456 Intelligence and Miscellaneous Articles. 



RESEARCHES ON THE ELECTRICAL CONDUCTIBILITY OF GASES AT 

 HIGH TEMPERATURES. BY M. EDMOND BECQUEREL. 



The apparatus employed in these researches consists of a long 

 platinum tube without a joint, surrounded by an earthen tube which 

 traverses a furnace horizontally. This tube, which is to receive the 

 gases submitted to experiment, is of sufficient thickness to allow of 

 a vacuum being produced in it without disfigurement, even when a 

 portion of it is at a red heat. 



Two platinum wires, completely insulated, are stretched lengthwise 

 through the tube parallel to one another, in such a manner that if 

 each of them communicates with one pole of the battery, the elec- 

 trical current can only circulate when the gaseous medium sepa- 

 rating the wires becomes a conductor. These two wires are some- 

 times replaced by a rod of platinum or iron, also insulated and parallel 

 to the tube, when the rod and the tube are employed as electrodes 

 instead of the two platinum wires. 



In the course of the circuit are interposed a galvanometer of 

 extreme sensibility, and a rheostat of peculiar construction. This 

 rheostat consists of a column of fluid of very small diameter con- 

 tained in a divided capillary tube like that of a thermometer, and so 

 arranged that its length can be varied at pleasure whilst kept at the 

 same temperature. The circuit now containing the battery, the gas 

 which has acquired conductive power, the rheostat and the galvano- 

 meter, it is easy, by always bringing the deviation of the needle to 

 the same degree, to compare the conductive power of the gas with 

 that of the fluid in the rheostat. 



By these means of investigation the author has measured exactly 

 the resistance of the gases in different conditions, as that of solids 

 and liquids has been measured. t The gas being contained in a pla- 

 tinum tube, he was able to change its elastic force at pleasure at 

 the same time that he raised its temperature. He has arrived at the 

 following results : 



Gases do not become conductors of electricity to an appreciable 

 extent until towards a red heat ; from this point they conduct better 

 in proportion to the elevation of their temperature. They then afford 

 a passage for the weakest currents of electricity that can be pro- 

 duced by means of a small pair of plates. 



The quantity of electricity which passes is augmented as the size 

 of the negative electrode is increased. The same effect is observed 

 in the transmission of electricity through liquids. 



The resistance of a gas varies according to the number of pairs of 

 which the battery consists, and the intensity of the electric current 

 traversing it. 



Below red heat there is no appreciable difference between the 

 conductibility of a rarefied gas and one at the ordinary pressure ; 

 they neither of them conduct electricity. Above this limit, differ- 

 ences show themselves, and the dilated gas always proves the best 

 conductor. 



When the elasticity of a gas brought to a red heat is dimi- 

 nished, its conductibility increases ; when brought to the highest 

 degree of rarefaction possible with pneumatic apparatus, the gaseous 



