1889.] On Salts of a Base containing Chromium and Urea. 321 



[If an iron ring which has never been magnetised has its curve of 

 magnetisation determined for an ascending series of forces, if it be 

 then thoroughly demagnetised by a succession of reversed currents of 

 descending intensity, and the curve of magnetisation is redetermined, 

 I find that the two curves differ materially. The demagnetising 

 currents do not reduce the iron to its virgin state. For small forces 

 the second curve is below the first, indicating less induction for the 

 vsame magnetising force ; for medium forces the second curve is above 

 the first, whilst for large forces the two curves agree. 



If a ring be heated with a current through the primai-y coil and the 

 heating be continued till the ring has ceased to be magnetic, if then 

 the current be stopped and the ring be allowed to cool, I find that 

 the ring is not entirely demagnetised by the heating, but that it 

 recollects its state of magnetisation before heating. It would seem 

 that the magnetic molecules of the iron, having been directed by the 

 magnetising force whilst they were magnetic, retain in part their 

 direction when they have ceased to be magnetic by heating, and that 

 when they again become magnetic by cooling its effect is apparent. 

 February 14, 1889.] 



I have tested a sample of manganese steel, and find that at no tem- 

 perature above the normal temperature does it become substantially 

 magnetic. 



II. " On a Series of Salts of a Base containing Chromium and 

 Urea. No. 2." By W. J. SELL, M.A., F.I.C. With 

 Cry stallo graphic Determinations by Professor W. J. LEWIS, 

 Cambridge. Communicated by Professor G. D. LlVElNG, 

 F.R.S. Received February 1, 1889. 



In a former paper (' Roy. Soc. Proc.,' vol. 33, 1882) a number of 

 salts were described derived from a base formed by a combination of 

 chromium with urea. It was stated that the chief product of the 

 regulated action of chromyl dichloride on dry urea, and subsequent 

 treatment with water, i's a green crystalline powder, insoluble in 

 alcohol, ether, or chloroform. The compound thus obtained contains 

 chlorine as an essential component, while, as noted, the product of 

 crystallisation from hot water is the pure dichromate of the base. At 

 the date of the previous publication the nature of this green salt, as a 

 preliminary to the study of the reaction by which it is produced, was 

 under investigation. The present paper deals with these subjects, 

 and describes a number of additional salts of the base. 



The failure in the attempt to purify the green salt by crystallisa- 

 tion from water, added to its insolubility in all other available neutral 



