THE CHEMISTRY OF ALBUMINS 207 



remembered that metaphosphoric acid was used for the pre- 

 cipitation of the amylase of saliva. 



Tannic acid also precipitates peptone bodies, and it is 

 probable that the difficulty of extracting certain enzymes 

 from plants depends on the fact that they exist in the plant 

 in combination with tannic acid. It was for this reason that 

 Brown and Morris, in their research on the amylase of foliage 

 leaves, obtained better results by using powdered dry leaf 

 than by using a watery extract. 



In order to illustrate the preparation of a specific albumin 

 from its natural source, and the separation of other bodies, the 

 following description of the preparation of a typical vegetable 

 albumin, viz., edestin, may here be given. 



A quantity, say 500 grams, of hemp-seed is ground up and 

 the fat thoroughly extracted by shaking in a large flask with 

 b'ght petroleum and pouring off the solution. After draining 

 off as much as possible of the petroleum, the remainder may 

 be allowed to spontaneously evaporate. The residue is then 

 digested at 60 C. with 350 c.c. of 5 per cent, salt solution, with 

 continual stirring. The liquid is filtered through calico and 

 allowed to cool. A precipitate forms, which can be washed 

 by decantation with distilled water. It is redissolved in 

 250 c.c. of 5 per cent, salt solution, and the solution filtered 

 through a warm filter. On cooling crystals of edestin separate, 

 which can be washed successively with cold 5 per cent, salt 

 solution, distilled water, alcohol and ether. 



CLASSIFICATION OF ALBUMINS 



We are now in a position better to appreciate the following 

 classification of albumins and related substances. Where 

 the name of the substance does not indicate its source or 

 characteristic properties, short explanatory notes are added. 



