410 



RECENT PROGRESS IN PHYSICS. 



manner : In the circuit of a constant battery besides a platinum wire, 

 which could conveniently be surrounded by an atmosphere of different 

 gases, a voltameter was inserted. The intensity of ignition in the pla- 

 tinum wire was found to be very different in the different gases, but, at 

 the same time^ the rate of the decomposition of water in the voltameter 

 was also changed, so that in equal times the quantity of detonating 

 gas obtained was greater as the heat evolved by the wire was less. The 

 following quantities of detonating gas were obtained per minute in 

 the voltameter when the platinum was immersed in the gases enume- 

 ated: 



In hydrogen 7.7 cubic inches. 



defiant gas 7.0 " 



carbonic oxide 6.6 " 



carbonic acid 6.6 " 



oxygen 6.5 " 



nitrogen.... 6.4 *' 



atmospheric air 6.4 " 



do. condensed 6.5 " 



do. rarified 6.3 '' 



chlorine 6.1 " 



With the appearance of light in the wire, the heat produced in it 

 also is greater, as is demonstrated by the following experiment: The 

 bulb of a thermometer was placed at a certain distance from a coil of 

 wire, which was heated to redness by a battery of 4 cells. When the 

 coil remained in atmospheric air the thermometer rose 15° in five min- 

 utes, but when it was immersed in hydrogen the rise, during the same 

 interval, was only 7.5°. 



Poggendorf, in a note, expresses the opinion that this phenomenon 

 may be connected with the observation formerly made by Dulong and 

 Petit, that a heated body is more rapidly cooled in hydrogen than in 

 atmospheric air. To me this view seems inadmissible, for if the wire 

 in hydrogen gives out more rapidly the heat developed in it, the 

 thermometer ought to rise more rapidly when the wire is placed in 

 this gas, provided the quantity of heat produced in the wire by the 

 galvanic current is always the same in whatever gas it is placed. 



This experiment, however, is not yet decisive ; but another one, 

 described by Grove in a later memoir on the same subject, beyond a 

 doubt refutes the above explanation of Poggendorf. — (Phil. Magazine, 

 XXXY, 114 ; Fog. Ann. LXXVIII, 366.) Two glass tubes, A and 



B, fig. 50, 1.5 inch in length 

 and 0.3 inch interior diame- 

 ter, were closed at both ends 

 with corks, which were 

 penetrated by copper wires, 

 connected inside of the tube 

 by a spiral of platinum wire 

 Jy inch in diameter and 3.7 

 inches in length. The tube 

 A was filled with oxygen, B with hydrogen, and the tubes were then 

 placed in separate vessels, similar in every respect, and containing 



Fig. 50. 



