SPECIFIC HEATS OF SOME COMPOUND GASES. 577 
§7. Ethylene (C,H,). 
For the material I was indebted to the kindness of Professor DEwaAR, who gave me 
a cylinder of compressed ethylene. As the critical temperature of ethylene is near 
the ordinary atmospheric temperature, the bottle was placed in a freezing mixture to 
ensure the contents being liquefied, and so to keep back by fractional distillation any 
ether and water that had escaped the preliminary washing and drying of the gas. 
AMAGAT’S experiments on the compressibility of ethylene enable us to calculate 
the correction due to deviation from Bovis Law. Since, however, the lowest 
pressure used by AMAGAT was 30 atmospheres, the correction term must be put in a 
slightly different form. Using VAN DER WAALS’ equation 
(p + a/v’) (v — b) = Rt 
to express the relation between jp, v, and ¢, it is easily shown that the correction term 
takes the form 1 + a/pv? — b/v. 
Baynes has calculated VAN DER WAALS’ constants from AMAGAT’s observations, 
and finds (‘ Nature, vol. 22, p. 186) a =-00786, b = ‘0024. Hence since in my 
experiments p = 1 and v = 288/273, we get the correction 1:007. 
Two determinations of the velocity of sound at atmospheric pressure gave the 
following results, the theoretical value of the density of the gas being used in the 
calculation of y. 
TABLE XIV. 









| ld 
t. 1. } eZ Dp. 1 ——— . vee . 
| as f ar Aan pe 1 B 
| | 
| 15°4 | 46°32 48:51 9675 1-007 ° 1-251 
15 46°32 48°54. | i: ae 1-249 
Mean 1 1:250 1:740 
| | | 



§ 8. Vinyl Bromide (C,H,Br). 
The material was made by gently warming ethylene dibromide with alcoholic 
potash. The issuing gas was condensed, fractionated, allowed to stand over calcium 
chloride, and again fractionated. 
Four weighed tubes to contain the liquid for vapour-density determinations were 
filled in a freezing mixture, but on coming to the temperature of the room two burst, 
so that only two were left for use. These gave the following results :— 
MDCCCXCV.—A. 4 E 
