240 CHEMICAL DISCOVEKY AND INVENTION 



ever, that in view of the complicated chemical constitution of 

 such substances it cannot be regarded as certain whether these 

 are chemical individuals or aggregates of two or more chemical 

 units, especially in view of the commonly recognised tendency 

 to association exhibited in the liquid state by many chemical 

 compounds. There is in fact a gradual mergence of granules 

 into molecules among these minute particles. The subject is 

 comparatively new, and the further study of colloids may lead 

 to still more wonderful results. 



The molecule, however, is not the ultimate limit of subdivision 

 of matter. Molecules are made up of atoms, and as the whole 

 is always greater than the part, atoms are smaller than mole- 

 cules. Spectrum analysis proves that an atom is itself a com- 

 plex structure, and what is the nature of the attraction which 

 binds atoms closely together into molecules and the law of this 

 attraction is at present unknown. The spaces between the atoms 

 in a molecule are doubtless small as compared with the volume 

 of the molecule as a whole. Nevertheless there are strong reasons 

 for believing in the independence and entity of each atom. The 

 capacity for heat of each atom, that is its " specific heat," is, for 

 example, nearly the same, whether the element is in the " free " 

 state or in chemical combination. The facts of stereo-chemistry 

 (see Chapter XII) also afford strong evidence. 



At the end of the nineteenth century every chemist and 

 physicist believed in the permanence of the atom as the funda- 

 mental unit of mass. Since that time it has been shown not only 

 that certain special types of atoms break up spontaneously, but 

 that all atoms under cathodic discharge yield smaller bodies, 

 electrons, which have only about T^oTyth part of the mass of an 

 atom of hydrogen. Attempts to conceive or to express such 

 dimensions are vain and ineffectual. It is calculated that the 

 absolute mass of an electron is 6xlO~ 28 gram and its 

 radius 10~ 14 of a millimetre, but such figures convey no 

 idea to the mind, since dimensions of such an order correspond 

 to nothing within human experience. 



