1874.1 Physics. 135 
tions. Gladstone finds, as a rule, the effect of heat is equivalent to a concen- 
tration of the solution, and amounts to an increase in the amount of absorption. 
In a paper ‘“‘ On the Change of Colour produced by Heat in Certain Chemical 
Compounds,” E. J. Houston pointed out the curious and novel fad, that, in all 
cases where no chemical change was involved, solutions, as well as solids, 
changed to tints lower in the spe&trum on the application of heat. The loss 
of fluorescence in a few substances when heated appears to extend (with cer- 
tain limitations) to all the uranium compounds, both in their solid state and in 
solution. We find that in the case of the anhydrous ammonio-uranic sulphate, 
fluorescence is sensibly diminished at 140° C., and is almost destroyed at 
260° C. The hydrate does not show any marked loss of fluorescence below 
the point at which it begins to part with its water. The same is true of the 
potassium sulphate. The sodio-uranic acetate is much more sensitive. 
Experiments were made with it and other salts. It was observed that at 
about 50° C. the brightness of the fluorescence was reduced, and that the 
uppermost decided band (81°8) lost its distin@tness. At about 116° C. it 
seemed to reach aminimum. At that temperature the uppermost band had 
vanished, and the lower ones were too faint for measurement. No further 
change was noticed on carrying the temperature to 150°. Solutions are still 
more sensitive. The authors next enter upon a detailed examination of 
various uranium compounds, from which we seleé the following passages : — 
Uranic Acetate (normal), U203;3C,H303+2HO.—This substance fluoresces 
very brightly, different specimens, however, differing, probably from the pre- 
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sence of minute traces of foreign matter. Its solution yields a very bright 
fluorescence, which is reduced by the addition of a trace of alcohol, ether, 
glucose, or sucrose, and is destroyed by a very small amount of hydrochloric 
acid. The fluorescent light of the solution yields a continuous spectrum, 
