OF THALLIUM, INDIUM, AND TIN 35 



Thus the dilution of the tin amalgams gives a small cooling effect a 

 conclusion wholly in accord with the deviation of its potential from the 

 equation of von Turin and Meyer. If more concentrated amalgam could 

 have been used, the result would undoubtedly have been greater. 



If possible, it would be well to verify these values of heats of dilution 

 by actual experiment. Unfortunately, however, an accurate determination 

 of the heat of dilution is only possible with the more concentrated amal- 

 gams, and even in these cases it is difficult. Five millionths of a volt in 

 the potential of a concentration cell corresponds to the development of 

 one joule during the transport of an univalent gram-atom. A mass of 

 amalgam containing a gram-atom of thallium dissolved in 99 times its 

 weight of mercury, when diluted with an equal volume of mercury would 

 involve a heat capacity not far from 6000 mayers ; hence one joule would 

 produce a temperature change of less than 0.0002. On account of the 

 high inertia of mercury, the liquids do not mix easily ; and for the same 

 reason the plentiful stirring evolves much heat. The exact evaluation of 

 the stirring correction is very difficult. Moreover, the dilution must be 

 carried out in an indifferent gas in order to avoid oxidation with its 

 attending heat effect. 



Nevertheless, in spite of these difficulties the attempt was made to 

 determine the heat of dilution in the cases of the more concentrated amal- 

 gams of thallium and indium. 1226 grams of a I per cent thallium amal- 

 gam were diluted with an equal bulk of mercury and found to cause a rise 

 of 0.015 in a calorimetric system having a heat capacity of 431 mayers. 

 On further diluting by an equal bulk of mercury the mixture resulting 

 from this first experiment, the increased system (having now a heat 

 capacity of 762 mayers) was raised through only 0.002. These effects 

 were in the expected direction, but not of the expected magnitude. 



The experiments were conducted in the apparatus of Richards and 

 Forbes, in which the mixing was conducted by a clock-work stirrer. Lack 

 of time had prevented the proposers of this apparatus from testing it 

 thoroughly. Our present experience indicates that the clock-work stirring 

 was inadequate, and hence that an inadequate change of temperature must 

 have been observed in all cases. Nevertheless, in spite of the quantitative 

 inadequacy of these results, they are qualitatively of value ; for they afford 

 experimental evidence that the conclusions drawn from the equation of 

 Helmholtz are at least in the right direction, and therefore that the data 

 upon which the conclusions are based are not seriously in error. 



In the case of indium, 150 grams of an amalgam containing 1.92 per 

 cent of indium was diluted with 600 grams of mercury in a small calo- 

 rimeter, the total heat capacity being 157 mayers. Here, in this smaller 

 apparatus, the stirring was more effective, and the temperature rose 0.048, 



