Michael Faraday, his Life and Works. 415 



of hydrogen in a liquid state, which was found to be a mixture 

 of several compounds endowed with various degrees of volatility, 

 and which could be separated by distillation. Every one knows 

 the advantage, in the production of colours, derived from this by 

 the illustrious chemist Hofmann, when he extracted aniline 

 from it. 



The discovery of this bicarburet of hydrogen was only an in- 

 cident in the researches which Faraday had undertaken in 1823, 

 upon the condensation of gases into liquids. His mode of ope- 

 ration in this investigation consisted in placing, in one extremity 

 of a recurved tube closed at both ends, the necessary ingredients 

 for the production of the gas, and plunging the other extremity 

 in a freezing-mixture. The gas, evolved in a closed space, spee- 

 dily condensed into a liquid state in the refrigerated extremity of 

 the tube. In this way chlorine, sulphurous acid, sulphuretted 

 hydrogen, carbonic acid, protoxide of nitrogen, cyanogen, am- 

 monia, and hydrochloric acid were successively reduced to a 

 liquid state. With the exception of chlorine, all these liquefied 

 gases were colourless and perfectly transparent ; and all of them 

 had a refractive power superior to that of water. The attempts 

 made to reduce the other gases, especially hydrogen, oxygen, 

 and nitrogen, to a liquid state were fruitless. Twenty years 

 later (in 1844) Faraday resumed these experiments by directly con- 

 densing the gases by mechanical processes in very strong and 

 hermetically sealed tubes, refrigerating them by means of the 

 mixture of ether with solid carbonic acid produced by Thilorier's 

 method. The condensation could be brought to fifty atmospheres, 

 and the lowering of temperature to —166° F., or 110° C. be- 

 low 0°. In this way Faraday succeeded in liquefying, besides 

 the gases which I have already mentioned, defiant gas, phos- 

 phuretted hydrogen, and arseniuretted hydrogen, as also fluosilicic 

 acid; but he did not succeed in solidifying them. On the 

 other hand, by applying his new process to the gases which he 

 had previously liquefied, he brought them not only to a liquid 

 state, but even to that of transparent and crystalline solids; hy- 

 drochloric gas alone of these latter would not become solid, 

 whilst hydriodic and hydrobromic gas were successively liquefied 

 and solidified. 



It is easy to understand all the importance of an investigation 

 the result of which was to modify completely the received ideas 

 as to the constitution of the permanent gases by causing them 

 to enter into the category of simple vapours ; this was to intro- 

 duce into molecular physics a new and important notion, the 

 consequences of which have gradually unfolded themselves. 



It is also to a question of molecular physics that we must 

 refer the memoir on the relations of gold and the other metals 



