258 PIGMENTS 



7. Ferric chloride gives a pinkish-brown precipitate. 



8. Boiled with nitric acid a yellow colour results which 

 turns to orange on adding an excess of ammonia. 



9. Boiled with Millon's reagent a deep red colour results. 



10. The addition of a caustic soda solution followed by 

 a drop or two of dilute copper sulphate gives a greenish tint. 



11. Digestion with pepsin, in the presence of hydrochloric 

 acid, has no result. 



1 2. On digestion with trypsin in the presence of sodium 

 carbonate, the phycoerythrin loses its colour, and the solution 

 contains a very small amount of leucin, but no tyrosin. 



13. On hydrolysis with acids, tyrosin is found in very 

 small amounts, but leucin occurs in greater quantities. 



From these and other facts it is concluded that phycoerythrin 

 is a colloidal nitrogenous substance allied to the proteins ; it is 

 not a true protein, since its nitrogen content is too low and it 

 does not give the biuret reaction. It is impossible to say any- 

 thing more definite regarding its chemical nature until it has 

 been prepared in a pure state in quantities sufficient for analysis. 



Physiologically, phycoerythrin acts as a pigment com- 

 plementary to chlorophyll. It absorbs the blue-green rays, 

 and degrades them to yellow and red light of just those wave- 

 lengths which the chlorophyll can absorb. 



PHYCOPHAEIN. 



As is well known, a brown colouring matter may be 

 extracted by water from the Phaeophyceae and other brown 

 Algae. Hitherto this has generally been considered to be 

 due to the presence within the cells of a definite colouring 

 matter of a protein nature. According, however, to the work 

 of Molisch * and Tswett,f this is not the case. The brown 

 colouring matter is really due to post-mortem changes, th< 

 oxidation of a water soluble chromogen. An extract pn 

 pared with distilled water is at first colourless, but will tui 

 yellow if the solution is made alkaline in reaction, e.g. by ta] 

 water, and finally brown owing to oxidation. If the reactioi 

 be made acid decolorization will result. With regard to th( 

 chemistry of this substance little, if anything, is known. 



* Molisch : " Bot. Ztg.," 1894, 52, 181; 1895, 53, 131 ; 1905. 63, 131. 

 fTswett: " Ber. deut. bot. Gesells.," 1906, 24, 235. 



