OF ARTS AND SCIENCES. 



33 



so that the salt when containing an atom of water of crystallization, 

 certainly becomes anhydrous a little below 125° C. 

 The structural formula of the salt is : — 



NH3— NH3— 0— N<Q>N ^ 



NHj— NH3— 0— N<^>N 



-N<^>N 

 .0, 



Co, 



NHg— NH3— 0- 



NH3— N H3— 0— N < Q > N 

 NH3— NH3— O— N <Q> N 



NH3— NH3— 0- 



Co, 



In this case, as in formulating Fischer's salts (p. 17), I have as- 

 sumed that six units of affinity of the hexatomic complex, Co^, on the 

 right, are saturated by six units of affinity of nitrogen, which is of 

 course equivalent to supposing that a nitrite may be R — N<a, and 



not, according to the usual view, = N — OR. It seems to me that 

 the first view exhibit's more clearly the mutual relations of the am- 

 monia and nitroxyl compounds of cobalt, and the existence of such 

 intermediate compounds as the salts of Erdmanu's series. But it is 

 also possible that, while the alkaline nitrites have the structural for- 

 mula, O = N — OM, very stable compounds, like Co^(NO^)i2Kg, have 

 the different structure which I have above assumed. It will be seen that 

 the difterence corresponds to that between ethylic nitrite, O = N — O 



C„H„ and the far more stable nitro-ethan a>N 



i o (J 



C2H3 



When the luteocobalt salt just described, and which we may more 

 briefly express by the formula Co2(N02)i2Lc, is digested with a solu- 

 tion of thallous nitrate, T1N0„, containing a little free nitric acid, the 

 yellow salt soon becomes red, and finally assumes a fine scarlet tint, 

 while the supernatant liquid becomes yellow, and contains nitrate of 

 luteocobalt. After washing with hot water and drying, a fine crystal- 

 line scarlet salt of thallium is obtained, which has the formula, 



Co,(NO.,),2Tl,+20H2, 

 as the following analyses show : — 

 0-3964 gr. gave 0-3724 gr. sulphates of cobalt and thalliums 



93-94%. 

 0-9879 gr. gave 0-0034 gr. water at 102° C. = 0-34%, 0-010 gr. at 



130°-135^ C.= 1-02%, and 0-0318 gr. at 150* C. = 3-22%. 



VOL. XI. (n. S. II.) 3 



