to yield distinct crystals of chrysoberyl. It is probable that in Nature the formation of gem-stones has occurred in the presence of water, and under very great pressure continued for a long time. Indeed, it may be concluded that the agency of a very high temperature has not been generally at work, but that the important elements in the production of natural crystals have been time, mass, and pressure.
Chemists have devoted much time and skill to devising methods for producing diamonds. These methods have rarely been successful, but M. Henri Moissan has really made a number of small—very small—diamonds by causing carbon to dissolve in molten iron at the high temperature of the electric furnace and then, by sudden cooling of the metallic mass, causing the formation of a rigid shell and so producing great pressure in the interior: the iron mass treated with acid left a residue containing small diamond crystals: by slow cooling graphite only was formed.