250 PIGMENTS 



by decantation with 70 per cent alcohol ; the pigment, in a 

 pasty mass, is placed in a clock glass and dried in a vacuum. 



Reactions. 



The following reactions are among those recorded by 

 Hanson : — 



1. Phycoerythrin is precipitated from its solution by 

 alcohol, by small quantities of mercuric chloride, and by 

 saturation with ammonium sulphate and magnesium sulphate. 



2. When dilute acids are added gradually, the fluorescence 

 first disappears, leaving a somewhat opalescent solution of 

 a lilac-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 



