1863.] 713 



account of the examination of two idiots' brains preserved in the 

 museum of St. Bartholomew's Hospital, and also of a series of wax 

 models of foetal brains in the museum of Guy's Hospital. 



The result of the additional information so obtained is entirely to 

 confirm the descriptions and explanations given of the structure and 

 mode of formation of the idiot brain, 



XXIII. " On Fermat's Theorem of the Polygonal Numbers/' 

 By the Eight Hon. Sir FREDERICK POLLOCK, F.R.S., 

 Lord Chief Baron. Received June 18, 1863. 



[An abstract will be given in a future Number.] 



COMMUNICATIONS RECEIVED SINCE THE END OF THE SESSION. 



I. " On Mauve or Aniline-Purple." By W. H. PERKIN, Esq., 

 F.C.S. Communicated by J. STENHOUSE, LL.D., F.R.S. 

 Received August 19, 1863. 



(Abstract.) 



The discovery of this colouring matter in 1856, and its introduc- 

 tion as a commercial article, have originated that remarkable series of 

 compounds known as Coal-tar colours, which have now become so 

 numerous, and, in consequence of their adaptability to the arts and 

 manufactures, are of such great and increasing importance. The 

 chemistry of mauve may appear to have been rather neglected, its 

 composition not having been established, although it has formed the 

 subject of several papers by continental chemists. Its chemical nature 

 also has not been generally understood ; and it is to this fact that 

 many of the discrepancies between the results of the diiferent expe- 

 rimentalists who have worked on this subject are to be attributed. 



On adding a solution of hydrate of potassium to a boiling solution 

 of commercial crystallized mauve, it immediately changes in colour 

 from purple to a blue violet, and, on standing, deposits a crystalline 

 body, which, after being washed with alcohol and then with water, 

 presents itself as a nearly black glistening body, not unlike pul- 

 verized specular iron ore. 



This substance is a base which I propose to call Mauveine ; it 



