1896.] on New Besearches on Liquid Air. 139 



Direct determinations with an exhausted glass cylindrical vessel 

 displacing about 22 c.c. gave 1-1378. Fizeau's parabolic law for 

 the variation of the coefficient of expansion holds down to —183^. 

 The solid which showed the greatest contraction was a block of 

 compressed iodine ; the one that contracted least being a compressed 

 cylinder of silver iodide. Wroblewski gave the density of liquid 

 oxygen at the boiling point as 1*168, whereas Olszewski found 1 • 124. 

 The variation of density is about +0'0012, for 20 mm. barometric 

 prc>:sure. Much work requires to be done in the accurate deter- 

 mination of the physical constants of liquid gases. 



Liquid Air. — A large silver ball weighed in liquid air gave the 

 density of the latter as 0-910, and the corresponding density of 

 nitrogen at its boiling point - 850. It is difficult to be quite certain 

 that the constituents of liquid air are in the same proportion as the 

 gaseous ones, so that further experiments must be made. Liquid air 

 kept in a silvered vacuum vessel gradually rises in boiling point from 

 the instant of its collection, the rate of increase during the first hour 

 being nearly directly proportional to the time. As the increase 

 amounted to 1° in ten minutes, the boiling point of oxygen ought to 

 have been reached within two hours. The density of liquid air, 

 however, does not reach that of pure oxygen even after thirty hours' 

 storage. The large apparatus of the Eoyal Institution for air lique- 

 faction can be arranged to deliver liquid air containing 49 per cent, 

 of oxygen, which gives off gas containing 20 per cent, of oxygen, 

 rising after six hours to 72-6 per cent. 



Combustion in Liquid Oxygen. — A small ignited jet of hydrogen 

 burns continuously below the surface of liquid oxygen, all the water 

 produced being carried away as snow. There is a considerable 

 amount of ozone formed, which concentrates as the liquid oxygen 

 evaporates. In the same way graphite or diamond, when projjerly 

 ignited, burns continuously on the surface of liquid oxygen, pro- 

 ducing solid carbonic acid and generating ozone. If liquid oxygen 

 is absorbed in wood charcoal, or cotton-wool, and a part of the body 

 heated to redness, combustion can start with explosive violence. 



Gas Jets containing Liquid. — The experiments of Joule and Thom- 

 son and Reguault on the temperature of gas jets issuing under low 

 pressures are well known. The following observations refer to the 

 pressure required to produce a lowering of temperature sufficient to 

 yield liquid in the gas jet. 



The apparatus used in the study of highly compressed gas jets is 

 represented in Fig. 2 ; where C is a vacuum tube which holds a coil 

 of pipe about 5 mm. in diameter surrounded with carbon dioxide or 

 liquid air for cooling the gas before expansion, and A is a small 

 hole in the silver or copper tube about i mm. in diameter, which 

 takes the place of a stopcock. When carbon dioxide gas at a pressure 

 of 30 or 40 atmos. is expanded through such an aperture, liquid can 

 be seen where the jet impinges on the wall of the vacuum tube, along 

 with a considerable amount of solid. If oxygen gas escaj^es from the 

 gmall hole at the pressure of 100 atmos. having been cooled previously 



