Note:  Do not rely on this information. It is very old.

Clarkes Test

Clarke's Test, a test used for determining the hardness of water. The test is performed by adding a "standard" soap solution to a known quantity of water, and shaking until a permanent lather is formed. The quantity of solution required is an indication of the hardness of the water, which is stated in degrees, corresponding to a certain weight of calcium carbonate per gallon of water.