556 



PRINCIPLES OF CHEMISTRY 



of three lines a red line corresponding with the Frauenhofer line- 

 C, a green line corresponding with the line F, and a violet line corre- 



w 



a 



8 1 



t- 



i 1 



I i 



im 10 in us ^ 



iSl I II II I M MS I ! ! 



_li7l I 





 I I 



Sign I I 1.1 is II 





IfelSsSl M M I M M 



| | O I i * 



' ' ^* 



* X $ S?'- "~ 5; 



5V] !o| i 



1 1 



S 

 s 



i i i i 



ggSii M M 



Hi 





I I3i 1 



bo 



IMIMIlS 



M 



1 M 



'M i 



ii i 



M M M M M I I M 



5'i 



5 ! I I M II Ig M ll 



M M M lll| M M M 



M 



!Ste I M I I 1 I I 1*1 



,-i 1 







1 1 i 



I I I 



M IS M 1 ^^^SS 



1 I 



o 



x 



blue from 490 to 420, and the violet 

 from 420 to 380 millionth parts of 

 a millimetre. Beyond 380 the lines are 

 scarcely visible, and belong to the 

 ultra-violet. 



In this table, which is arranged in 

 conformity to the image of the spectra 

 as they are seen (the red lines on the 

 left hand and the violet on the right 

 hand side), the figures in black type 

 correspond with lines which are so 

 bright and distinctly visible that 

 they may easily be made use of, both 

 in determining the relation between 

 the divisions of the scale and the 

 wave lengths, and in determining 

 the admixture of a given element 

 with another. The brackets join those 

 lines between which several other 

 lines are clearly visible if the disper- 

 sive power of the spectroscope per- 

 mits distinguishing the neighbouring 

 lines. In the ordinary laboratory 

 spectroscopes with one prism, even 

 with all possible precision of arrange- 

 ment and with a brilliancy of light 

 permitting the observations being 

 made with a very narrow aperture, 

 the lines whose wave lengths only 

 differ by 2-3 millionth parts of a mil- 

 limetre, are blurred together ; and 

 with a wide aperture a series of lines 

 differing by even as much as 20* 

 millionths of a millimetre appear as 

 one wide line. With a faint light 

 (that is, with a small quantity of 

 light entering into the spectroscope) 

 only the most brilliant lines are* 

 clearly visible. The length of the 

 lines does not always correspond 

 with their brilliancy. According to 

 Lockyer this length is determined 

 by placing the carbon electrodes 

 (between which the incandescent 

 vapours of the metals are formed), not 

 horizontally to the slit (as they are 

 generally placed, to give more light), 

 but vertically to it. Then certain 

 lines appear long and others short. 

 As a rule (Lockyer, Dewar, Cornu), 

 the longest lines are those with which 

 it is easiest to obtain reversed. 



