708 
of this appears in the tables. In the tables of the 3"¢ kind also, 
where it would have been quite possible to apply a different perio- 
dicity to the time-intervals and to the synodic ares, this has not been 
done; they ran practically parallel, differing only by an unimportant 
computational quantity; and the method of calculation which is used 
in the tables of the first and second kind exeludes any possibility 
of taking into account the varying velocity of the sun. 
Chemistry. — “On the System Mercury-lodide.” By Prof. A. Smits. 
(Communicated by Prof. P. Zeman.) 
(Communicated in the meeting of September 27, 1916.) 
As was already discussed more at length before mercury iodide 
exhibits a very peculiar phenomenon on being heated, which phe- 
nomenon consists in this that after the red phase has been converted 
to the yellow phase at 127°, the substance remains yellow up to 
about 188°, but then gradually assumes a more and more pronounced 
red colour, and finally melts to a dark red liquid at + 255°,5. 
This, combined with the fact that the vapour is colourless or light 
yellow, tells us that as far as the composition is concerned the solid 
phase lies between the vapour and the liquid at the three-phase- 
equilibrium solid-liquid-gas. In virtue of these data a pseudo figure 
was derived that took these above facts into account, and gave, 
moreover, an exceedingly simple explanation of the fact that on 
sudden cooling of the vapour the yellow modification always makes 
its appearance first. 
Yet this figure had a drawback, which was felt by me and also 
by others, and which gave an indication that the view would still 
have to be modified somewhat. This drawback consisted in this that 
it was assumed that above the point of transition the yellow rhombic 
mixed crystals wouid continuously pass into red tetragonal ones. 
As was communicated in the last paper on this subject, Dr. A. L. 
W. E. van DER Veen had at my request undertaken the erystallo- 
graphic study of mereury iodide in the hope that this research 
would bring the problem nearer its solution. This has actually been 
the case. By making use of a special sublimation arrangement Dr. 
v. D. Vern ') has succeeded in making crystals of yellow mercury 
iodide, 2 em. long above 127°.2, and in studying them accurately 
microscopically at different higher temperatures. It then appeared 
that the originally yellow crystal begins to gradually assume an 
1) Verslag van de gewone vergaderingen der wis- en nat. afd. Kon. Akademie 
5 +e) 5 ’ 
Vol. XXIV (1916) Pp. WD 
