ON SPONGIOPORPHYUTN. 341 



still thinner layer a band from about A 610 to X 515 appears, 

 and on diluting further or diminishing the layer we get sp. 

 3, and in a still thinner layer or more dilute solution sp. 4. 

 An aqueous and caustic potash solution, a few drops only of 

 the alkali having been used for the extraction, having a fine 

 deep thick purple colour, gave the following measurements 

 for the bands : — First including shadings from X 602 to X 552, 

 dark from X 595 to X 560, centre about X 577 ; second, X 545 

 to X 522, centre about X 534. A thin layer or a dilute solu- 

 tion has a beautiful lavender tint. 



Although the spectrum obtained by adding an excess of 

 a mineral acid to a feebly acid solution finally shows the 

 spectrum of sp. 9, yet there is evidence of the presence of 

 some intermediate substance which may show five or six 

 bands. I have not yet investigated this substance or 

 substances. As stated above, an excess of caustic alkali does 

 not seem to produce any change of spectrum. Nitric acid 

 added to a weak aqueous solution acidulated with hydro- 

 chloric acid produces the change just mentioned. Sulphuric 

 acid produces a similar effect. 



Is this Pigment Respiratory ? — The addition of 

 ammonium sulphide to a neutral aqueous solution of 

 Spongioporphyrin lightens the colour of the solution and 

 diminishes the intensity of the bands, and on vigorously 

 shaking with air the bands did seem darker and the colour 

 deeper. The addition of formol produces no change. The 

 slight change produced by reducing agents does not enable 

 one to conclude whether the pigment is respiratory or not. 



The Action of Strong Sulphuric Acid. — It was 

 necessary to find out if strong sulphuric acid produces any- 

 thing like ha3matoporphyrin, when made to act on Spongio- 

 porphyrin, as it does in the case of turacin.^ Accordingly 

 some pigment isolated as described below was treated with 

 pure sulphuric acid, and filtered through asbestos. The 

 filtrate, which was of a purple-red colour and showed a 

 spectrum closely resembling sp. 5, was poured into water, 



* 'Pbilos. Trans.,' vol. clxxxiii, p. 516. 



