# Page:Popular Science Monthly Volume 44.djvu/439

Worlds and Molecules.—In his lectures at Geneva and Lausanne, M. Raoul Pictet presented mechanics as an exact science, comprising chemistry and physics in its domain. The principal phenomenon of physics is astronomy. The laws of sidereal gravitation apply likewise to the smallest bodies on the earth, to infinitely small ones like the molecules, and also to the atoms. Thus we have a unity of matter in which atoms, uniting from molecules, these group themselves into bodies, and these form worlds. The attraction which controls infinitely large bodies may therefore be regarded as similar to that which unites infinitely little ones. If the atoms touched in a molecule, there would be no force capable of separating them. We are, however, acquainted with dilatation and various ways of separating the atoms and augmenting the distance between them. The hypothesis that they touch is, therefore, not admissible. To explain the theory of chemical phenomena, let us suppose a molecule, A, placed somewhere in sidereal space, having a rectilineal motion toward another molecule, B, immovable, and very remote. In its approach to B there will come a moment when A's motion will slacken. Then astronomical phenomena will end and the phenomena special to physics will begin. At last the molecule A will stop; it has become inert, and can not advance further toward B. It is bound by cohesion. If, now, we suppose a pressure to be imposed on A, to bring it down to B, physical phenomena will cease, the resistance of A will diminish with the distance, and finally the molecule will ally itself with B without touching it; then we have chemical phenomena. The force that unites A and B is affinity. M. Pictet supposes that the absolute zero of temperature, when bodies can no longer react upon one another, is found between these last two phases, and his idea is confirmed by experiment. When sulphuric acid with potash is cooled down to ${\displaystyle -}$150º C. (${\displaystyle -}$236º Fahr.), no reaction is apparent. The bodies are no longer able to combine at that temperature, when occurs a complete death of such action. At ${\displaystyle -}$80º C. (${\displaystyle -}$112º Fahr.), potassium remains unattacked in alcohol and water for whole days. A slight warming produces a small reaction; and if the temperature is raised a little more, combination takes place with energy and an explosion is produced.