108 Mr. J. P. Joule on the Electric Origin 



should be straight. It is in fact so nearly a straight line, that 

 its slight discrepancies therefioni may be properly referred to 

 unavoidable errors of experiment. Produce the straight line 

 C D so as to meet A B in X, and the straight line A X, equal 

 to 2*8, will indicate the number of pairs necessary to decom- 

 pose water. 



42. Fig 5 represents an experiment of the same kind, with 

 a solution of sulphate of oxide of zinc in the decomposing cell. 

 Oxide of zinc was decomposed, the oxygen being evolved at 

 the positive, and the zinc being reduced at the negative elec- 

 trode. The intensity necessary to decompose oxide of zinc is 

 equal to that of 3-7 of Mr. Smee's pairs. 



43. With sulphate of protoxide of iron I did not at first 

 succeed, on account of the formation of peroxide at the posi- 

 tive electrode. However, by placing the negative electrode 

 among some crystals of the salt, pouring water thereon, and 

 suspending the positive electrode in the water, 1 obviated that 

 difficulty, and obtained the results which are projected in fig. 6, 

 and which indicate 3*3 pairs as the intensity necessary to de- 

 compose protoxide of iron. 



44. Now from (41.) and (42.) we have (usijig the same let- 

 ters as before) 2-8 pairs = h, and 3-7 pairs = ;:; whence 

 2*8 z = 3'7 h, and z =1-32 h; or, in other words, the intensity 

 required to separate oxide of zinc into metal and gas is to the 

 intensity required to separate water into its gaseous elements 

 as 1*32 :1. But from (35.), the intensity produced by the 

 union of iio?i-gaseoiis oxygen with zinc is to the intensity neces- 

 sary to separate water into no?i-gaseotis oxygen and gaseous 

 hydrogen as 1-93 : 1 ; and 1-32 : 1 : : 1-93 + 1'9 : 1 + J-9. 

 Wherefore, the intensity necessary to give oxygen the gaseous 

 form is to the intensity necessary to separate water into non- 

 gaseous oxygen and gaseous hydrogen as 1*9 : 1. 



45. Thus we see that a very great intensity of current is 

 employed in changing the condition of bodies, as well as in 

 separating them from their combinations. The field of investi- 

 gation here opened is very extensive, but 1 may not at present 

 enter further upon it. I will only remark, that if the intensity 

 necessary to convert a body into a different state, compared 

 with the heat or cold due to the mechanical or other produc- 

 tion of that different state, be such as accords with the rela- 

 tions of intensity and heat which we observe in the voltaic ap- 

 paratus, we have a proof that some of the effects which are 

 usually referred to " latent heat," are in fact nothing more than 

 the recondite operations of resistance to electric current*. 



46. In our investigation into the cause of the heat of com- 



* Some experiments, which I have not time to refer to at present, ren- 

 der this hypothesis more than probable. 



