176 INTRODUCTION TO GENERAL SCIENCE 



b. Test your soap with litmus. Do you think that your 

 soap would make a good toilet soap? 



c. Soft soap may be made by using potassium hydrate and 

 no salt. There is a great excess of the alkali in soft soap. 



124. HARD WATER 



Water is called hard or soft according to the ease with which 

 soap forms suds in it. If water is rendered soft by boiling, it 

 is called temporarily hard, and the hardness was due to calcium 

 carbonate, which was dissolved in it. This calcium carbon- 

 ate, or lime, is deposited on the bottom and sides of the tea- 

 kettle. If tested with hydrochloric acid, it shows itself to be 

 a carbonate. See Section 90, The Chemical Engine. 



On the other hand, if the water is not changed by boiling, it 

 is called permanently hard. In this case calcium sulphate or 

 magnesium sulphate is present; both may be present. Per- 

 manently hard water can be rendered soft only by chemical 

 means. Boiling alone has no effect on it. By the addition of 

 soaps, chemical compounds are formed with the calcium sul- 

 phate, or magnesium sulphate, which are insoluble, and 

 collect as a scum which may be removed. The softened 

 water is not fit to drink, but is excellent for cleansing pur- 

 poses. It must be remembered, however, that it is costly 

 to use hard water, since the soap used to soften it is wasted 

 as far as the real cleansing is concerned. For the testing of 

 water, see Section 196, Water Analysis. 



References : 



1. 1703 : 47. Hard and Soft Water. 



2. 1710:67-68. Hard Water. 



a. 1701 : 309-310. Temporary and Permanent Hardness of 

 Water. 



