Royal Society, 391 



density of the surrounding medium, and their effect will increase 

 as the density and convection-currents diminish. 



These forces would appear, if their magnitude is sufficient, to 

 afford an explanation of all Mr. Crookes's results if the medium 

 is not in a state of saturation ; but when, as in my experiments, 

 the medium is steam, and water is present in the receiver, or, as 

 I suppose in Mr. Crookes's experiments, mercury was present, 

 and the medium was vapour of mercury, or at any rate sulphuric 

 acid, then it would be impossible for the medium to communi- 

 cate heat to the ball or surface without condensation ; and hence 

 in such cases it seems to me that the effects must be due to the 

 forces of condensation. 



LIV. Proceedings of Learned Societies, 



ROYAL SOCIETY. 



[Continued from p. 309.] 



March 19, 1874. — Joseph Dalton Hooker, O.B., President, in the 



Chair. 



'npHE following communications were read : — 

 -*- " Preliminary Notice of Experiments concerning the Chemical 

 Constitution of Saline Solutions." By Walter Noel Hartley, E.C.S. 



The author has been engaged in investigating the above subject 

 during the last eighteen months ; and his experiments being still in 

 progress, he thinks it desirable to place the following observations 

 on record. 



In the examination of the absorption-spectra, as seen in wedge- 

 ehaped cells, of the principal salts of cerium, cobalt, copper, chro- 

 mium, didymium, nickel, palladium, and uranium, to the number of 

 nearly sixty different solutions, it was noticed that the properties 

 of the substances in regard to changes of colour could be ascer- 

 tained by noticing the absorption-curves and bands, so that, pro- 

 vided water be without chemical action, it could be foreseen what 

 change would occur on dilution of a saturated solution. 



The effect of Beat on Absorjrtion-sjyectra. 



"When saturated solutions of coloured salts are heated to 100° C, 

 1st, there are few cases in which no change is noticed. 2ndly, ge- 

 nerally the amount of light transmitted is diminished to a small 

 extent by some of the more refrangible, the less refrangible or both 

 ]dnds of rays being obstructed. 3rdly, there is frequently a com- 

 plete difference in the nature of the transmitted light. Anhydrous 

 salts not decomposed, hydrated compounds not dehydrated at 100° 

 C, and salts which do not change colour on dehj'dration, give little 

 or no alteration in their spectra when heated. 



Solutions of hydrated salts, and most notably those of haloid 



