Experiment No. 43
Testing Hard and Soft Waters
Partially fill a large cylinder with very hard water. This may be prepared by dissolving 0.1 to 0.2 gm. calcium chloride in 500 cc. of ordinary water. Add to this a measured quantity of soap solution. Mix well and notice how many cubic centimeters of soap solution must be used before a permanent lather is formed, also notice the precipitate of "lime soap." Repeat this experiment, using either rain or distilled water, and compare the cubic centimeters of soap solution used with that in former test. Repeat the test, using tap water.
Soap Solution.—Scrape 10 gms. of castile soap into fine shavings and dissolve in a liter of alcohol, dilute with 1/3 water. Filter if not clear and keep in a tightly stoppered bottle.
1. Why is more soap required to form a lather with hard water than with soft water? 2. What is meant by "lime soap"? Describe its appearance. 3. How may hard waters be softened for household purposes?