NEW RESEARCHES ON LIQUID AIR. 141 



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 pressure. Much 

 work requires to be done in the accurate determination 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 nitro- 

 gen at its boiling point 0.850. 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 liquefaction 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 properly ignited, burns continu- 

 ously on the surface of liquid oxygen, producing 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 Thomson 

 and Regnault on the temperature of gas jets issuing under low pres- 

 sures 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, Plate V, where O 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 | mm. in diameter, which takes the place 

 of a stopcock. When carbon dioxide gas at a pressure of 30 or 40 atmos- 

 pheres is expanded through such an apperture, liquid can be seen 



