110 METHODS OF ANALYSIS [Chap. 



60 Direct Acid Hydrolysis (Modified Sachsse Method). — Official. 



(In this method there will be included as starch the pentosans and other carbo- 

 hydrate bodies present which undergo hydrolysis and conversion into reducing 

 sugars on boiling with hydrochloric acid.) 



Stir a quantity of the sample, representing 2.5-3 grams of the dry material, in a 

 beaker with 50 cc. of cold water for an hour. Transfer to a filter and wash with 

 250 cc. of cold water. Heat the insoluble residue for 2^ hours with 200 cc. of water 

 and 20 cc. of hydrochloric acid (sp. gr. 1.125) in a flask provided with a reflux con- 

 denser. Cool, and nearly neutralize with sodium hydroxid. Complete the volume 

 to 250 cc, filter, and determine the dextrose in an aliquot of the filtrate as directed 

 under 52 or 54. The weight of the dextrose obtained multiplied by 0.90 gives the 

 weight of starch. 



The factor 0.9 is the theoretical ratio between starch and glucose but, according 

 to Noyes" and other investigators, the factor 0.93 more nearly approaches the actual 

 yield. 



Diastase Method with Subsequent Acid Hydrolysis. — Tentative. 



61 REAGENT. 



Malt extract. — Digest 10 grams of fresh, finely ground malt for 2-3 hours at or- 

 dinary temperature with 200 cc. of water and filter. Determine the amount of dex- 

 trose in a given quantity of the filtrate after boiling with acid, etc., as in the starch 

 determination, and make the proper correction in the subsequent determination. 



62 DETERMINATION. 



Extract a convenient quantity of the substance (ground to an impalpable powder 

 and representing 4-5 grams of the dry material) on a hardened filterwith 5 successive 

 portions of 10 cc. of ether ; wash with 150 cc. of 10% alcohol and then with a little strong 

 alcohol. Place the residue in a beaker with 50 cc. of water, immerse the beaker in boil- 

 ing water, and stir constantly for 15 minutes or until all the starch is gelatinized ; cool 

 to55°C., add 20 cc. of malt extract, and maintain at this temperature for an hour. 

 Heat again to boiling for a few minutes, cool to55''C., add 20 cc. of malt extract, and 

 maintain at this temperature for an hour or until the residue treated with iodin shows 

 no blue color upon microscopic examination. Cool, make up directly to 250 cc, and 

 filter. Place 200 cc. of the filtrate in a flask with 20 cc. of hydrochloric acid (sp. gr. 

 1.125) ; connect with a reflux condenser and heat in a boiling water bath for 2^ hours. 

 Cool, nearly neutralize with sodium hydroxid solution, finish the neutralization 

 with sodium carbonate solution, and make up to 500 cc. Mix the solution well, pour 

 through a dry filter, and determine the dextrose in an aliquot as directed under 

 52 or 54. Conduct a blank determination upon the same volume of the malt 

 extract as used upon the sample and correct the weight of reduced copper accord- 

 ingly. The weight of the dextrose obtained multiplied by 0.90 gives the weight of 

 starch. 



PENTOSANS.— TENTATIVE. 



63 REAGENT. 



Phloroglucin. — Dissolve a small quantity of the phloroglucin in a few drops of 

 acetic anhydrid, heat almost to boiling, and add a few drops of concentrated sul- 



