8 PROCEEDINGS OP 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 

 Kilt : — 



0-4583 gr. gave 0-24C6 gr. SO,Co = 24-11% cobalt. 



The formula |Co,(XIl3),J jCo,(NH3),{NO,)j3 requires 24-20%. 



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

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

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

 standing, large crystals of cobaltic nitrate, Co(XO.,)2, being formed 

 together with crystalline scales of the corresponding salt of xantho- 

 cobalt already described. 



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



Co,(NO,),,Na„ 

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

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

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

 alcohol may be expelled by evaporation. This solution gives with 

 one of nitrate of pur[)ureocobalt, 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^(^«0^,)^^,Tl^, 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 : — 



lCo,(NIl3),,(NO,)j3 \ Co,(NO,),3 L+90H,, 



which rc<iuires 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,(NIl3),,(NO,),( , |Co,(NO.,),,t,+12TlNO, = 3.Co2(NH3),o 

 (NO,),(NOj,-|-2.Ca,(N0,),;n,. 



The compound therefore belongs in reality to the xanthocobalt series ; 

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

 The formali(jn of this remarkable salt may very probably be expressed 

 by the equation : — 



