458 
MR. T. H. LABY ON THE SUPERSATURATION AND 
This formula has been used to find y as shown in the following table. In the 
calculations, as air is one of the component gases, 
p" = 0-00130 gm./c.c., y" = D404, p = \ molecular wgt. x 0-00009 gm./c.c., 
p = [tt x p'+ (760 — 77i)p"]/760, 
where tt 1 has the values given in the table on p. 460, have been used. 
y for Air Saturated with a Vapour. 
Vapour. 
/ 
7- 
Observed for 
vapour. 
7- 
Calculated by 
formula. 
S. 
S x if 
y = 1-404. 
Acetic acid .... 
1-147 
1-395 
9-3 
9-6 
Methyl alcohol . 
1-256 
1-382 
3-1 
3-4 
Ethyl alcohol 
1133 
1 • 367 
2-3 
2-6 
Chloroform .... 
1-11 
1-264 
3 
— 
Water. 
1-307 
1-401 
4-15 
4-19 
The supersaturation Sj in the last column is that obtained when y = 1‘404 is used 
in calculating it. The above values of y are from Landolt, Bornstein, and Meyer- 
hoefer’s tables, and y could not be found for any of the other vapours used in these 
experiments. Assuming y is not less than 1T # for propionic to iso-valeric acids and 
propyl to iso-amyl alcohols, it can be shown that Sj for these substances would have 
closely the values (S) given in the table on p. 460. For the esters S x would be in the 
same ratio as the values of S given, but would be smaller. For formic y' = 1‘27 has 
been assumed ;f it gives Sj = 25T, while, if y = 1’404 is used, S = 26T.| 
The values for the least expansion for condensation in the case of the alcohols are 
those of Przibram (except the value IT 82 for iso-amyl alcohol, which is the writer’s), 
who used both radium and Rontgen rays as ionising agents. Though he does not 
explicitly state what ionising agent was used to obtain these particular values, it 
would appear the rays from radium were used in the case of ethyl, propyl, iso-butyl, 
and iso-amyl alcohols. 
* ■/' for iso-butane with 14 atoms in the molecule is 1 • 108. 
t y’ for penta atomic CH 4 is 1 • 27. 
1 I admit that this application of Richarz’ formula is open to criticism. Previously the presence of the 
vapour has not been taken into account at all. The calculations I give are intended to show that the 
values for S are not greatly altered when the presence of the vapour is taken into account. The paucity of 
data (such as the value of y, and the association constant) for the vapours used in these experiments makes 
a satisfactory treatment impossible. It is trusted that the calculations given are not without value. 
