1095 
Tinca vulgaris, Perca fluviatilis. An emptied air-bladder was never 
filled again after the Rami intestinales Vagi had been cut through on 
both sides. 
Finally I have tried to ascertain if, for some time after the air- 
bladder has been emptied, an increased absorption of oxygen could 
be observed. Theoretically there is of course every reason to expect 
this, and the strong almost asphyxial respiratory movements of the 
fish after the bladder has been emptied, render it very probable. 
The experimental proof is difficult to give. I omit here the tech- 
nical details relating to the oxygen determinations. On comparing the 
oxygen consumed by a fish in rest, before the bladder has been 
emptied and after it, it is found that in the latter case an increase 
may be observed. It is a remarkable fact, which is difficult to 
explain, that often immediately after the gas-extraction the oxygen- 
consumption fell below the average. 
Chemistry. — “On critical end-points and the system ethane-naph- 
talene’. By Dr. Apa Prins. (Communicated by Prof. A. F. 
HOLLEMAN). 
(Communicated in the meeting of Jan. 30, 1915). 
After Smits’ investigation of the system ether-anthraquinone *) no 
other binary system has been found which shows in a similar way 
the critical end-points. It was, therefore, my intention to search for 
such a case. Should [ succeed in finding end-points p and g. 
which might be easily realized, it would be possible by an appro- 
priate choice of the components to obtain one of the types of ternary 
systems theoretically developed by Sirs *) by combination of two 
binary ones. As the following shows, I have not been successful 
in finding a system analogous to ether-anthraquinone; so I had to 
give up the research of a ternary system. 
Obviously either ether or anthraquinone recommended itself as 
one of the components. As the melting-point of the less volatile 
component must be above the critical temperature of the more vola- 
tile one, and the solubility of the former substance must be slight 
even at the critical temperature of the latter, and moreover no 
decomposition may occur, the number of substances suitable for 
investigation, is not large. 
The preliminary experiments, showing whether critical end-points 
occurred or not, were made in small sealed tubes, which were heated 
1) Z. Phys. Chem. 51, page 193. 
2) Proc. R. Acad. Amsterdam June 1912. 
