70 Scientific Proceedings, Royal Dublin Society. 



The bleached solution in the 5 mm. cell transmitted the coloured rays, while 

 showing a continuous absorption in the ultra-violet like that of the original 

 colour in the same cell, but at a dilution of 15 c.e. ; and in the 2 mm. cell, the 

 bleached solution showed a continuous absorption in the ultra-violet resembling 

 that of the original colour at a dilution of 40 c.c. through 5 mm. The measure- 

 ments of the spectra are as follows : — 



Alcoholic solution bleached by exposure to sunlight. 



Concentration one part in 800 approximately. 



0"005 grm. in 5 c.c. of absolute alcohol. 



Thickness of cell, 5 mm. Coloured rays all transmitted. 



Spectrum strong to 1/X 3002 A 3332 



feeble to 3510 2850 



Total absorption beyond 3510 2850 



Thickness of cell, 3 mm. Coloured rays all transmitted. 



Ai 



Spectrum strong to 1/A 3464 



feeble 3523 2838 



Total absorption beyond 3523 2838 



The alcohol alone through 5 mm. transmits all rays to 1/A 4555, or 

 A 2196. 



There is no absorption-band in the ultra-violet.' 



Inquiries into previous work upon these bacterial colouring-matters 

 disclosed a paper, " Sur une nouvelle espece de microbe chromogene 

 Bacterium Rosaceum Metalloides," par G. F. Dowdeswell, M.A. (" Annales 

 de Micrographie," vol. i, 1888-89), in which the examination of the colouring- 

 matter was described by Professor W. N. Hartley. Unfortunately no definite 

 weight of substance was taken, but the spectra of different thicknesses of 

 solution were examined. It was decided to examine the violet colouring- 

 matter in a similar manner and to compare the curve obtained with the curves 

 of other similar colouring-matters from different sources. 



A second paper, which was not obtainable till after all the experimental 

 work was finished, was, " Die Bedeutung der Bakterienfarbstoffe fiir die 

 TJaterscheidung der Arten," von Dr. Paul Schneider (Karlsruhe, 1895). 



Schneider describes the colour-reactions and spectra of some thirty different 

 colouring-matters obtained from various organisms, among which are Bacillus 



1 This distinguishes the colouring-matter from the violet and blue triphenylmethaue dyes, the 

 indophenols, and indigo, all of which have a chromogenio nucleus with an aromatic origin. Curves 

 of these are shown in the Chem, Soe. Trans., li, 1887. See also XJhler and Wood's Atlas of 

 Absorption- Spectra. 



