CIRCULAR No. 7, REVISED EDITI 



United States Department of Agriculture, 



DIVISION OF CHEMISTRY. 



H. W. WILEY, Chief. 



AMENDED METHODS ADOPTED AT THE EIGHTEENTH ANNUAL 



CONVENTION OF THE ASSOCIATION OF OFFICIAL 



AGRICULTURAL CHEMISTS. 



DIASTASE METHOD FOR STARCH. 



Extract 3 grams of the finely powdered substance on a hardened filter with 

 five successive portions of 10 c. c. of ether, wash with 150 c. c. of 10 per cent 

 alcohol, and then with a little strong alcohol. Place the residue in a beaker 

 with 50 c. c. of water, immerse the beaker in a boiling water bath, and stir the 

 contents constantly until all of the starch is gelatinized ; cool to 55 C. ; add 

 20 c. c. of malt extract and maintain at this temperature for an hour. Heat 

 again to boiling for a few minutes, cool to 55 C., add 20 c. c. of malt extract, 

 and maintain at this temperature until a microscopic examination of the residue 

 with iodin reveals no starch. Cool and make up directly to 250 c. c. ; filter. 

 Place 200 c. c. of the filtrate into a flask with 20 c. c. of 25 per cent hydro- 

 chloric acid (specific gravity, 1.25) ; connect with a reflux condenser and heat 

 in a boiling water bath for two and a half hours ; nearly neutralize while hot 

 with sodium hydrate, and make up to 500 c. c. Mix the solution well, pour 

 through a dry filter, and determine the dextrose in an aliquot part. Convert 

 the dextrose into starch by the factor 0.90. 



Preparation of malt extract. Digest 10 grams of fresh, finely ground malt 

 two or three hours at ordinary temperature, with 200 c. c. of water, and filter. 

 Determine the amount of dextrose in a given quantity of the filtrate after 

 boiling with acid, etc., as in the starch determination, and make the proper 

 correction. 



PROVISIONAL METHOD FOR THE DETERMINATION OF PENTOSANS BY MEANS OF 



PHLOROGLUCOL. 



A quantity of the material, chosen so that the weight of the phloroglucid 

 obtained shall not exceed 0.300 gram, is placed in a flask, together with 100 c. c. of 

 12 per cent hydrochloric acid (specific gravity, 1.06), and several pieces of recently 

 heated pumice stone. The flask, placed upon wire gauze, is connected with a 

 condenser and heat applied, rather gently at first, using a gauze top to distribute 

 the flame, and so regulated as to distill over 30 c. c. in about ten minutes, the 

 distillate passing through a small filter paper. The 30 c. c. driven over are 

 replaced by a like quantity of the dilute acid added by means of a separatory 

 funnel and in such a manner as to wash down the particles adhering to the sides 

 of the flask, and the process continued until the distillate amounts to 360 c. c. 

 To the completed distillate is gradually added a quantity of phloroglucol (puri- 

 fied if necessary) dissolved in 12 per cent hydrochloric acid, and the resulting 

 mixture thoroughly stirred. The amount of phloroglucol used should be about 

 double that of the furfural expected. The solution first turns yellow, then 

 green ; and very soon an amorphous greenish precipitate appears, which grows 



