98 . THE DOCTRINE OF PART i. 



water weighing ten pounds, an energy is expended, the 

 atoms clash together with a force, equal to that of a ton 

 weight let fall from a height of 23,757 feet ; and in the 

 change from the state of vapour to water, an energy is 

 exerted equal to that of a ton weight falling from a 

 height of 3,700 feet, or of a hundredweight falling from 

 a height of 74,000 feet. The moving force of the stone 

 avalanches of the Alps is but as that of snowflakes 

 compared with the energy involved in the formation of 

 a cloud. In passing finally from the liquid to the solid 

 state,' that is from water to ice, 'the atoms of ten 

 pounds exercise an energy equal to that of a ton weight 

 falling down a precipice of 550 feet of perpendicular 

 height.' 



From Mr. Joule's investigation of the relation existing 

 between chemical affinity and mechanical force, it ap- 

 pears that when affinity is feeble it can be overcome 

 mechanically. He formed amalgams of different metals, 

 that is he combined them with mercury, by electricity. 

 The affinity of iron for mercury is so feeble that the 

 amalgam is speedily decomposed when left undisturbed 

 by the pressure of the atmosphere, and if a greater 

 pressure be added, almost all the mercury is driven out. 

 The efficacy of mechanical force to overcome feeble 

 chemical affinities is strikingly illustrated by the amal- 

 gam of tin, out of which nearly the whole of the mercury 

 is driven by long continued pressure. In these cases 

 the force of affinity did not amount to chemical equiva- 

 lency, otherwise the mercury could not have been driven 

 out by so small a force. Instances from the weakest to 

 the strongest affinity show that it is only when the 

 power reaches a definite point that the law of chemical 

 equivalents comes in. The intense energy which then 

 begins to be exerted has just been shown. 



It is vain to hope for a knowledge of the absolute 

 weight of the ultimate atoms of matter, and nothing 



