AMMONIA-COBALT BASES. 



13 



by Prof. Dana. The observed forms are represented in Figs. 1, 2, and 3. The 

 measured angles are as follows : 



1:1= 10T°20' 



1 : tt = 126° 20' 



ii : li= 13?° 21' 



: It = 132° 35' (calc. 132° 39') 



a = 1.0866. 



Prof. Dana remarks that the angles are very close to those of Cerasine; and also 

 to those of Scheeletine or tungstate of lead, if 1* be § and 1 be li. 



The sulphate of Eoseocobalt is nearly insoluble in cold water, but is soluble in 

 much boiling water, and crystallizes readily as the solution cools. By slow evapo- 

 ration, it may be obtained iu large crystals, which, however, seldom exhibit very 

 perfect faces. Ammonia in dilute solution dissolves the sulphate, giving a fine 

 purple solution, from which the salt crystallizes unchanged. The neutral solution 

 is readily decomposed by boiling, ammonia being evolved, and a dark brown preci- 

 pitate of the hydrated magnetic oxide of cobalt, Co 3 4 + 3HO, thrown down, while 

 sulphate of Luteocobalt remains in solution. The decomposition in this case 

 extends to the sulphate of Luteocobalt also, so that much less than one equivalent 

 of this salt is obtained for two equivalents of the sulphate of Eoseocobalt decom- 

 posed. 



Strong ammonia poured upon dry sulphate of Eoseocobalt usually changes its 

 color almost immediately from a red to a buff yellow, while the liquid itself be- 

 comes red. The buff colored substance formed in this case, is the sulphate of Luteo- 

 cobalt ; the red solution contains sulphate of Eoseocobalt. 



When dry sulphate of Eoseocobalt is carefully heated in a porcelain or platinum 

 crucible, ammonia is evolved, and there remains a lilac-red mass, which contains 

 sulphate of Luteocobalt, sulphate of Purpureocobalt, and a leek-green crystalline 

 substance which we have called provisionally Praseocobalt. 



We shall speak of all these reactions more fully when treating of the sulphate 

 of Luteocobalt. 



A current of the red gas which arises from the action of nitric acid upon starch, 

 and which probably consists chiefly of N0 4 , converts an acid, neutral, or ammonia- 

 cal solution of sulphate of Eoseocobalt into one of the nitrate of Xanthocobalt. 



A solution of sulphurous acid gently heated with sulphate of Eoseocobalt gives, 

 in a few minutes, an orange precipitate of a substance containing ammonia, sesqui- 

 oxide of cobalt, sulphurous and sulphuric acid, and which we shall describe fully 

 in the second part of our memoir. 



Strong sulphuric acid digested with sulphate of Eoseocobalt yields, under some 

 circumstances, sulphate of ammonia and sulphate of Luteocobalt. In other cases 



