94) Sir H. Davy on the Relations 



value of the quantity sought was known, it became a point of 

 great importance to ascertain, by varying the circumstances 

 of the experiment, whether that quantity always retained the 

 same value independently of the different states of the at- 

 mosphere ; and all the trials that have been made favour the 

 conclusion that it is neai'ly constant. But the constancy of 

 the factor is now proved a prioii by the theory here laid 

 down, and is no longer merely an induction from experiments. 



Taking -^- = | , we are entitled to enunciate the following 



proposition, which solves the proposed problem : 



The heat extricated from air 'when it undergoes a given con- 

 densation, is equal to ^ of the diminution of temperature re- 

 quired to produce the same condensation, the pressure being 

 constant. 



Air, under a constant pressure, diminishes 4^o^h of its vo- 

 lume for every degree of depression on Fahrenheit's scale ; 

 and therefore one degree of heat will be extricated from air 

 when it undergoes a condensation equal to ^^-^ x f = y^Q. 

 If a mass of air were suddenly reduced to half its bulk, the 

 heat evolved would be i -h ^i^ = 90°. 



Having now solved the proposed problem, I shall reserve 

 what further is important on this subject to a future occasion. 



Jan. 8, 1827. J. IvoRY. 



XXII. The Bakerian Lecture. On the Relations of Electrical 

 and Chemical Changes. By Sir Humphry Davy, Bart. 

 Pres. R.S. 



[Continued from p. 38.] 



IV. On the electrical and chemical effects exhibited by com- 

 binations containing single metals and one fluid. 



T KNOW of no class of phsenomena more calculated to give 

 -■- just views of the nature of electro-chemical action than those 

 presented by single metals and fluids ; and as their results are, 

 with one or two exceptions, entirely new, I shall describe them 

 with some degree of minuteness. — When two pieces of the 

 same polished copper, connected with the platinum wires of 

 the multiplier, were introduced at the same time into the same 

 solution of hydro-sulphuret of potassa, there was no action ; 

 but if they were introduced in succession, there was a distinct 

 and often, if the interval of time was considerable, a violent 

 electrical effect — the jiiece of metal first plunged in being ne- 

 gative, and the other positive. 



This result depends upon the circumstance of the produc- 

 tion 



