Berzelius is inclined to consider, that the true com position of the acid is 100 selenium, 71.26, 40 33 cxygen, 28.74; and that it contains I atom of selenium, and 2 of oxy gen. If so, the number for selenium is 4.959, that of oxygen being I.
Dr. Thomson, from calculation founded on the for mer of these experiments, infers that the acid is com posed of 100 selenium, 38 oxygen.
The cause of this inherence is owing to a difference entertained with respect to the constittriou of the preci pitate, d by the nitrate of silver. According to Thomson, the equivalent number for selenium is 5.125, that for the 7.125.
Chloride of Selemum.—When selenium is kept in chlorine, the gas is absorbed, the metal becomes hot, and a brown-coloured liquid is formed, which assumes a white colour as the absorption of the gas proceeds. According to Berzelius, the product of this experiment is selenic and muriatic acids. According to Sir H. Davy's doctrine, it is a chloride. When dissolved in water, it forms a transparent colourless acid solution.
When this compound is heated in contact with se lenium, a yellowish fluid is formed, which, when put into water, decomposes it, and generates muriatic and selenic acids, and deposits selenium. It is probable that this is another compound of selenium and chlo rine, containing less chlorine. If so, it is the proto chloride, and the former is the perchloride of the metal.
Seleniuretted Hydrogen.—Selenium combines with hydrogen, and forms a gaseous fluid, called seleniuret ted hydrogen, which is procured by adding muriatic acid to the compound called seleniuret of potassa. It is absorbed by water, forming a transparent colourless solution, having a hepatic taste, and which stains the skin red, and reddens litmus. The solution, after be ing kept for some time, becomes turbid, front the de position of selenium. NVhen exposed to the air, the seleniuretted hydrogen is decomposed. The same takes place when the gas is brought in contact with a moist body, and what is remarkable, the selenium pe netrates the substance, if porous, and communicates to it a red colour.
Nitric acid causes no change oil the solution of sele niuretted hydrogen in water.
The solution, when added to the metallic salts, throws down precipitates from them, which are in ge neral black or brown. Those from a salt of zinc, man
ganese, and cerium, are however of a red colour. The former are considered seleniurets, the latter hydro seleniurets, and according to Berzelius, when exposed to the air, are converted into seleniurets of the oxide of the metals.
Seleniuretted hydrogen produces remarkable effects on the organs of respiration. When admitted into the nostrils, it excites a painful sensation, and destroys completely for several hours the sense of smell, follow ed by severe catarrh, deep pain of the chest, and ex pectoration of mucus, having the taste of the vapour of corrosive sublimate.
These effects are produced by a very minute quan tity of the gas. Berzelius supposes that the seleniu retted hydrogen is decomposed by the moisture, and that the selenium adheres to the membrane of the nos trils and trachea. The eyes are likewise affected with inflammation when exposed to this gas.
Scleniuretted hydrogen, according to the experiments of Berzelius, is composed of 97.4 selenium, 2.6 hydrogen.
This compound of selenium may be considered analogous to sulphutetted hydrogen.
No compound of selenium and carbon has yet been formed, though from some experiments, it is conjectured that these do unite.
Phoathuret of Selenium is formed, when selenium and phosphorus are heated together. The compound is fusiblt, and is of a dark colour, having a vitreous Fracture. When digested in water, it decomposes this fluid; seleniuretted hydrogen is formed, and selenium is deposited.
Szilithuret of selenium may be procured by passing a stream of sulphuretted hydrogen through a solution of selenic acid, and then adding a few drops of muriatic acid, by which the sulphuret of selenium is precipitated of an orange colour. This compound is very fusible, passing into the liquid state at a temperature a little below that of boiling water. By the application of a stronger heat it volatilizes, and again condenses of an orange colour. Sulphuret of selenium, when heated in the air, burns, and emits the odour of sulphurous acid and of horse-raddish. When exposed to heat with selenic acid, it is decomposed, and the sulphur combines with the oxygen.