OILS AXD FATS. 379 



acids of fruits, etc., exist in the plant? How may some organic acids be 

 distinguished from mineral acids ? 509. From what sources is tannic acid 

 obtained ? What is its character? What is said of the products of its de- 

 composition ? 510. Describe the mode of obtaining it. 511. What is tan- 

 nin ? To what is it compared ? Give the chemical explanation of the 

 black color of leather. Why do drops of tea on a knife-blade become 

 dark? 512. Explain the common mode of making writing-ink. What is 

 said of securing permanency in writing ? What substances are added to 

 ink, and for what purposes ? 513. In what parts of plants are oils and fats 

 formed ? Name some of the principal ones, with their sources. 5U. What 

 is said of their composition ? What is stearin ? Olein ? 515. What are the 

 properties of glycerin ? To what class of bodies does it belong ? What is 

 nitroglycerin ? What is dynamite? 516. How can stearic acid be ob- 

 tained ? Of what are candles best made ? 517. What is soap, chemically 

 considered ? Explain the action of caustic soda on olive-oil. Of what are 

 natural fats composed ? 518. What is the difference between hard and soft 

 soaps ? Upon what does the cleansing power of soap depend ? Mention 

 some of the uses of soap. What is the best application for burns? 519. 

 What is said of the properties of fats, and of the uses to which they are ac- 

 cordingly applied ? 520. How do fats become rancid ? What are varnish 

 oils? How is linseed-oil prepared for varnishing? What are oil-cloth and 

 oil-silk? 521. State in full what is said of spontaneous combustion. 

 522. What is said of the combustion of fats ? 523. What are the nature 

 and composition of wax ? What is said of its occurrence in plants ? What 

 of its preparation by bees ? 524. How do volatile oils differ from fixed ? 

 How can adulteration of a volatile with a fixed oil be detected? In what 

 parts of plants are the volatile oils found ? 525. Give the three classes of 

 volatile oils, and what is said of them. 526. What is said of camphor? 

 f>27. What are resins ? What is said of their indestructibility ? 528. What 

 of their uses ? 529. What is said of caoutchouc ? What of gutta-percha ? 

 530. What of vulcanized India-rubber. 531. What are vegetable alkaloids? 

 Mention some of them, and the sources from which they are obtained. 

 What is said of their crystals? What of their composition? 532. What 

 are the two classes of coloring matters ? What is said of indigo ? 533. 

 What is said of mordants? 534. What is said of modifying color by mor- 

 dants ? In what way can different colors be put upon the same piece of 

 calico ? 



