152 Royal Society : — 



the force of chemical affinity. If then one cubic inch had been altered 

 under this pressure, it would have overcome a mechanical force equal 

 to that required to raise 1200 lbs. through the space of -107 inch, 

 which is equivalent to raising twenty-one times its own weight to the 

 height of 1 metre; and under the same circumstances 1*278 cubic 

 inch would have been altered when no such mechanical force had 

 to be overcome. Supposing then that in both cases the total energy 

 at work was the same, but in one was altogether expended in pro- 

 ducing a chemical result, and in the other in producing partly a 

 chemical and partly a mechanical effect, we may say that the force 

 which gives rise to the purely chemical change, taking place at a 

 particular rate, is equal to that which gives rise to this chemical 

 effect, taking place at '783 of that rate, and to a mechanical 

 effect equal to the force required to raise in the same space 

 of time 34*87 times the weight of the Witherite altered to the 

 height of 1 metre. Supposing also that the power of chemical 

 force varies as the rate at which it gives rise to a chemical change, in 

 the same manner as the power of a mechanical force varies as the 

 velocity of motion imparted by it, we may perhaps conclude that this 

 mechanical force is equal to *21 7 of the chemical force, and that the 

 whole energy of the chemical action under the conditions of the ex- 

 periment was equal to the mechanical power required to raise in the 

 same period of time 160 times the weight of the Witherite altered to 

 the height of 1 metre. If these principles are correct, a pressure 

 of more than 370 atmospheres would have entirely counterbalanced 

 the force of chemical affinity, since to produce any chemical change 

 it would then have had to overcome a greater force than it possessed. 

 This is so great a pressure that I fear it will be difficult to prove 

 the deduction by experiment ; and until some such case can be 

 found, capable of being verified, these calculations must be considered 

 as little more than suggestions, which future investigations may con- 

 firm or disprove. 



When calcite is sealed up in a mixed and rather strong solution of 

 chloride of sodium and sulphate of copper, slow double decomposi- 

 tion gives rise to malachite, sulphate of lime, and carbonic acid ; and 

 though this case is extremely complicated, and it is very difficult to 

 determine what would be the change in volume, yet, so far as I am 

 able to make out, until the solution becomes saturated with sulphate 

 of lime, there is a decrease in volume equal to about 8 per cent, of 

 that of the calcite altered, so that, under pressure, mechanical 

 force is the very reverse of being opposed to the chemical change. 

 Three experiments, all indicating the same fact, and in which, on an 

 average, the pressure was about 90 atmospheres for two weeks, show 

 that, as a mean of the whole, the amount of chemical change was 1 7 

 per cent, more with the pressure than without • thus proving that 

 pressure had, as it were, increased the force of chemical affinity. Cal- 

 culating according to the principles described above, we may con- 

 clude that a pressure of 530 atmospheres would have caused the 

 action to take place at double the rate, and that therefore the che- 

 mical action is equivalent to the expenditure of that amount of 



