ATTAINMENT OF VERY LOW TEMPERATURES. 3 



Mascart, qui veiilent bien m'autoriser a invoquer leur temoignage j'ai 

 leussi a observer des indices de liquefaction de I'hydrogene, dans les 

 conditions d'evidence qui n'ont paru douteuses a aucum des savants 

 temoins de Texperience. Celle-ci a ete repetee un grand nombre de 

 fois. En operant avec de I'hydrogene pur comprime vers 280 atmos- 

 pheres, puis brusquement detendu, nous avons vu se former un 

 brouillard excessivement fin et subtil, suspendu dans toute la longueur 

 du gaz et qui disparaissait subitement. La production meme de ce 

 brouillard, malgre son extreme subtilite, a paru incontestable a tous 

 les savants. ..." 



In the light of our present knowledge of the properties of liquid 

 hydrogen some other explanation must be given to the phenomenon 

 observed by M. Cailletet and his colleagues. Possibly the mist was 

 caused by the condensation of some impurity in the hydrogen. 



Next year M. Pictet published a similar statement* Hydrogen 

 was generated by heating potassium formate with caustic potash in a 

 closed apparatus connected with a steel tube terminating in a stopcock. 

 When the pressure had risen to 650 atmospheres, and the tube was 

 cooled to about — 140° C, the cock was opened. The jet of hydrogen 

 issuing from the cock appeared steel-blue in color, and opaque for a 

 length of twelve centimeters. The substance forming the jet struck 

 the ground with a sound like that of hail falling on the earth. It is 

 probable that the explanation of the phenomenon lies in the formation 

 of carbon monoxide and carbon dioxide by the decomposition of the 

 sodium formate. 



The earliest experiments leading to results which can in any way 

 be considered as reliable are those of the Polish chemists Wroblewski 

 and Olszewski, which were commenced in 1882, and were carried out 

 partly in conjunction, partly independently, during the succeeding 

 years. That the work presented great difificulties may be imagined 

 when we read of six cubic centimeters of liquid air referred to as " a 

 large quantity." 



The earlier experiments, described in letters to the Cracow Academy 

 and in communications to the French Academy, are probably of little 

 direct value, except in so far as they show the efforts which were being 

 made. The following is an extract from one of Wroblewski's papers :!" 



" L'hydrogene soumis a la pression de 180 atm. jusqu'a 190 atm. 

 refroidi par I'azote bouillant dans le vide (a la temperature de sa 

 solidification) et detendu brusquement sous la pression atmospherique 

 presente une mousse bien visible. De la couleur grise de cette mousse, 

 ou I'oeil ne pent distinguer des grouttelettes incolores, on ne pent pas 

 encore deviner quelle apparence aurait I'hydrogene a I'etat de liquide 



* Comptes Rendns, 86, 106. 



t Comptes Rendus, 1885, 100, 981. 



