XVIII.] 



LITHIUM. 



243 



with Steinheil's apparatus it yielded normal results without any 

 trace of a blue band. I am just now reading the report of your dis- 

 course in the Chemical News, and I find that you have noticed the 

 same thing. Whence does this blue line arise ? Does it really 

 belong to the lithium, or are the carbon points or ignited air guilty 

 of its production ? I find these blue bands with common salt, but 

 they have neither the definiteness nor the brilliancy of the lithium 

 band. When lithium wire burns in air it emits a somewhat crim- 

 son light ; plunge it into oxygen, and the light changes to bluish 

 white? This seems to indicate that a high temperature is necessary 

 to bring out the blue ray." 



Flame. 



Suiu 



Feeble 

 spark. 



Arc. 



FIG. 92. The various intensities of the lines of Lithium under different 

 conditions. 



FIG. 93.- 



-The various intensities of the lines of Lithium arranged in order of 

 increasing temperatures. 



Postscript, November 22, 1861. "I have just made some further 

 experiments on the lithium spectrum, and they conclusively prove 

 that the appearance of the blue line depends entirely on the temper- 

 ature. The spectrum of lithic chloride, ignited in a Bunsen's burner 

 flame, does not disclose the faintest trace of the blue line ; re- 

 place the Bunsen's burner by a jet of hydrogen (the temperature of 

 which is higher than that of the Bunsen's burner) and the blue line 

 appears, faint, it is true, but sharp and quite unmistakable. If 

 oxygen now be slowly turned into the jet, the brilliancy of the blue 



B 2 



