IN POPULAR CHEMISTRY. 103 



On account of the formation of humus, which contains car- 

 bon in excess. 



9. How would you show that C exists in sugar ? 



By heating it until the H and O are all driven off. A mass 

 of porous charcoal remains on the plate. 



1O. Whyr do fruits lose their sweetness when over-ripe ? 



(See Miller's Organic Chemistry, p. 875.) 



The vegetable acid contained in the fruit when green, oxi- 

 dizes as the ripening process continues, O being absorbed, and 

 CO 3 evolved. If this continues too long, the sugar itself be- 

 comes oxidized. 



11. Why does maple-sap lose its sweetness when the leaf 

 starts ? 



The sugar of the sap is applied to the wants of the grow- 

 ing tree. 



12. Should yeast-cakes be allowed to freeze? 



A cold of 32 will kill the ferment. 



13. Why will ivine sour if the bottle be not well corked ? 



The presence of air will cause the continuation of the oxi- 

 dizing process into the second or acetic stage. 



14. W7iy can vinegar be made from sweetened water 

 and brown paper ? 



The paper acts as a ferment, while the sugar or molasses is 

 oxidized into alcohol, and thence into acetic acid. 



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

 place ? 



Fermentation takes place to the best advantage at a special 

 temperature, about 70 F. 



16. Why does "scalding" check the "working" of 

 preserves ? 



The ferment which causes the fermentation is killed by the 

 heat. 



