26o PIGMENTS 



a ]ilac-pink tint. After the lapse of two days a pink precipitate 

 comes down. 



3. Ammonium hydrate in small quantities removes the 

 fluorescence ; in excess, a yellowish-brown coloration results. 



4. Caustic soda or potash in small quantities causes the 

 red colour to disappear, the solution turning opalescent and 

 yellowish-brown in colour; on standing, a brownish precipitate 

 comes down. 



5. The solution is immediately decolorized by bleaching 

 powder, bromine water or a solution of iodine in potassium 

 iodide. 



6. Mercuric chloride solution in small quantities gives a 

 lilac-grey precipitate, the solution then being yellowish in colour. 



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. 



12. 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 



