Spring and Mineral Waters. 55 
be conceived that the sp. gravity cannot 
constitute a test of the hardness of water, 
when we find that onegrain of earthy salt dis- 
solved in 2000 grains of pure water converts 
it into the hardest spring water that is com- 
monly found. 
We shall now proceed to notice some of 
the most useful tests im the analysis of 
waters. 
1. Soap test. When a piece of soap is agi- 
tated in distilled or pure rain water a part of 
it is dissolved, producing a milky liquid, 
which continues for many days unaltered. 
But when soap is agitated with hard spring 
water, the milkiness produced almost instantly 
degenerates into a curdy substance, which 
rises to the surface and leaves the liquid below 
nearly transparent. This curdy substance is 
understood to be the earth of the salt combined 
with the oil of the soap. It has a glutinous, 
unpleasant feel when rubbed upon the hands, 
and soils glass and other vessels so as to require 
hard pressure of a cloth to remove it. Though 
this test sufficiently distinguishes hard water 
from soft or pure water, it is not equal to form 
an accurate comparison of the hardness of 
two kinds of water. 
2. Lime water test. Most spring water 
fresh from the well will exhibit milkiness by 
