258 



Hartley — The Action of Heat on the Absorption Spectra and 



PART I. 

 The Absorption Spectra described. 



The spectra of metallic solutions are principally of three kinds :— 



(1) Continuous spectra^ or bands of rays uninterruptedhj transmitted. 



(2) Groups of rays of different refrangibilities separated by one or more broad 



absorption bands. 



(3) Spectra interrupted by sharp black bands or lines. 



Substances showing such spectra as the second — for instance, chromium salts 

 — are markedly dichroic. I propose to take the simplest spectra first. 



The Spectra of hot and cold Solutions of Copper and Nickel Salts. — A continuous 

 absorption in the red, or in botli red and blue, characterises these substances, and 

 they are therefore generally green or blue in colour. 



The Spectra of Nickel Salts. (Plate XVII.; 



