Ws 
( 311 ) 
size of the molecule of the normal substance has influence on the 
course, has also lost its direct importance. For mixtures of ethane 
with an alcohol the separation between the two types lies between 
methyl- and ethylalcohol; the question whether this separation takes 
place between two higher terms of the alcohol series, if we take 
instead of ethane a higher term of the series of carbonhydrogene 
compounds, which seemed very important before is now no longer 
of primary interest '). It seems to me that I have to return in many 
respects tO my original meaning, namely that we have to inquire 
after the circumstance which causes the spinodal curve to show a 
protuberance towards the side of the small volumes. In mixtures of 
a normal substance with an associating one this cause can perhaps 
Op 
be found in the circumstance that the quantity Ge can obtain ab- 
U Dv 
normous high values for such a mixture. As the equation: 
dpdwp — (dp)? 
Ov Ow? (5) 
Op 
applies to the spinodal curve, the value of — ay ay also be abnor- 
vb 
mously high in this case. If this is really the case an explanation 
for the protuberance is given which is certainly satisfactory. Yet a great 
distance exists between this observation and an adequate calculation. 
In any case these experiments of KuerNeN, to which I hope that 
he will add many others, are an important contribution to our know- 
ledge of the critical phenomena of not miscible substances. 
Physics. — “The influence of variation of the constant current 
on the pitch of the singing arc” By J. K. A. Wurrumm 
SALOMONSON. (Communicated by Prof. P. Zeman). 
In the course of some experiments on the physiological action of 
alternating currents of very high frequency, I tried the currents 
generated by means of Depprerr's singing are. <A constant current 
are between solid carbons shunted by a self-inductive resistance and 
a condenser emits a note, the pitch of which corresponds with the 
frequency of the alternate current generated in the condenser-circuit. 
1) An experiment in order to investigate whether for propane the limit lies between 
ethyl- and propylalcohol was already in preparation for a long time in the laboratory 
of Amsterdam. But other labour which could not be delayed prevented each time 
those who would undertake the investigation. 
Proceedings Royal Acad. Amsterdam. Vol. V. 
