of the Heat of Combustion. 99 



chemical combination is the same as calculation founded on 

 these facts would lead us to expect, no reasonable doubt can 

 be entertained that it also is the product of resistance to elec- 

 tric conduction. 



3. In studying the character of the heat of combustion, the 

 first point was to determine the intensities of the affinities of 

 different combustibles for oxygen. For this purpose I have, 

 in accordance with the views which were first stated by Davy, 

 and have since been adopted by the most eminent electricians, 

 made use of the measure of these intensities which is afforded 

 by the electric current. 



4. I had not proceeded far before some curious phaenomena 

 were observed, which, though not very well understood, have 

 long been known* to electricians. I shall notice these first, 

 because of their important bearing upon subsequent reason- 

 ings and conclusions. 



5. I was working with an arrangement consisting of iron, 

 platinized silver, and dilute sulphuric acid. The circuit was 

 closed by a galvanometer, the coil of which consisted of 119 

 turns of thin-silked copper wire, forming a rectangle, measu- 

 ring 1 foot by 6 inches. The needle indicated a pretty con- 

 stant deviation of 20°, but on moving the platinized silver 

 backwards and forwards the needle advanced gradually to 40°, 

 where it was kept for some time by continuing the agitation. 

 As soon as the motion of the platinized silver was disconti- 

 nued, the needle resumed its former position. Similar effects 

 were produced by stirring the liquid, and thus causing it to 

 impinge against the platinized silver. 



6. 1 repeated the above experiment many times with si- 

 milar results, but I found that whenever a large quantity of 

 hydrogen had been evolved from the liquid by the action of 

 the pair, or otherwise, the phasnomena wevQ not well produced. 

 This circumstance convinced me that the effects were due to 

 atmospheric air held in solution by the liquid, and that the 

 displacement of a part of it by the hydrogen had occasioned 

 their partial prevention. My opinion was confirmed by the 

 following experiment. 



7. 1 filled three quarters of the contents of a glass flask with 

 dilute sulphuric acid, and then placed it over the flame of a 

 spirit-lamp until I judged that all the atmospheric air had been 



• In IS.'JO, Mr. Sturgeon remarked that when two pieces of iron are 

 placed in dilute muriatic acid, the agilalion of one of them will make it ope- 

 rate as copper in the copper-zinc battery : also, that if two pieces of iron 

 are iiimiersed in succession in a solution of nitrous acid, the iron last im- 

 mersed will act as copper in the copper-zinc battery. — Recent Experimental 

 Researches, p. 4G— 49. We shall hereafter see the true cause of these phae- 

 nomena. 



H2 



