294 Hartley — The Action of Heat on the Absorption Spectra and 



from the spectra of other saline solutions, such as those of cobalt, nickel, and 

 copper, the following deduction was drawn : — 



The ahsoi'ption spectra of different salts of the same metal, ivhether solid or in 

 solution, are not identical, even when the spectrum is a marked characteristic of the 

 metal. 



From the examination of organic substances, whether salts of bases or other- 

 wise, it was concluded that — 



Molecules of compounds — that is to say, molecules composed of dissimilar atoms — 

 vibrate as wholes or units, and the fundamental vibrations give rise to secondary vibrations, 

 which stand in no visible relation to the chemical constituents of the molecule, lohether 

 these be atoms or smaller molecules* 



This conclusion is generally applicable also to metallic salts of inorganic 

 origin, as well as to organic compounds. 



When anhydrous compounds are examined the same effect of heat is observed, 

 but the only substance experimented upon was potassium permanganate, the 

 absorption spectrum of which was first described by Vierordt. As there are 

 seven bands in the yellow, green, and blue, of diminishing intensity, and not 

 very sharply defined, it was necessary to examine solutions of different strengths 

 so as to bring into prominence some of the weaker bands. Of course, the 

 stronger bands increase in width, and even become confused as the weaker gain 

 in intensity when stronger solutions are used ; hence the measurements are not all 

 comparable with those of Lecoq de Boisbaudran, who used one solution of fixed 

 strength, containing O'l gr. of KMnOj per litre. 



Potassium Permanganate, KMn04. — A freshly prepared solution. Thin wedge- 

 cell. 



The mean of the numbers at 16° are 474, 490, 508, and 531-5. The figures 

 of Lecoq de Boisbaudran, representing the maximum intensity of absorption, 

 and for apparently the same bands, are 469-4, 486-1, 504-5, and 524-6. That 

 they are not more nearly in agreement with the above is due to the fact that the 

 maximum of intensity is not in a position intermediate between the two edges of 

 a band, but lies a little to one side or the other. This particular solution shows 



* " Eesearches on the Relation between the Molecular Structure of Carbon Compounds and their 

 Absorption Spectra." Part VII.— Trans. Chem. Soc, vol. 47, p. 685, 1885. 



