Chemistry. — “The Thermo-electric Determination of Transition 
Points”. 1. By Prof. A. Smits and J. Spurman. Communicated 
by Prof. P. Zeeman. 
(Communicated at the meeting of June 26, 1920). 
In 1912 the transition point of tetrogonal tin into rhombic tin 
was determined by means of very lengthy and laborious determina- 
tions. Small quantities of mercury accelerated this transformation, | 
but at the same time brought about a lowering of the transition 
point. Through extrapolaticn up to the quantity of mercury = 0 
200°.5 was found as transition temperature, the subsequent experi- 
ments with pure tin, which gave a great deal of difficulty, yielding 
+ 202°.8 in the end.) Though it has appeared that also in other 
cases mercury is a catalyst for the transition from one metal modi- 
fication to another, so that this expedient may often be successfully 
applied, it seemed very desirable to try and find another reliable 
and quicker method. 
That thermo-elements can only be used over a range of tempe- 
rature, within which no points of transition of the metals used 
occur, is known, and likewise the conclusion of the existence of a 
transition point was drawn before from a discontinuity of the change 
of the electomotive force with the temperature. 
Thus among others in the examination of the thermo-elements 
Niekel-Copper*) and Nickel-Lead*) a discontinuity was found between 
350° and 360°, which points to a transition point of Nickel, with 
which also the study of the magnetic and mechanic properties and 
also the investigation of the change of length carried out by JÄNECKE, *) 
is in agreement. Further BripGMAn °) investigated the thermo-electric 
force of thermo-elements under pressure; we may, accordingly, say 
that the thermo-element has been used already several times to 
discover a point of transition in one of the metals of the thermo-element. 
That, however, on rational application the thermo-electric method 
1) Smits and pe Leeuw, These Proc. Vol. XV, p. 676. 
2) Harrison, Phil. mag. 3, 192, 1902; Wiener Z. f. anorg. Chem. 83, 310 (1913). 
3) Proc. Roy. Soc. Edinburg, 8, 182 (1872—1873). 
4) Z. f. Electr. Chem. 9 (1919). 
5) Proc. Amer. Acad. 53, 269 (1918). 
