464 Intelligence and Miscellaneous Articles. 



separated by a perfectly visible meniscus. I have attained this 

 result by the following method : — Having liquefied at — 142° C. 

 a certain quantity of air in the tube of the apparatus which I 

 employ for using permanent gases as cooling mixtures, I allow a 

 quantity of gaseous air to enter the tube, such that the pressure of 

 the gas having become equal to 40 centim. and its optical density 

 equal to that of the liquid, the meniscus entirely disappears, after 

 which I slowly lessen the pressure ; the moment the manometer 

 indicates a pressure of about 37*6 atmospheres, I see that a new 

 meniscus forms at a point in the tube much higher than the place 

 previously occupied by the vanished meniscus. A few minutes after- 

 wards the lirst meniscus reappears at the place at which we had 

 seen it disappear, and at the same moment two liquids are distinctly 

 seen, different in character, one on the top of the other. The 

 two liquids remain separated for several seconds. After this a 

 current of very small bubbles forms, which ascend, detaching them- 

 selves from the meniscus which separates the two liquids. In 

 consequence of this phenomenon the upper liquid becomes a little 

 opaque ; the meniscus, gradually destroyed by the current, ulti- 

 mately disappears altogether, and the last result is a single liquid 

 homogeneous in appearance. * 



By means of a small metal tube introduced into the apparatus 

 I have been able, without destroying the meniscus, to take at will 

 either from the bottom or top layer a quantity of liquid sufficient 

 for analysis. AVhile the lower liquid contains 21*28 to 21*5 of 

 oxygen, the upper one only contained 17*3 to 18*7. 



This experiment is of great importance in the theory of the 

 critical state of gases. It shows in fact, contrary to the assertion 

 made some years ago by certain physicists, that the disappear- 

 ance of the meniscus of a liquid, when it is obtained by increasing 

 the pressure exerted by a gas on a superposed liquid, does not effect 

 a solution of the liquid in the gas. — Comptes Rendxis, Sept. 28, 1885. 



ON THE SOURCE OF THE HYDROGEN OCCLUDED BY ZINC DUST. 

 BY GREVILLE WILLIAMS, F.R.S. 

 In my paper "On the Synthesis of Trimethylamiue and Pyrrol 

 from Coal-Gas, and on the Occlusion of Hydrogen by Zinc Dust,"t 

 I showed that, under certain conditions, zinc dust behaved towards 

 hydrogen like palladium; and 1 inferred, from the phenomena 

 observed, that the zinc dust occluded hydrogen at ordinary tempe- 

 ra! area, and gave it off in an active condition when heated. In my 

 second paper, "Note on the Occlusion of Hydrogen by Zinc Dust 

 and the Meteoric Iron of Lenarto " J, 1 gave the results of determi- 



* In this experiment air, which is a completely colourless liquid, shows 

 moreover a singularly enigmatical optica] phenomenon, which immedi- 

 ately precedes the appearance of the upper meniscus. The part of this 

 tube where th<> meniscus should form, assumes a feebly orange coloration, 

 which disappears the moment the meniscus appears. A like phenomenon 

 never precedes the appearance of the lower meniscus, which separates the 

 two Liquids. 



t See 4 Journal of Gas Lighting/ vol. adv. p. 15. J Loc. oit. p. 486\ 





