90 PRINCIPLES OF CHEMISTRY. 



Decomposition by electricity. It has been shown in Chapter 4 

 that electricity exerts under certain conditions a strong decomposing 

 influence on many compounds. It was also stated that this process 

 of decomposition is called electrolysis, while the term electrolyte is 

 given to the material acted upon. This material must be a conductor 

 of electricity, and either in the liquid or gaseous state. The electro- 

 lyte is brought into the liquid state either by melting it if solid or 

 dissolving it in some other molten medium, or, as is most frequently 

 the case, by dissolving it in water, which in some cases is rendered 

 acid or alkaline, before electrolysis is carried out. 



Electricity is widely used at the present day in chemical industries 

 and in quantitative chemical analysis. Some examples of chemicals 

 obtained thus are metallic sodium and potassium, caustic potash, 

 chlorine which is converted into bleaching powder, potassium chlor- 

 ate, aluminum by electrolysis of a solution of aluminum oxide in 

 molten cryolite, pure copper from the impure product, pure iron, 

 nitric acid by a powerful electric discharge through air. 



Decomposition by light. Another cause of decomposition is, in 

 many cases, the action of light. The art of photography is based 

 upon this kind of decomposition. Many substances, easily affected 

 by light, have to be kept in the dark to prevent them from being 

 decomposed. 



The phenomena of heat, light, and electricity resemble each other in so far 

 as they are phenomena of motion. Heat is the consequence of the motion of 

 material particles (molecules) ; light is the consequence of the vibratory motion 

 of the hypothetical medium ether ; probably the same is true of electricity. 



These motions, in being transferred, have, as shown above, frequently the 

 tendency of splitting up the molecules of compound substances. 



Mutual action of substances upon each other. As a general 

 rule, it may be said that no chemical action takes place between two 

 substances both of which are in the solid state, because the molecules 

 do not come in sufficiently close proximity to exchange their parts. 

 The free motion of the molecules in liquid or gaseous substances 

 facilitates such a proximity, and consequently chemical action. It is 

 often sufficient to have but one of the acting substances in the gaseous 

 or liquid state, while the second one is a solid. By converting two 

 solids into extremely fine powder and mixing them together thor- 

 oughly, chemical combination may follow, provided the affinity 

 between them be sufficiently strong. 



