282 CHEMISTRY. 



Where the centre of actinic power ? Where the point of greatest heat ? 

 394. State the experiments with paper charged with nitrate of silver. How 

 can you charge paper with chloride of silver ? What is said of the effect 

 of light upon it ? What experiments can be tried with variously colored 

 glasses? 395. State in full what is represented in Figs. 103 and 104. 

 396. What is said of "fixing" the picture obtained with the chloride of 

 silver ? 



CHAPTER XXII. 



SPECTEUM ANALYSIS. 



398. Continuous Spectra. You have learned in Part I. 

 that when light from the sun passes through a prism it is 

 separated into its different colors, because rays of differ- 

 ent colors are unequally refracted. The first band in the 

 figure on p. 287 represents roughly the spectrum thus ob- 

 tained. 



Suppose light from other sources than the sun is thus 

 analyzed by a prism, what are the results ? Briefly, the 

 results vary according to the nature of the light emitted ; 

 how this is we will now explain to you. In the first place, 

 the emission of light is a question of temperature ; any solid 

 body heated high enough emits light. Now it is found 

 that all solid bodies heated to incandescence that is, until 

 they glow with light produce spectra resembling in the 

 main that of the sun, at least so far as the nature and order 

 of the colors are concerned. For example, a glowing plat- 

 inum wire, a candle, and a gas flame give the same sort 

 of spectrum, uninterrupted in the shading of its colors and 

 containing them all. Such spectra are termed continuous. 



399. Discontinuous Spectra. There is another kind of 

 spectrum called discontinuous or broken. These are pro- 

 duced by glowing gases. You have already learned that 



