AMMONIA-COBALT BASES. 31 



with ammonia, and allowed to crystallize by slow evaporation, the sulphate of 

 Koseocobalt is also obtained, but by rapid evaporation dark-red, prismatic crystals 

 are sometimes formed, which we have not yet obtained in sufficient quantity for a 

 complete analysis. They may prove to be the neutral sulphate of Purpureo- 

 cobalt. 



The acid sulphate of Purpureocobalt crystallizes in fine, red, prismatic crystals, 

 which, according to Prof. Dana, belong to the trimetric system, and are hemihedral. 

 The observed forms are I, it, %l, r -f, is (?) or in other symbols oo, co-Sb , ^--ob, 1 ^, 

 00-2 (?): 



Fia. 8. 

 1:1= 106°. 



I : il = 121° (126° 50'— 127° 10') 

 i'i :i'i= 122° 42'. 



12 : 12"= 67° 54 a : b : c = 1.092*7 : 1 : 1.3211 



Fig. 8 represents an end view of a crystal of this salt ; 12 is hemihedral and 

 i2 usually so : the symbol i2 is probably correct, though the observed angle varies 

 much. 



The acid sulphate is very soluble in water, and has a distinct though not strongly 

 acid taste. It reddens litmus, and expels carbonic acid from the carbonates. 

 The formula of this salt is 



5NH 3 .Co 2 3 ,4S0 3 +5HO 



as the following analyses show : 



0.620 grs. gave 0.2577 grs. sulphate of cobalt = 15.82 per cent, cobalt. 

 1.1402 grs. gave 0.4756 grs. " " = 15.86 " 



1.5317 grs. gave 1.9270 grs. sulphate of baryta = 43.19 " sulphuric acid. 

 1.5843 grs. gave 0.7570 grs. water = 5.31 per cent, hydrogen. 



1.1869 grs. gave 189.5 c. c. of nitrogen at 15° C. and 775 mm .2 (at 15°.3 C.) = 179.6 c. c. at 0° 

 and 760""° = 19.00 per cent, nitrogen. 



The formula requires 



Eqs. Calculated. Found. 



Cobalt . . 2 15.81 15.82 15.86 



Sulphuric acid . 2 42.89 43.19 



Hydrogen . . 20 5.36 5.31 



Nitrogen . . 5 18.76 19.00 



The acid sulphate gives no precipitate with 3KCy,Co 2 Cy 3 , but only a fine red 

 liquid, which, on evaporation, yields a red mass. Boiled with chlorhydric acid the 

 sulphate yields the chloride of Purpureocobalt, easily recognized by oxalate of 

 ammonia, with which, however, the acid sulphate itself gives no precipitate. 

 When precipitated with nitrate of baryta the acid sulphate yields a red liquid 

 which probably contains a nitrate of Purpureocobalt, but which on evaporation 

 gives crystals of nitrate of Roseocobalt. It is well worthy of notice, that this red 

 liquid contains a large quantity of sulphate of baryta in solution, which it deposits 

 during evaporation. 



The products of the decomposition of the acid sulphate are similar to those of 



