ON ELECTROLYSIS IN ITS PHYSICAL AND CHEMICAL BEAEINGS. 227 



with an electroscope, and charged statically; the terminals were then joined by 

 a strip of thm platinum foil, whose length could he varied at will by means of 

 insulating handles. The strip when shortened became more and more heated by 

 the increased current, but only when a red heat was reached did I observe that the 

 statical charge of the cell began to escape. 



This would seem to show that (in daylight at any rate) dissociated atoms are 

 not found at the surface of the metal at a temperature below that of a red heat. 



The rate of escape of charge was much increased by holding an earth-connected 

 conductor near to the red-hot platinum. This would increase the density of charge 

 at the surface of the platinum, and therefore the electric force at the sui-face, i.e.. 

 the directive force on the free atoms. 



9. By hanging side by side, in a large Bunsen flame, a sheet of copper and a 

 sheet of platinum, which were connected outside the flame by a wire bavin"- in 

 circuit a galvanometer of about 200 ohms resistance, a feeble current of about 

 2 X 10 « amperes was obtained, the flame appearing to act as an electrolyte of 

 very high resistance through which the cm-rent passed from the more oxidizable 

 copper to the less oxidizable platinum. 



_ When, however, two sheets of platinum were hung in the flame so that one 

 just touched the outside, while the other bisected the flame, a current of about the 

 same magnitude was obtained, and in either direction at will, according to the 

 relative positions of the plates in the flames, and the observation of Messrs. Elster 

 and Qeitel was confirmed, that the outer mantle of the flame is at a hio-her 

 potential than the interior of the flame. The eflect of this seemed to over-ride'and 

 obscure any eflect due to the difference of the material of the two plates. 

 _ 1 have not been able to obtain any more direct experimental evidence that there 

 18 an excess of + ve atoms on the outside, and of- ve on the inside of the flame. 

 • I V^^^. "°^^ experiment mentioned in this paper that I can suppose to be new 

 18 that of the air-blast ; but in the light of this, the significance of the other experi- 

 ments cited seems considerably changed, and the inference that a charge of either 

 sign, indistinguishable from the charges that are produced by friction, may be 

 obtained on a non-conductor in air, by the liberation of free atoms on its surface, 

 IS not at present so familiar that any excuse seems required for emphasising it. 



Note.— Professor Poynting has suggested to me since the above was written, 

 that the charges of the dissociated atoms might be so great and their masses so 

 smaU, that the acceleration communicated under the electric stress would suffice 

 to enable the original atoms present in the flame to traverse the air-blast. 



Report of the Committee, consisting of General Testing {Chair- 

 man), Dr. H. E. Armstrong (Secretary), Captain Abney, and 

 Professor W. N. Hartley', on the Absorption Spectra of Pure 

 Compounds. 



During the past year the research has not progressed so rapidly as it was 

 hoped would have been the case, owing to various causes ; but a consider- 

 able advance has been made in the methods to be employed in the 

 research. Considerable difficulty was encountered in devising the method 

 to employ with the various liquids, and a long series of observations 

 were undertaken with the object of ascertaining what was the really most 

 practicable plan. It was hoped at one time that a modified diffraction 

 method might have been adopted, but experiment showed that although 

 such a method was not impossible, it was impracticable. Eventually 

 a double hollow prism was found to give the best results, with a com- 

 pletely difPcrent arrangement of collimator and lens to that usually 

 adopted. It would be premature to describe the apparatus in detail, 

 ibis will be communicated when the results from the photographs of the 

 compounds already taken have been tabulated. 



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