VOLTAIC IGNITION. 



345 



Fig. 4 . 



B 



could I detect any difference in the resulting heat, whether 

 the current passed in the same or in a different direction 

 through each wire respectively. 



My next object was to ascertain whether, in cases of ordi- 

 nary ignition, the same apparent annihilation of heat took 

 place in hydrogen gas as with voltaic ignition. Two iron cy- 

 linders, A B, fig. 4, each weighing 390 grains, were attached 

 to long iron wires bent back in the form shown in the figure. 

 The cylinders were placed together 

 in a crucible of fine sand, and the 

 whole heated to a uniform white heat. 

 The cylinders were now taken out of 

 the sand, placed at the surface of 

 equal portions of water in the vessels 

 C and D ; two inverted tubes, e, f, the 

 one of hydrogen, the other of atmo- 

 spheric air, were placed over them, 

 and the whole quickly immersed in 

 the water, and retained by a little 

 contrivance, which I need not parti- 

 ticularise, in the position shown in the figure. The tempe- 

 rature of the water at the commencement of the experiment 

 was 60 Fahr. In four minutes the water surrounding the 

 hydrogen had risen to 94, and became stationary there, while 

 that surrounding the air had only reached 87 ; in ten minutes 

 the water surrounding the hydrogen had sunk to 92^5, while 

 that surrounding the air had risen to 93, which was the highest 

 temperature it reached ; thus the respective maxima were 94 

 and 93 ; but considering the greater time which the water 

 surrounding the air required to attain its maximum tempera- 

 ; '. nd t hat, being during this time at a temperature above 

 that of the surrounding atmosphere, it must have lost some- 

 thing of its acquired heat, we may fairly consider the maxima 

 to be the same, and that the difference of effect in the two 

 gases had reference solely to the time occupied in the trans- 

 ference of the heat. In a second experiment the results were 

 similar, the maximum being in this experiment 92*5 in 

 hydrogen, and 91 in air.* 



* Iron wire produces a similar effect to platinum wire in the voltaic experi- 

 ments. 



