112 § 80. BASES AND ACIDS WITH EE AGENTS. 



amount of these can be determined by evaporating the 

 solution of starch and inorganic salts to dryness, and in- 

 cinerating the residue at a low red heat (§ 91). 



Or, the starch may be extracted with a concentrated 

 solution of malt instead of with acid, in wliich case no in- 

 organic salts will be taken into solution. Prepare the 

 solution of malt and perform the operation as directed 

 above. 



If much mucus is present, a concentrated solution of 

 sodic chloride mixed with 5°\^ of hydrochloric acid should 

 be used instead of pure water and acid. 



GUM. 



80. The gums, which abound in the juices of plants, 

 are very soluble in water, forming thick, viscid solution «; 

 they are insoluble in alcohol. 



Quantitatiye estimation. — This depends upon their in- 

 solubility in alcohol. A quantity of from 500 to 1000 c.c. 

 of the aqueous extract of the substance in which the gum 

 is to be determined is evaporated almost to dryness on 

 the water-bath, and the moist residue is digested with al- 

 cohol of 80 to 85° 1^ until it is no longer colored by mat- 

 ters taken into solution. 



Sugar is dissolved, while gum, albuminoids, and some 

 inorganic salts, remain unaffected ; collect the insoluble 

 substance on a dried and weighed filter, dry at 100° C, 

 and weigh. Then incinerate this residue at a low red heat 

 (§ 91), and subtract from the total weight of the residue 

 insoluble in alcohol, the sum of the weights of the ash 

 just determined, and the albuminoids, which are deter- 

 mined by another process (§ 85). The remainder may be 

 considered as gum, mixed with some vegetable acids. 



GLUCOSE. GRAPE SUGAR. CeHijOeH^O. 180 + 18. 



81 . This sugar is soluble in water, and somewhat solu- 

 ble in aqueous alcohol. 



