526 report— 1884. 



H is the unknown quantity to be determined, and its determination 

 involves four separate measurements, Hj, H 2 , H 3 , h. 



The only one of these at all easy to observe is h, and this my assistant, 

 Mr. Butler, bas done. Proportions of zinc and copper sulphate, con- 

 taining equal weights of zinc and copper, are dissolved in as little water 

 as will keep in solution any double salt that may be formed on mixing. 

 The zinc sulphate is enclosed in a thin bulb or tube inside the other solu- 

 tion, and left, screened from stray heat, for some hours. The bulb is then 

 broken, or the liquid otherwise blown out of it, and the liquids mixed. 

 No certain rise of temperature so great as a hundredth of a degree has 

 been observed. 



27. In thinking over what metals were more suitable, it struck me 

 that the heat of formation of amalgams was a subject easy of direct attack. 

 I therefore, as a preliminary, have dissolved a little granulated tin in 

 mercury. Of course the latent heat of liquefaction of tin has to be 

 allowed for, and the actually observed result is a cooling ; but I hoped that 

 the cooling observed would be less than what the latent heat would account 

 for, and that I might then calculate the real evolution of heat due to com- 

 bination. Unfortunately the only data I know of with reference to the 

 latent heat of tin relate to its ordinary melting point, at which point it is 

 given by Rudberg as 13"3 and by Person as 14" 25. We have no ground 

 whatever for believing latent heat to be constant, and I am therefore utterly 

 in the dark as to what the latent heat of tin at ordinary temperature may 

 be. That liquid tin could be super-cooled to ordinary temperatures with- 

 out solidification is unlikely. I give, however, the data of my experiment 

 (which was carefully performed) in case better latent heat data are known 

 to someone else :— 2*10 grammes of thin granulated tin at 12 0- 4 were 

 dropped into 502 - 00 grammes of mercury at a steady temperature of 

 10° *85, contained in a large thin protected test-tube, of which the part 

 sharing the temperature of the mercury weighed 8 grammes. After 

 solution, which took ten minutes, the resulting temperature was found to 

 be 8°"82. Three minutes later it had risen to 8 - 99 from surrounding 

 influences. The thermal capacity of the immersed part of the ther- 

 mometer 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 . . 3045 units 

 Disappearance of heat actually observed .... 43 - 57 



more than can be accounted for, without any combination heat at all I 

 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° Centigrade. 



Ignorance of the true latent heat thus effectually prevents our obtain- 

 ing 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 temperatures 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 



