^ 76, 77. DEXTRIN, ETC—SAPONIN 67 



amount of sugar thus produced. The majority of the iiiulin is, 

 however, left in the residue insoluble in, water, from which it 

 may be extracted as directed in § 102. 



§ 76. Dextrin, etc. — The filtrate and wash-alcohol from the 

 mucilage precipitate {§ 73) are evaporated aa rapidly as possible, 

 at a temperature of 70° to 80°, to a syrupy consistence and again 

 precipitated with 4 volumes of absolute alcohol. Certain car- 

 bohydrates soluble in dilute alcohol, such as dextrin, levulin, 

 sinistrin and triticin, are thus thrown down and shciuld be 

 filtered off ias rapidly as possible. 



These carbohydrates may be distinguished from mucilage by 

 their being more easily convertible into sugar and by their not 

 being precipitated by basic acetate of lead. Dextrin is dextro- 

 rotatory in aqueous solution, and yields grape sugar on boiling 

 with a dilute acid. Levulin, sinistrin, and triticin vield levu- 

 lose. The first of these three is optically inactive ; sinistrin and 

 triticin are laevo-rotatory {ao - -32'456 and— 43"579° respec- 

 tively). None of the four are coloured either blue or red by 

 iodinfe.! Sinistrin and triticin are precipitated by caustic baryta 

 from solution in 40 per cent, alcohol. Carbonic acid liberates the 

 carbohydrate from the compound thus produced (§ 198), 



Qmn^aiive Estirmtiaa (§§ 199, 201 to 204).— The carbo- 

 hydrates mentioned in the preceding paragraph are best esti- 

 mated by boiling with a dilute acid and determining the amount 

 of sugar thus produced by titrating with Fehling's solution. The 

 barium precipitates of levulin^ triticin and sinistrin. may be treated 

 directly with acid. 



If dextrin and glucose are present together, the results yielded 

 by the estimation are as a rule somewhat too high, as a little 

 sugar is precipitated with the dextrin. 



It should, however, be ascertained whether the dextrin-precipi- 

 tate contain much nitrogen, and, if this is the case, whether the 

 amido-acids discussed in §§ 101 and 242 are present. 



EXAMINATION FOR SAPONIN AND ALLIED SUBSTANCES. 



§ 771 Extraction of. Saponin. — If the precipitate obtained with 

 alcohol in § 76 is rapidly filtered oflF, the majority of the saponin 



■ It was formerly thought tliat dextrin was coloured red by iodine. This 

 colouration was due to an impority (soluble starch — erythmdextrin) contained 

 in the dextrin examined. 



5—2 



