Hartley — On a Violet Colouring- Matter, Sfc. 71 



violaceus, and Bacillus iantlunm, the colouring-matters of which he says are 

 identical. The reactions he obtained with this pigment proved to be similar 

 to those I had obtained, except where the quantity of reagent is different. 

 He used a Bunsen-Kirchlioff spectroscope with a photographed scale for 

 examining the visible rays. The scale was entirely arbitrary and without 

 reference to Fraunhofer's lines or to wave-lengths. The weight of substance 

 dissolved is not stated, nor is tlie thickness of the layer of liquid recorded. 



He states tliat the red rays are entirely transmitted, whioli is not the 

 case according to either optical examination or the photographed spectra of 

 the violet solutions I have described. 



It is interesting to compare the absorption curve of this natural 

 colouring-matter with that of Hoffmann's violet (Chem. Soo. Trans, li, 

 152-202, 1887). 



0'416 grm. of Hoffmann's violet was dissolved in 100 c.e. of alcohol 

 and diluted to 600 c.c, 2500 c.c, and 12,500 c.c, which dilutions were 

 examined through 5, 4, 3, 2, 1 mm. Expressed in dilutions only, the same 

 curve would be given by 0'208 grm. of solid, dissolved in 5 c.c. of alcohol, 

 observed through 5 mm., and diluted to a concentration of 0'0208 grm., in 

 625 cc, when absorption ceases.' The spectrum of Hoffmann's violet, in the 

 above-mentioned paper, is therefore strictly comparable with the spectrum 

 of the bacterial colour violet, 0'022 grm. of which was dissolved in 5 c.c. of 

 alcohol, and diluted to 160 c.c, when absorption ceases. 



It is clear that Hoffmann's violet at similar dilutions shows four absorption- 

 bands instead of one as does the natural colour, and that absorption continues 

 to a greater dilution in the case of Hoffmann's violet, the colour intensity of 

 which is nearly four times as great. Kopp' examined methyl violet (Geigy) 

 and describes a sharp absorption-band overlying D, which withstood dilution 

 to 1 grm. in 250 litres. 



Farther inquiries into research on plant and animal colouring-matters" 

 showed thftt the colours of somewhat similar appearance have been more or 

 less briefly examined : — 



Lecoq de Boisbaudran extracted a violet colouring-matter from a 

 bacterium grown on a starch-paste, which he does not describe.' The colour 

 dissolved in alcohol gave an absorption-band about D, or from A 600 to X 563, 

 with a maximum intensity at X 581. Thick layers of the solution transmit 

 the red rays fully only as far as X 670, and fidntly to 662, with a trace of 

 light at 481. 



' Bull. Soo. Industr. de Mulhouss, xlviii, 946-950. 1878. 

 - Kayser's Handbuch der Speotroskopie, vol. iv. 

 ^ Comptes Eendus. xciv, 1882. 

 SOIENT. PEOC. B.D.S., VOL. XIV., NO. IV. L 



