400 



Mr. Alex. McAulay. On the 



[Apr. 28, 



\ 589. It probably arises from the presence of traces of the green 

 alteration-product of turacin formed during the preparation of that 

 pigment in the isolated condition, an alteration -pro duct which is 

 likely to prove identical with Krukenberg's turacoverdin. 



5. Turacin in ammoniacal solution remains unchanged after the 

 lapse of twenty-three years. 



6. Turacin in the dry state, when suddenly and strongly heated, 

 yields a volatile copper- containing red derivative, which, though 

 undissolved by weak ammonia- water, is not only soluble in, but may 

 be crystallised from, ether. 



7. Turacin in the dry state, when heated in a tube surrounded by 

 the vapour of boiling mercury, becomes black, gives off no visible 

 vapour, is rendered insoluble in alkaline liquids, and is so pro- 

 foundly changed that it evolves no visible vapour when afterwards 

 strongly heated. 



8. The accurate analysis of turacin offers great difficulty. The 

 percentage composition, as deduced from those determinations which 

 seem most trustworthy, is — 



Carbon 53'69 



Hydrogen 4*60 



Copper 7*01 



Nitrogen 6*96 



Oxygen 27*74 



These numbers correspond closely with those demanded by the 

 empirical formula CgsHgiCiisNgC^, although the author lays no stress 

 upon this expression. 



9. Turacin presents some analogies with heematin, and yields, by 

 solution in oil of vitriol, a coloured derivative, turacoporphyrin. The 

 spectra of this derivative, both in acid and alkaline solution, pre- 

 sent striking resemblances to those of heematoporphyrin, the corre- 

 sponding derivative of hsematin. But copper is present in the 

 derivative of turacin, w hile iron is absent from its supposed analogue, 

 the derivative of hsematin. 



III. " On the Mathematical Theory of Electro-magnetism." By 

 Alex. MoAulay, M.A., Ormond College, Melbourne, Com- 

 municated by the Rev. N. M. Ferrers, D.D., F.R.S. 

 Received January 8, 1892. 



(Abstract.) 



It will conduce to clearness to give some account here of the 

 objects and aims of what is to follow. The part of the paper suc- 

 ceeding this Introduction is in three main divisions : The groundwork 



