90 



NATURE 



[May 25, 1S93 



compressor as gas and liquefied, and thence, again, into the 

 chamber as required. A similar cycle of operations was carried 

 out with the nitrous oxide. There was a hundredweight of 

 liquid ethylene prepared for the experiment. Ethylene was ob- 

 tained from alcohol by the action of strong sulphuric acid. Its 

 manufacture was exceedingly difficult, because dangerous, and 

 .IS the efficiency of the process only amounted to 15 or 20 per 

 cent, the preparation of a hundredweight of liquid was no light 

 task. The cycle of operations, which, for want of time, was 

 nit fully explained, was the same as that commonly employed 

 in refrigerating machinery working with ether or ammonia. 



The lecturer then exhibited to the audience a pint of liquid 

 oxygen, which by its cloudy appearance shov.ed that it con- 

 tained traces of impurity. The oxygen was filtered, and then 

 appeared as a clear transparent liquid with a slightly blue tinge. 

 The density of oxygen gas at - 182° C. is normal, and the 

 latent heat of volatilisation of the liquid is about 80 units. The 

 capillarity of liquid oxygen at its boiling-point was about one- 

 sixth that of w.ater. The temperature of liquid oxygen at 

 atmospheric pressure, determined by the specific heat method, 

 using platinum and silver, was - 180° C. 



Reference was then made to a remarkable experimental 

 corroboration of the correctness for exceedingly low tempera- 

 tures of Lord Kelvin and Prof. Tait's thermo-electric diagram. 

 ]f the lines of copper and platinum were prolonged in the 

 direction of negative temperature, they would intersect at 

 ~ 95° C. Similarly, the copper and palladium lines would cut 

 one another at - 170° C. Now, if this diagram were correct, 

 the E. M.F. of the thermoelectric junctions of these two pairs 

 of metals should reverse at these points. A Cu - Pt junction 

 connected to a reflecting galvanometer was then placed in 

 oxygen vapour and cooled down. At - 100° C. the spot of 

 light stopped and reversed. A Cu - Pd junction w,is after- 

 wards placed in a tube containing liquid oxygen, and a similar 

 reversal took place at about - 170° C. 



Liquid o.xygen is a non-conductor of electricity : a spark 

 taken from an induction coil, one millimetre long in the liquid 

 requires a potential equal to a striking distance in air of 25 

 millimetres. It gave a flash now and then, when a bubble of 

 the oxygen vapour in the boiling liquid came between the 

 terminals. Thus liquid oxygen is a high insulator. When the 

 spark is taken from a Wimshurst machine the oxygen appears 

 to allow the passage of a discharge to take place with much 

 greater ease. The spectrum of the spark taken in the liquid is 

 a continuous one, showing all the absorption bands. 



As to its absorption spectrum, the lines A and B of the solar 

 spectrum are due to oxygen, and they came out strongly when 

 the liquid was interposed in the path of the rays from the 

 electric lamp. Both the liquid and the highly compressed gas 

 show a series of five absorption bands, situated respectively in 

 the orange, yellow, green, and blue of the spectrum. 



Experiments prove that gaseous and liquid oxygen have 

 substantially the same absorption spectra. This is a very note- 

 worthy conclusion considering that no compound of oxygen, so 

 far as is known, gives the absorptions of oxygen. The per- 

 sistency of the absorption through the stages of gaseous con- 

 ■ lensation towards complete liquidity implies a persistency of 

 molecular constitution which we should hardly have expected. 

 The absorptions of the class to which A and B belong must be 

 those most easily assumed by the diatomic molecules (O;) of 

 ordinary oxygen ; whereas the diffuse bands above referred to, 

 seeing they have intensities proportional to the square of the 

 density of the gas, must depend on a change produced by com- 

 pression. This may be brought about in two ways, either by 

 the formation of more complex molecules, or by the constraint 

 to which the molecules are subjected during their encounters 

 with one another. 



When the evaporation of liquid oxygen is accelerated by the 

 action of a high expansion pump and an open test-tube is 

 inserted into it, the tube begins to fill up with liquid atmospheric 

 air, produced at the ordinary barometric pressure. 



Dr. Janssen had recently been making prolonged and careful 

 experiments on Mont Blanc, and he found that these oxygen 

 lines disappeared more and more from the solar spectrum as he 

 reached higher altitudes. The lines at all elevations come out 

 more strongly when the sun is low, because the rays then have 

 to traverse greater thicknesses of the earth's atmosphere. 



Michael Faraday's experiments made in 1849 on the action of 

 magnetism on gases opened up a new field of investigation. The 



NO 1230, VOL. 48] 



following table, in which 4- means "magnetic" and - means 

 " negative," summarises the results of Faraday's experiments. 



Magnetic Relations of Gases (Faraday). 



I., a:- In Carbonic In Hydro- t f. 1^ 



In Air. .-, ^' Int^oaloas. 



Acid. gen. 



Becquerel was before Faraday in experimenting upon this 

 subject. Becquerel allowed charcoal to absorb gases, and then 

 examined the properties of such charcoal in the magnetic field. 

 He thus discovered the magnetic properties of oxygen to be 

 strong, even in relation to a solution of ferrous chloride, as sel 

 forth in the following table : — 



Specific Magnetism, Equal Weights {Becquerel). 



Iron -f 1,000,000 



Oxygen + 377 



Ferrous chloride solution, sp. gr. i'4334-+- it/ci 



Air -t- 8S 



Water - 3 



The lecturer took a cup made of rock salt, and put in it some 

 liquid oxygen. The liquid did not wet rock salt, but remained 

 in a spheroidal state. The cup and its contents were placed 

 between and a little below the poles of an electro-magnet. 

 Whenever the circuit was completed, the liquid oxygen rose 

 from the cup and connected the two poles, as represented in the 

 cut, which is copied from a photograph of the phenomenon. 

 Then it boiled away, sometimes more on one pole than the 

 other, and when the circuit was broken it fell off the pole in 

 drops back into the cup. He also showed that the magnet would 

 draw up liquid oxygen out of a lube. A test-tube containing 



liquid oxygen, when placed in the Hughes balance, produced no, 

 disturbing effect. The magnetic moment of liquid oxygen is- 

 about looo when the magnetic moment of iron is taken as 

 i,ooo,oco. On cooling some bodies increased in magnetic 

 power. Cotton wool, moistened with liquid oxygen, was strongly 

 attracted by the magnet, and the liquid oxygen was actually 

 sucked out of it on to the poles. A crystal of ferrous sulpliatej ' 

 similarly cooled, stuck to one of the poles. 



The lecturer remarked that fluorine is so much like oxygen in 

 its properties, that he ventured to predict that it will turn out 

 to be a magnetic gas. 



Nitrogen liquefies at a lower temperature than oxygen, and ^ 

 one would expect the oxygen to come down before the nitrogen 

 when air is liquefied, as stated in some text-books, but un- i 

 fortunately it is not true. They liquefy together. In evaporat- j 

 ing, however, the nitrogen boils off before the oxygen, llepoured j 

 two or three ounces of liquid air into a large test-tube, and a i 

 smouldering splinter of wood dipped into the mouth of the tube 



