136 Professor Dewar [March 27, 



reached, numbers of heads and hands are disposed to take over the 

 problem from the scientific researcher." 



Solid Air. — As Professor Olszewski has recently alleged that 

 air does not solidify at the lowest pressures,* the author's former 

 experiments were repeated on a larger scale. If a litre of liquid 

 air is placed in a globular silvered vacuum vessel and subjected to 

 exhaustion, as much as half a litre of solid air can be obtained 

 and maintained in this condition for half an hour. At first the 

 solid is a stiff, transparent jelly, which, when examined in the 

 magnetic field, has the liquid oxygen drawn out of it to the poles. 

 This proves tLat solid air is a nitrogen-jelly containing liquid 

 oxygen. This statement was made in a paper " On the Refraction 

 and Dispersion of Liquid Oxygen, and the AbsorjDtion Spectrum of 

 Liquid Air" (Professors Liveing and Dewar), published in the 

 Phil. Mag. for September 1895, yet Professor Olszewski, in 1896t 

 is declaring " that Professor Dewar has stated that liquid air 

 solidifies as such, the solid product containing a slightly smaller 

 percentage of nitrogen than is present in the atmosphere. My 

 experiments have proved this statement to be incorrect." The Cracow 

 professor may well have the satisfaction of correcting a statement 

 which was never made by me. He seems also to forget that in 

 1893, Proc. Roy. Inst. Lecture on Liquid Air, it is distinctly stated 

 that " all attempts to solidify oxygen by its own evaporation have 

 failed." Solid air can only be examined in a vacuum or in an 

 atmosphere of hydrogen, because it instantly melts on exposure to 

 air cooled to the temperature of its boiling point, giving rise to 

 the liquefaction of an additional quantity of air. It is strange to see 

 a mass of solid air melting in contact with the atmosphere, and 

 all the time welling up like a kind of fountain. The apparatus 

 shown in Fig. 3 is well adapted for showing the direct liquefaction 

 of the air of a room and its solidification. A large vacuum vessel G, 

 is mounted on a brass stand containing another smaller vessel B of 

 the same kind. By means of the two cocks C and D, either the large 

 vessel G or the bulb B can be connected to the air pump circuit. 

 Liquid oxygen is placed in A, which can, by opening the stopcock D, 

 be cooled to —210° by exhaustion. If the stopcock C is shut and a 

 barometric gage is joined on at F, the dropping of the liquid air from 

 the outside of A will go on even at as low a pressure as 4 in. of mer- 

 cury ; w^hich is equivalent to saying that this apparatus would 

 liquefy air if taken by a balloon ten miles high. If F is now opened, 

 giving a supply of air at atmospheric pressure, the cup B soon fills 

 with liquid air. Unless the air supply is passed over soda lime and 

 strong sulphuric, the liquid is always turbid from the presence of 

 ice crystals and solid carbonic acid. Now on shutting F and 

 opening C, the air in B is placed under exhaustion and soon solidifies 

 to a jelly-like mass. When the vacuum is about 14 mm. then the 

 temperature of the solid air is — 232° by the platinum resistance 



* rhih Mag. Ftbniary 1895. f See ' Nature,' Aug. 20, p. 378. 



