862 PRINCIPLES OF CHEMISTRY" 



tesquioxide of cobalt, cobaltic oxide, Co 2 O 3 than nickel, especially in 

 the presence of hypochlorous acid. If a solution of a cobalt salt be' 



of cobalt ; the green colour of the prazeo-salts already forms a step towards the blue.) 

 Jorgenson obtained salts for ethylene-diamine, N 2 H 4 C 2 H4 which replaces 2NH 3 . After 

 being kepi a long time" 'in aqueous solution they give rosetetramine salts, just as met% 

 phosphoric acid gives orthophosphoric acid, while the rosetetramine salts are converted 

 into prazeo-salts by Ag 2 O and NaHO. Here only one X is ionised out of the X 3 . There 

 are also basic salts of the same type; but the best known is the chromium salt called the 

 fhodozochromic salt, Cr 2 (OH) 3 Cl 3 ,6NH 3 ,2H 2 O, which is formed by the prolonged action 

 of water upon the corresponding roseo-salt.- 



The cobaltamine compounds differ essentially but little from the ammoniacal com* 

 pounds of other metals. The only difference is that here the cobaltic oxide is obtained 

 from the cobaltous oxide in the presence of ammonia. In any case it ia a simpler question 

 than that of the double cyanides. Those forces in virtue of which each a considerable 

 number of ammonia molecules are united with a molecule of a cobalt compound, apper- 

 tain naturally to the series of those slightly investigated forces which exist even in the 

 highest degrees of combination of the majority of elements. They are the same forced 

 which lead to the formation of compounds containing water of crystallisation, double 

 salts, isomorphous mixtures and complex acids '( Chapter XXI., Note 8 bis). The 

 simplest conception, according to my opinion, of cobalt compounds (much more so than 

 by assuming special complex radicles, with Schiff, Weltzien, Claus, and others), may be 

 formed by comparing them with other ammoniacal products. Ammonia, like water, com* 

 bines in various proportions with a multitude of molecules. Silver chloride and calcium 

 chloride, just like cobalt chloride, absorb ammonia, forming compounds which are some- 

 times slightly stable, and easily dissociated, sometimes more stable, in exactly the same 

 way as water combines with certain substances, forming fairly stable compounds called 

 hydroxides or hydrates, or less stable compounds which are called compounds with water 

 of crystallisation. Naturally the difference in the properties in both oases depends on 

 4he properties of those elements which enter into the composition of the given substance, 

 and on those kinds of affinity towards which chemists have not as yet turned their 

 attention. If boron fluoride, silicon fluoride, &c., combine with hydrofluoric acid, if 

 platinic chloride, and even cadmium chloride, combine with hydrochloric acid, these 

 compounds may be regarded as double salts, because acids are salts of hydrogen. But 

 evidently water and ammonia have the same saline faculty, more especially as they, like 

 haloid acids, contain hydrogen, and are both capable of further combination for instance, 

 ammonia with hydrochloric acid. Hence it is simpler to compare complex ammoniacal 

 with double salts, hydrates, and similar compounds, but the ammonio-metallic salts 

 present a most complete qualitative and quantitative resemblance to the hydrated salts 

 of metals. The composition of the latter is MXjiwH^O, where M = metal, X = the 

 haloid, simple or complex, and n and m the quantities of the haloid and so-called water 

 of crystallisation respectively. The composition of the ammoniacal salts of metals is 

 MXnmNHj. The water of crystallisation is held by the salt with more or less stability, and 

 some salts even do not retain it at all ; some part with water easily when exposed to the air, 

 others when heated, and then with difficulty. In the case of some metals all the salts com- 

 bine with water, whilst with others only a, few, and the water so combined may then be 

 easily disengaged. All this applies equally well to the ammoniacal, salts, and therefore the 

 combination of ammonia may be termed the ammonia of crystallisation. Just as the 

 water which is combined with a salt is held by it with different degrees of force, so it is with 

 ammonia. In combining with 2NH 3 , PtCl 2 evolves 81,000 cals. ; while CaCl 9 only evolves 

 14,000 cals. ; and the former compound parts with its NH 3 (together with HC1 in this 

 case) with more difficulty, only above 200, while the latter disengages ammonia at 180. 

 ZnCl 2 ,2NH 3 in forming ZnCl 2 , 4NH 3 evolves only 11,000 cals., and splits up again into 

 its components at 80. The amount of combined ammonia is as variable as the amount 

 of water of crystallisation for instance, Snl48NE 3 ,CrCl 2 8NH 5 ,CrCl 5 6NH 3 ,CrCl 3 5NH3, 

 PtCMNH*, &c. are Tmown. Very often NH X is replaceable by OH-, and conversely. A, 



