210 JONES AND SCHUMB. 



amalgams (varying from 44.6% to 55.68% Tl) he finds the amalgam 

 0.0008 volt more positive than the metal itself. 



Shukoff ^^ measured (incidentally to some work on thallie diethyl 

 chloride) the potential of a saturated thallium amalgam in a saturated 

 thallous chloride solution against the normal calomel electrode at 25° 

 and obtained +0.727 volt. This result differs only by about one 

 millivolt from the later measurements discussed below. 



Kurnakow and Puschin ^^ have investigated the freezing points of a 

 series of thallium amalgams. They find a maximum in the liquidus 

 curve at 15.0°C. with 33.33 atomic per cent, of thallium and two 

 eutectic points at -60°C. with 8.34% thallium and +3.5°C. with 40% 

 thallium. These authors conclude that thallium forms a solid com- 

 pound, TlHgo. As will be pointed out below, this work of Kurnakow 

 and Puschin has been discredited by later investigators. 



Sucheni ^'^ has measured the potential of a series of thallium amal- 

 gams in contact with 0.1 N potassium cUoride saturated with thallium 

 chloride, against the decinormal calomel electrode. He was interested 

 principally in unsaturated amalgams but states that saturated two- 

 phase amalgams have the same potential as metallic thallium. Con- 

 trary to his expectations based upon Kurnakow's work, he failed to 

 find a break in the concentration-potential curves at the point cor- 

 responding to the compound TlHg2. Accepting the existence of 

 the compound TlHgo as proved by the work of Kurnakow, he con- 

 cludes that Tl and TlHg2 form no solid solutions but that Hg and 

 TlHg2 form solid solutions. (It will be shown below that this con- 

 clusion is incorrect, because based upon the erroneous work of Kurna- 

 kow.) Sucheni found the potential of the cell: TlHgx, TlCl sat., 

 0.1 N KCl, 0.1 N KCl, HgoCb, Hg; containing a saturated two-phase 

 amalgam, to be +0.830 volt at 37° and +0.820 volt at 0°. The 

 interpolated value for 25° is +0.827 volt. 



Some measurements (unpublished) were made by R. W. Kent (1906) 

 in this laboratory upon the thallium metal and amalgam electrodes 

 in solutions of N/10 thallous sulphate at 25°. His cell consisted of: 

 Tl or TlHg,, O.INTI2SO4, O.lNNaNOg, l.NKCl, HgsClo, Hg. 

 His corrected measurements, recorded to milli^•olts, for the metal 

 electrodes — electrol^'tically prepared metal was used — varied from 

 0.685 to 0.690 v., with an average of 0.689 v. The degree of dis- 

 sociation of thallous sulphate is here 61.5% (data of Hunt ^^), from 



25 J. Shukoff, Ber., 38, 2691 (1905). 



26 N. S. Kurnakow and N. A. Puschin, Z. anorg. Chem., 30, 86 (1902). 



27 A. Sucheni, Z. Elektrochemie, 12, 726 (1906). 



28 F. L. Hunt, Jour. Amer. Chem. Soc, 33, 795 (1911). 



