322 A CENTURY OF SCIENCE 



substance depends upon the force of its affinity and upon 

 the mass which is present in a given volume. " The 

 development of this idea, which is fundamentally correct, 

 was greatly hindered by the fact that Berthollet drew the 

 incorrect conclusion that the composition of chemical 

 compounds depended upon the masses of the substances 

 combining to produce them, a conclusion in direct con- 

 tradiction to the law of definite proportions, and since 

 this view was soon disproved by Proust and others, 

 Berthollet 's law in its other applications received no 

 immediate attention. Mitchell, however, pointed out 

 in the Journal (16, 234, 1829) the importance of 

 Berthollet 's work, and Heinrich Rose in 1842 again 

 called attention to the effect of mass, mentioning as one 

 illustration the effect of water and carbonic acid in 

 decomposing the very stable natural silicates. Some- 

 what later several other chemists made important contri- 

 butions to the question of the influence of concentration 

 upon chemical action, but it was the Norwegians, Guld- 

 berg and Waage, who first formulated the law of mass 

 action in 1867. 



This law has been of enormous importance in chemical 

 theory, since it explains a great many facts upon a 

 mathematical basis. It applies particularly to equilib- 

 rium in reversible reactions, where it states that the 

 product of the concentrations on the one side of a simple 

 reversible equation bears a constant relation to the 

 products of the concentrations on the other side, provided 

 that the temperature remains constant. In cases of this 

 kind where two gases or vapors react with two solids, 

 the latter if always in excess may be regarded as con- 

 stant in concentration, and the law takes on a simpler 

 aspect in applying only to the concentrations of the 

 gaseous substances. For example, in the reversible 

 reaction 



3Fe + 4H 3 O^ZFe,O 4 -f 4H a , 



which takes place at rather high temperatures, a definite 

 mixture of steam and hydrogen at a definite temperature 

 will cause the reaction to proceed with equal rapidity in 

 both directions, thus maintaining a state of equilibrium, 

 provided that both iron and the oxide are present in 



