Professor Liveing, On the Influence of Temperature, etc. 213 



On the Influence of Temperature, and of Various Solvents, on 

 the Absorptio?i Spectra of Didymium and Erbium Salts. By 

 Professor Liveing. 



[Read 27 November, 1899.] 



Prof. Liveing exhibited a number of photographs prepared to 

 illustrate his paper on the absorption spectra of solutions of salts 

 of Didymium and Erbium in various conditions of dilution, and 

 temperature, and in various solvents, which was communicated to 

 the Society at the Stokes Jubilee meeting. These photographs 

 shewed that dilution produced no increase of the intensity of the 

 absorptions when the thickness of the absorbent was proportioned 

 to the dilution. In strong solutions of the chlorides a diffuse 

 continuous absorption creeps down the spectrum from the most 

 refrangible end and extends further as the solution is more con- 

 centrated. This is not seen with most chlorides, not even with 

 that of aluminium, but is shown by strong solutions of hydrochloric 

 acid in water and in alcohol. The nitrates shew a somewhat 

 similar general absorption, and also a widening of some of the 

 bands as the solutions become more concentrated. 



The effect of acidifying the solutions is to make the absorptions 

 generally more diffuse, but not sensibly to weaken them, and to 

 extend the general absorptions at the most refrangible end. A 

 rise of temperature from about 20° C. to 97° or 98°, also makes 

 the bands more diffuse, but does not increase their intensity. It 

 seems to the author improbable that the metallic atoms should 

 maintain such independence in combination as to have the same 

 absorptions in such different compounds as chloride, nitrate and 

 sulphate, and it is more probable that the common absorptions 

 are due to common products of decomposition. These might be 

 the metallic ions, but the facts that neither dilution nor rise of 

 temperature increases the intensity, and that acidifying does not 

 weaken the intensity of the common absorptions are against that 

 supposition. Ionization implies an electrification of the ions, 

 which again implies a communication of energy to the field, which 

 may probably depend on the circumstances of the encounter when 

 the molecule of salt is broken up, and so some molecules may 

 be broken up without being charged; while there is no reason 



