METHODS FOR DETERMINING SUGAR. 21 



With this method very line pulp is necessary and the greatest care 

 must he exercised to remove all of the air from the beet cuttings to 

 insure an even digestion. For accurate readings the polarization 

 should be made at the standard temperature of the instrument and 

 flasks and allow of no evaporation. This method is but little used. 



HOT ALCOHOL DIGESTION METHOD. 



The same procedure is followed as in the preceding method up to the 

 point of adding more alcohol. In this method add only enough 90 per 

 cent alcohol to fill the flask three-fourths full. Then connect the flask 

 with a return condenser, place in a water bath, and allow to boil 

 for 20 minutes. Cool the flask and contents to the standard tempera- 

 ture and bring up to the mark with 90 per cent alcohol, shake and 

 allow to stand for awhile, filter, and polarize. 



This method does not require so fine a pulp as the former one 

 and is not open to error from entrained air bubbles, but to obtain 

 correct results it must be worked carefully to prevent evaporation 

 and changes of temperature during polarization. 



ALCOHOL EXTRACTION METHOD. 



The alcohol extraction method has been recognized as the standard 

 method for sugar determination and is the one with which other 

 methods are compared, but its execution is difficult and the results 

 are liable to error if the greatest care is not exercised. For the 

 inexperienced chemist it is not a suitable method, but by familiarizing 

 oneself with its details and difficulties, correct results can be obtained. 



A Soxhlet extraction apparatus is necessary for this method. The 

 usual form has been improved by opening the siphon tube with a 

 short tube and cork as shown in the frontispiece, K. In this way one 

 can test the progress of the extraction by withdrawing a sample 

 without interfering with the work. The best procedure for this 

 method is to weigh 26 grams of the beet pulp and transfer to a 100 cc 

 flask with about 50 cc of 90 per cent alcohol and from 3 to 5 cc of 

 basic lead-acetate solution. Connect a return condenser to the flask 

 and place in a boiling water bath for from 10 to 15 minutes. Then 

 pour the whole into the extractor, washing out the flask with fresh 

 portions of 90 per cent alcohol. A return condenser is connected 

 with the Soxhlet extractor and also a 100 cc flask, the latter by 

 means of a cork. Add more 90 per cent alcohol until the siphon 

 is started and the lower flask is about three-fourths full. Place the 

 containing flask in a covered water bath held at a heat that will 

 make the alcohol boil freely. Continue the extraction for from one to 

 four hours, or until a test of the alcohol in the extractor gives no 

 color with <*-naphthol solution (see p. 22). Remove the flask and 

 add 90 per cent alcohol to the mark after cooling to the standard 

 temperature, shake and filter. Polarize in 200 mm tube. 



