212 JONES AND SCHUMB. 



thallium, we must use an electrode of pure metallic thallium or some 

 electrode that is its equivalent. It was shown by Kurnakov and 

 Puschkin ^^ [sic] that thallium and mercury form no solid compound 

 above 15°. Sucheni ^^ showed that mercury does not dissolve to any 

 extent in solid thallium, and that a saturated solution of thallium in 

 mercury therefore has the same potential as pure thallium. This 

 fact, which we have also corroborated,^^ enables us to use a paste of 

 thallium and thallium amalgam in place of solid thallium, which like 

 all solid metals gives an inconstant potential owing to uncontrollable 

 surface variations." They found the potential of a saturated two- 

 phase amalgam in contact with a saturated thallous chloride solution 

 measured against the normal calomel electrode to be 0.7257 volt at 

 25°C. The normal potential of the thallium electrode is computed 

 to be 0.6170 volt. 



However, since this paper of Lewis and von Ende was published, the 

 work of Kurnakow and Puschin, on which they relied, has been dis- 

 credited by three independent investigations. P. Pavlovich, ^* in a 

 repetition of the work of Kurnakow and Puschin, finds, as did the 

 earlier workers, a eutectic at — 60°, corresponding to 8 at. per cent, 

 thallium; another eutectic at +2°, with 40% thallium; but his 

 dystectic occurs at 14.8°, covering a range of from 28.7 to 29.7 at. 

 per cent, thallium. Pavlovich postulates the existence of the com- 

 pound TlHg3, and notes that solid solutions separate between the 

 limits 21 to 31% Tl, as well as between 86-100 at. per cent. Tl. 



G. D. Roos ^^ has also repeated the work of Kurnakow and Puschin 

 on the freezing points of thallium amalgams and obtains results of a 

 quite different character. He finds that the solid compound of 

 thallium and mercury has the formula TloHga instead of TlHgo. This 

 compound forms solid solutions with both excess of mercury and of 

 thallium within the limits 20% Tl and 31.3% ^^ Tl. Of more import- 

 ance for the present purpose, however, is the proof by measurements 

 of eutectic halts in the cooling curves, that metallic thallium forms 

 solid solutions with mercury, which may contain as much as 18% of 

 mercury at the eutectic temperature, wliich was found to be +0.6°C. 

 instead of 3.5°C. as observed by Kurnakow and Puschin. The work 



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



32 A. Sucheni, Z. Elektrochemie, 12, 72r3 (1906). 



33 No details of this corroboration are given. 



34 P. Pavlovich, Jour. Russ. Phys. Chem. Soc, 47, 29 (1915); Bull. Soc. 

 Chim., 20, 2 (1916). 



35 G. D. Roos, Z. anorg. Chem., 94, 369 (1916). 



36 Atomic percentages; in the present case nearly equal to percentages 

 by weight. 



