Bromine is a very heavy fluid, which should be preserved by keeping it in a bottle covered with water; when required, a few drops may be removed by means of a small tube, and dropped into a warm bottle, which is quickly filled with the orange-red vapour. If some phosphorus is placed in a deflagrating spoon, and exposed to the action of bromine vapour, it takes fire spontaneously. _Second Experiment._ Powdered antimony sprinkled into the vapour of bromine immediately takes fire. _Third Experiment._ A burning taper immersed in a bottle containing the vapour of bromine is gradually extinguished. _Fourth Experiment._ Liquid bromine exposed to a freezing mixture of ice and salt, or reduced to a temperature of about eight degrees below zero, solidifies into a yellowish-brown, brittle, crystalline mass. _Fifth Experiment._ A solution of indigo shaken with a small quantity of the vapour of bromine is quickly bleached. Many substances, when brought in contact with liquid bromine, combine with explosive violence, and therefore experiments with liquid bromine are not recommended, as all the most instructive and conclusive results can be obtained by the use of the vapour of bromine, which is easily procured by allowing a few drops to fall into a warm, dry bottle. Bromine, as already mentioned, is used in the art of photography. FLUORINE. Symbol, F. Combining proportion, 19. This singular element seems almost to embody the ancient idea of the alchemists, being a sort of _alkahest_, or universal solvent; or in plainer language, its affinities for other bodies are so powerful, that it attacks every substance (not even excepting gold), at the moment of its liberation, and combines therewith, so that its isolation has not yet been effected. Chemists who assert that they have been able to obtain fluorine in the elementary condition, pronounce it to be a gas which possesses the colour of chlorine; but the experiments, as hitherto conducted, render that statement extremely doubtful. [Page 151] The only interesting fact connected with fluorine, is the remarkable property of attacking glass and other silicious bodies, belonging to its combination with hydrogen gas, called hydrofluoric acid. This acid is easily obtained and used by placing some powdered fluorspar in a leaden tray six inches square and two inches deep. If sulphuric acid is now mixed with the powdered spar, so as to form a thin paste, and heat applied, the vapour of the hydrofluoric acid quickly rises, and can be employed to etch a glass plate upon which a drawing may have been previously traced by scratching away the wax, with which it is first coated. By heating the glass plate before a fire, a sufficient quantity of wax is soon melted on to it by merely rubbing the wax against the glass plate; any excess should be avoided, if a well-executed drawing is required to be etched on its surface. (Fig. 144.)