a 
362 Prof. Oliver Lodge on the Seat of the 
Three minutes later it had risen to 8°99 from surrounding 
influences. The thermal capacity of the immersed part of the 
thermometer was equivalent to ‘48 gramme of water. 
Working on these data, and taking the specific heat of tin 
as ‘056, latent heat 14:25, specific heat of glass 19, and of 
mercury ‘033, we find :— 
Heat disposed of in cooling and liquefying tin . 30°45 units. 
Disappearance of heat actually observed . . . 48°07, 
More than can be accounted for without any combination- 
heat at all! This is rather depressing; but it only shows 
how wrong is the estimate of 14:25 for the latent heat of 
liquid tin at 10°C. - 
Ignorance of the true latent heat thus effectually prevents 
our obtaining any information whatever, about the heat of 
combination of tin and mercury, from the experiment. It 
seems indeed easier to observe the combination-heat by a 
process of dissolving the amalgam and the metals separately 
in acid, as already explained for brass, and then to use the 
above experiment to calculate latent heat from. One might 
perhaps thus get the latent heats of fusion at various tempe- 
ratures for metals soluble in mercury. 
Another alternative, however, presents itself. Instead of 
trying to reduce the latent heat to ordinary temperatures, one 
might form the amalgam at a temperature just below the 
melting-point of tin, and obtain, if possible, the net evolution 
of heat then. 
Suppose the heat of combination of the 2°1 grammes of tin 
with mercury to be somehow or other determined, we have 
next to suppose the amalgam made otherwise, bringing the 
molecules together ina reasoned way. Let the same quantity 
of tin be brought to within molecular distance of the mercury 
in successive pieces of very thin foil, first made to touch at 
one corner and then laid down. 
It is quite true that each flake would be charged with a 
Volta H.M.F. of, say, *6 volt, and so would attract the mer- 
cury and do a certain amount of work in laying itself down. 
But it is not fair to compare an operation thus conducted in 
air with the dropping of a solid mass of tin into mercury: to 
be able to compare the two operations, one must perform the 
foil experiment in absolute vacuum. This being done, the 
contact H.M.F. is no longer ‘6 volt, but only about 00015 
volt according to the experiments of Matthiessen. Good data 
for this quantity are, however, wanting. Mercury is not one 
of the metals included in Professor Tait’s series. It was ob- 
served by Gaugain; and by rather hypothetical deduction 
