290 CHEMISTRY. 



scopy. A description of the methods employed, the instru- 

 ments used, and the results obtained would be interesting, 

 but must be passed by in the present work. 



QUESTIONS. 



398. Do lights from other sources than the sun yield spectra ? Upon 

 what does the emission of light depend ? Give examples. What are 

 continuous spectra ? 399. What produces discontinuous spectra ? What 

 bodies color flames ? What kind of a spectrum does sodium give ? What 

 strontium ? 400. Explain the use of a narrow opening for the passage of 

 light. What produces the banded appearance of discontinuous spectra ? 

 401. Describe and explain the spectroscope. How does the light pass ? 

 402. Who invented this instrument ? When ? How is it made prac- 

 tical ? What can be detected by it at the temperature of a Bunsen burn- 

 er ? What kind of a spectrum does barium yield ? What is said of the 

 delicacy of this instrument ? 403. What elements were discovered by 

 Bunsen and Eirchhoff? How? From what source? What other ele- 

 ments have been discovered by this means ? 404. How can spectra of 

 heavy metals be obtained ? 405. State in full what is said of celestial 

 spectroscopy. 



CHAPTER XXIII. 



ORGANIC CHEMISTRY. 



406. Introduction. Formerly the term Organic Chemistry 

 was applied to that branch of chemistry treating of sub- 

 stances which derived their existence from the operations 

 of either vegetable or animal life ; it was erroneously sup- 

 posed that the production of these substances was due to a 

 mysterious power, called vital force, residing in the organs 

 of plants and animals, and that this class of substances could 

 not be artificially formed. Under this view organic chem- 

 istry was considered as the Chemistry of Life. 



Within from twenty to thirty years, however, many sub- 



