Capy.| Theory of Solutions. 83 
they differ from them markedly in properties; for instance, 
metallic sodium attacks water vigorously, the sodium ion does 
not; chlorin is a gas having a greenish-yellow color, disagree- 
able odor, ete., chlorin ion has none of these properties. This 
great difference is due to the fact that the ions are very heavily 
charged with electricity. 
Action of Solvents.—Comparatively few solvents have this 
power of breaking up or dissociating dissolved substances, and 
of these water is the most powerful. But by no means all sub- 
stances can be broken up into ions, even when dissolved in 
water; sugar, glycerol, alcohol, etc., are not dissociated to a 
perceptible degree, and their solutions do not conduct elec- 
tricity. 
Degree of Dissociation.—The degree of dissociation of an ion- 
izable substance depends upon the concentration of the solution ; 
the more dilute the latter is, the greater the degree of dissocia- 
tion. In solutions as dilute as most mineral waters, the sub- 
stances may be regarded as being completely dissociated, and 
therefore the properties of such mineral waters are simply the 
sum of the properties of the ions present. 
Combination of Elements in Water Analysis.—The question of 
how to combine the results of an analysis of a mineral water 
has always been a vexed one. But with the modern view of 
solutions all these difficulties disappear, for most waters are so 
dilute that the substances are not combined but are present as 
ions; or if the solution is more concentrated, the same ions will 
be present, together with all the possible salts. [or instance, 
if a dilute solution of sodium chlorid which will contain simply 
sodium ions and chlorin ions but not an appreciable quantity 
of the compound sodium chlorid, be mixed with a dilute solu- 
tion of magnesium sulfate, which will contain simply magne- 
sium ions and sulfate ions, there will be no reaction, and the 
solution will contain only these four ions and none of their 
possible compounds. Such a solution is absolutely identical in 
physical, chemical and therapeutic properties with one which 
is made by dissolving in the same quantity of water an equiva- 
