Chemistry mid Physics. 149 



change in the composition of the liquid, the nitrogen evaporating 

 more rapidly than the oxygen and the boiling point approaching 

 that of oxygen, — 18r5°. When evaporated in oxygen, the ten- 

 sion steadily diminishes and the temperature passes through a 

 series of maxima and minima. But more than this. The liquefied 

 air may separate into two distinct layers differing in appearance 

 and in composition and defined by a sharp meniscus. To obtain 

 this separation, a certain quantity of air is liquefied at —142°, and 

 gaseous air allowed to enter into the tube until the pressure is 40 

 c. m. and its optical density is equal to that of the liquid, the 

 meniscus entirely disappearing. The pressure is then slowly re- 

 duced, and when it reaches 3 7 '6 atmospheres, a new meniscus 

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

 occupied by the vanished meniscus. Presently the former menis- 

 cus reappears in its old position and two liquids are distinctly seen 

 superposed. In some seconds bubbles form at the lower meniscus, 

 rendering the upper liquid opaque and ultimately destroying the 

 dividing meniscus and leaving a homogeneous liquid. By the in- 

 troduction of a small metal pipette the author has removed por- 

 tions both of the upper and of the lower layer and has analyzed 

 them. The lower liquid contained 21*28 to 21*5 of oxygen, the 

 upper one 17'3 to 18 # 7. This experiment clearly shows that the 

 disappearance 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. — C. P., ci, 

 6C5, Sept. 1885 ; Phil. Mag., V, xx, 463, Nov. 1885. g. f. b. 



2. On the Velocity of the Explosive wave in Liquid and Solid 

 Petonants. — Berthelot has supplemented his researches on the 

 velocity of propagation of the wave of exploding gases, by a simi- 

 lar series of investigations on the velocity of the explosive wave 

 in detonating solids and liquids. For this purpose the explosive 

 was placed in a tube of block tin or lead, or an alloy of the two, 

 one to two millimeters in interior diameter and of varying length 

 up to 100 or 200 meters. It was distributed as uniformly as pos- 

 sible, and in some cases compi-essed in the tube. The explosives 

 used were gun cotton, both in the ordinary form and granulated, 

 nitro-starch, nitro-mannite, dynamite, nitroglycerin and panclas- 

 tite. Most of the measurements were made on Sebert's velocime- 

 ter, though a fall-chronograph and a Le Boulenge chronograph 

 were also used. At the ends and at 25 meter intervals, the tube 

 containing the explosive was surrounded by fine conducting wires 

 leading to the registering electro-magnets. These wires being 

 successively ruptured by the explosion, the order of the phenome- 

 non was registered on a smoked surface, simultaneously with the 

 vibrations of a tuning fork of known rate. A single experiment, 

 made on the 27 Sept., 1882, will show the method of operating. 

 Tubes 6 mm. interior and 10 mm. exterior diameter, were filled 

 with nitroglycerin. The progress of the wave of explosion was 

 registered on a Le Boulenge chronograph by the breaking of the 

 copper wires attached to the tube. The explosion was effected by 



