VOLTAIC IGNITION. 341 



In oxygen. In associated nitrogen. 



Exp. ist. From 60 to 71-5. From 60 to 73. 



2nd. 60 to 77. 60 to 76. 



3rd. 60 to 75. 60 to 76. 



Mean . . 60 to 74-5. 60 to 75. 



The battery had increased somewhat in power after the 

 first experiment ; but as both wires formed part of the same 

 circuit in each experiment, the variations in battery power do 

 not affect the comparative results. The second experiment 

 gives a variation in the position of oxygen and nitrogen with 

 reference to the first and third experiments, but the gases so 

 nearly approach in their cooling effects, that these slight 

 differences are not much to be relied upon ; however, I 

 applied a farther test. I associated in turn oxygen and 

 nitrogen with carbonic acid ; the following were the results. 

 In five minutes the thermometer rose 



In oxygen. In carbonic acid. 



Exp. ist. From 60 to 75. From 60 to 75. 



2nd. 60 to 76. 60 to 75. 



In nitrogen. In carbonic acid. 



Exp. ist. From 60 to 74. From 60 to 73. 



2nd. 60 to 73. 60 to 72-5. 



The battery had in the last experiment a little decreased 

 in power ; the oxygen and nitrogen both produced a less cool- 

 ing effect than the carbonic acid, but the oxygen came nearer 

 to it than the nitrogen, thus according with the previous ex- 

 periments. Upon the whole it would appear that oxygen 

 produces a somewhat greater cooling effect on the ignited wire 

 than nitrogen, but these gases may, for the purposes of this 

 paper, be fairly regarded as equal. Atmospheric air produces 

 a similar effect to oxygen and nitrogen separately, though I 

 am inclined to think that a slight chemical change takes place 

 when atmospheric air is exposed to the ignited wire, and that 

 nitrous acid is formed ; for if litmus-paper be held over a vol- 

 taically ignited platinum wire in the air, a slight but very per- 

 ceptible tinge of red marks the portion of it immediately over 

 the wire. 



With the view of ascertaining whether the specific heat of 



