Ixx PROCEEDINGS. 



solution, purple in color, absorbs certain light, colored glasses absorb light, 

 etc., but all manganese salts, colored or uncolored, do not absorb light, 

 nor if the solutions are of different colors, though of the same element, 

 do they absorb the same portions of light. Gases absorb light, and on 

 looking towards the sun with a spectroscope, faint bands are to be seen 

 in the spectrum. Certain metals when heated, give certain varieties of 

 light as, ]STa yellow, potassium blue, copper green, etc., and these same 

 substances, converted into vapour, absorb the same light that in their 

 white hot condition they emitted, but here we have the phenomenon of 

 a colorless solution acting like a colored solution or like a gas. This of 

 course gave a test for Di. as soon as the absorption bands were mapped 

 and thoroughly defined. This to the rare earth chemist was a valuable 

 discovery, but in its application it calls forth the highest skill of the 

 chemist, for he must be able to fix upon the exact bands and say this is 

 given by Di., this by Er., etc. Here' is displayed a fresh peculiarity of 

 the rare earths, for while there are no elements outside these which 

 give bands, there are several within the group which do, viz., 

 Di. gives 31 well defined bands, Sin. 12 not so well defined (and 

 some of them disputed, the subject is being thoroughly investigated by 

 Boisbaudran), Ho. 16, Er. 8 ; Yb. shows none in the visible part of the 

 spectrum, but many have been mapped in the ultra red portion. 



The qualitative application of this knowledge is as follows : A mix- 

 ture, say of Di. and Ce., is to be freed from Di., this being most familiar 

 to myself. The oxalate, first well-washed in dilute IIC1, is dried and 

 ignited to the condition of an oxide, and then dissolved in HN0 3 and a 

 preliminary examination is made with the spectroscope to make sure of 

 the presence of Di., and incidently to judge of its abundance. The 

 intensity of that band known as the a band is especially noted. It lies 

 near the Na. band (yellow.) The mixed solution is then subjected to one 

 of the separation processes, and as strong a solution in as deep a layer as 

 possible, is examined with the spectroscope and the intensity of the a 

 band is noted. This process is repeated until the most intense baud has 

 entirely disappeared. When I remind you, however, that the removal 

 of the Di. by what was undoubtedly the best method known until 

 lately, required a seven times repetition the Di. bands growing gradually 

 fainter and dying out one by one until what had been the most intense 

 finally faded entirely from view it will be seen that this fractional 

 method forces one to the conclusion that possibly all the Di. has not 



