1890 - 91 .] Prof. Tait on Isothermals of Ethyl Oxide . 
267 
lower than the critical range, I assumed 3-5 as an inferior critical 
volume, and obtained 
jp=27-2^1 
(v- 3-5) 3 \ 
v 2 (v - 1-5)/ ’ 
As will he seen by the numbers in column C above, which are 
calculated from them, these formulae represent the experimental 
results very closely : — but I am not quite satisfied with the first of 
them, because the value (3), which it assigns to a, seems to he too 
large in comparison with v. But, on the other hand, if we much 
reduce this value of a, the closeness of representation of dp/dt is 
much impaired. Again, the value ( — 1*5) which is assigned for a 
in the second of these formulae is inconsistent with the fact that at 
0° C and 1 atm. the volume of one gramme is 1*4 e.c. nearly. But 
a very small change of a will entirely remove this objection, and 
will not perceptibly impair the agreement of the formula with 
experiment. 
The general formula is applicable to temperatures considerably 
under that of the critical point, for volumes greater than 4. In fact 
Drs Ramsay and Young seem to assert that at any constant volume 
p is a linear function of t. But I think even their own experiments 
show that, for v< 4, there is diminution of the value of dpjdt as soon 
as the temperature falls below the critical value : — i.e., as soon as we 
begin to deal with liquid alone. And certainly such is the result 
which theory would lead us to expect. 
[It is curious to note that if, in my general formulae (Trans. 
R.S.E., xxxvi. p. 265), we assume 
we have 
a = y, 
A-C eC 
v + y (y + y) 2 3 
and this leads to 
p=p ( 1 
with the condition 
(v - v ) 3 
v(y + y) ! 
)+ E ( 1 + dq) 
t-t 
3v + 2y = R t/p. 
This formula differs by want of one disposable constant from (C) 
of the paper referred to, but approximates much more closely to it 
than does either (A) or (B).] 
