Uranous chloride

In 1823 J. A. Arfwedson reduced the green oxide of uranium (then believed to be the lowest oxide) with hydrogen, and obtained a brown powder which he took to be the metal, but which is now known to be uranous oxide, U02 (25, 30). In 1841 Peligot, on analyzing anhydrous uranous chloride, UC14, found that 100 parts of this chloride apparently yielded about 110 parts of its elements uranium and chlorine. His explanation of this seemingly impossible result was that the uranous chloride reacts with water in the following manner ... 

Uranium Arsenide, U3As4, may be obtained i by passing hydrogen over a fused mixture of sodium uranous chloride and sodium arsenide. It is a greyish powder which readily burns in the air. Sometimes it is obtained in a pyrophoric condition. An aluminium-containing product results when the aluminothermic process, using an oxide of uranium and arsenious oxide, is employed. The purest arsenide is obtained, in the crystalline form, when a mixture of hydrogen and arsenic vapour is passed over sodium uranium chloride. It is rapidly decomposed by nitric acid. 

Preparation of Uranium.—The isolation of the metal in a state of purity is accomplished only with difficulty. Three methods of procedure have been suggested, namely, (1) by reduction of urano-uranic oxide, (2) by reduction of uranous chloride, and (3) by electrolysis. The best results have been obtained by the first method, which also possesses an advantage in using as the starting material an oxide which is a commercial product. 

Electrolytic Methods.—Moissan obtained the metal by electrolysis of the double sodium uranium chloride in an atmosphere of hydrogen, using carbon electrodes. Feree, by electrolysis of an aqueous solution of uranous chloride, using a mercury cathode, obtained a uranium amalgam, from which he isolated the uranium by distilling off the mercury in vacuo. However, uranium cannot be obtained in any quantity by this means. 

Double Chlorides of the type R2UCI5 (R=Na, K, Li R2=Ca, Sr, Ba) have been obtained by passing uranous chloride vapour over the chloride of the alkali or alkaline earth metal heated to dull redness. The salts, which are green, are hygroscopic, and darken as they absorb moisture from the air. They are unstable, and their solutions oxidise slowly at ordinary temperature and more rapidly when heated. When evaporated in a vacuum over sulphuric acid they decompose, so that the salts cannot be obtained in the crystalline form. 

Uranium Pentachloride, UClg, is formed in small quantity during the preparation of uranous chloride by chlorination of uranium or its oxides, either by heating in a stream of chlorine or of carbon tetrachloride vapour (see p. 294) it forms as a sublimate further from the heated material than the tetrachloride. It exists in two forms ... 

It is formed in solution by oxidising uranous chloride with nitric acid by dissolving uranic oxide in concentrated hydrochloric acid or by adding barium chloride to a concentrated solution of uranyl sulphate until precipitation is complete. Its aqueous solution on evaporation yields the monohydrate, UOaClj.HaO." The solution is unstable at ordinarj temperatures and slowly deposits uranic hydroxide, which after a time partly redissolves. The uranyl chloride may be reduced in solution to black uranous oxide by the action of magnesium or aluminium powder. The densities of aqueous solutions of uranyl chloride have been determined as follows ... 

Uranium Sulphite.—The existence of normal uranous sulphite has not been established. The addition of a saturated solution of an alkali sulphite to uranous chloride solution precipitates a greyish-green basic sulphite of composition UO.SO3.2H2O. When solutions of uranyl salts are treated with sodium bisulphite, a reddish-browm precipitate is produced which dissolves in excess of the reagent by boiling such solutions the above basic sulphite is again precipitated. It is insoluble in water, but dissolves in a solution of sulphurous acid. 

Uranous Phosphide, U3P4, is obtained in the form of a black microcrystalline powder by fusing together sodium uranous chloride and aluminium phosphide at 1000° C. in a stream of hydrogen or... 

All acid uranium phosphate, UH2(P04)2 or UO2.P2O5.H2O, is obtained as a gelatinous 23recipitate when ordinarj " sodium phosphate, or excess of sodium metaphosphate, is added to a solution of uranous chloride. It may be obtained in the crystalline form as UH2(P04)2.oH20. Aloy also describes a uranous chlorophosjihate of composition UH2(P04)2.UCl4 (see p. 295). 

Uranous Antimonide, UgSb4, is not obtained by the ordinary methods used for the arsenide (see p. 332). By fusing a mixture of sodium uranous chloride, antimony, and aluminium Colani obtained a silvery white mass practically free from aluminium. The product resembled the phosphide and arsenide in properties, and produced vivid sparks when projected into the Bunsen flame. 

Uranous Antimonate.—-By the addition of sodium metanti-monate to a solution of uranous chloride, a precipitate, aiiparently uranous metantimonate, is obtained. It is insoluble in acids. 

Uranous Carbonate has not been prepared. The addition of an alkali carbonate to uranous chloride solution causes an evolution of carbon dioxide and precipitates an unstable basic carbonate. 

Fig. 10 Principle of electrolytic reduction of uranyl chloride to uranous chloride...

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