!4 RESEARCHES ON THE 



it yields the acid sulphate of Purpureocobalt. By double decomposition with salts 

 of barium the sulphate of Roseocobalt yields the other salts of this base. 



The reactions of the sulphate are somewhat different from those of the chloride, 

 as will be seen from the following statement. 



Ferridcyanide of potassium gives no precipitate at first, but after two hours very 

 distinct and well defined small augitic crystals. 



Cobaltidcyanide of potassium behaves in a precisely similar manner, giving red 

 crystals. 



Neutral chromate of potash gives no precipitate. The bichromate gives none at 

 first, but after two or three hours, groups of reddish brown needles. 



We shall hereafter state our reasons for believing that in certain cases there is 

 a conversion of the triacid Roseocobalt in the sulphate of this base, into the biacid 

 Purpureocobalt. 



ANHYDROUS NITRATE OF ROSEOCOBALT. 



The ammoniacal solution of nitrate of cobalt absorbs oxygen very readily from 

 the air, and the oxidation is usually complete after a few days. As a general rule, 

 a considerable quantity of nitrate of Luteocobalt is formed under these cir- 

 cumstances, and being insoluble in the ammoniacal liquid, forms a bright yellow 

 crystalline precipitate upon the bottom and sides of the vessel. During the 

 process of the oxidation, crystals of the compound described by Fremy as the 

 nitrate of Oxycobaltiaque are frequently formed in some quantity, but these disap- 

 pear at a later stage of the oxidation, when the liquid takes a deep wine-red color. 

 The crystals of nitrate of Oxycobaltiaque were first observed by Leopold Gmelin. 

 We have not particularly examined or analyzed them, though Fremy's analyses do 

 not appear to us satisfactory. 



The dark-red liquid formed under these circumstances contains nitrate of Roseo- 

 cobalt. When nitric acid is added to this solution, a brick-red precipitate is thrown 

 down, which is the hydrated nitrate of Roseocobalt. This nitrate is readily solu- 

 ble in water, and exists unchanged in the solution, but by boiling with niti'ic acid, 

 the solution yields a fine violet-red crystalline precipitate of the anhydrous nitrate 

 of Roseocobalt. The presence of nitrate of ammonia facilitates the oxidation 

 and formation of nitrate of Roseocobalt, but is not indispensable. 



The preparation of pure nitrate of Roseocobalt is attended with difficulty, as the 

 precipitated crystalline nitrate almost always contains a little nitrate of Luteocobalt. 

 It is best to dissolve the crude nitrate in water, to which a little ammonia has been 

 added, to filter and allow the solution to evaporate spontaneously. After some 

 days, large and well defined crystals of the nitrate are formed, while the bottom of 

 the evaporating vessel is covered with minute red crystals of the same salt. The 

 difference between the appearance of the large and small crystals is so great that 

 we suspected a difference in their constitution. Analysis and the behavior of the 

 two kinds towards reagents, showed, however, no difference. A marked variation 

 in the color of the large and small crystals of the same substance is very commonly 



