EQUATION AND THE NATURE OF COHESION. 37 



8. Acetylene. C%H 2 . 



(a), a = 2.03 RT c V r \\ .03 -- P V C 2 . P c =01.0; d c = 0.2300; 

 7' c =30S.5; V c = 112.72; M= 26. (Cardoso an. i 

 Baume) a == 4.91 X 10 12 



(/,). a = 6.5 L\V 2 , a = 5.16 X 10 2 



The mean of these two is 5.04 X 10 12 . Van Laar gives the 

 value of 4.35 X 10 12 which is probably many per cent too low. 

 If there are 10 valences in the molecule we compute by the for- 

 mula a = 1.1763 X 10 u (i/X Valf\ which is the easiest way 

 of making the computation from the gravitational attraction and the 

 number of valences 4.79 X I0 12 which is somewhat lower than either 

 of these values but which agrees better with them than does van 

 Laar's. If acetylene were acetylidene one carbon being bivalent, 

 then there would be 8 valences and a still lower value would be 

 found. If there were 11 valences to the molecule a would be 

 computed as 5.11 X 10 12 which agrees better with the found value. 

 I have not been able to find the surface tension or latent heat of 

 liquid acetylene to make the computation from them. 



9. Ethylene. C 2 H±. 



{a), a = 2.03 RT c Vj\M — P C F C 2 . T c = 282.5 ; P c = 50.05 

 (Cardoso and Arni). M = 28 ; V c = 133.3; d e = 0.21 

 (Cailletet and Mathias). S= 3.43. . . . a = 5.26 X 10' 2 



(b). a=(J. r oP i ,F c 2 a = 5.93 X I0 12 



The mean of these two values is 5.59 X 10 12 . It think it pro- 

 bable from the low value of S and the lack of agreement of these 

 two computations that perhaps the critical density should be a little 

 higher. De war gives 0.32 for d c , but this is obviously too high 

 since it makes S over 4. The value 5.59 agrees very well with 

 that computed from the valences and molecular weight. Taking 12 

 valences to the molecule a is computed to be 5.69 X 10 12 - Van 

 Laar's value is 4.44 X 10 12 . This is again as usual too low being 

 in fact over 20 °/ too low. I could not find data for the surface 

 tension and latent heat calculations. 



10. Ethane. CJI & . 



(ft). «=2.03 UT c V r l\m--P c V?. 1\ = 48.85; T c = 305.1 

 (Cardoso and Belt,). I could not find the critical density 

 of ethane, so I have assumed S to be 3.55. This gives 

 V c = 144.35. With these values a = 6.19 X 10 12 



(6). a=G.bP c F c 2 a = 6.71X10 12 



