304 | Scientific Intelligence. 
sidered pure, were fixed, by means of gum, upon a piece of mica, 
placed in the phosphoroscope and excited by the light of the 
electric are. They emitted a red light, which, however, was much 
weaker than that given out by alumina containing chromium 
under the same circumstances. But after having calcined this 
pure alumina for fifteen minutes in a porcelain crucible in a blast 
furnace, it became quite as luminous in the phosphoroscope as the 
alumina containing chromium and of the same color. Hence he 
concludes that the alumina upon which de Boisbaudran operated, 
was not sufficiently calcined. The experiment was then repeated 
upon pure alumina prepared by himself by calcining pure am- 
monia alum. The light emitted was the characteristic red light 
so long ago studied. The addition of chromium then does not 
change the color of the phosphorescent light, but simply increases 
its intensity. Becquerel also calls attention to the difference in 
the luminous phenomena according as they are produced by the 
electric light in the phosphoroscope or by the electric discharge 
in vacuo; the former effects being simpler, but not obtainable 
with all bodies.— C. #., ciii, 1224, Dec., 1886. G. F. B. 
2. On the Crimson Line of Phosphorescent Alumina,— 
Crookes has presented to the Royal Society a paper on the - 
color emitted by pure alumina when submitted to the electric dis- 
charge in vacuo, in answer to the statements of de Boisbaudran. 
In 1879 he had stated that ‘next to the diamond, alumina in the 
form of ruby is perhaps the most strikingly phosphorescent stone 
I have examined. It glows with a rich full red; and a remark- 
able feature is that it is of little consequence what degree of color 
the earth or stone possesses naturally, the color of the phosphores- 
cence is nearly the same in all cases; chemically precipitated 
amorphous alumina, rubies of a pale reddish yellow and gems of 
the prized ‘pigeon’s blood’ color glowing alike in the vacuum.” 
These results, as well as the spectra obtained, he stated further, 
corroborated Becquerel’s observations. In consequence of the 
opposite results obtained by de Boisbaudran, Crookes has now 
reéxamined this question with a view to clear up the mystery. 
On examining a specimen of alumina prepared from tolerably 
pure aluminum sulphate, shown by the ordinary tests to be free 
from chromium, the bright crimson line, to which the red phos- 
phorescent light is due, was brightly visible in its spectrum. The 
aluminum sulphate was then, in separate portions, purified by 
various processes especially adapted to separate from it any 
chromium that might be present; the best of these being that 
given by Wohler, solution in excess of potassium hydrate and 
precipitation of the alumina by a current of chlorine. The 
alumina filtered off, ignited and tested in a radiant matter tube 
gave as good a crimson line spectrum as did that from the ori- 
ginal sulphate. A repetition of this purifying process gave no - 
change in the result. Four possible explanations are offered of 
the phenomena observed: ‘‘(1) the crimson line is due to alumina, 
but it is capable of being suppressed by an accompanying earth 
