PHYSICAL BASIS OF SOLAR CHEMISTRY 853 



system of bands; zinc gives its system; and brass, wbicli 

 is an alloy of copper and zinc, gives a spectrum made up 

 0,f tbe bands belonging to both metals. 



Kot only, however, when metals are united like zinc 

 and copper to form an alloy is it possible to obtain the 

 bands which belong to them. No matter how we may dis- 

 guise the metal — allowing it to unite with oxygen to form 

 an oxide, and this again with an acid to form a salt; if 

 the heat applied be sufficiently intense, the bands belong- 

 ing to the. metal reveal themselves with perfect definition. 

 Into holes drilled in a cylinder of retort carbon, pure cul- 

 inary salt is introduced. When the carbon is made the 

 positive electrode of the lamp, the resultant spectrum 

 shows the brilliant yellow lines of the metal sodium. 

 Similar experiments made with the chlorides of stron- 

 tium, calcium, lithium,* and other metals, give the bands 

 due to the respective metals. When different salts are 

 mixed together, and rammed into holes in the carbon, a 

 spectrum is obtained which contains the bands of them all. 



The position of these bright bands never varies, and 

 each metal has its own system. Hence the competent 

 observer can infer from the bands of the spectrum the 

 metals which produce it. It is a language addressed to 

 the eye instead of the ear; and the certainty would not 

 be augmented if each metal possessed the power of audi- 

 bly calling out, "I am here!" Nor -is this language af- 

 fected by distance. If we find that the sun or the stars 



* The vividness of the colors of the lithium spectrum is extraordinary; the 

 spectrum, moreover, contained a blue band of indescribable splendor. It was 

 thought by many, during the discourse, that I had mistaken strontium for 

 lithium, as this blue band had never before been seen. I have obtained it 

 many times since; and my friend Dr. Miller, having kindly analyzed the 

 substance made use of, pronounces it pure chloride of lithium. — J. T. 



