OF THALLIUM, INDIUM, AND TIN 5 



the amalgam, except the osmotic pressure of the ion dissolved in the 



electrolyte. Thus P and P' include the effect of the chemical free 



p 

 energy change connected with dilution ; and if such exists 7 can not be 



equal to . This explanation appears to be necessary, because of the 



C-i 



misconception of Carhart concerning the significance of the Nernst 

 equation. 9 



The equation of Cady 10 and of Lewis " is an attempt to take account of 

 the heat of dilution, thus resolving the tendencies P and P' into their most 

 important components. This equation may only be supposed to hold true 

 when there is no change of heat capacity during the reaction. Further 

 explanation may be deferred until the present research has been described, 

 when a still more recent suggestion of Lewis, concerning the application 



of the law of Raoult [ = - ] to osmotic work, will also be con- 



\p N+nJ 



sidered. 



Before beginning a description of our experimental work it will be well 

 to consider the accuracy with which the various quantities in the equations 

 are defined. 



In a previous contribution from this laboratory" the results of Ray- 

 leigh, 13 F. and W. Kohlrausch, 14 Kahle, 15 and Patterson and Guthe, 1 ' con- 

 cerning the value of Faraday's equivalent F, have been compared ; and 

 the conclusion was reached that 96,580 coulombs are associated with 107.93 

 grams of silver, if the silver is weighed in a form free from mother-liquor, 

 after having been deposited in a manner avoiding anode complications. 

 The more recent work of Smith, Mather and Lowry, and others, has not 

 changed our opinion on this point." Since Richards, Collins and Heim- 

 rod, 18 and Richards and Stull 19 have established the universality of Fara- 

 day's law on a firmer basis than ever, the same value can be used for a 

 gram equivalent of thallium or indium with reasonable accuracy. If the 

 atomic weight of silver is taken as 107.88, a value probably nearer the 



8 H. S. Carhart, Phys. Rev., 26, 216 (1908). 

 10 Cady, Journ. Phys. Chem. 2, 551 (1898). 



11 Lewis, Proc. Am. Acad. 35, 34 (1899). 



12 Proc. Amer. Acad., 37, 415 (1902). 

 "Phil. Trans., 175, 411 (1884). 

 14 Wied. Ann., 27, I (1886). 

 "Wied. Ann., 67, I (1889). 



16 Phys. Rev., 7, 257 (1898). 



17 Smith, Mather and Lowry, Phil. Trans. Roy. Soc. London, Series A, 207, 545 

 (1908) ; also see especially T. W. Richards, Proc. Am. Acad., 44, 91 (1908). The 

 Report of the International Conference on Electrical Units and Standards, " Science," 

 28 (1908), recommends F = 96,540 for the same atomic weight without these pre- 

 cautions. This probably amounts to about the same thing. 



18 Zeit. phys. Chem., 32, 301 (1900). 



19 Proc. Amer. Acad., 35, 123 (1899). 



