8 PROCEEDINGS OF THE AMERICAN ACADEMY 



very soluble in cold, but dissolve quite easily in hot water. The solu- 

 tion gives the characteristic reaction with argentic nitrate. Of this 

 salt : — 



0-4583 gr. gave 0-2466 gr. SO^Co = 24-11 <;^ cobalt. 



The formula ^Co2(XH8),„^ |Co2(NH3),(N02)8}3 requires 24-20%. 



The solution of this salt does not give the reactions of xanthocobalt at 

 first, but after some days ammonic oxalate throws down the character- 

 istic wine-yellow oxalate. The solution is decomposed by long 

 standing, large crystals of cobaltic nitrate, Co(NO.,)o, being formed 

 together with crystalline scales of the corresponding salt of xantho- 

 cobalt already described. 



Cohalto-nitrite. — The sodium salt of Fischer's series, 

 Co,(X'0,),,Na„ 

 is soluble at the instant of formation in an excess of sodic nitrite. 

 Alcohol precipitates, after a time, some of the yellow insoluble 

 sodic salt, and gives a very deep orange-red sokition, from which the 

 alcohol may be expelled by evaporation. Tliis solution gives with 

 one of nitrate of purpureocobalt, after a short time, fine deep orange- 

 red to ruby-red octahedral crystals, which are very slightly soluble 

 in water even on boiling. This salt gave by digestion with a solu- 

 tion of thallous nitrate the characteristic scarlet crystalline salt, 

 Co^(N02)i2Tly, which I shall describe further on. On analysis : — 



0-5598 gr. gave 0-3290 gr. SO.Co = 22.38% cobalt. 

 0-7324 gr. gave 188.5 c.c. nitrogen (moist) at 6°C and 773-4'"'" = 

 31-87% nitrogen. 



The ratio is here exactly that of one atom of cobalt to six atoms of 

 nitrogen ; and the analyses lead to the formula : — 



|Co,(NH,),,(NO,),f3 \ CX(NO,),, l,+90H,, 



which requires 22-33% cobalt, and 31-79% nitrogen. The constitu- 

 tion of the salt is fully established by these analyses, and by the reac- 

 tion with the thallium salt given above, since we have : — 



lCo,(NH3),„(NO,),^ 3 |Co,(NO,)„j,+12TlN03 = 3.Co,(NH3),, 

 (NO,),(NO,),-i-2.Co,(NO,),2Tl,. 



The compound therefore belongs in reality to the xanthocobalt series ; 

 it gives the reactions of the ordinary salts of that series distinctly. 

 The formation of this remarkable salt may very pVobably be expressed 

 by the equation : — 



