CHAPTER V. 
THE THEORY OF SOLUTIONS. 
BY PROF. H. P. CADY. 
The modern theory of solutions is of especial interest in con- 
nection with a discussion of mineral waters, because of the 
light which it throws upon the condition and properties of the 
dissolved mineral matter. 
Solutions Defined.—A solution may be defined as a homoge- 
nous mixture of two or more substances which resembles a 
chemical compound in that the constituents cannot be separated 
by ordinary mechanical means, but which differs from a chem- 
ical compound in that the relative proportions of the con- 
stituents may vary between wide limits. Solutions may be 
divided into two classes: First, solutions which will conduct 
electricity ; second, solutions which will not conduct electricity. 
Solutions of the first class are of the most interest here because 
in this class are included solutions of acids, bases and salts in 
water, and hence it embraces all mineral waters which are 
simply aqueous solutions of various mixtures of the above-men- 
tioned substances. 
Theory of Lonization.—There are a good many reasons for be- 
lieving that in solutions which will conduct electricity the mole- 
cules of the dissolved substances are broken up by the action of 
the solvent into smaller parts, called ions. This belief rests 
upon a great body of experimental facts which are too numer- 
ous and complex to be discussed here. According to this theory, 
when common salt, sodium chlorid, is dissolved in water, the 
molecules of sodium chlorid are broken up by the action of the 
solvent into sodium ions and chlorin ions, each of which is en- 
tirely free, uncombined, and independent of the others. These 
ions are not to be confused with the atoms of the elements, for 
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