1879.] The Physical Properties of Liquid Acetylene. 211 



the point is closed, the acetylene becomes rapidly charred and blows 

 out, a small portion of it being consequently decomposed, and thus 

 interfering materially with the accuracy of the results. 



The tube for the tension determinations was of the usual shape 

 used in the Cailletet pump, the internal diameter of the capillary part 

 being about 2*5 mm. This was found to be more convenient than a 

 narrower tube, as a larger reservoir could be used, and consequently a 

 larger quantity of liquid obtained. 



The pressure at the different temperatures was always observed 

 when a very slight layer of liquid was formed on the surface of the 

 mercury, as the gas not being entirely free from air, the pressure was 

 slightly increased on filling completely the upper part of the tube. 



The following are the tensions obtained compared with those of 

 Cailletet : — 



Cailletet. 



Temp. 



Pressure. 



Temp. 



Pressure. 



-23° C. . . 



.. 11-01 



atm. 







-10 



. . 17-06 



3 3 











.. 21-53 



33 



+ l D c. 



. . . . 48 atm. 



+ 5-25 .. 



. . 25-48 



33 



2-5 



.... 50 „ 



13-5 



. . 32-77 



33 



io-o 



... 63 „ 



20-15 . . 



. . 39-76 



55 



18-0 



.... 83 „ 



27-55 . . 



. . 48-99 



33 



25-0 



. . . . 94 „ 



31-6 



. . 56-20 



33 



31-0 



... 103 „ 



36 



. . 65-36 



33 







36-5 



. . 65-89 



55 







36-9 



. . 67-96 



33 







The temperatures above zero were kept constant to within ^th of a 

 degree, by allowing a constant stream of water to flow over the tube 

 from a reservoir holding about 10 gallons, in which it had been pre- 

 viously thoroughly mixed. The temperature of —10° was obtained by 

 cooling down alcohol with ice and salt, and that at —23° by surround- 

 ing the tube with a narrow glass cylinder containing liquid chloride 

 of methyl, which boils constantly at this temperature; this cylinder 

 being again enclosed in a wider one containing a little phosphoric 

 anhydride to prevent moisture from condensing on the sides. 



It was thought interesting to compare the tensions of liquid 

 acetylene with those of the saturated vapour of benzene, being 

 polymeric bodies, although having totally different properties. For 

 this purpose curves were plotted for the two substances, that for the 

 benzene being taken from Regnault's results (" Mem. Acad. Sci., 

 Paris," vol. xxvi, p. 420). They do not, however, run parallel to 

 each other, the benzene having a slower rate of increase at low tem- 

 peratures, but a quicker rate than the acetylene as the temperature 



