328 METHODS OF ANALYSIS [Chap 



STARCH. 



10 Direct Acid Hydrolysis. —Tentative. 



Weigh 4 grams of the sample, if unsweetened, or 10 grams if sweetened, into a 

 small porcelain mortar, add 25 cc. of ether and grind. After the coarser materia) 

 has settled, decant the ether, together with the fine suspended matter, onto an 11 

 cm. paper of sufficiently fine texture to retain the crude starch. Repeat this treat- 

 ment until no more coarse material remains. After the ether has evaporated from 

 the filter, transfer the fat-free residue to the mortar by means of a jet of cold water 

 and rub to an even paste, filtering on the paper previously employed. Repeat this 

 process until all the sugar is removed. In the case of sweetened products the fil- 

 trate should measure at least 500 cc. Determine crude starch in the extracted 

 residue as directed under VIII, 60. 



11 Diastase Method. — Tentative. 



Remove fat and sugar from 4 grams of the sample, if unsweetened, or 10 grams if 

 sweetened, as directed under 10. Wash carefully the wet residue into a beaker with 

 100 cc. of water, heat to boiling over asbestos with constant stirring and continue 

 the boiling and stirring for 30 minutes. Replace the water lost by evaporation and 

 immerse the beaker in a water bath kept at 55°-60°C. When the liquid has cooled 

 to the temperature of the bath, add 20 cc. of freshly prepared malt extract [VIII, 

 61] and digest the mixture for 2 hours with occasional stirring. Boil a second 

 time for 30 minutes, dilute, cool and digest as before with another 20 cc. portion 

 of the malt extract. Heat again to boiling, cool and transfer to a 250 cc. flask. Add 

 3 cc. of alumina cream, make up to the mark and filter through a dry paper. The 

 residue on the paper should show no signs of starch when examined microscopically. 

 Continue from this point as directed under VIII, 62, beginning with the words 

 "Place 200 cc. of the filtrate in a flask with 20 cc. of hydrochloric acid". 



12 FAT.-TENTATIVE. 



Dry 2 grams of the material over sulphuric acid until all the moisture is practi- 

 cally removed. (Products rich in fat show a tendency to cake at the temperature 

 of boiling water. Hence, drying by means of heat must be avoided.) Extract with 

 anhydrous ether in a continuous extractor until no more fat is removed. Grind 

 and repeat the extraction. Introduce the ether extract into a tared dish, allow the 

 ether to evaporate and dry the residue to constant weight at 100°C. 



The rapid centrifugal method^, though useful and accurate under ordinary con- 

 ditions, is unreliable during the summer months or in warm latitudes and has not 

 been approved. 



13 FAT CONSTANTS.-TENTATIVE. 



Separate the fat in a manner similar to that described under 1 5 and determine 

 the melting point, index of refraction, iodin absorption, saponification, Reichert- 

 Meissl and Polenske numbers as directed under XXIII. Melting point determi- 

 nations upon this material do not become normal until the fat has been kept for at 

 least 24 hours in a cool place. 



1 4 MILK FAT IN MILK CHOCOLATE.-TENTATIVE. 



Estimate the amount of milk fat in milk chocolate from the following formula 

 based on a Reichert-Meissl number of 0.5 for cocoa butter: 



