CONSTITUENTS OF PLANTS, ETC. 327 



tained ; it is known, however, that the green color is due to 

 the mixture of a blue with a yellow substance. Chloro- 

 phyll is not soluble in water, but is easily soluble in alcohol 

 and ether, which are used to extract it from green leaves. 

 Light is necessary for its formation, as we know by the 

 white color of plants that grow in darkness. 



QUESTIONS. 



428. What is said of the variety of vegetable substances ? 129. What is 

 wood, chemically speaking ? 430. What is the essential part of woody 

 fibre? 431. What is said of linen and cotton ? 132. What of the uses of 

 wood ? 433. How is gun-cotton made ? Why is it explosive ? What is 

 its chemical constitution? What is collodion? For what is it used? 

 434. What are the chief products of the distillation of wood ? 435. De- 

 scribe them. 436. Of what is pyroligneous acid composed? What are the 

 properties of creosote? 437. What is said of wood-naphtha ? 438. What 

 of wood-tar and its uses ? 439. What coals are found in the earth ? 

 Wherein do they differ? How are they formed? 440. What are the 

 chief products of the imperfect combustion of coal ? For what is coal-tar 

 used ? What is benzol ? What is nitro-benzol ? What is aniline ? U I . 

 What is said of nature's products from bituminous coal ? What is asphal- 

 tum? Whence comes it? 442. Give the history of petroleum. 443. 

 What is its composition ? Name some of the hydrocarbons occurring in 

 petroleum. 444. What is said of refining petroleum? Name some of the 

 products of distillation of petroleum ? 445. What makes kerosene unsafe ? 

 446. What is said of white rotten wood ? 447. What is chlorophyll ? 

 What is necessary to its formation ? 



CHAPTER XXVI. 



CONSTITUENTS OF PLANTS (CONTINUED). 



448. Starch. This vegetable constituent, while it is pres- 

 ent to some extent in all plants, is especially abundant in 

 particular parts of some of them. It is one of the principal 



