— 
360 Prof. Oliver Lodge on the Seat of the 
If we intend to make brass, must we not regard the air 
surrounding the plates as a simple accident, and imagine all 
air-films removed before beginning the operation? Work 
with the zinc and copper plates in absolute vacuum, where 
(on my hypothesis at any rate) the only difference of potential 
between them is a minute thermoelectric one; there will be 
an attraction caused by this difference of potential, and work 
will be done in shutting the book, but to get any appreciable 
amount of heat the plates must be terribly thin. How much 
heat really is produced in the formation of brass I don’t 
believe any one knows; but if it be enough to warm the 
metals sixty degrees, the lower limit to the size of atoms 
becomes greatly depressed. 
In a note near the end of this paper I show that a rise of from 
+ to 2 degrees is all that is probable, on the usual estimate of 
atomic dimensions; the smaller evolution of heat being caused 
by alloying the metals at 10° C., the larger being produced by 
alloying them at 400 °C. 
26. Js there much heat produced in the formation of brass ? 
Is there any way of attacking the question simply? 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 undertake this observation, which is doubtless a delicate 
one, for he was engaged in some thermo-chemieal 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 doubt be readily 
found. 
Adhering to zine and copper as convenient for explanation, 
the argument, though obviously not the order of experiment, 
will stand as follows:—Take definite weights of zinc and 
copper, dissolve them separately, getting heats H, and H, 
respectively; then mix the solutions, getting a possible further 
heat-production 4. ‘This is one plan of passing from separate 
zinc and copper to a solution of a salt of brass. 
* It occurred in conversation with Professor 8. P. Thompson and Dr. 
J. A. Fleming on board the Quebec excursion steamer ‘Canada’, and I 
am unable to say who suggested it. 
