§ 131. FODDEK. 255 



its volume in the azotometer. {See Fresenius^s Quan- 

 titative Analysis.) 



e. Sugar aad Gum in Aqueous Extract.— Evaporate 

 500 to 1000 c.c. nearly to dryness, as quickly as it can be 

 done without loss, and, if j^ossible, in a space where the 

 air can be rarefied, and exhaust the moist residue with 

 alcohol of 80-85" 1^, by repeated boiling with fresh por- 

 tions of the solvent, as long as it is colored. Filter the 

 liquid, add water to the filtrate, expel the alcohol by heat, 

 filter through animal charcoal, if necessary, bring this 

 filtrate to a certain volume, and estimate glucose and 

 saccharose (§ 81). 



Dry the residue insoluble in alcohol at 100° C, weigh, 

 and incinerate it. Subtract the ash and protein com- 

 pounds, as may be estimated from determinations already 

 made, from the total amount of the residue insoluble in 

 alcohol, and call the remainder gu7n and vegetable acids. 



f. IVitric Acid. — To control the determination of nitro- 

 gen already made in a portion of the aqueous extract, 

 nitric acid may be determined, in addition to the ammonia 

 already estimated; thus it may be learned how much 

 of the nitrogen is present in the form of these inorganic 

 substances. 



Evaporate 500-1000 c.c. of the aqueous extract to a 

 small bulk, and determine nitric acid by Schlossing's 

 method (§ 62, a). 



Frtihling and Grouven {Landwirthsch. Yersuchs-Sta- 

 tionen, 9, 9) prepare the aqueous extract of the plant, 

 particularly for the determination of nitric acid, as fol- 

 lows : Put 100-500 grms. of the finely divided but not 

 ground air-dried substance in strong beakers of a capacity 

 of two litres; add enough 50" 1^ alcohol, so that the whole 

 mass of the solid will be completely covered, when pressed 

 down firmly with a pestle and kept down by a plate 

 weighted with a glass filled with mercury. 



