302 PRINCIPLES OF CHEMISTRY 



metallic uranium as a grey metal, having a specific gravity of 187, and 

 liberating hydrogen from acids, with the formation of green urarious 

 salts, UX 4 , which act as powerful reducing agents. 14 



rated. The solution of uranous chloride in water is green. It is also formed by the 

 action of zinc and copper (forming cuprous chloride) on a solution of uranyl chloride, 

 UO.^Cli, especially in the presence of hydrochloric acid and sal-ammoniac. Solutions of 

 uranyl salts are converted into uranous salts by the action of various reducing agents, 

 and among others by organic substances or by the action of light, whilst the salts UX 4 

 are converted into uranyl salts, UO 2 X^, by exposure to air or by oxidising agents. Solu- 

 tions of the green uranyl salts act as powerful reducing agents, and give a brown precii 

 pitate of the uranous hydroxide, UH 4 O 4 , with potash and other alkalis. This hydroxide 

 is easily soluble in acids but not in alkalis On ignition it does not form the oxide UO 2l 

 because it decomposes water, but when the higher oxides of uranium are ignited in a 

 stream of hydrogen or with charcoal they yield uranous oxide. Both it and the chloride 

 UC1 4 dissolve in strong sulphuric acid, forming a green salt, U(SO 4 )o,2H 2 O. The same 

 salt, together with uranyl sulphate, UO^SO.^, is formed when the green oxide, U 5 O 8 , is 

 dissolved in hot sulphuric acid. The salts obtained in the latter instance may be 

 separated by adding alcohol to the solution, which is left exposed to the light ; the alcohol 

 reduces the uranyl salt to uranous salt, an excess of acid being required. An excess of 

 water decomposes this salt, forming a basic salt, which is also easily produced under 

 .other circumstances, and contains UO(SO 4 ),2H 2 O (which corresponds to the uranic salt). 



14 The atomic weight of uranium was formerly taken as half the present one, U = 120, 

 And the oxides U 2 O 3 , suboxide UO, and green oxide U 3 O 4 , were of the same types as the 

 oxides of iron. With a certain resemblance to the elements of the iron group, uranium 

 presents many points of distinction which do not permit its being grouped with them. 

 Thus uranium forms a very stable oxide, 17.^05(11 = 120), but does not give the corre- 

 sponding chloride U 8 C1 6 (Roscoe, however, in 1874 obtained UC1 5 , like MoCl 3 and WC1 5 ), 

 and under those circumstances (the ignition of oxide of uranium mixed with charcoal, in 

 a~stream of chlorine), when the formation of this.compound might be expected, it gives 

 XU = 120) the chloride UClj, which is characterised by its volatility; this is not a pro- 

 perty, to such an extent, of any of the bichlorides, RC1 8 , of the iron group. 



The alteration or doubling of the atomic weight of uranium i.e. the recognition of 

 U = 240 was made for the first time in the first (Russian) edition of this work (1871), and 

 in my memoir of the same year in Liebig'a Annalen, on the ground that with an atomic 

 weight 1'20, uranium could not be placed in the periodic system. I think it will not be super- 

 fluous to add the following remarks on this subject : (1) In the other groups (K Rb Cs, 

 Ca Sr Ba, Cl Br I) the acid character of the.oxides decreasesand their basic charac- 

 ter increases with the rise of atomic weight, and therefore we should expect to find the 

 same in the group Cr Mo W U, and if CrO 3 , Mo0 3 , W0 3 be the anhydrides of acids 

 then we indeed find a decrease in their acid character, and therefore uranium trioxide, 

 JJO 3 , should be a very feeble anhydride, but its basic properties should also be very 

 feeble. Uranic oxide does indeed show these properties, as was pointed out. above (Note 

 10). (2) Chromium and its analogues, besides the oxides RO 3 , also form lower grades of 

 oxidation RO 2 , R%Qz> and the same. is seen in uranium; it forms U0 3 , UO 2 , U^O.-, and 

 their compounds. (3) Molybdenum and tungsten, in being reduced from RO- >( easily and 

 frequently give an intermediate oxide of a blue colour, and uranium shows the same 

 property ; giving the so-called green oxide which, according to present views, must 

 be regarded as U 3 O 6 = UO 2 2y0 3 , analogous to Mo 3 O 8 . (4) The higher chlorides, RCl d , 

 possible for the elements of this group, are either unstable (WC1J or do not exist at all 

 {Cr) ; but there is one single lower volatile compound, which is decomposed, by water, 

 and liable to further reduction into a non-volatile chlorine product and the metal. The 

 same is observed in uranium, which forms an easily volatile chloride, UC1 4 , decomposed 

 by water. (5) The high sp. gr. of uranium (18'6) is explained by its analogy to tungsten 

 <i(sp. gr, 19'1). (6) For uranium, as fox chromium and tungsten, yellow tints pre- 



