340 CHEMISTEY. 



and casein have nearly the same chemical composition, 

 and are convertible into each other. The name, protein 

 compounds, has been given to them because they were sup- 

 posed to have a common base, which, from its importance 

 in the chemistry of life, was called protein, from the Greek 

 word protos, first. This supposition has been abandoned, 

 but the name has been retained, and these substances are 

 often spoken of still as the protein compounds. They are 

 often also spoken of as the albuminoids, especially in rela- 

 tion to the nutrition of animals. Then, again, they are 

 styled the plastic elements or constituents, because they are 

 used in building up structure in animals, this word being 

 derived from a Greek word meaning to form. Another 

 term still is often applied to them azotized because they 

 contain, unlike starch, gum, sugar, etc., nitrogen, or azote. 

 There is always in these substances a small amount of both 

 sulphur and phosphorus. It varies much, however, in dif- 

 ferent cases. 



QUESTIONS. 



448. What is starch? What proportion of bread is starch? What is 

 arrow-root? What is sago? 449. How can starch be obtained ? 450. 

 Describe the grains of various kinds of starch. What is the composition 

 of starch? 451. What are the properties of starch? What causes the 

 swelling of rice when boiled ? 452. What curious property has iodide of 

 starch ? 453. What are gums ? What is a mucilage ? What is pectine ? 

 454. How is dextrin made from starch ? To what uses is dextrin ap- 

 plied ? Describe another way of making dextrin. 455. Explain the 

 chemistry of this change. 456. What is said of the production of sugar in 

 nature? What of the mingling of sugar and acids in fruits? 457. What 

 are the different kinds of sugar ? 458. What is the source of cane-sugar ? 

 How is it obtained from the cane ? What is rock-candy ? 459. What is 

 said of milk-sugar ? 460. How does grape-sugar differ from cane-sugar in 

 properties? How in composition? 461. How can sugar be made from 

 starch and wood? Explain the change. 462. What is said of the adul- 

 teration of cane-sugar ? 463. What of the conversion of starch and wood 



