OF ARTS AND SCIENCES. 31 



Ammoma-cohalt-nitrate of Xanthocohalt. — When a solution of po- 

 tassic ammonia-cobalt nitrite is added to one of nitrate of xanthocohalt, 

 a beautiful crystalline precipitate is formed, of a deep orange-red color, 

 which requires a rather large quantity of boiling water for solution, and 

 which may be recrystallized without decomposition. The solution 

 gives the reactions of salts of xanthocohalt, and gives also, with argentic 

 nitrate, the characteristic silver salt Co2(NH3)^(N02)3Ag2. Of this 

 salt 



0-5074 gr. gave 0-3172 gr. SO^Co = 23-77 per cent cobalt. 

 0-4731 gr. gave 135 c.c. nitrogen (moist) at 12°Cand 757-8™" = 33-69 

 jaer cent nitrogen. 



The formula |Co2(NH3)jo(N02)2^ lCo2(NH3),(N02)j2 requires 23-79 

 per cent cobalt, and 33-87 per cent nitrogen. This salt is metameric 

 with the corresponding salt of the octamin series already described, 

 and with Erdmann's salt, Co2(NH3)g(N02)6) since we have 



lCo2(NH3),„(N02)2nCo2(NH3),(N02),i2 = 

 3Co2(NH3),(N02)e. 



In endeavoring to obtain measurable crystals by allowing a solution 

 of this salt to stand for some time, and evaporate at ordinary tempera- 

 tures, I found that the salt was partially decomposed, a considerable 

 quantity of cobaltic nitrate being formed. 



Oxalate of Xanthocohalt. — In the first part of this memoir, in con- 

 sequence of an oversight, the formula given for the oxalate of xantho- 

 cohalt contains (old style) five atoms of water of crystallization. Tlie 

 salt is really anhydrous, and the analyses given agree with the formula 

 Co2(NH3),||(N02) 2(020^2' The salt is obtained from hot solutions iu 

 granular crystals. Its solution in hot dilute nitric acid deposits abun- 

 dant crystals of the nitrate, the oxalate being almost completely decom- 

 posed. Sulphate and nitrate of xanthocohalt may be readily prepared 

 from the oxalate by boiling with a small excess of mercurous sulphate 

 or nitrate, adding, in the first case, a little dilute sulphuric, in the last, 

 a little nitric, acid. As the oxalate can be precipitated by ammonic 

 oxalate from the crude nitrate, this furnishes a cheap and expeditious 

 method of obtaining the pure sulphate. 



The formulas of the salts of xanthocohalt at present known become 

 in the new notation : — 



Chloride, Co2(NH3),o(NO.,)2Cl, 



Bromide, Co2(NH3),o(N02).,Br, 



Iodide, Co,(NH3),,(.N02)2l, 



