454 PRINCIPLES OF CHEMISTRY 



molecular motion in solid bodies, could the famous Spring have hoped to 

 attain any result by mixing carefully-dried powders of potash, saltpetre and, 

 sodium acetate, in order to produce, by pressure, a chemical reaction between 

 these substances through the interchange of their metals, and have derived, 

 for the conviction of the incredulous, a mixture of two hygroscopic though 

 solid salts sodium nitrate and potassium acetate ? 



In these invisible and apparently chaotic movements', reaching from the 

 stars to the minutest -atoms, there reigns, however, a harmonious order which 

 is commonly mistaken for complete rest, but which is really & consequence 

 of the conservation of that dynamic equilibrium which was first discerned 

 by the genius of Newton, and which has been traced by his successors in the 

 detailed analysis of the particular consequences of the great generalisation, 

 liamely, relative immovability in the midst of universal and active movement. 

 But the unseen world of chemical changes is closely analogous to the 

 visible world of the heavenly bodies, since our atoms form distinct portions 

 of an invisible world, as planets, satellites, and comets form distinct portions 

 of the astronomer's universe ; our atoms may therefore be compared to the 

 solar systems, or to the systems of double or of single stars: for example, 

 ammonia (NH 3 ) may be represented in the simplest manner by supposing 

 the sun, nitrogen, surrounded by its planets of hydrogen ; and common salt 

 (NaCl) may be looked on as a double star formed of sodium and chlorine. 

 Besides, now that the indestructibility of the elements has been acknow- 

 ledged, chemical changed cannot otherwise be explained than as changes of 

 motion, and the production by chemical reactions of galvanic qurrents, of 

 light, of heat, of pressure, or of steam power, demonstrates visibly that the 

 processes of chemical reaction are inevitably connected with enormous though 

 unseen displacements, originating in the movements of atoms in molecules* 

 Astronomers and natural philosophers, in studying the visible motions of the 

 heavenly bodies .and of matter on the earth, have Tinderstood and have esti- 

 mated the valuer of this store of energy. But the chemist has had to pursue 

 a contrary course. Observing in the physical and mechanical phenomena 

 which accompany chemical reactions the quantity of energy manifested by 

 the atoms and molecules, he is constrained to acknowledge that within the 

 molecules there exist atoms in motion, endowed with an energy which, like 

 matter itself, is neither being created nor capable of being destroyed. There- 

 fore, in chemistry, we must seek dynamic equilibrium not only between the 

 molecules, but also in their midst among their component atoms. Many 

 conditions of such equilibrium have been determined, but much remains to be 

 done, and it is not uncommon, even in these days, to find that some chemists 

 forget that there is the possibility of motion in the interior of molecules, and 

 therefore represent them as being in a condition of death-like inactivity; 



Chemical combinations take place with so much ease and rapidity, 

 possess so many special characteristics, and are so numerous, that their sim- 

 plicity and order were for a long time hidden from investigators. Sympathy, 

 relationship, all the caprices or all the fancifulness of human intercourse, 

 seemed to have found complete analogies in chemical combinations, but with 

 this difference, that the characteristics of the material substances such as 

 eilver, for example, or of any other body remain unchanged in every sub- 



