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Dr. J. Monckman. Occluded Gases and [May 31, 



These experiments appear to prove that absorbed gases increase 

 the resistance of conductors, and that hydrogen renders metals more 

 negative (thermo-elecfcrically) whilst carbon becomes more positive. 



I have introduced the experiment (fig. 1) which caused this work 

 to be undertaken, although I do not think that it is entirely caused 

 by the occlusion of gases, where the best results are obtained by 

 electrolysis which produces them in a nascent or more energetic 

 state. 



Thermo-electric and other Properties of Graphite and Carbon. 



In making the previous experiments, I had occasion to place the 

 heated end of one carbon rod in contact with the cold end of another. 

 The temperature of the hot end was varied from 30° 0. to a red heat, 

 whilst the cold end was kept at about 17° C. 



Currents of electricity were of course produced. When the tem- 

 perature of the hotter rod was raised but slightly, the current was 

 from cold to hot through the point of contact, but when it was raised 

 to a red heat the current passed from hot to cold; between these 

 temperatures the direction of the current varied, appearing at first 

 sight to obey no rule, and as nothing was known that would explain 

 these results, I was led to examine the matter more carefully. 



There were several difficulties to be overcome before any satisfac- 

 tory results could be obtained. 



Firstly, it was necessary to get two rods of such pure material, that 

 they would not produce a current when placed in contact end to end 

 and heated, or at any rate weak enough to be neglected in presence 

 of that produced by the contact of the two rods at different 

 temperatures. 



I tried several specimens of gas-carbon, but as no two pieces were 

 found to fulfil the condition before mentioned, they were useless. 

 I was more fortunate with the rods prepared for arc lamps in electric 

 lighting, readily finding two that answered my purpose. 



A small portion of one of them gave on combustion less than one 

 part of incombustible matter in 200 of carbon. They were heated 

 repeatedly to a red heat and allowed to cool slowly. The ends were 

 filed flat to prevent difference of shape producing any current. 



When placed in contact end to end and heated, one rod was 

 slightly positive to the other, but not sufficiently to prevent the 

 experiments from succeeding. 



Secondly, the manner of making contact caused the currents to 

 vary much in strength, and the surface of the heated rod required 

 filing at intervals, in order to preserve a clean flat face. 



It was found also that the heat of the hot rod passed so quickly to 

 the cold one that even after a very short contact the current fell, so 

 that the rods could be placed together once only and for a very short 



