1891.] The Faraday Centenary. 483 



Specimens, arranged and tabulated by himself, of Faraday's last 

 research on the optical properties of gold leaf in a highly attenuated 

 form were exhibited and described. 



Turning then to the special subject of the evening's discourse, the 

 liquefaction of gases, Prof. Dewar stated that although Faraday made 

 his first researches in this direction as early as 1823, the matter 

 lay dormant for many years, until his interest in it was reawakened 

 by Thilorier's discovery that solid carbonic acid could be produced 

 in the form of a snow-like substance, boiling at — SCO., and capable 

 of being handled. Faraday was the first to introduce this discovery 

 into England in a lecture given at the Royal Institution on the 18th 

 May, 1888 ; and, thereafter, by its aid, he resumed his work on the 

 liquefaction of the various gases which had resisted his former efforts. 

 All through the summer of 1844 he was busily employed at this 

 work, using the low temperatures, which Thilorier's new product 

 enabled him to obtain, combined with great pressures. (Specimens 

 of gases thus liquefied by Faraday shown.) This important work 

 was the subject of a Friday evening lecture given at the Royal 

 Institution early in 1845, a full abstract of which appeared in the 

 Times of that date, the Institution itself not having then commenced 

 the publication of its proceedings. In the course of that address 

 Faraday produced a small quantity of ethylene ; and he expressed the 

 opinion that if a method could be found of producing liquid nitrous 

 oxide in large quantities, that would be the material which would 

 enable him to liquefy oxygen and the other gases which had hitherto 

 resisted all his efforts. (Experiments showing the comparative 

 boiling points of solid carbonic acid, nitrous oxide, and ethylene at 

 ordinary pressure and under diminished pressure given.) Faraday 

 hoped that the production of solid nitrous oxide would enable him to 

 get temperatures as far below the boiling point of carbonic acid as 

 the temperature of that body was below ordinary temperatures. As 

 a matter of fact, it is impossible to reach such low temperatures by 

 the agency of solid nitrous oxide, and such great depression of 

 temperature was not attained until such time as liquid ethylene 

 became available. The lecturer here showed and described a diagram 

 of the machinery and apparatus now employed at the Royal Institu- 

 tion for the liquefaction and solidification of gases, see Fig. 1. The 

 method of producing liquid ethylene, and of employing it over and 

 over again in the apparatus was described. 



The work done in connection with this subject since the time of 

 Faraday, and especially the investigations of Andrews and Van der 

 Waals, had enabled scientists of the present day to calculate exactly 

 the temperature of the boiling point of hydrogen, the gaseous body 

 which has in the liquid state the lowest boiling point of all the 

 elementary substances, and which has up to the present time resisted 

 liquefaction. The temperature of boiling hydrogen would be — 250^ 

 C. The lowest point attained by Faraday was 110° C, and the 

 lowest temperature yet reached was — 210° C. 



