APPLYING THE SOAP-TEST.
In making the tests, a measured quantity of the Cedar water was put into a stoppered bottle. One ounce of water put into a two-ounce bottle is a convenient quantity. The soap-solution was then measured out with a pipette made to hold thirty drops, and the bottle was well shaken after each measure till it was found that a lather was formed which held on for five minutes. The operation was then repeated; and the last charge from the pipette was put in, drop by drop, till the point where a permanent lather formed was noted. A similar performance was gone through with the bad well-water, and very little practice enabled the operator to ascertain where a specimen of water stood between the range of the good and bad water.
The soap-solution must be kept in a properly stoppered bottle; and, every time a new solution is made, its strength must be tested in the above fashion. The solution deteriorates when kept longer than a month or six weeks.
The degree of turbidity caused by the first charge of soap-solution, is an indication to the practiced experimenter of the degree of hardness of the water.
Most men interested in ascertaining the condition of boiler-water, can devise means for obtaining water of known hardness wherewith to make comparative tests.
If water under examination prove very hard, the test will be more accurately done by diluting it with its own volume of distilled water.
The soap-test is good for lime in all its forms, and magnesia; but the latter impurity uses up more soap than lime does. So, where magnesia abounds in water, the specimen under trial will seem harder than it actually is. Magnesia is also slower than lime in acting upon the soap. Water that contains magnesia will produce a lather when enough solution is put in to overcome the lime present; but if it be allowed to stand a few minutes, till the magnesia acts, the lather will not then form. The presence of certain alkaline salts in water, such as the carbonates and sulphates of soda and potash, injuriously affects the soap-test by making the water appear softer than it is; since they accelerate the forming of a permanent lather. Keeping these facts in mind will often prove of valuable service in making tests of water.
When the soap-test indicates that water contains hardening ingredients, representing more than fifteen grains to the gallon, other tests should be at once made to ascertain what the leading ingredients are.