1887.] Crimson Line of Phosphorescent Alumina. 



29 



The filtrate from the alumina, which should contain all the 

 chromium present in the form of potassium chromate, was super- 

 saturated with hydrochloric acid and boiled till free from volatile 

 chlorine compounds. Alcohol was then added, and it was again 

 boiled to reduce to the state of sesquichloride of chromium any- 

 chromic acid which might be present. Ammonia in excess was now 

 added, and the whole was boiled ; a very small precipitate of a brownish 

 colour fell down ; it was filtered and washed. This precipitate, which 

 was not more than the 5 q th part of the alumina from which it 

 was derived, contained no chromium whatever ; it was too small in 

 quantity to admit of a complete analysis being made, but all the tests 

 which I could apply showed it to be a mixture of ferric oxide and 

 alumina. 



One part of this precipitate was mixed with 100 parts of the pure 

 alumina from which it had just been separated, and the mixture was 

 tested in the radiant matter tube. The phosphorescence was the same 

 as in the two previous experiments, the crimson line being neither 

 better nor worse. 



I now prepared aluminium chromate, and tested its action in the 

 radiant matter tube. It was almost black after ignition, and refused 

 to phosphoresce. A mixture was then made of aluminium chromate 

 and alumina in the proportion of one part chromium to 100 parts of 

 aluminium. After ignition the colour of the mixture was almost 

 white. Tested, it gave very poor phosphorescence ; the alumina line 

 was faintly visible. 



• Aluminium acetate was mixed with 5 per cent, of ammonium 

 bichromate, ignited with sulphuric acid, and tested in the radiant 

 matter tube. There was no phosphorescence. The same mixture was 

 heated to a high temperature before the blowpipe, when it gave a 

 very feeble phosphorescence, but I could detect no line in the 

 spectrum. 



Pure alumina was mixed with 5 per cent, of ammonium bichromate, 

 and moistened with sulphuric acid. After ignition it phosphoresced 

 with a reddish colour, and the spectrum showed a concentration of 

 light in the orange, but no alumina light was visible. The tube was 

 opened, and the contents heated to a very high blowpipe temperature. 

 In the radiant matter tube it gave the same results as before. 



A mixture of 0'5 per cent, ammonium bichromate, 10 per cent, of 

 lime, and 89*5 per cent, of pure alumina was ignited with sulphuric 

 acid, and tested in the usual way. The calcium brought oat a trace 

 of yttrium and samarium bands, but no crimson line was to be seen. 



Alumina precipitated from its ammoniacal solution by boiling was 

 found to glow with a green light in the vacuum tube and to give no 

 crimson line in its spectrum. The tube was now opened, and some of 

 its contents removed and heated in a hot blast blowpipe to the 



