PRINCIPLES UNDERLYING METAMORPHIC PROCESSES 507 
affinity is ordinarily employed it is fallacious and misleading. For 
example, consider the following reactions: 
AgNO;+BaCl, =2AgC/+Ba(NO,), 
Ba(NO;).-+-Ag.SO,= BaSO,+2AgNO, 
From the first of these, we should, according to the above 
reasoning, conclude that silver was a stronger base than barium; 
while from the second, we reach the directly opposite conclusion. 
As another example, take the statement (which appears in the 
majority of textbooks on organic chemistry) that tetramethylam- 
monium hydroxide (N(CH;),OH) cannot be displaced from aqueous 
solutions of its salts (e.g., the chloride) by potassium hydroxide 
because the former is the stronger base. But it has been shown 
that if we choose a medium (methyl alcohol) in which one of the 
products (potassium chloride) of the reaction is insoluble, the reac- 
tion 
N(CH,),Cl+-KOH = N(CH,),OH+KCI 
takes place and yields practically the theoretical amount of the 
tetramethylammonium hydroxide.t These two examples, which 
are typical of a very large number of similar cases,- demonstrate 
that the relative strength of the competing acids and bases is a 
negligible factor in determining the product which separates out 
following a reaction in aqueous (or other) solution; the important 
factor is the relative solubility limits of the original substances and 
of the possible products of reaction.? This behavior is in thorough 
accordance with the law of mass action and with the currently 
accepted theory of solution; so that if we knew the solubility rela- 
tions of all possible products (including complex salts, e.g., the 
double cyanides and oxalates, if such are possible) we could predict 
quantitatively the course of the reaction. 
Another good example, which at the same time illustrates 
another point, is this. If we add hydrochloric acid to a solution of 
sodium silicate, sodium chloride will be formed and silicic acid (in 
t Walker and Johnston, Jour. Chem. Soc., LXX XVII (1905), 955. 
2This statement is subject to slight limitations, which, however, are of minor 
importance, and hence need not be discussed here. Their effect is such that a lack 
of concordance of 1 or 2 per cent may be found between theory and practice. 
