178 



NATURE 



[yan. 3, 1878 



the employment of sulphurous acid, by giving the gas time 

 to cool after compression. M. Cailletet has not yet ob- 

 tained, at all events, so far as we yet know, oxygen in a 

 liquid form, as M. Pictet has done ; on being separated 

 from its enormous pressure it has merely put on the 

 appearance of a cloud. 



M. Pictet's arrangements are more elaborate. He uses 

 four vacuum- and force-pumps, similar to those which 

 were recently exhibited in the Loan Collection of Scien- 

 tific Apparatus for makmg ice, driven by an engine of 

 15-horse power. Two of these are employed in procuring 

 a reduction of temperature in a tube about four feet long 

 containing sulphurous acid. This is done in the follow- 

 ing way : the vacuum pump withdraws the vapour from 

 above the surface of the liquid sulphurous acid in the 

 tube, which, like all the others subsequently to be men- 

 tioned, is slightly inclined so as to give the maximum of 

 evaporating surface. The force-pump then compresses 

 this vapour, and sends it into a separate reservoir, where 

 it is again cooled and liquefied ; the freshly-formed 

 liquid is allowed to return under control to the tube first 

 referred to, so that a complete circulation is maintained. 

 With the pumps at full work there is a nearly perfect 

 vacuum over the liquid and the temperature falls to — 65° 

 or - 70° C. 



M. Pictet uses this sulphurous acid as a cold-water 

 jacket, as we shall see. It is used to cool the carbonic acid 

 after compression, as water is used to cool the sulphurous 

 acid after compression. 



This is managed as follows : — In the tube thus filled 

 with liquid sulphurous acid at a temperature of — 60° C. 

 there is another central one of the same length but 

 naturally of smaller diameter. This central tube M. 

 Pictet fills with liquid carbonic acid at a pressure 

 of four or six atmospheres. This is then let into 

 another tube four metres long and four centimetres in 

 diameter. When thus filled the liquid is next reduced 

 to the solid form and a temperature of — 140° C, the 

 extraction of heat being effected as before by the pump, 

 which extracts three litres of gas per stroke and makes 

 100 strokes a minute. 



Now it is the turn of the oxygen. 



Just as the tube containing carbonic acid was placed 

 in the tube containing sulphurous acid, so is a tube con- 

 taining oxygen inserted in the long tube containing the 

 now solidified carbonic acid. This tube is five metres 

 long, fourteen millimetres in exterior diameter, and only 

 four in interior diameter — the glass is very thick. The 

 whole surface of this tube, except the ends which project 

 beyond the ends of the carbonic acid tube, is surrounded 

 by the frozen carbonic acid. 



One end of this tube is connected with a strong shell 

 containing chlorate of potash, the other end is furnished 

 with a stop-cock. 



When the tube was as cold as its surroundings, 

 heat was applied to the chlorate, and a pressure of 

 500 atmospheres was registered ; this descended to 320. 

 The stop-cock was then opened, and a liquid shot out 

 with such violence that none could be secured, though we 

 shall hear of this soon. 



Pieces of lighted wood held in this stream sponta- 

 neously inflamed with tremendous violence. 



In this way, then, has oxygen been liquefied at last. 



But this result has no sooner filled us with surprise than 

 it has been completely eclipsed. On the last day of 

 December, a week after the meeting of the Academy to 

 which we have referred, M. Cailletet performed a series of 

 experiments in the laboratory of the Ecole Normale at 

 Paris, in the presence of Berthelot, Boussingault, St. 

 Claire Deville, Mascart, and other leading French 

 chemists and physicists, using the same method as that 

 formerly employed for oxygen and he then and there 

 liquefied hydrogen, nitrogen, and air ! 



M. Cailletet first introduced pure nitrogen gas into the 

 apparatus. Under a pressure of 200 atmospheres the tube 

 was opened, and a number of drops of liquid nitrogen were 

 formed. Hydrogen was next experimented with, and this, 

 the lightest and most difficult of all gases, was reduced to 

 the form of a mist at 280 atmospheres. The degree of 

 cold attained by the sudden release of these compressed 

 gases is scarcely conceivable. The physicists present at 

 the experiment estimated it at — 300° C. 



Although oxygen and nitrogen had both been liquefied, 

 it was deemed of interest to carry out the process with 

 air, and the apparatus was filled with the latter, carefully 

 dried and freed from carbonic, acid. The experiment 

 yielded the same result. On opening the tube a stream 

 of liquid air issued from it resembling the fine jets forced 

 from our modern perfume bottles. 



These more recent results are all the more surprising 

 as, at an earlier stage, hydrogen, at a pressure of 300 

 atmospheres, has shown no signs of giving way. 



These brilliant and important results, though, as we 

 have said, they give us no new idea on the constitution of 

 matter, open out a magnificent vista for future experi- 

 ment. First, we shall doubtless be able to study solid 

 oxygen, hydrogen, and air, and if MM. Pictet and Caille- 

 tet succeed in this there will then be the history to write 

 of the changes of molecular state, probably accompanied 

 by changes of colour, through which these elemental 

 substances pass in their new transformations. 



There is a distinct lesson to be learnt from the sources 

 whence these startling tours de force have originated. 

 The means at the command of both MM. Cailletet and 

 Pictet arise from the industrial requirements of these 

 gentlemen, one for making iron, the other for making ice. 



Why then in England, the land of practical science, 

 have we not more men like MM. Cailletet and Pictet to 

 utilise for purposes of research the vast means at their 

 disposal, or at all events to allow others to use them 1 



It is also clear that to cope with modern requirements 

 our laboratories must no longer contain merely an anti- 

 quated air-pump, a Leyden jar, and a few bottles, as many 

 of them do. The professor should be in charge of a 

 work- instead of an old curiosity-shop, and the scale of 

 his operations must be large if he is to march with the 

 times — times which, with the liquefaction of the most 

 refractory gases, mark an epoch in the history of science. 



HUXLEY'S PHYSIOGRAPHY 

 Physiography : an Introduction to the Study of Nature. 

 By T. H. Huxley, F.R.S. (London: Macmillan and 

 Co., 1877.) 



AMONG educational works which are calculated to 

 afford real assistance to the teacher in his all-import- 

 ant labours, we may recognise two distinct classes. One 



