Below a red heat it enters into a state of fusion; at a high temperature it becomes converted into a yellow vapour. It burns in air, when strongly heated, with a blue flame having a green rim, and giving off white fumes that have a peculiar odour. When taken internally, even in very minute quantities, tellurium imparts to the breath an offensively powerful odour of garlic. Tellurium dissolves
in cold concentrated sulphuric acid, to which it imparts a rich purple-red colour. If the acid solution be diluted with water the tellurium precipitates unchanged. There are two oxides of tellurium: the dioxide (TeO2) and the trioxide (TeO3), the first of which corresponds to sulphurous, and the second to sulphuric anhydride.
Tellurous acid (H2TeO3) is obtained by pouring a solution of tellurium on nitric acid of 1·25 into water, when the tellurous acid is precipitated as a bulky hydrate. This hydrate is slightly soluble in water and reddens litmus. It forms salts called tellurites.
Telluric acid (H2TeO4). When tellurium or tellurous acid is gently heated with nitre a potassic tellurate is formed, this being decomposed by a salt of barium, whilst the resulting barium tellurate is in its turn decomposed, and the telluric acid separated by sulphuric acid. The telluric acid occurs in hexagonal prismatic crystals, which, when heated usually to redness, becoming converted into telluric anhydride, which then assumes an orange-yellow colour. This telluric anhydride (TeO3) is entirely insoluble in water, nitric and hydrochloric acids, and alkaline solutions. Although it has but a feeble attraction for bases, telluric acid forms salts which are called tellurates. There are two chlorides of tellurium: the dichloride (TeCl2) and the tetrachloride (TeCl4). They may both be obtained by the direct action of chlorine on tellurium.
Telluretted hydrogen, or dihydric telluride. (H2Te). This compound presents a striking analogy to seleniuretted and sulphuretted hydrogen. Like both of these it is gaseous, but resembles the latter in smell more than the former. It burns with a blue flame, reddens litmus, and when fused into water forms a colourless solution, which becomes brown by exposure to the air, owing to the oxidation of hydrogen and the deposition of tellurmin. The salts of most of the metals are decomposed when a current of telluretted hydrogen is passed through these solutions, from which the metals are then thrown down as tellurides. These tellurides present a close resemblance to the corresponding sulphides. The tellurides of the alkali metals, like the sulphides, are soluble in water.
Tests. The most distinctive character of tellurium compounds is the reddish-purple solution of potassium telluride they furnish when fused with potassic carbonate and charcoal and treated with water.
TEM′PERATURE. In English pharmacy it is customary to measure the degree of heat by Fahrenheit’s thermometer. When a boiling heat is directed, 212° is meant. A gentle heat is that which is denoted by any degree between 90° and 100° Fahr.
Whenever specific gravity is mentioned, the substance spoken of is supposed to be of the temperature of 62° Fahr. (Ph. L.)
In the B. P., Ph. E., & D., and in chemical
works in this country generally, the specific gravities of bodies are taken at, or referred to, the temperature of 60° Fahr. See Thermometers.