1883.] 



On Radiant Matter Spectroscopy. 



269 



distillation than to the separations in mineral chemistry as ordinarily- 

 adopted in the laboratory. 



Pure terbia ignited with -sulphuric acid and tested in the radiant 

 matter tube shows no citron band spectrum. A concentrated solution 

 of the purest terbia . obtained in this way, when examined by the 

 spectroscope, showed no absorption lines whatever : proving the 

 absence of erbium, bolminm, and thulium. 



I did not 'attempt any separation of erbium, holmium, and thulium 

 from each other, as the evidence obtained was sufficient to show that 

 the element giving the ■citron band spectrum was not one of these 

 three metals. Likewise I had far too little material to enable me to 

 enter on a work of such, difficulty with any prospect of success. 



The chemical characters of mosandra are so little known that I 

 could not attempt to search for it. 'But as the citron band-forming 

 earth always appeared -concentrated amongst those whose double sul- 

 phates were most soluble in potassic sulphate — and, of these, amongst 

 those having the palest colour -and lowest atomic weight — it was 

 scarcely conceivable that the earth I was in search of should ulti- 

 mately prove to be one whose properties did not in vany. case corre- 

 spond to these — of a dark oranges-yellow colour, forming a difficultly 

 soluble double potassic sulphate, and having the very high equivalent 

 of M = 51'2 ; these being the properties ascribed to mosandra by the 

 discoverer, Professor Lawrence Smith. 



Ytterbia -was prepared from gadolinite, as this mineral \ is said by 

 Nilson to contain most ytterbia. It was separated from accompanying 

 earths by processes described in the paper. The resulting earth gave 

 at first a faint citron band spectrum, evidently due to impurity ; on 

 repeating the purification several times I at last succeeded in obtain- 

 ing -a white earth which gave only the merest trace of citron band 

 spectrum. Its hydrogen equivalent, 58'0, and its chemical properties 

 showed that it was probably Marignac's ytterbia. Subsequent ex- 

 periments satisfied me that this earth did not contain more than 

 x l^o P ar t f yttria. The extreme tediousness of the chemical 

 operations necessary to obtain this high degree of purity, and the 

 long time they required, prevented me from pushing these lesults 

 beyond what was necessary to prove the special point at issue. 



The yttria, purified as already described, might still contain traces 

 of terbia, together with erbia, holmia, -and thulia. These were 

 gradually removed by the fusing nitrate process. The atomic weight 

 gradually got down to 31°Q, ! but the spectra did not vary .very much ; 

 that from the earth of lowest atomic weight being, however, the most 

 brilliant. 



Pure yttria is quite white. That from gadolinite on testing in the 

 radiant matter tube gave a spectrum absolutely identical with that 

 given by the zircon, cerite, thorite, orangite, and samarskite yttria. 



