94 THE LAW OF PART i. 



different liquids are often condensed into a solid, and 

 the result of the chemical combination of two different 

 gases or vapours in quantitative proportions may be 

 solid, liquid or aeriform, a fact which could only have 

 been discovered by experiment. The powers of the 

 atoms are changed and often highly exalted by chemical 

 union as in ammonia, a chemical compound of three atoms 

 of hydrogen and one of nitrogen, which absorbs 1,195 

 times more radiant heat than its constituents whether 

 simple or mixed. During chemical combination light 

 and electricity are often evolved, heat always. The 

 quantity given out is exactly proportional to the energy 

 of the chemical action, and is often so great and so 

 rapidly evolved as to produce an explosion by the 

 sudden expansion of the air around. Whatever the 

 temperature may be, which is given out during the union 

 of the atoms, the very same quantity of heat is requisite 

 to dissolve their union, and the atoms are separated in 

 the same definite proportions in which they were com-, 

 bined. 



Voltaic electricity both combines and resolves sub- 

 stances into their component parts, strictly according to 

 the law of definite proportions. It combines eight parts 

 by weight of oxygen and one part by weight of hydrogen 

 into water ; and again when it decomposes water, one 

 part by weight of hydrogen is given out at the negative 

 pole of the battery, and eight parts by weight at the 

 positive or zinc pole. For an electric current weakens 

 or neutralizes the force of affinity in one direction and 

 strengthens it in the other, so that the heterogeneous 

 atoms of the substance under its influence have a 

 tendency to go in different directions and appear at 

 opposite poles. Mr. Faraday has established as a 

 general law, that the quantity of electricity requisite 

 to unite the atoms of matter, is precisely equal to the 

 quantity requisite to separate the same atoms again. 



