466 



THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



bablement le plus grand nombre de liquides que 

 nous connaissons, se transformeraient en montagnes 

 solides. 



" L'air dans eette supposition, ou du moins une 

 partie des substances aeriformes qui le composent, 

 cesserait, sans doute, d'exister dans l'etat de fluide 

 invisible, faute d'un degre de chaleur suffisant ; il 

 reviendrait done a, l'etat de liquidity, et ce chauge- 

 ment produirait de nouveaux liquides dont nous 

 n'avons aucune id£e." 



When Faraday in the year 1823 (at the age 

 of thirty-one) began the researches indicated in 

 the last paragraph quoted by M. Dumas, and first 

 liquefied chlorine and then several other gases, 

 he had no idea that he had been anticipated, as 

 he had been, by Monge and Clouet, who condensed 

 sulphurous acid before the year 1800, and by 

 Northmore, who liquefied chlorine in 1805. If 

 the great experimenter were among us now, how 

 delighted he would be to see one of the greatest 

 iron-masters of France employing the enormous 

 resources at his disposal at Ch&tillon-sur-Seine, 

 and a descendant of the Pictet, the firm friend 

 of his great friend De la Rive (who was the first 

 to whom he communicated his liquefaction of 

 chlorine), thus engaged in carrying on the work 

 which he made his own ! 



The methods employed by MM. Pictet and 

 Cailletet are quite distinct, and are the result of 

 many years' preparatory study, as testified by 

 M. H. St.-Claire-Deville and M. Regnault. It is 

 difficult to know which to admire most, the sci- 

 entific perfection of Pictet's method or the won- 

 derful simplicity of Cailletet's. It is quite certain 

 that the one employed by the latter will find fre- 

 quent use in future experiments. We may briefly 

 refer to both these methods. 



M. Cailletet's apparatus has already been 

 briefly alluded to in these columns. It consists 

 essentially of a massive steel cylinder with two 

 openings ; through one hydraulic pressure is com- 

 municated. A small tube passes through the 

 other, the sides of which are strong enough to 

 withstand a pressure of several hundred atmos- 

 pheres, and which can be inclosed in a freezing 

 mixture. It opens within the cylinder into a 

 second smaller cylinder serving as a reservoir 

 for the gas to be compressed. The remainder 

 of the space in the large cylinder is occupied by 

 mercury. M. Cailletet's process consists in com- 

 pressing a gas into the small tube, and then, by 

 suddenly placing it in communication with the 

 outer air, producing such a degree of cold by the 

 sudden distention of the confined gas that a large 

 portion of it is condensed, a process perfectly 

 analogous to that used to prepare solid carbonic 



[ acid by the rapid evaporation of the liquefied 

 gas. In M. Cailletet's experiment with oxygen it 

 was brought to a temperature of —29° C. by the 

 employment of sulphurous acid, and a pressure 

 of 300 atmospheres ; the gas was still a gas. But 

 when allowed to expand suddenly, which, accord- 

 ing to Poisson's formula, brings it down to 200° 

 below its starting-point, a cloud was at once 

 formed. The same result has since been obtained 

 without the employment of sulphurous acid, by 

 giving the gas time to cool after compression. 

 M. Cailletet has not yet obtained, 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 Scientific Apparatus for making 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 con- 

 taining sulphurous add. This is done in the fol- 

 lowing way: The vacuum-pump withdraws the 

 vapor from above the surface of the liquid sul- 

 phurous acid in the tube, which, like all the others 

 subsequently to be mentioned, is slightly inclined 

 so as to give the maximum of evaporating sur- 

 face. The force-pump then compresses this va- 

 por, 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 circula- 

 tion 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 tempera- 

 ture of — 60° C. there is another central one of 

 the same length but naturally of smaller diame- 

 ter. This central tube M. Pictet fills with liquid 

 carbonic acid at a pressure of four or six atmos- 

 pheres. 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. 



