OF ARTS AND SCIENCES. 19 



solubility and the facility with which it crystallizes in tabular lustrous 

 crystals have made it of great service in my investigations, especially in 

 distinguishing salts containing Co2(NH3)^(N02)sfrom those which con- 

 tain Co.,(N02)i2. Compounds of ammonia-cobalt-nitrite with barium, 

 strontium, &c., are easily formed by double decomposition, the metallic 

 chlorides being digested with a solution of the argentic salt. They are 

 pale orange-yellow, soluble salts which I have not further examined. 

 A solution of the potassic salt gives beautiful crystalline precipitates 

 with salts of various organic alkaloids, especially with those of brucin. 

 and strychnin. These are soluble in hot water without sensible decom- 

 position, and may be recrystallized. Salts of anilin give a bi-ight yel- 

 low precipitate with potassic ammonia-cobalt-nitrite, which is, however, 

 immediately decomposed, phenol being set free. The potassic salt 

 gives also splendid crystalline precipitates with salts of croceocobalt, 

 xanthocobalt, luteocobalt, &c. I have already noticed the salt of 

 croceocobalt, and will describe the salts of the other bases in due 

 course. 



Erdmann has not attempted to explain the formation of this class of 

 salts. He remarks that a yellow insoluble compound is formed at the 

 same time with the potassic salt Co2(NH3)^(N02)8K2' which appears to 

 be a mixture which cannot be obtained pure for analysis. I have also 

 obtained this body, and also regard it as consisting mainly of Fischer's 

 salt, Co.,(N02)i2Kg, though, as Erdmann states, it contains a small per- 

 centage of ammonia. The formation of the salt Co2(NH3)^(N02)jjK2 

 may be expressed by the equation 



2C0CI2 + 4NH,C1 -f 8KNO2 + O = Co2(NH3),(N02)sK2 + 

 6KCI + 2HCI + OH2, 



if we suppose oxygen to be absorbed from the air. In consequence, 

 however, of the formation of free chlorhydric acid, NgOg is set free, 

 and it is much more probable that this is reduced by the nascent- 

 hydrogen ; so that we have 



N203 + 2H = 2XO-fOH2. 



The potassium salt is also formed, as I shall show, in various other 

 cases : the similarity of some of its reactions to those of a solution of 

 Co.,(NO.,)]oNag in sodic nitrite for a long time misled me; but its 

 relations to salts of silver, mercury, and thallium enable us to recognize 

 its presence with absolute certainty. The salt does not enter into com- 

 bination with iodine. 



