In
the case of waters containing salts of both calcium and magnesium, I
found that if the salts of the latter metal were in solution in
quantities sufficient to give more than 10 deg. of hardness, no evidence
could be obtained of their presence so long as the salts of calcium in
the same water exceeded 6 deg.; in such a case a perfect and permanent
lather was produced when soap had been added equivalent to 7 deg. of
hardness.
If any water be diluted so as to reduce the proportions of the salts
of calcium and magnesium below those stated above, perfectly reliable
results will of course be obtained.
Instead of dilution I found that heating the water to about 70 deg. C. was
sufficient to cause a complete reaction between the soap and the salts
of calcium and magnesium, even if these were present in far larger
quantities than any given here.
The experiments so far had all been made with a solution of Castile
soap of the strength suggested by Mr. Wanklyn in his book on "Water
Analysis." My attention was next directed to the use of any one of the
compounds of which such a soap is composed. I commenced with sodium
oleate, and found that by employing this substance in a moderately
pure condition, perfectly reliable results could be obtained in very
hard waters without the trouble of either diluting or heating. I was
unable to try sodium stearate directly because of the slight
solubility of this substance in cold water or dilute alcohol; but I
found that a mixture of sodium oleate and stearate behaved in exactly
the same manner as the Castile soap.
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