6 979 
sooner transformed than the thread of the same combination which 
is immersed in paraffin oil’). 
If this is actually the case, the electromotive force of the differ- 
ential thermo-element will undergo a rather sudden change, and the 
initial point of this change will correspond with the transition point 
of one of the metals of the element. On application of this simple 
and very sensitive differential method it was found that the electro- 
motive force was practically zero throughout the temperature range 
that we examined, for it was less than 0,001 milli Volt. We did 
not consider the investigation as finished then, and we once more 
examined the same differential thermo-element Cu—Ag—Cu, taking 
care that one pair of wires was not only immersed in a solution 
of CuSO,, but in such a way that the etched copper wire, the 
soldering place, and a small piece of the silver wire were in contact 
with powdery copper. 
This procedure in our experiment, however, did not bring about 
the slightest change in the results, for now too the electromotive 
force of the circuit between 40° and 80° remained certainly smaller 
than 0,001 milli-Volt. 
We will still mention here that the times of observation have 
been taken very long here on purpose, and amount to 2x 24 hours. 
Notwithstanding this prolonged heating at temperatures above and 
below those at which dilatometrically indications were found for a 
transition point, the electromotive force of the differential thermo- 
element appeared to be smaller than 0,001 milli-Volt. In the first 
place this result shows that both the silver wire and the copper 
wire were very homogeneous, and in the second place that neither 
the silver wire nor the etched copper wire, though they were in 
contact with a solution of CuSO, and with fine copper powder over 
a length of 20 cm., showed appreciable transformation. 
The differential method discussed here is now being applied to 
the other important metals. In the following paper also the theory 
will be discussed. 
Laboratory of General and Inorganic 
Chemistry of the University. 
Amsterdam, December 13, 1920. 
1) For ConeN found that contact with an electrolyte has an accelerating effect 
on the transformation of one metal modification into another. This accelerating 
action must probably be ascribed to this, that when the stable modification has 
appeared only in one point, this gives rise to local currents, which greatly promote 
the transformation. ; 
