Strontia resembles barytes in every circumstance, except that the salts it forms with acids have somewhat different properties; and it will probably be found that potash and soda, barytes and strontia, lime and magnesia, are very nearly and respectively connected. The specific gravity of strontia is about 3.7. One part of strontia requires 162 parts of cold water, but boiling water dissolves it more freely. In cooling, the earth is deposited in thin quadrangular plates, which are often parallelograms: occasionally they adhere and form cubes, containing about 0.68 of water. It is not poisonous; and though it has been tried in medicine, it does not seem to possess any peculiar medicinal powers.

Lime is an earth well known, and has already been particularly noticed (see Calx). We may add here, for the sake of the connection, that its specific gravity is about 2.4, and that it is soluble in 450 times its weight of water. Its neutrals are supposed to be astringent. It combines, in the form of lime water, with the oxides of mercury and lead; but we know not that these compounds have been employed in medicine.

Magnesia was first pointed out as a distinct earth by Dr. Black. Its properties are less strikingly alkaline than the preceding earths, and it does not melt in the strongest heats that can be employed; nor does it become acrid by calcination, though the air which it loses in the fire is rapidly regained on exposure to the atmosphere. If, therefore, the calcined magnesia is not care-iuiiy kept from the air, it soon differs little from the common earth. Its specific gravity is 2.33, and its compounds, with acids, are soluble; yet even with the vegetable acid, the neutral is deliquescent and not pleasing to the taste. The fossils in which it predominates are soft and unctuous to the touch.

Alumine is an earth of the highest importance in medicine, since its sulphat, the common alum, is a very valuable remedy; and the boles, in which it is often a principal ingredient, are useful in sheathing membranes deprived of their mucus. The earth is soft to the touch, and adheres to the tongue, in consequence of absorbing its moisture. Its specific gravity is 2.0. It absorbs water, and is diffusible through it: but alone it is wholly insoluble; and in fire infusible. It unites with alkalis, and many different earths.

Of the remaining earths our account will be necessarily short, as they are useless in medicine.

Yttria appears in the form of a tasteless, white powder. It is insoluble in water, and does not change vegetable blues. It refuses all union with fixed alkalis, but unites with the carbonate of ammonia. With acids it forms salts of a sweetish but somewhat austere taste, and in fire it is unaltered.

Glucina is obtained in white, light masses, adhering strongly to the tongue, unaffected by fire, and insoluble in water. This earth unites with all the alkalis, with acids, and with sulphurated hydrogen.

Zircona appears also as a white powder, soft to the touch, without taste or smell; of a specific gravity equal to 4.3. Though infusible by heat alone, when surrounded by charcoal its particles unite to a flinty hardness. It combines with carbonated alkalis, and is soluble in all the acids, though insoluble in water.

Of agustina, the existence as a distinct earth has been disproved. If Tromsdorf 's experiments may be trusted, though the results have not been supported by other chemists, it resembles alumina, and refuses to unite with all alkalis. It hardens when heated without acquiring any taste, and its salts are tasteless.

Silica is well known by its common appellation, flint. It melts with alkalis, forming the well known and useful compound, glass; but it is insoluble in acids, and wholly useless in medicine. It occurs in vegetable substances; and must consequently admit of such a minute division that we may expect to find it also in the animal fluids. It occurs, we find from late experiments, in the Bath waters; but we have no reason to think that it contributes to their medicinal virtues. Its source is unknown; but if potash is only lime united to hydrogen, as this salt dissolves flint, on the separation of the hydrogen, the latter will necessarily form distinct concretions, in which state we find it. We regret that this system of De Morveau's is not better established, since it elucidates so clearly various facts in mineralogy, many more indeed than we dare hint at. Silica combines with barytes, and, when recently formed, unites with about 1000 parts of its weight of water.

Inflammables. These are sulphur, phosphorus, the various kinds of pitcoal, charcoal, and amber. Of these the two former only are medicinal, and to them we must return; but to preserve the connection we shall give a very short outline of the chemical properties of each.

Sulphur is known to be a yellow substance, brittle, fusible, electric, insoluble in water, of the specific gravity of nearly 2.0. It sublimes at 170°, melts at 185°, burns with a pale blue flame at 300°, and with a bright white flame at 570. It combines with different proportions of oxygen, and occurs in a variety of minerals. particularly metallic ores.

Phosphorus is a concrete oxide, generally prepared from urine or bones, of the consistence of wax, of a reddish colour, which it loses by being kept in the dark. It is soluble in essential, and with some precautions in expressed, oils. When the oil of cloves is employed, a Hash of light follows each time the bottle is opened. Phosphorus in the dark emits a pale light, but at about 100° of Fahrenheit melts and burns with a vivid flame and violent heat. It is brittle under 32°, and its fracture is vitreous and somewhat lamellated. It unites with oxygen, but attracts it only when nitrogen or some other intermede is added. This union would appear to be a mixture, but that phosphorus attracts oxygen from the oxy-muriatic acid. With oxygen, as we have said, the phosphoric acid is produced. The union of phosphorus with oxygen takes place with considerable violence if the ingredients are struck only. Nitrate of silver, or oxygenated muriat of potash, forms, with phosphorus, the most violent fulminating powders, in consequence of percussion only; but even common muriates, with heat, will have the same effect. This is a fact of more importance, as phosphorus has been lately given internally; but great inconveniences have arisen from its exhibition, which seems sometimes to have proved fatal. Its specific gravity is 2.0382, taste acrid, smell alliaceous. It is raised into vapour by a heat of 180°, and boils at 534°.