Lines in tJte Sj>arl Spectra of the Element*. 



449 



rersely, metals which are the best conductors and the most volatile exhibit 

 spectra with their principal lines largely extended. 



The following metals are good conductors, that is to say, suffi- 

 ciently good not to impede the spark when broad electrodes are used, 

 and they are more or less volatile. They show a large extension of 



eir principal lines : 



Atomic mass. 



Copper Not volatilised by ordinary means. . 63'33 



Silver Boils about 1570 C 107'93 



Mercury 357 C 200'1 



In these examples the extension of the lines is least in the case of 

 the least volatile metals, which are also those of least atomic mass, 

 ind it is greatest with those which are most volatile and of greatest 



3m ic mass. 



The continuous spectrum in these examples is very weak, and the 

 iir lines are almost absent from the thallium and mercury spectra, 

 air spectra being suppressed by the excess of dense vapour in the 



rack of the spark. The lines most extended are the following : In 



, ^ 



cadmium spectrum, those with wave-lengths 3611 '8, 3609'6 



(a pair), 3466'8, 3465-4 (a pair). These pairs appear as single lines 

 the dispersion is insufficient and the definition imperfect. 

 The most refrangible line of each pair is the more extended. The 

 rther lines in this spectrum are 3402'9, 2747' 7, 2572'2, 2313'6, and 

 265*9, all with fine extensions. In the spectrum of thallium, wave- 

 sngths 3775-6, 3528'8, 3518'b', and 29177. 



In the spectrum of mercury, the Hues with wave-lengths 4358, 

 1)6-5, and 3984 are well extended, but the most important exten- 

 sions in this spectrum are the lines with wave-lengths 3662'9, 3654'4, 

 J2'9 ; the last of these, which form a well-marked triplet, is by far 

 most extended. The pair of lines 3130'4 and 3124'5 are greatly 

 extended, and the same remark applies to 2966'4 and 2946'6. 



The dimensions of the principal lines in the cadmium, thallium, 



