of the Heat of Combustion. 101 



showing the increase of intensity arising from the presence of 

 oxygen. Some dilute sulphuric acid was agitated with chlo- 

 rine until the former had taken up as much of the gas as it 

 could. By pouring a solution of sulphate of oxide of silver 

 into the liquid, I now precipitated chloride of silver, leaving 

 sulphuric acid and oxygen in solution. When a pair, con- 

 sisting of platinized silver and iron, was placed in the acid thus 

 prepared, the galvanometer was permanently deflected 50°, and 

 by agitating the platinized silver the needle advanced as far as 

 60°. When a piece of amalgamated zinc was substituted for 

 the iron the permanent deflection of the needle was 65°, and 

 by agitating the negative element as before, the needle ad- 

 vanced to 70°. Had the same pairs been immersed in a sim- 

 ple solution of sulphuric acid, the permanent deflections would 

 have been no greater than 30'^ and 63°. 



13. Similar results were obtained with the solution of chlo- 

 rine, as might have been anticipated from its strong affinity for 

 hydrogen. 



14. From the above experiments, we see that the agitation 

 of the negative element is productive of an increase of inten- 

 sity, simply because it is thereby brought into contact with 

 bodies capable of combining with the hydrogen, which would 

 otherwise have been evolved from it. When those bodies ai'e 

 present in considerable quantities, as in (10.), (12.) and (13.), 

 the intensity of the current is great, even though the pair be 

 left quiet, because then the negative plate can collect them 

 readily upon its surface. Again, by causing the current to 

 encounter great resistance, the effects of agitation which we 

 have noticed are proportionally increased, because then the 

 number of particles required for neutralizing the hydrogen is 

 less. Hence it is that when I have used a resistance of 500 or 

 600 yards of thin wire, I have frequently found the deviation of 

 the needle (even when the pair was left quiet in a common 

 solution of sulphuric acid) considerably greater than was due 

 to that resistance. This is also the probable reason why De 

 la Rive in one instance* found the intensity of the copper-zinc 

 pile the same, whether charged with water or nitric acid. 



15. In the course of the preceding experiments I was forci- 

 bly struck with the very great intensity of the pairs at the mo- 

 ment of their immersion, compared with that which they were 

 able to maintain permanently. It appeared to me that the 

 theories which had been put forth to explain the first effect of 

 immersion, though seemingly plausible with regard to the zinc 

 battery, were not at all equal to account for the same phteno- 



* Ann. de Chmk; 18;j6, part i. p. \7i). 



