274 GENERAL SCIENCE 



bacteria by previously wetting them with vinegar. The 

 shavings are held in a barrel (Figure 237) having a number 

 of holes cut in it to admit a plentiful supply of air. The 

 change from alcohol to vinegar in such an apparatus takes 

 place in a few minutes. 



Uses of Acids. Acids have many commercial uses. 

 Shortly after the great European war broke out the prices 

 of inorganic acids rose perceptibly. Both nitric and 

 sulphuric acids are used in the manufacture of many 

 high explosives such as nitro-glycerine, nitro-cellulose, 

 and guncotton. 



In addition to its many direct commercial uses, sul- 

 phuric acid is used in the manufacture of other acids. 

 With the present high prices, all the old sulphuric acid 

 plants, even those using obsolete methods of manufac- 

 ture, have been placed in operation and have proved 

 very profitable. The world's annual production of sul- 

 phuric acid is several million tons. Hydrochloric acid is 

 now made on a large scale by the action of sulphuric acid 

 on Chile saltpeter. 



Alkalies and Bases. A base is a substance which has 

 a number of properties just the opposites of the properties 

 of acids. Their solutions reverse the color changes pro- 

 duced by acids on sensitive dyestuffs. Litmus paper or 

 litmus solutions which have been colored red by acids are 

 changed back to blue by basic solutions. Soluble bases 

 have a bitter taste quite different from the sour taste of 

 acids. 



Common bases are sodium hydroxide (caustic soda), 

 potassium hydroxide (caustic potash), ammonium hy- 

 droxide, and calcium hydroxide. It will be noticed that 

 the chemical term hydroxide occurs in each of the above 

 names. This means that oxygen and hydrogen are 



