300 PRINCIPLES OP CHEMISTRY 



salts UO 2 X 2 . The property of uranic oxide, U0 3 , of forming salts 

 UO 2 X 2 is shown in the fact that the hydrated oxide of uranium, 

 UO 2 (HO). 2 , which is obtained from the nitrate, carbonate, and other 

 salts by the loss of the elements of the acid, is easily soluble in acids, 

 as well as in the fact that the lower grades of oxidation of uranium are 

 able, when treated with nitric acid, to form an easily crystallisable 

 uranyl nitrate, UO 2 (N0 3 ) 2 ,6H 2 ; this is the most commonly occurring 

 uranium salt. 11 



Uranium, which gives an oxide, UO 3 , and the corresponding salt 

 tT0 2 X 2 and dioxide U0 2 , to which the salts UX 4 correspond, is rarely 

 met with in nature. Uranite or the double orthophosphate of uranio 



11 Uranyl nitrate, or uranium nitrate, UO^NO^jBH^O, crystallises from its solu- 

 tions in transparent yellowish- green prisms (from an acid solution), or in tabular crystals 

 (from a neutral solution), which effloresce in the air and are easily soluble in water, 

 alcohol, and ether, have a sp. gr. of 2'8, and, fuse when heated, losing nitric acid and water 

 in the process. If the salt itself (Berzelius) or its alcoholic solution (Malaguti) be 

 heated up to the temperature at which oxides of nitrogen are evolved, there then remains 

 a mass which, after being evaporated with water, leaves uranyl hydroxide, UO a (HO) 4 

 (sp. gr. 5'93), whilst if the salt be ignited there remains the dioxide, UO^, as a brick-red 

 powder, which on further heating loses Oxygen and forms the dark olive uranoso- uranio 

 oxide, U 3 O 8 . The solution of the nitrate obtained from the ore is purified in the following 

 manner : sulphurous anhydride is first passed through it in order to reduce the arsenic 

 acid present into arsenious acid ; the solution is then heated to 60, and sulphuretted 

 hydrogen passed through it ; this precipitates the lead, arsenic, and tin, and certain 

 other metals, as sulphides, insoluble in water and dilute nitric acid. This liquid is then 

 filtered and evaporated with nitric acid to crystallisation, and the crystals are dissolved 

 in ether. Or else the solution is first treated with chlorine in order to convert the ferrous 

 chloride (produced by the action of the hydrogen sulphide) into ferric chloride, the 

 oxides are then precipitated by ammonia, and the resultant precipitate, containing the 

 oxides Fe 2 O3,UO3, and compounds of the latter with potash, lime, ammonia, and other 

 bases present in the solution (the latter being due to the property of uranic oxide of 

 combining with bases), is washed and dissolved in a strong, slightly-heated solution of 

 ammonium carbonate,,which dissolves the uranic oxide but not the ferric oxide. The 

 solution is filtered, and on cooling deposits a well-crystallising uranyl ammonium car- 

 bonate, U0. 4 (NH 4 ) 4 (CO3)3, in brilliant monoclinic crystals which on exposure to air slowly 

 give off water, carbonic anhydride, and ammonia; the same decomposition is readily 

 effected at 300, the residue then consisting of uranic oxide. This salt is not very soluble 

 in water, but is readily so in ammonium carbonate; it is obvious that it may readily be 

 converte'd into all the other salts of oxides of uranium. Uranium salts are also purified 

 in the form of acetate, which is very sparingly soluble, and is therefore directly precipi- 

 tated from a strong solution of the nitrate by mixing it with acetic acid. 



We may also mention the uranyl phosphate, HUPO 6 , which must be regarded as an 

 orthophosphate in which two hydrogens are replaced by the radicle uranyl, UO.^, i.e. as 

 H(UO 2 )PO 4 . This salt is formed as a hydrated gelatinous yellow precipitate, on mixing 

 a solution of uranyl nitrate with disodium phosphate. The precipitation occurs in the 

 presence of acetic acid, but not in the-presence of hydrocMoric acid. If moreover an 

 excess of an ammonium salt be present, the ammonia enters into the composition of 

 the bright yellow gelatinous precipitate formed, in the proportion UO. 2 NH 4 PO 4 . This 

 precipitate is not soluble in water and acetic acid, and its solution in inorganic acida 

 when boiled entirely expels all the phosphoric acid. This fact is taken advantage of for 

 removing phosphoric acids from solutions for instance, from those containing salts of 

 calcium and magnesium. 



