THE SOAP-TEST FOR HARDNESS.
Most people are aware that hard water has a peculiar effect upon soap, making it curdle instead of lather when used for washing purposes. This peculiarity was made use of some years ago by Dr. Clark of Aberdeen, Scotland, in devising a test for the hardness of water, in which the quantity of a standard soap solution needed to produce a permanent lather on water, indicated the degree of hardness of the water. A modification of the Clark process can be used very conveniently by master mechanics in making superficial tests of the hardness of water, and the plan has the advantage of being easily applied. With a test tube and a small bottle of soap-solution, the investigator is ready at any time or place to make tests; and a few minutes spent over each specimen will give him an idea of the value of the water for boiler purposes.
The original Clark soap-test was made with a soap-solution of known strength, of which a certain measured quantity was required to produce a permanent lather on a gallon of water containing a given quantity of carbonate of lime. The degrees of hardness of other specimens were computed according to the quantity of the soap-solution required to produce a permanent lather. Preparing soap-solution of a certain strength, and water of a certain hardness, for the purpose of indicating a point for beginning the computations, is a tedious operation; and the soap-test can be used in a much simpler way. While making numerous tests of water on the Burlinglington, Cedar Rapids, and Northern Railway some years ago, to ascertain the condition of water tanks at different seasons of the year, and in examining the supply of proposed water stations on extensions of the road, I used the following modification of the Clark process:—