I8o GENERAL SCIENCE 



The hardness of water is sometimes calculated from the amount of 

 soap consumed in ridding a measured amount of water of its lime by 

 chemical action. This is considered accomplished when lather from 

 the soap remains for some time after it has been formed. 



Exercises 



1. Explain the use of borax in toilet and bath waters. 



2. When only will soap added to dish-water or wash- water give a suds? How 

 determine in either case when enough washing powder has been added 

 before making free use of soap? 



3. Why use bluing in the rinse water only in laundry work, and never in the 

 wash water? 



4. Account for any lessened wearing qualities in garments by reason of fre- 

 quent laundering. 



6. How proceed to rid a garment of a grease spot by use of gasoline without 



leaving the spot much enlarged? What is meant by "dry cleaning"? 

 6. Explain the cleansing power of soap. 



ACIDS, BASES, AND SALTS 



Any accurate use of the terms acid, base, and sail requires a 

 more extended knowledge of Chemistry than can be taught 

 in the study of General Science. Their very common use 

 in general science readings, however, almost necessitates 

 some knowledge of the distinctions to be observed in their 

 use, and something of what these terms imply. The use 

 of litmus paper is only an aid in testing for acids and bases, 

 indicating as it does acid, alkaline, or neutral effects. Some 

 salts show acid effects on litmus paper, and others turn red 

 litmus paper blue, i.e., they are alkaline. 



Vinegar contains from 3 to 4 per cent of acetic acid, 

 and sour milk has in it lactic acid; the juices of oranges, 

 lemons, and grape fruit have citric acid; rhubarb and grapes 

 have tartaric acid 1 . But there are acids lacking any sour 



1 In the gastric juice of the stomach there is a small amount of free hydro- 

 chloric acid whose presence neutralizes the alkaline saliva, and tends to prevent 

 fermentation of food in the stomach by its destructive effect on bacteria. 

 The digestive ferment pepsin requires the presence of an acid, too, for its 

 action. 



