( 886 ) 
gen is always available, which with the present apparatus is now a 
matter of no difficulty. Formerly, when quite pure hydrogen was a 
costly commodity, many experiments were obstructed by the precau- 
tions necessary to properly collect the hydrogen that had evaporated ; 
but now one need no longer be afraid of sacrificing pure hydrogen, 
if necessary, and since this is the case, the great objection to its 
being sent away is removed. 
Physics. — “On the motion of a metal wire through a piece of ice.” 
By Dr. J. H. Merrpure. (Communicated by Prof. H. A. Lorentz). 
(Communicated in the meeting of March 27, 1909). 
EE 
A paper by G. Quincke') which had escaped my notice at the 
time of my first communication on the above-mentioned subject *) 
and which I happened to come across only some time ago, induced 
me take the subject up again. In this paper by QuinckE the phenomena 
are dealt with, caused by occlusions of salt in the ice and it is 
shown that even with ice, formed from distilled water, these play a 
part. From this point of view the phenomena are also studied, that 
are observed when a metal wire sinks through ice; the turbidity 
where the wire has cut through, is ascribed *) to occluded salt-solution 
with a different refractive power from the ice between which it lies. 
If this view is right, differences must be expected in the velocity of 
descent with ice of different origin. For then the slower descent 
— slower than theory would lead us to expect — is also a consequence 
of the fact that probably the salt-containing water does not re-freeze 
above the wire and this cause would be the more effective as the 
percentage of salt is greater. 
So I repeated part of the experiments with ice, formed from 
distilled water. Boiled distilled water was frozen by means of a 
mixture of snow and common salt in a glass tube of about 4 em. 
diameter, the freezing progressing, after BUNsEN’s advice *), from above 
downwards. If the freezing took place sufficiently slowly a quite 
clear rod of ice was formed in this way *). Undoubtedly even this 
1) G. Quincke Ann. d. Phys. 18. p. 1. 
2) These proceedings Vol. IX, p. 718. 
%) G. Quincke |. c. p. 46. 
4) G. Quincxe I. ce. p. 14. 
5) Sometimes a turbidity appeared in the middle of the tube, starting as a plume 
in the axis, the fine ramifications extending upwards in gentle curves. It is curious 
