; that of the planets towards 

 each other, and the attractions of electricity and magnetism. 

 But that attraction, which comes under the more immediate 

 cognizance of chemists, subsists between the particles of 

 bodies ; and when it operates between particles of the same 

 species, it is called the attraction of cohesion, or the attrac- 

 tion of aggregation ; but when between the particles of dif- 

 ferent substances, it is called the attraction of composition, 

 chemical attraction, or chemical affinity. The attraction 

 of cohesion, then, is the power which unites the integrant 

 particles of a body : the attraction of composition that which 

 combines the constituent particles. When particles are 

 united by the attraction of cohesion, the result of such a 

 union is a body of the same kind as the particles of which it 

 is formed ; but the attraction of composition, by combining 

 particles of a dissimilar nature, produces compound bodies 

 quite different from any of their constituents. If, for in- 

 stance, you pour upon a piece of copper, placed in a glass 

 vessel, some of the liquid called nitric acid {aquafortis) for 

 which it has a strong attraction, every particle of the copper 

 will combine with a particle of acid, and together they will 

 form a new body, totally different from either the copper or 

 the nitric acid. If you wish to decompose the compound 

 which you have thus formed, present to it a piece of iron, 

 for which the acid has a stronger affinity than for copper ; 

 and the acid will quit the copper to combine with the iron, 

 and the copper will be what the chemists call precipitated, 

 that is to say, it will be thrown down in its separate state, 

 and reappear in its simple form. In order to produce this 

 effect, dip the blade of a knife into the fluid, and when you 

 take it out you will observe that, instead of being wetted 

 with a bluish liquid like that contained in the glass, it will 

 be covered with a thin coat of copper. 



