ELKCTllOMOTIVi; FOKCKS IN TIIK VOLTAIC CELL. 



52."> 



, Clil'tdn, 

 water. 

 s it (loon 

 on of ;iiv 

 ■present u 

 d air and 

 mcl water, 

 iviously (I? 

 ' tlie slow 

 ctrical.]* 

 nore avoid 

 ectromek': 

 10 one disc 

 Bore lippe- 



eally clctcr- 

 wliich are 



5 is by the 



it are not a: 

 ore contiict, 



lowever, no*j 

 itrolyto, iti:i 



vmiuato tliB 

 a-isc in con- 

 smallness of 

 to indicate, 

 is argntnent 

 ^'olta s force. 

 made in Sir 

 his paper be 

 [c and copper 

 ■es of a book 

 ^k. Directly 

 ,nd attracted 

 ■ making the 

 •lose enougli. 

 quantities Oi 

 as masses ot 

 lick. So far 

 consider tuc 

 the work lie 

 Is. But if^-e 

 combustioa 



act, not odIJ 



tako the plates several atoms thick, but wo must suppose filni.s of air of 

 Hullioient thickness to ]n'osorvo their normal activities in the wayofcliemical 

 (itrain to bo shut up witli the plates, (iiven these, the amount of wo>'k 

 wliicli he has calculated would certainly bo done in shutting the book, 

 ami a corrospondini^ amount of heat rrcnerated. Ihit would this heat have 

 luivdiing to do with the making of brass ? So far as I can see, nothing 

 wliii fever. 



It wo intend to make brass, must we not regard the air .surrounding 

 the plates as a simple accident, and imagine all air-iilms removed before 

 lu'giniiing the operation? Work Avith the zinc and copper plates in 

 nhsdlnto vacuum, where (on my hj'pothesi.s at any rate) the only 

 dill'ercuco of potential between them is a minute thermoelecti'ic one ; 

 there will be an attraction caused by this ditl'erence of potential, and 

 work will bo done in .shutting the l)ook ; but to get any appreciable 

 amount of heat the plates must be terribly thin. How much heat is 

 rcallv produced in the formation of brass I do not believe anyone knows ; 

 hut if it be enough to warm tlie metals sixty degrees, the lower limit to 

 the size of atoms becomes greatly dei)ressed. 



lu a note at the end of this paper I show that a rise of from -\ to 

 1 degrees is all that is probable, on the usual estimate of atomic 

 dimensions ; the smaller evolntion of heat being caused by alloying the 

 metals at 10° C, the larger being produced by alloying them at 4(J0° C. 



2<!. Is there much heat produced in the formation of brass ? Is there 

 finy way of attacking the question simj)ly ? The only way which has 

 occurred ' to me is to dissolve brass in acid, and to see whether one gets 

 appreciably less heat than by dissolving its constituent copper and zinc 

 separately. When an alloy is dissolved, I suppose the affinities of its con- 

 stituents are unloosed, or the combination undone ; hence the heat developed 

 during the solution of an alloy, subtracted from that produced during the 

 solution of its constituent metals and mixing of those solutions, ought to 

 measure the heat of formation of the alloy. Dr. Forster Morley, of 

 University College, London (also on the boat), said he might be willing to 

 nmdertake this observation, which is doubtless a delicate one, for he was 

 engaged in some thermo-chemical researches. It may not be practicable 

 for the actual case of brass, because of the complication and uncertainty 

 introduced by secondary products, but a better pair of metals may no 

 doul)t be readily found. 



Adhering to zinc and copper as convenient for explanation, the argu- 

 ment, though obrionsly not the order of experiment, will stand as follows : 

 Take dt'finite weights of zinc and copper, dissolve them separately, getting 

 beats H] and H2 respectively, then mix the solutions, getting a possible 

 further heat production h. This is one plan of passing from separate zinc 

 and copper to a solution of a salt of brass. 



Next take the same weights of zinc and copper as before and alloy 

 them, getting heat H, then dissolve the brass in the same acid as before, 

 getting heat H3. This is another plan of passing from separate zinc and 

 copper to a solution of a salt of brass. 



Now, unless external work and secondary products are different in the 

 vo cases, we are justiBed in writing the heats evolved in the two cases 

 equal: — • , , , 



H, + Ho+ /i = lI + H3. 



' It occurred in conversation with Professor S. P. Thompson and Dr. Fleming' on 

 lioard the Quebec excursion steamer Canada, and I am unable to sny who suggested it. 



