IRON, COBALT, AND NICKEL 361 



tion, and in general the relation of nickel, it is important to observe 

 that cobalt more easily forms a higher degree of oxidation namely, 



Co 2 2 (S04) 2 . The whole process of oxidation will be as follows : first of all 03X4, a 

 cobaltous salt, is in the solution (X a univalent haloid, 2 molecules of the salt being 

 taken), then Co 2 OX 4 , the basic cobaltic salt (4th series), then Co 2 O 2 X 4 , the salt of the 

 dioxide (2nd series); The series of basic salts with an acid, 2HX, forms water and a 

 normal salt, Co 2 Xe (in -8, 5, 6 series). These salts are combined with various amounts ol 

 water and ammonia. tJnder many conditions the salts .of fuscocobalt are easily trans- 

 formed into salts oi the next series. The salts of the series that has just been described 

 contain 4 molecules of ammonia to 1 atom of cobalt, 



(e) 'The roseocobaltic (or rosepentamine), CoXaBLjOjSNHj, salts, like the luteo- 

 cobaltic, correspond with the normal cobaltic salts, but contain less ammonia, and an 

 extra molecule of water. Thus the. sulphate is obtained from cobaltous sulphate 

 dissolved in ammonia and left exposed to the air until transformed into a brown solution 

 of the fuscocobaltic salt ; when this is treated with sulphuric acid a crystalline powder 

 of the roseocobaltic salt, Co2(S04)3,10NH3,5H 2 O, separates. The formation of this salt 

 is easily understood : cobaltous sulphate in the presence of ammonia absorbs oxygen, and 

 the solution of the fuscocobaltic salt will therefore contain, like cobaltous sulphate, one 

 part of sulphuric acid to every part of cobalt, so that the whole process of formation may 

 be expressed by the equation: 10NH 3 + 2CoSO 4 + H2SO4 + 4H 2 + O = Co2(S0 4 ) 3) iONH 3 , 

 6H 2 O. This salt forms tetragonal crystals of a red colour, slightly soluble in cold, but 

 readily soluble in warm water. Wh6n the sulphate is treated with baryta, roseocobaltio 

 hydroxide is formed in the solution, which absorbs the carbonic anhydride of the air. 

 It is obtained from the next series by the action of alkalis. 



(/) The rosetetramine cobaltic salts CoCl 2 ,2H 2 0,4NH 5 were obtained by Jorgenson, 

 and belong to the type of the luteo-salts, only with the substitution of 2NH 3 for H 2 O. 

 Like the luteo- and roseo-salts they give double salts with PtCl4, similar to the alkaline 

 double salts, for instance (Co2H 2 O,4NH 3 )2(SO 4 )2Cl 2 PtCl4. They are darker in colour 

 than the preceding, but also crystallise well. 'They are formed by dissolving CoC0 3 in 

 sulphuric acid (of a given strength), and after NH 3 and carbonate of ammonium have 

 been added, air is passed through the solution (for oxidation) until the latter turns red. 

 It is then evaporated with lumps of carbonate of ammonium, filtered from the precipi- 

 tate and crystallised. A salt of the composition Co 2 (CO 3 ) 2 (SO 4 ), (2H 2 O,4NH 3 ) 3 is thus 

 obtained, from which the other salts may be easily prepared. 



(<7) The purpureocobaltic salts, CoX 3 ,5NH 3 , are also products of the direct oxidation 

 of ammoniacal solutions of cobalt salts. They are easily obtained by heating the roseo- 

 cobaltic and luteo-salts with strong acids. They are to all effects the same as the 

 roseocobaltic salts, only anhydrous. Thus, for instance, the purpureocobaltic chloride, 

 Co 2 Cl 6 ,10NH 3 , or CoCl 3 ,5NH 3 , is obtained by boiling the oxycobaltamine salts with 

 ammonia. There is the same distinction between these salts and the preceding ones as 

 between the various compounds of cobaltous chloride with water. In the purpureo- 

 cobaltic only X 2 out of the X 3 react (are ionised) To the rosetetramine salts (/) there 

 correspond the purpureotetramine salts, CoX 3 H 2 0,4NH 3 . The corresponding chromium 

 purpureopentamine salt, CrCl 3 ,5NH 3 is obtained with particular ease (Christensen, 1898). 

 Dry anhydrous chromium chloride is treated with anhydrous liquid ammonia in a 

 freezing mixture composed of liquid CO 2 and chlorine, and after some time the mixture 

 is taken out of the freezing mixture, so that the excess of 'NH 3 boils away ; the violet 

 crystals then immediately acquire the red colour of the salt, CrCl 3 ,5NH 3 , which is formed. 

 The product is washed with water (to extract the luteo-salt, CrCl 3 ,6NH 3 ), which does not 

 dissolve the salt, and it is then recrystallised from a hot solution of hydrochloric acid. 



(h) The prazeocobaltic salts, CoX 3 ,4NH 3 , are green, and form, with respect to the 

 fosetetramine salts (/), the products of ultimate dehydration (for example, like meta- 

 phosphoric acid with respect to orthophosphoric acid, but in dissolving in water they give 

 neither rosetetramine nor tetramine salts. (In my opinion one should expect salts with 

 a still smaller amount of NH 3 , of the blue colour proper to the low hydrated compounds 



