FLUORINE.
In many parts of England, especially in Devonshire, Cornwall, and above all in Derbyshire, is found a very beautiful mineral, known by the name of Fluor Spar, Derbyshire Spar, and called by the miners Blue John, to distinguish it from another mineral found, in the same locality, called Black Jack. It occurs in very regular and frequently large crystals in the form of cubes, and occasionally in octoëdra. It is a compound of calcium with fluorine, and is very abundant in certain fossil bones. This element, in combination with hydrogen and called hydrofluoric acid, acts so energetically upon all substances containing silica, that it cannot be preserved in vessels of glass or porcelain—very few of the metals are capable of resisting its action, lead being nearly the only common metal possessed of this power. Gutta percha may also be employed for vessels to hold it.
This property of dissolving silica, has caused this acid to be used for engraving on glass.
EXPERIMENT.
Mix one part of powdered fluor-spar, quite pure, with two parts of oil of vitriol, in a saucer, and apply a gentle heat, when the acid will be disengaged in the form of vapour. Prepare a piece of glass after the manner of engraving on copper, by coating it with a thin covering of wax, placing a paper over the wax, and then drawing any design with a sharp-pointed instrument, when, on removing the paper, the wax-coating will be found to be removed wherever the instrument has passed over it. Now invert, this glass over the fumes of the acid for half an hour or so, and then heat the glass so as to soften the coating, and wipe it off; the design will then appear “bitten in” as the term is, that is, the acid will have dissolved the glass wherever it was not protected by the wax, and will exhibit the design indelibly fixed on the glass.
This acid requires the greatest care in handling, for it is extremely corrosive, producing very troublesome ulcers if it comes in contact with the skin; even the fumes will produce smarting if the skin is long exposed to them.
CARBON.
The next substance in our list of elementary bodies is named carbon.
The purest form of carbon is the precious stone called diamond, which consists entirely of carbon in a crystallized form. The French chemist Lavoisier was the first who proved the combustibility of the diamond; and Sir H. Davy found that when once set on fire it would continue to burn in oxygen gas air, and that the product of the combustion was carbonic acid gas, exactly equal in quantity to the gas produced by burning an equal weight of pure charcoal, the most common form of carbon.