| Alumina | 55.4% |
| Silica | 32.6 |
| Fluorine | 20.6 |
| ——— | |
| 108.6 |
The oxygen equivalent to 20.6 per cent. fluorine may be found by multiplying the percentage of fluorine by 0.421; it is 8.7 per cent., and must be deducted. The analysis would then be reported thus:—
| Alumina | 55.4% |
| Silica | 32.6 |
| Fluorine | 20.6 |
| ——— | |
| 108.6 | |
| Less oxygen equivalent to fluorine | 8.7 |
| ——— | |
| 99.9 |
Take as an illustration the following actual analysis by F.W. Clarke and J.S. Diller:—
| Alumina | 57.38% |
| Silica | 31.92 |
| Fluorine | 16.99 |
| Potash | 0.15 |
| Soda | 1.33 |
| Water | 0.20 |
| ——— | |
| 107.97 | |
| Deduct oxygen equivalent | 7.16 |
| ——— | |
| 100.81 |
In calculating the factor for the "oxygen equivalent," divide the weight of one atom of oxygen (16) by the weight of two atoms of the halogen; for example, with chlorine it would be 16/71 or 0.2253; with bromine, 16/160 or 0.1000; with iodine, 16/254 or 0.063; and with fluorine, 16/38 or 0.421.
CHLORINE AND CHLORIDES.
Chlorine occurs in nature chiefly combined with sodium, as halite or rock salt (NaCl). With potassium it forms sylvine (KCl), and, together with magnesium, carnallite (KCl.MgCl2.6H2O). Of the metalliferous minerals containing chlorine, kerargyrite, or horn silver (AgCl), and atacamite, an oxychloride of copper (CuCl2.3Cu(HO)2.) are the most important. Apatite (phosphate of lime) and pyromorphite (phosphate of lead) contain a considerable amount of it. Chlorine is a gas of a greenish colour, possessing a characteristic odour, and moderately soluble in water. It does not occur native, and is generally prepared by the action of an oxidising agent on hydrochloric acid. It combines directly with metals at the ordinary temperature (even with platinum and gold), forming chlorides, which (except in the case of silver) are soluble.
It is important in metallurgy, because of the extensive use of it in extracting gold by "chloridising" processes. It is also used in refining gold.
Detection.—Compounds containing the oxides of chlorine are not found in nature, because of the readiness with which they lose oxygen. By reduction they yield a chloride; the form in which chlorine is met with in minerals. In testing, the compound supposed to contain a chloride is boiled with water, or, in some cases, dilute nitric acid. To the clear solution containing nitric acid a few drops of nitrate of silver solution are added. If, on shaking, a white curdy precipitate, soluble in ammonia, separates out, it is sufficiently satisfactory evidence of the presence of chlorides.