§ 134. POTATOES. 261 



hour ; decant the supernatant liquid on a dried and 

 weighed filter, and finally transfer the insoluble residue to 

 the same filter ; wash the filter well with cold water, re- 

 move most of the water from its contents by pressure 

 between folds of filter-paper, dry the whole at 100°, and 

 weigh. Treat the filter and its contents with extract of 

 malt, and determine glucose in the product (§ 81). 



POTATOES. 



134. Prepare them for examination as directed in § 133,a. 



a. Water. — Dry 250-500 grms. of the potatoes, and 

 determine hygroscopic water also, as directed in § 133, a, 

 in the examination of roots. 



I. Dry substance soluble in water. — Cut several pota- 

 toes very fine, and crush 30 grms. )f the carefully mixed 

 sample with cold water, in a mortar, and separate the 

 soluble from the insoluble part in the same manner as di- 

 rected in § 133, g. 



Dry the insoluble residue at 100° C, weigh it, inciner- 

 ate it in the muffle (§ 123, c), and weigh the ash ; thus we 

 have determined the organic and the inorganic matter in- 

 soluble in water. The difference between the weight of 

 the dried insoluble residue and the amount of substance 

 taken gives the weight of soluble matter in it. 



Bring the aqueous solution to any easily divisible vol- 

 ume, and heat about ^ I3 of it to boiling. Albumen is pre- 

 cipitated, and may be collected on a weighed filter, dried 

 at 100°, and weighed. 



Evaporate the filtrate from the albumen to dryness on 

 the water-bath, Aveigh the residue, ignite it, and weigh the 

 ash ; thus organic and inorganic matters, soluble in 

 water, are determined. 



c. Albuminoids. — Evaporate another third of the solu- 

 tion almost to dryness, mix the moist residue with calcined 



