120 



Mr. W. Crookes. 



[Feb. 17, 



Cadmium 1 per cent., calcium 99 per cent. — Similar to calcium 

 sulphate, q. v. 



Calcium sulphate was prepared from a colourless and transparent, 

 rhomb of Iceland spar which had been used for optical purposes. Itr. 

 was dissolved in nitric acid, the nitrate was decomposed with distilled 

 sulphuric acid, and the ignited sulphate tested in the tube. The 

 phosphorescence is bright greenish-blue without bands or lines. In 

 the phosphoroscope the colour is a rich green ; the spectrum shows 

 the red and orange entirely cut off, leaving the green and blue ; the 

 blue is especially strong. 



Calcium sulphates prepared from Professor Breithaupt's calcites* 

 were re-examined. All phosphoresce with the normal greenish- blue^ 

 glow of calcium, except ISTo. 11, which gives a reddish glow. A 

 minute trace of samarium was found in this calcite, but not enough 

 to affect the colour of the glow. In the phosphoroscope all the 

 specimens give a continuous spectrum beyond the yellow, the red and 

 orange being cut off as usual. 



Chromium 5 per cent., calcium 95 per cent., as sulphates, gives a, 

 pale reddish phosphorescence. In the phosphoroscope the colour is. 

 green, and the red and orange are cut off. 1 per cent, of chromium 

 with calcium phosphoresces green in the cold, and becomes a red 

 when slightly heated. The behaviour of chromium with aluminium 

 has already been described.*!" 



Copper sulphate with 95 per cent, calcium sulphate behaves like 

 calcium sulphate. 



Diamonds phosphoresce of various colours. Those glowing pale 

 blue have the longest residual glow, next come those phosphorescing: 

 yellow ; I am unable to detect any residual glow in diamonds 

 phosphorescing of a reddish colour. A large diamond of a greenish 

 hne, very phosphorescent, shines almost as brightly in the phosphoro- 

 scope as out of it. 



Glucina phosphoresces of a rich blue colour. There appears to be 

 no residual glow with this earth in the phosphoroscope. 



Lanthanum. — All the specimens of lanthanum sulphate I have 

 examined in the radiant-matter tube phosphoresce of a reddish 

 colour, and give a broad hazy band in the orange, with a sharp line 

 — 1/X. 2 280 — superposed on it. This is identical with the line of Ge, 

 one of the constituents of the samarium phosphorescent spectrum.. 

 Calcium added to lanthanum changes the colour of the phosphorescence 

 from red to yellowish, and brings out yttrium and samarium lines,, 

 these metals being present as impurities ; the Gr£ and Go. lines are also 

 seen, but the space which should be occupied by the G/3 green is now 

 a dark space. I have shown that when G£, Ga, and G/3 are present- 



* ' Phil. Trans.,' 1885, Part II (p. 697). 

 t ' Roy. Soc. Proc.,' vol. 42, p. 28, et seq. 



