_Silicon._--The reaction between fluorine and silicon is one of the most beautiful of all these extraordinary manifestations of chemical activity. The cold crystals become immediately white-hot, and the silicon burns with a very hot flame, scattering showers of star-like, white-hot particles in all directions. If the action is stopped before all the silicon is consumed, the residue is found to be fused. As crystalline silicon only melts at a temperature superior to 1,200 deg., the heat evolved must be very great. If the reaction is performed in the fluorspar tube, the resulting gaseous silicon tetrafluoride, SiF_{4}, may be collected over mercury. Amorphous silicon likewise burns with great energy in fluorine. ACTION OF FLUORINE UPON METALS. _Sodium_ and _potassium_ combine with fluorine with great vigor at ordinary temperatures, becoming incandescent, and forming their respective fluorides, which may be obtained crystallized from water in cubes. Metallic _calcium_ also burns in fluorine gas, forming the fused fluoride, and occasionally minute crystals of fluorspar. _Thallium_ is rapidly converted to fluoride at ordinary temperatures, the temperature rising until the metal melts and finally becomes red hot. Powdered _magnesium_ burns with great brilliancy. _Iron_, reduced by hydrogen, combines in the cold with immediate incandescence, and formation of an anhydrous, readily soluble, white fluoride. _Aluminum_, on heating to low redness, gives a very beautiful luminosity, as do also _chromium_ and _manganese_. The combustion of slightly warmed zinc in fluorine is particularly pretty as an experiment, the flame being of a most dazzling whiteness. _Antimony_ takes fire at the ordinary temperature, and forms a solid white fluoride. _Lead_ and _mercury_ are attacked in the cold, as previously described, the latter with great rapidity. _Copper_ reacts at low redness, but in a strangely feeble manner, and the white fumes formed appear to combine with a further quantity of fluorine to form a perfluoride. The main product is a volatile white fluoride. _Silver_ is only slowly attacked in the cold. When heated, however, to 100 deg., the metal commences to be covered with a yellow coat of anhydrous fluoride, and on heating to low redness combination occurs, with incandescence, and the resulting fluoride becomes fused, and afterward presents a satin-like aspect. _Gold_ becomes converted into a yellow deliquescent volatile fluoride when heated to low redness, and at a slightly higher temperature the fluoride is dissociated into metallic gold and fluorine gas.