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Sir TV". Crookes 



water, and the liquid well boiled. A white precipitate of basic nitrate 

 forms, while the undecomposed nitrates remain in solution. These are 

 separated by filtration, the precipitate going to the right and the solu- 

 tion to the left. The basic nitrate is dissolved in nitric acid, and the 

 right and left solutions are then evaporated to dryness and fused as 

 before. Partial decomposition by heat again divides each of these 

 portions into two lots, soluble and insoluble. The soluble from the 

 left-hand lot goes still further to the left, and its insoluble portion to 

 the right. The soluble from the right-hand portion goes to the left, 

 where it mixes with the insoluble from the other portion, while its 

 insoluble goes still further to the right. This series of operations is 

 continued for as long a time as the material will hold out.* From a 

 description the process seems to be more complicated than it really is, 

 but a study of the diagram and the direction of the arrows make it 

 clear. The number of times this operation is performed varies with 

 each lot of earth fractionated. The portions submitted to fusion 

 rapidly diminish in quantity, and the operation is continued until the 

 material becomes too scanty. 



The last horizontal line of fractions spectroscopically examined in a 

 radiant matter tube shows differences in the visible spectrum. For 

 many years I recorded these differences in coloured drawings, which 

 have served on several occasions to illustrate papers before this Society.! 

 In the year 1893 I commenced to record the differences between the 

 various spectra by photographing them in a spectrograph having a 

 complete quartz train, and since that time attention has chiefly been 

 directed to the variations in the number, character, and positions of the 

 lines and bands in the ultra-violet spectrum : these are more striking 

 than those which are visible, and as they are self-recording, results are 

 more rapidly attained. A description of this instrument is given 

 further on. 



On placing the photographed spectra of one of the horizontal lines 

 of earths in order, several differences are detected. One striking 

 difference is seen in the behaviour of a group of lines in the ultra-- 

 violet. It is nearly absent in the end fractions, gradually becoming 

 stronger towards the middle, and attaining a maximum in the fractions 

 situate about two-thirds towards the right. This shows that at least 

 three different bodies are present : one, the great bulk, having a nitrate 

 difficult to decompose ; another whose nitrate is easiest to decompose ; 

 and a third body, occupying an intermediate position, whose nitrate 

 decomposition occurs at temperatures between that required by the 

 others, but nearer that of the nitrate easiest decomposed. 



* " On the Methods of Chemical Fractionation," British Association, Birming- 

 ham Meeting, 1886; ' Chemical Xews,' vol. 54-, p. 131. 



f "On some ~Ne\v Elements in Gadolinite and Samarskite detected Spectro- 

 scopically, 1 Roy. Soc. Proc.,' No. 245, 188G, vol. 40, p. 502." 



