18 PROCEEDINGS OF THE AMERICAN ACADEMY 



The manner in which these compounds may be derived from each 

 other by replacement is sufficiently obvious, and is best seen by assum- 

 ing chloride of luteocobalt and Fischer's salt as the two extreme terms 

 of the series in which the other three are intermediate. 



Erdmann's analyses leave no reasonable doubt as to the constitution 

 of the ammonia-nitrites. I have thought it worth while, however, to 

 make a few additional analyses in support of his view. In the potas- 

 sium salt, 



0-4497 gr. gave 0-3397 gr. SO, Co and 80,1^2 = 75-54 per cent. 

 0-7338 gr. gave 0-oGlo gr. „ „ =76-52 per cent. 



0-5937 gr. gave 127 c.c. nitrogen at 65° C, and 773-4""" = 26-45 

 per cent nitrogen. 



The formula Co2(NH3),(N02)8K2 requires 76-58 per cent (280,00 + 

 SO^Kj) and 26-58 per cent nitrogen. In the silver salt, 



0-3580 gr. gave 0-2902 gr. SO,Co and 80,Ag,„ 

 0-5937 gr. gave 0-1675 gr. silver = 28-21 per cent. 



The cobalt by difference amounts to 15-33 per cent. The formula 

 Co.,(NH3),(N02)8Ag2 requires 28-05 per cent silver and 15-32 per cent 

 cobalt. 



Thallium Salt. — When a solution of the potassium salt is added to 

 one of thallous nitrate, a beautiful sherry-wine-colored crystalline pre- 

 cipitate is thrown down, which on recrystallization gives very well- 

 defined prismatic crystals, having apparently the same form as the 

 corresponding potassium and ammonium salts. 



Mercurous Salt. — A solution of potassic ammonia-cobalt-nitrite gives 

 immediately in solutions of mercurous nitrate a beautiful orange-colored 

 crystalline precipitate, which may be dissolved in boiling water, but not 

 without partial decomposition. The salt does not crystallize well from 

 the solution. Of this salt, 



0-7785 gr. gave 0-1775 gr. SO,Co = 8-68 per cent cobalt. 



The formula Co2(NH3),(N02)s(Hg,)2 requires 8-71 per cent. 



A solution of the potassic salt gives no precipitate with salts of cobalt, 

 nickel, barium, and copper, and none at first with plumbic acetate. 

 After standing, however, a lead salt separates in fine aciiular leafy 

 crystals of a brown-orange color, soluble in hot water, but with partial 

 decomposition. The same is true of the silver salt, but small quantities 

 of this may usually be dissolved and recrystallized without change. 

 The silver salt is extremely well characterized ; its moderate degree of 



