CHROMIUM, MOLYBDENUM, TUNGSTEN, URANIUM, ETC. 



forming fluorescent yellowish-green salts of the composition U0 2 X 2 , 

 and in this respect uranic trioxide, U0 3 , differs from chromic anhydride, 

 CrO 3 , although the latter is able to give the oxychloride, Cr0 2 Cl 2 . In 

 molybdenum and tungsten, however, we see a clear transition from 

 chromium to uranium. Thus, for example, chromyl chloride, Cr0 2 Cl 2 , 

 is a brown liquid which volatilises without change, and is completely 

 decomposed by water ; molybdenum oxychloride, MoO 2 Cl 2 , is a crys- 

 talline substance of a yellow colour, which is volatile and soluble in 

 water (Blomstrand), like many salts. Tungsten oxychloride, WO 2 C1 2 , 

 stands still nearer to uranyl chloride in its properties ; it forms yellow 

 scales on which water and alkalis act, as they do on many salts (zinc 

 chloride, ferric chloride, aluminium chloride, stannic chloride, &o.), and 

 perfectly corresponds with the difficultly-volatile salt, UO 2 C1 2 (obtained 

 by Peligot by the action of chlorine on igniteil uranium dioxide, UO 2 ), 

 which is also yellow and gives a yellow solution with water, like all the 



an excess of the reagent, and particularly so if the acid carbonates be taken. This is 

 due to the fact that (4) the uranyl salts easily form double salts with the salts of the 

 alkali metals, including the salts of ammonium. Uranium, in the form of these double 

 salts, often gives salts of well-defined crystalline form, although the simple salts are little 

 prone to appear in crystals. Such, for example, are the salts obtained by dissolving potas- 

 sium uranate, K 2 U 2 O 7 , in acids, with the addition of potassium salts of the same acids. 

 Thus, with hydrochloric acid and potassium chloride a well-formed crystalline salt, 

 K 2 (UO S )C1 4 ,2H 2 O, belonging to the monoclinic system, is produced. This salt decom- 

 poses in dissolving in pure water. Among these double salts we may mention the 

 double carbonate with the alkalis, R 4 (UO 2 )(CO S ) 3 (equal to 2R 2 CO 3 + UO 2 CO 3 ) ; the 

 acetates, R(UO 2 )(C i H 3 O v ) 3 for instance, the sodium salt, Na(UO 2 )(OjH 3 O 2 ) 3 , and the 

 potassium salt, K(UO 2 )(C 2 H 3 O 2 ) 5 ,H 2 O; the sulphates, R. 2 (UO 2 )(SO 4 ) 3 ,2H 2 O, &c. In the 

 preceding formula R = K, Na, NH 4 , or R 2 = Mg, Ba, &"c. This property of giving 

 comparatively stable double salts indicates feebly developed basic properties, because 

 double salts are mainly formed by salts of distinctly basic metals (these form, as it were, 

 the basic element of a double salt) and salts of feebly energetic bases (these form the acid 

 element of a double salt), just as the former also give acid salts ; the acid of the acid 

 salts is replaced in the double salts by the salt of the feebly energetic base, which, like 

 water, belongs to the class of intermediate bases. For this reason barium does not 

 give double salts with alkalis as magnesium does, and this is why double salts are 

 more easily formed by potassium than by lithium in the series of the alkali metals. 

 (5) The most remarkable property, proving the feeble energy of uranic oxide as a base, is 

 Been in the fact that when their composition is compared with that of other salts those of 

 oranic oxide, always appear as basic salts. It is well known that a normal salt, R a X 6; 

 corresponds with the oxide R 2 O 3 , where X= Cl, NO 3 , &c.,orX-, = S0 4 , CO 3 , &c. ; but there 

 also exist basic salts of the same type where X = HO or X^ = O. We saw salta of all 

 kinds among the salts of aluminium, chromium, and others. With uranic oxide no salts 

 are known of the types UX 6 (UC1 6 , U(SO 4 ) 3 , alums, &c., are not known), nor even salts, 

 U(HO)iX 4 or UOX 4 , but it always forms salts of the type U(HO) 4 X 2 or UO 2 X 2 . 

 Judging from the fact that nearly all the salts of uranic oxide retain water in crystallising 

 from their solutions, and that this water is difficult to separate from them, it may be 

 thought to be water of hydration. This is seen in part from the fact that the composition 

 of many of the salts of uranic oxide may then be expressed without the presence of water 

 Of crystallisation; for instance, U(HO) 4 K 2 C1 4 (and the salt of NH 4 , U(HO) 4 K 2 (S0 4 ) , 

 U(HO) 4 (C 8 H 3 O 2 ) 2 .. Sodium uranyl acetate however does not contain water. 



