(Study pages 55-65)
Strips of litmus paper may be obtained at a drug store or will be sent from the School on request. Moisten the blue paper in vinegar, lemon juice, tomato, solution of cream of tartar, etc., and then in ammonia (even the vapor will change it), in solution of washing soda, baking soda, borax, soap, and various washing powders. If the paper is washed in running water after being turned blue with ammonia, a test for acid may usually be found in milk, molasses, and sometimes butter. One piece of paper will be found to turn from blue to red and back again to blue an indefinite number of times when wet with solutions of acids and alkalies alternately.
Buy five cents' worth of hydrochloric acid and a little caustic soda at the druggist's. As caustic soda is unpleasant to handle, it is best to have the druggist dissolve it in water. Now pour a part of the acid into a saucer or glass, with a little water, and add the solution of caustic soda until the mixture begins to turn the litmus faintly blue. In an agate-• ware dish, free from worn places, evaporate the solution to dryness. A whitish substance will be found, which by testing will be recognized as common salt.
From two very active chemical substances has been formed a neutral substance - salt. Not all salts, however, are neutral. Sodium carbonate (washing soda) is chemically a salt, but it is made up of a very strong alkali forming element - sodium - and a very weak acid - carbonic acid - and the alkali properties predominate. Cream of tartar is an example of an acid salt. It is acid potassium tartrate, which is a double salt, that is, tartaric acid is added to neutral potassium tartrate, the result being a substance which has acid properties. Common alum is slightly acid to litmus paper.
Soap chemically considered is a salt, made up of a fat acid and the metallic substance sodium. The fatty acid can be separated by adding any acid like vinegar to a solution of soap. If the solution is warm, it rises as a scum to the top. It can be dissolved in ammonia, forming an ammonia soap. The sodium part of the soap unites with the acid and forms a salt. If hydrochloric acid is added to a soap solution (a sufficient quantity to make the solution very slightly acid), the fatty acid removed, and the residue evaporated to dryness, common salt will be found.
If lime water be added to a solution of soap, white clots of "lime soap" will be formed which are insoluble in water, but on collecting and drying will be found to dissolve in gasoline, naphtha, or kerosene. This is why naphtha or gasoline is useful in cleaning bath tubs, bowls, etc. Quite a good varnish can be made of aluminum soap, made from alum and white soap, dried and dissolved in gasoline.
It is not difficult to get some idea of the composition of the various washing powders on the market. When acid is added to a solution, if there is effervescence, washing soda is probably present. A skum would indicate that soap formed a part of the mixture.
In the experiment with cabon dioxide it was shown how carbonate of lime might be dissolved by an excess of carbon dioxide gas, the bicarbonate of lime being formed, which is soluble in water. This is an example of an "unstable" chemical compound. Simply boiling drives off the excess of carbon dioxide gas, leaving the ordinary carbonate of lime which is insoluble and is deposited on the sides of the tea kettle or other vessel. This may be shown by blowing into lime water until the cloudiness which at first appears begins to dissolve. As it is difficult to dissolve it completely, the solution may be filtered. On boiling the clear solution, the milkiness will appear again.
Hardness that is brought about by the sulphate of lime - "permanent hardness " - is difficult to remedy by any household means. Washing soda helps a little, but not very much. The so-called alkali waters of the west, in addition to sulphate of lime contain sulphate of soda and other salts, so that they are beyond remedy.
Reference: Chemistry of Daily Life - The Manufacture of Soda. Page 194.