146 EXPERIMENTAL GENERAL SCIENCE 



water and rubbed through the fingers, have a slimy feel. Most 

 bases consist of a metal combined with oxygen and hydrogen. 

 Lime-water and ammonia are good examples of bases. When 

 a base is added to a solution of phenolphthalin it is turned a 

 bright scarlet, but the solution becomes colorless again when 

 sufficient acid is added. A strong base is called an alkali. 

 Caustic potash (potassium hydroxide) and caustic soda 

 (sodium hydroxide) are two other active bases which are 

 usually known as lyes. Both acids and bases attack other 

 substances and corrode them. 



124. Formation of Salts. If an acid be added drop by drop 

 to a base, a mixture may be formed which will not affect either 

 red or blue litmus paper, and which is not corrosive in its 

 action. Such a solution is said to be neutral. When a base 

 and an acid neutralize each other in this way, a chemical 

 reaction takes place which results in the formation of a salt, in 

 addition to more or less water. Common table salt (sodium 

 chloride) is a familiar example of a salt, and among others with 

 which we are familiar may be mentioned calcium chloride, 

 sodium nitrate, and calcium sulphate. If a mixture is not 

 quite neutral, we may have an acid salt or a basic salt accord- 

 ing to whether the base or acid predominates. Baking soda is 

 a basic salt and therefore affects litmus paper like a base. 

 Soaps are really mixtures of salts. When a potash base is 

 used, "soft" or liquid soap is formed. A soda base is used for 

 the hard soap commonly sold. Soft soap may be made hard 

 by the addition of table salt during the process of manufac- 

 ture. Laundry soaps usually have an excess of alkali which 

 renders them unfit for toilet use. 



Practical Exercises 



1. Test the substances in the following list with litmus paper and 

 decide which react as acids and which as bases. Those that are not 

 liquid should be dissolved in a little water before testing: 



