PHYCOERYTHRIN 257 



It is a matter of great difficulty to obtain a pure sample of 

 phycoerythrin, for, in an aqueous solution, it passes over into 

 an irreversible gel,* even when kept at o C. This, of course, 

 renders ordinary filtration extraordinarily slow, and thus in- 

 creases the difficulty of purification. 



The solid phycoerythrin may be prepared from the aqueous 

 solution by concentrating it under reduced pressure at a 

 temperature not higher than 38 C. ; any precipitate which 

 comes down during this process must be filtered off. Methyl- 

 ated spirit is then added to the concentrated solution until 

 the fluorescence disappears. The precipitated phycoerythrin 

 is allowed to settle and the more or less clear supernatant 

 fluid is filtered off, again treated with alcohol, and filtered. 

 The operation is repeated until the red colour has entirely 

 disappeared from the solution. The precipitates are washed 

 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. 



* See Section VIII., on the Colloidal State. 

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