512 
PROFESSOR J. J. THOMSON ON SOME APPLICATIONS OF 
therefore the existence of surface-tension diminishes the value of that is, it 
diminishes the precipitation. In the case mentioned above it seems to have been 
able to stop the precipitation altogether. The effects of surface-tension will be most 
noticeable when the heat developed by the chemical action is small. Some other 
effects produced by surface-tension on chemical action are considered in a paper read 
before the Cambridge Philosophical Society, February 1887, by Professor Liveixg-. 
Surface-tension will also affect the equilibrium when chemical combination produces 
a change in volume, even though the surface remains unaltered. 
Effects of Pressure. 
§ 17. If Q be the volume, p the pressure, k the coefficient of compressibility of the 
solution, then, just as in the case of solution, we have 
cl. Sco _ dQ cl /Qp 2 \ 
d% ~ ' p d% + ¥ d%\ k ) 
(65) 
Thus pressure produces two effects, the one being proportional to the pressure, the 
other to the square of it. 
If the volume increases as chemical combination goes on, external pressure will tend 
to stop the combination ; and, vice versa, the change in the coefficient of reaction due 
to this case is given by the equation 
or, approximately, 
Sco 
1 + 
p ic6d£ 
CO 
Sco 
1 
dQ 
CO 
k ~e p 
df 
( 66 ) 
If the coefficient of compressibility increases as chemical action goes on, external 
pressure will tend to facilitate the combination, and the change in the coefficient of the 
reaction due to this cause is 
Sco _ j 1 d / Qp 2 \ 
"co ~ ¥ K dd%\ff) ' 
(67) 
Horstmann’s Experiments on the Division of Oxygen between Carbonic Oxide and 
Hydrogen. 
§ 18. We shall now proceed to apply the Hamiltonian principle to this case, which is 
more complicated than any of the preceding. In these experiments hydrogen, carbonic 
oxide, and oxygen were mixed together and exploded, and the proportion of hydrogen, 
oxygen, carbonic oxide, carbonic acid, and water in the mixture after the explosion 
determined. 
