860 PRINCIPLES OF CHEMISTRY 



Nickel does not possess this property of absorbing the oxygen of the air 

 when in an aramoniacal solution. In order to understand this distinc- 



the art ; they absorb oxygen and become covered with a crust of oxycobaltamitie salts. 

 The latter are sparingly soluble in aqueous ammonia, have a brown colour, and are 

 characterised by the fact that with warm water they evolve oxygen, forming salts of the 

 following category : The nitrate may be taken as an example of this kind of salt ; its 

 composition is CoN 2 7 ,6NH 3 ,H 2 0. It differs from cobaltous nitrate, Co(NO 3 ) 2 , in con- 

 taining an extra atom of oxygen that is, it corresponds with cobalt dioxide, Co0 2 , in 

 the same way that the first salts correspond with cobaltous oxide ; they contain 5, and 

 not 6, molecules of ammonia, as if NH 3 had been replaced by O, but we shall afterwards 

 meet compounds containing either 5NH 3 or 6NH 3 to each atom of cobalt. 



(c) The luteocobaltic salts are thus called because they have a yellow (luteus) 

 colour. They are obtained from the salts of the first kind by submitting them in dilute 

 solution to the action of the air ; in this case salts of the second kind are not formed, 

 be'cause they are decomposed by an excess of water, with the evolution of oxygen and 

 the formation of luteocobaltic salts. By the action of ammonia the salts of the fifth 

 kind (roseocobaltic) are also converted into luteocobaltic salts. These last-named salts 

 generally crystallise readily, and have a yellow colour ; they are comparatively much 

 more stable than the preceding ones, and even for a certain time resist the action ol 

 boiling water. Boiling aqueous potash liberates ammonia and precipitates hydrated 

 cobaltic oxide, Co 2 O 3 ,8H 2 O, from them. This shows that the luteocobaltic salts corre- 

 spond with cobaltio oxide, Co 2 C>5, and those of the second kind with the dioxide. 

 When a solution of luteocobaltic sulphate, Co 2 (S0 4 ) 3 ,12NH 5 ,4H 2 O, is treated with 

 baryta, barium sulphate is precipitated, and the solution contains luteocobaltio 

 hydroxide, Co(OH) 3 ,6NH5, which is soluble in water, is powerfully alkaline, absorbs 

 the oxygen of the air, and when heated is decomposed with the evolution of am- 

 monia. This compound therefore corresponds to a solution of cobaltic hydroxide in 

 ammonia. The luteocobaltic salts contain 2 atoms of cobalt and 12 molecules of 

 ammonia that is, 6NH 3 to each atom of cobalt, like the salts of the first kind. The 

 CoXj salts have a metallic taste, whilst those of luteocobalt and others have a purely 

 saline taste, like the salts of the alkali metals. In the luteo-salts all the X's react (are 

 ionised, as some chemists say) as in ordinary salts for instance, all the C1 2 is pre- 

 cipitated by a solution of AgNO 3 ; all the (S0 4 ) 5 gives a precipitate with BaX 2 , &c. 

 The double salt formed with PtCl 4 is composed in the same manner as the potassium 

 salt, K 2 PtCl 4 = 2KCl + PtCl 4 , that is, contains (CoCl 3 ,6NH 3 ) ? ,8PtCl 4 , or the amount of 

 chlorine in the PtCl 4 is double that in the alkaline salt. In the rosepentamine (e), and 

 rosetetramine (/), salts, also all the X's react or are ionised, but in the (g) and (h) salts 

 only a portion of the X's react, and they are equal to the (e) and (/) salts minus water ; 

 this means that although the water dissolves them it is not combined with them, as 

 PH0 3 differs from PH 3 3 ; phenomena of this class correspond exactly to what has 

 been already (Chapter XXI., Note 7) mentioned respecting the green and violet salts of 

 oxide of chromium. 



(d) The fuscocobaltic salts. An ammoniacal solution of cobalt salts acquires a brown 

 colou in the air, due to the formation of these salts. They are also produced by the 

 decomposition of salts of the second kind ; they crystallise badly, and are separated from 

 their solutions by addition of alcohol or an excess of ammonia. When boiled they give 

 Up the ammonia and cobaltic oxide which they contain. Hydrochloric and nitric acids 

 give a yellow precipitate with these salts, which turns red when boiled, forming salts of 

 the next category. The following is an example of the composition of two of the fusco-* 

 cobaltic salts, Co 2 O(S0 4 ) 2 ,8NH 3 ,4H 2 O and Co 2 OCl 4 ,8NH 3 ,3H 2 O. It is evident that the 

 fuscocobaltic salts are aramoniacal compounds of basic cobaltic salts. The normal co- 

 baltic sulphate ought to have the composition Co 2 (SO 4 ) 3 - Co 2 O 3 ,8SO 5 ; the simplest 

 basic salts will be Co 2 O(SO 4 ) 2 =Co 2 3 ,2SO 3 , and Co 2 O 2 (S0 4 ) = Co 2 O 3 ,SO 3 . The fusco- 

 cobaltio salts correspond with the first type of basic salts. They are changed (in con- 

 centrated solutions) into oxycobaltamine salts by absorption of one atom of oxygen, 



