142 HOUSEHOLD CHEMICALS 



Some concentrated bases are so powerful in their action on 

 grease, cloth, and metal that they received the designation 

 caustic, and are ordinarily known as caustic soda, caustic potash 

 (lye), and caustic lime. These more active bases are generally 

 called alkalies in distinction from the less active ones like lime- 

 water. 



Neutral substances. To any acid solution add gradually a 

 small quantity of base, and test the mixture from time to time 

 with blue litmus paper. At first the paper will turn red quickly, 

 but as more and more of the base is added the blue litmus 

 paper will be affected less and less, and finally a point is 

 reached when a fresh strip of blue paper will not be affected 

 at all. Such a result indicates the absence of any acid quali- 

 ties in the solution. If now a red litmus paper is tested in the 

 same solution, its color also will remain unchanged ; such a 

 result indicates the absence of any basic quality. The solution 

 has the characteristic property of neither acid nor base and is 

 said to be neutral. A pinch of soda added to sour milk neutral- 

 izes the lactic acid and takes away the sour taste of the milk- 

 Ice cream is sometimes made of sour milk to which soda has 

 been added. A pinch of soda added to tomato soup neutral- 

 izes the acid of the tomatoes and prevents curdling of the milk. 



If to the neutral solution an extra portion of base is added, so 

 that there is an excess of base over acid, the neutralization is 

 overbalanced and the red paper turns blue. If to the neutral 

 solution an extra portion of acid is added, so that there is an 

 excess of acid over base, the neutralization is overbalanced in 

 the opposite direction, and the solution acquires acid character- 

 istics. 



Most acids and bases will eat and corrode and discolor, while 

 neutral substances will not. Soaps are very nearly neutral 

 substances and are the safest cleansing agent for laundry, bath, 

 and general work. Cheap soaps are carelessly prepared and are 



