Page:Proceedings of the Royal Society of London Vol 69.djvu/496

476 temperatures, viz., and 25 '2, the values of the constant were calculated at 10, 40, 60, 80, 100, by means of the integrated form of the van't Hoff equation :

1 T- 1 T-

log, K! - log,, R 2 = FT -

the value of q, the heat of reaction, being regarded as constant and equal to - 77 '4 centuple calories:* R is the "gas constant." The error introduced here can scarcely be very large.

Table VI.

Equilibrium constant.

Equilib. constant for 2, calc.

Absol. temp, for 1 observed.

Absol. temp, for 2 observed.

Absol. temp, for t calc. c =0-0114.

Eat-o of temperatures.

-0266

-02R5

8052

379-0

3804

2-1162

'0270

809 -5*

374 -0*

2 -1644

0-0275

0-0275

814-0

368-0

367-5

2-214S

-02SO

818 -0*

362 -0*

2 -2596

0-0285

0-0233

821-5

356 -0

357-3

2 -2988

0290

-0285

826-0

350 -0

351-6

2-3492

0-0295

0292

829-0

344-0

347-9

2 -3828

As can be seen from the above figures, the agreement between the calculated and determined values of the equilibrium constants is exceedingly good, especially when one considers how different the two reactions are in character and also that in one case the equilibrium constant increases, in the other case, diminishes with the temperature.

So far, this is the only case in which I have been able to test the application of the formula R = R' + c (t 1 - to the calculation of equilibrium constants. On account, however, of the analogy existing between the change of the vapour pressure, solubility, and equilibrium constant, with the temperature, it may be confidently expected that when other cases come to be tried, confirmation of the relationship will be obtained.

On account of the practical importance of the above relationships, I have thought it well, in this preliminary note, to publish them in the present empirical form. I hope, however, at a later time, to discuss the question in greater detail, with the help of a larger number of examples, and also to examine the subject from the theoretical stand- point. It may, however, be remarked here, that the whole work has been based on the form of the thermodynamic equation given by

van't Hoff, % eX = ^, an equation which at once shows the ~

Cut

Koeliclien, loc. cit.