IN CHEMISTRY. 135 



14. Why will wine sour if the bottle be not well corked ? 



The presence of air will cause the continuation of the 

 oxidizing process into the second or acetic stage. 



15. Why can vinegar be made from sweetened water and 

 brown paper ? 



The paper acts as a ferment, while the sugar or mo- 

 lasses is oxidized into alcohol and thence into acetic acid. 



1 6. Why should the vinegar-barrel be kept in a warm 

 place ? 



Heat promotes chemical change. 



17. Why does " scalding" check the "working" of pre- 

 serves ? 



The ferment which causes the fermentation is killed by 

 the heat. 



1 8. Is the oxalic acid in the pie-plant poisonous ? 



It is neutralized by the alkaline base, with which it is 

 combined in the plant. 



19. How may ink-stains be removed 1 ! 



By a solution of oxalic acid, forming an iron oxalate 

 which is soluble in water, and hence may be washed out. 



20. Why is leather black on only one side ? 



(See Chemistry^ page 211.) 



The solution of copperas, which blackens the leather, is 

 applied on only one side. 



