632 Prof. E. C. C. Baly on 



the method will probably be applicable also to the concen- 

 tration of products of thorium, actinium, and uranium. Some 

 experiments I made with solutions of mesothorium and 

 actinium have shown in fact that, by means of one filtration, 

 certain products may be collected on the filter. The proce- 

 dure may be further employed in the case of solutions of 

 uranium products. One filtration of aqueous solution of 

 uranium nitrate suffices to deprive uranium of the greater 

 part of its (3 activity, which remains on the filter. 



The method is convenient, not only because it is so very 

 simple, but also because it will allow the activity (the pro- 

 ducts) to be concentrated on extremely small quantities of 

 substance. It is applicable, however, in those cases only 

 when radioactive products behave as positive colloidal l^dro- 

 sols in solution : to take an instance, in the case of uranium 

 nitrate the solution must be very dilute (10 gr. of uranium 

 salt per litre at most). 



The results of experiments concerning the radioactive pro- 

 ducts of thorium, actinium, and uranium will be described in 

 full in a subsequent paper. 



Physical Laboratory of the Technical High School, 

 Lemberg (Lwow). 

 December, 1913. 



LXXI. Light Absorption and Fluorescence. By E. C. C. 

 Baly, M.Sc., F.R.S., Professor of Inorganic Chemistry in 

 the University of Liverpool*. 



IN two papers in conjunction with Miss E. G. Marsdenj 

 (Mrs. Solomon) and Mr. F. 0. Rice J, dealing with the 

 relationship between absorption spectra and chemical re- 

 activity, I have shown that it is possible for one substance to 

 exhibit different absorption bands when dissolved in different 

 solvents. If, for example, certain aromatic amino aldehydes 

 and ketones are dissolved in alcohol, their solutions exhibit 

 characteristic absorption bands in the ultra-violet region. 

 If now to these alcoholic solutions a small quantity of an 

 alcoholic solution of hydrogen chloride is added, the quantity 

 being much less than is required to convert the whole of the 

 amino compound into the hydrochloride, a second absorption 

 band is developed of longer wave-length. On adding a 

 further quantity of hydrogen chloride the absorption changes 

 to that characteristic of the hydrochloride of the base. These 



* Communicated by the Author. 



t Trams. Chem. Soc. xxiii. p. 2108 (1908). 



X Ibid. ci. p. 1475 (1912). 



