548 [April 30, 



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 

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

 mical action is equivalent to the expenditure of that amount of 

 mechanical force, being thus generated by it. Arguing then in a 

 manner similar to that already described, but modified to suit the 

 different conditions, if there be a contraction equal to 8 per cent, of 

 the bulk of the calcite, there must be a loss of mechanical force 

 capable of raising 28 times the weight of the calcite altered to the 

 height of 1 metre, in the time required for the chemical change ; 

 which amount of mechanical energy, as it were, becomes latent, and 

 is transformed into chemical action, and would again exhibit itself 

 as a mechanical force if, by any means, the chemical affinities could 

 be inverted and everything restored to its original state. 



In a like manner, other experiments indicate that in some cases 



