METHODS FOR DETERMINING SUGAR. 19 



hot water, and shake. Immerse the flask in a water bath at 80 C. 

 and shake at intervals by rotating. Add water from time to time so 

 that at the end of the heating, about 30 minutes, the water in the 

 flask is a little above the mark. Remove the flask from the water 

 bath and allow it to cool to standard temperature; add a sufficient 

 quantity of concentrated acetic acid to make the solution very 

 slightly acid in reaction (generally less than 0.5 cc is necessary) 

 and a few drops of ether to break the foam; complete the volume. 

 Mix thoroughly, filter, and polarize in a 200 mm tube. 



With this method a coarser beet pulp can be used than for the cold- 

 water methods, but over 30 minutes may be necessary for digestion, 

 if very coarse cuttings are used. To obtain correct results, care must 

 be exercised to make up to volume at the standard temperature of 

 20 C. (if the instrument and flasks are standardized at that tempera- 

 ture) and to digest the beet cuttings with as large a quantity of water 

 as possible. Not over 5 cc in any case should be added during 

 digestion and final cooling to complete the volume. Where smaller 

 quantities of water are used during digestion and then a large quantity 

 of water is added at the last to make to volume, the sugar has not 

 become equally diffused and the results are too low. Differences of 

 over 1 per cent in sugar content are often caused by lack of care in this 

 particular. 



HOT- WATER DIGESTION METHOD OF SACHS LE DOCTE. 



The procedure in the Sachs Le Docte cold-water extraction 

 method (p. 18) is modified as follows for hot digestion: The weighing 

 and the vessels used are the same, also the quantities of lead sub- 

 acetate and water are the same, namely, 177 cc. A special rubber 

 disk cover (7, frontispiece) is provided for the digestion vessels. Put 

 this in place and after shaking the vessel immerse it hi a water bath 

 kept at 80 C. for 30 minutes, or for 25 minutes if the temperature is 

 85 C. The temperature during extraction should not, however, 

 exceed this figure. Remove the cups and immerse in cold water, bring- 

 ing the temperature down to 20 C., shake, remove the covers, filter, 

 and polarize, after adding a drop or so of acetic acid. 



The chance of error due to contained air or unequal diffusion of 

 the pulp is removed by this method. As in the former case the 

 cuttings need not be so fine as with the cold-water extraction methods. 



HERZFELD'S MODIFICATION OF THE SACHS LE DOCTE METHOD. 



Instead of the tin-coated copper beakers used in the preceding 

 method, Herzfeld uses an extraction vessel of nickel-plated sheet 

 iron made us shown- in figure 5. The vessel is round. He also uses 

 small weighing glasses, holding 26 grams of material, which can be 

 introduced with the beet cuttings into the extraction vessel. These 



