.126 



HKPonr — 1881. 



t 



II is tho unknown qnantity to bo dcti rtninod, and iU dotorniinatiou 

 iiiv()lv(!H I'oni' Hcpanitc incasui-cmonts, Jl], II ,, 11,, h, 



Tlic only OIK) of tlicso at all easy to ohscrvo is//, and Uiisniy assistant, 

 !Mr. IJntlcr, has done. Proportions of zino and (;oj)|)or siiipliiilc, con. 

 tainin<,' ((((iial wciirlits oi" zinc and copiu'r, art; dissolved in as littlo wiitci- 

 ns will koc]! in solution iiny doalilo salt that may ho I'oniicil on niixiiifr. 

 Tho zinc sulphate is enclosed in a thin bulb or tube inside tho other Rr)lu. 

 tioii, and Icit, sc'eciicd from stray heat, lor sonu! hours. The bid!) is tlicii 

 broken, or tla? liipiid othei-wise blown out of it, and the litpiids niixod. 

 No certain rise of temperature so great as a hundredth of a degree lia- 

 been obsi-rvcd. 



'17. In thinking nver what metals wero more suitable, it struck mo 

 that th(i heat of fornaition of amalgams was a subject easy of direct attack. 

 I therefore, as a prelinunary, have dissolved ii little granidatcd tin in 

 mercury. Of course the latent heat of liciueliietion of tin has to bo 

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

 tho cooling observed would be less than what the liiteid. heat would aceonnt, 

 for, and that 1 nught then calculate tho real evolution of heat due to com- 

 bination. Unfortunately tho oidy data 1 know of with reference to the 

 latent heat of tin relate to its ordinary melting ])oint, at which jioint it is 

 given by Uudberg as V.Vo and by Person as li"2-'). AVo have no grouml 

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

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

 bo. That licpaid tin could be sn])er-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 Vl''\ wore 

 dropped into 502"0O grammes of mercury at a steady temperature of 

 10° '85, contained in a large tliin protected test-tube, of which the pan 

 sharing the temperature of the mercury weighed 8 grammes. After 

 solution, -which took ten iTiinutes, the resulting temperature was found to 

 be 8°'82. Three minutes later it had risen to 8'99 from surrouncliiii; 

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

 mometer was equivalent to '48 gramme of water. 



Working on these data, and taking the specific heat of tin as •O-jO, 

 latent heat 14"25, specific heat of glass "It), and of mercury "033, we find:— • 



Heat disposed of in cooling and liquefying tin . . 30*4r) units 

 Disappearance of heat actually observed .... 4u"57 



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 oi 

 14"2o for the latent heat of liquid tin at 10° Centigrade. 



Ignora,nce of the true latent heat thus efi'ectually 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 



