244 EXTRACTS. [CH. IX 



The residue from III. is placed in a flask fitted with 

 a reflux condenser, acid added, and heated on a water-bath 

 for two hours, or until a drop of the solution ceases to give 

 any iodine reaction. 



Instead of using dilute acid it is often better to use 

 solution of diastase (active malt- extract) to extract the 

 starch from the residue No. III. (see Chap. xiv.). 



The temperature for extracting with diastase must not 

 exceed 60 C. and the extraction takes considerably longer 

 it is best to allow the action to continue (with addition of 

 more malt-extract from time to time if necessary) till the 

 solution ceases to give any well-marked iodine reaction. 



It will generally be found sufficient to use 100 c.c. of 

 an extract, made by completely exhausting 300 grs. of 

 malt with water and making up the product to 500 c.c. 

 for each 10 grs. of substance originally taken. 



It is not generally required to examine further the 

 residue from IV., but if it is desired to estimate the cellu- 

 lose in it this may be treated in the manner described on 

 p. 293. 



The original drying at 100 C. and treatment with boil- 

 ing ether or benzene and boiling '85 alcohol tend to alter 

 the proteids and render them insoluble in cold water and 

 dilute acids, so that it frequently happens that the 

 extracts III. and IV. are almost completely free from 

 proteids. 



Preparation of extracts. 

 Nitrogenous plastic substances 



For nitrogenous plastic substances (proteids, amides, 



