210 



Mr. G. Ansdell. 



[June 19, 



constituent elements, has an especial interest for the chemist. The 

 chief physical constants of this substance are unknown, although 

 its polymerised modification, benzene, has been very thoroughly studied 

 in its physical relations by Regnault. Having one of M. Cailletet's in- 

 genious pumps for the liquefaction of gases at my disposal in the 

 laboratory of the Royal Institution, Professor Dewar suggested a 

 series of accurate determinations of its physical properties in the 

 liquid state, and the present communication deals with the critical 

 point, the tension of the vapour of the fluid at various temperatures, 

 together with the corresponding densities and coefficients of com- 

 pressibility. 



The only notice on the liquefaction of the gas appears to be a short 

 paper by M. Cailletet in the " Compt. Rendus," vol. lxxxv, No. 19, in 

 which he determines the tension of the vapour of the liquid at diffe- 

 rent temperatures. These tensions, as will be afterwards seen, differ 

 entirely from those obtained in the present paper, one of the reasons 

 appearing to be that instead of using a carefully calibrated air mano- 

 meter for determining the pressures, he used the ordinary metallic 

 gauge attached to the pump, which is far from being correct. 



The pump itself is too well known to need description, suffice it to 

 say, that two of the iron bottles or reservoirs were used, connected 

 with the pump by a piece of fine-bore copper tubing, so as to equalise 

 the pressure, one containing an air manometer registering the 

 pressures from ten atmospheres upwards, and the other the tube filled 

 with acetylene. The two bottles were then placed side by side, and 

 the height of the column of mercury in either read off by means of a 

 cathetometer. 



The formulae used for calibrating the tubes, and also for calculating 

 the volume of the liquefied gas, and the pressure by the air manometer, 

 were those given by Dr. Andrews in his researches on carbonic acid 

 ("Phil. Trans.," 1869 and 1876). The method of preparing the acety- 

 lene gas was by the action of alcoholic potash on bibro methylene, the 

 disengaged gas being collected in the form of the red acetylide of 

 copper, by passing it into a strong solution of subchloride of copper in 

 ammonia. This red compound, after being thoroughly washed and 

 boiled with distilled water, was transferred to a flask with dilute hydro- 

 chloric acid, the gas driven off by means of a gentle heat, and con- 

 ducted through a strong solution of caustic soda, to free it from traces 

 of hydrochloric acid, and finally through two small |J -tubes with 

 fused chloride of calcium. The perfectly pure and dry acetylene was 

 now passed through the tube to be used for its liquefaction in a slow 

 stream for several hours, and the latter carefully sealed off when all 

 the air had been expelled. 



The sealing off requires great care, as unless rapidly done, and the 

 pressure removed from the inside (by cooling the tube) immediately 



