Photographic Researches on Phosphorescent Spectra. 241 



than yttrium nitrate, but the difference is not sufficient to make this 

 reaction a good means of separating victorium and yttrium. Fusing 

 the nitrates can, however, be employed advantageously to separate 

 mixed victoria and yttria from the bulk of their associated earths. 



On the assumption that the oxide has the composition VC2O3, the 

 atomic weight of victorium is apparently not far from 117. 



The photographed phosphorescent spectrum of victoria consists of 

 a, pair of strong lines at about X 3120 and 3117 ; other fainter lines 

 are at 3219, 3064, and 3060. Frequently the pair at 3120 and 3117 

 merge into one, but occasionally I have seen them quite distinct. 

 The presence or absence of other earths has much influence on the 

 sharpness of lines in phosphorescent spectra, and it is probable that 

 these lines will be sharp and distinct when victoria is obtained quite 

 free from its associates. 



The best material for phosphorescing in the radiant matter tube is 

 not the earth itself, but the anhydrous sulphate formed by heating the 

 earth with strong sulphuric acid and driving off the excess of acid at 

 a red heat. The sulphate thus produced, probably also containing 

 some basic sulphate, is powdered and introduced into a bulb tube fur- 

 nished with a quartz window, and a pair of thick aluminium poles 

 sealed into the glass with stout platinum wires. The tube is well 

 exhausted, keeping the current from a good induction coil going all 

 the time. The pumping and sparking must continue until the earth 

 glows with a pure light free from haze or cloudiness, and continues so 

 to glow during the passage of the current without deterioration. 

 The exposure in the spectrograph usually occupies an hour. 



I give a diagrammatic plan of the two-prism spectrograph used in 

 this research. It is furnished with two quartz prisms, quartz lenses, 

 and condensers. The slit jaws are of quartz, cut and polished accord- 

 ing to the method I described in the ' Chemical News,' vol. 71, p. 175, 

 April 11, 1895. 



The prisms are made in two halves, according to Cornu's plan ; one 

 half of each being right-handed and the other half left-handed. One 

 of the lenses also is right-handed and the other left-handecl. By this 

 device the effect of double refraction is so completely neutralised that 

 with a five-prism instrument it is impossible, under high magnifying 

 power, to detect any duplication of the lines. 



The lenses are each of 52 mm. diameter and 350 mm. focus. The 

 focus of the least refrangible rays is longer than that of the most 

 refrangible rays, and the sensitive film must therefore be set at an 

 angle to get the extreme rays into focus at the same time. But this 

 alone is not sufficient. The focal plane is not a flat surface, but is 

 curved, and the film must therefore be curved,* and it is only when 



* ' Chemical News,' vol. 72, p. 87, August 23, 1895 ; and vol. 74, p. 259, Foyem- 

 ber 27, 1896. 



