=219. Pellet’s Method of Cold Diffusion.=—The impalpable pulp having been obtained, by one of the processes described, the content of sugar therein is determined as follows:[181] A normal or double normal quantity of the pulp is quickly weighed, to avoid evaporation, in a sugar dish with an appropriate lip, and washed into the flask, which should be graduated, as shown in Fig. 68, to allow for the volume of the fiber or marc of the beet. Since the beet pulp contains, on an average, four per cent of marc, the volume which is occupied thereby is assumed to be a little more than one cubic centimeter. Since it is advisable to have as large a volume of water as convenient, it is the practice of Pellet to wash the pulp into a flask graduated at 201.35 cubic centimeters. If a 200 cubic centimeter flask be used, the weight of the pulp should be 25.87 instead of 26.048 grams. After the pulp is washed into the flask, about six cubic centimeters of lead subacetate of 30° baumé are added, together with a little ether, to remove the foam. The flask is now gently shaken and water added to the mark and the contents thoroughly shaken. If the pulp is practically perfect, the filtration and polarization may follow immediately. The filter into which the contents of the flask are poured should be large enough to hold the whole quantity. It is recommended to add a drop or two of strong acetic acid just before completing the volume of the liquid in the flask to the mark. The polarization should be made in a 400 millimeter tube, which will give directly the percentage of sugar present. It is not necessary to heat the solution in order to insure complete diffusion, but the temperature at which the operation is conducted should be the ordinary one of the laboratory. In case the pulp is not as fine as should be, the flask should be allowed to stand for half an hour after filling, before filtration. An insufficient amount of lead subacetate may permit some rotatory bodies other than sugar to pass into solution, and care should be taken to have always the proper quantity of clarifying material added. The presence of these rotating bodies, mostly of a pectic nature, may be shown by extracting the pulp first with cold water until all the sugar is removed, and afterwards with boiling water. The liquor obtained from the last precipitation will show a decided right-handed rotation, unless first treated with lead subacetate, in which case the polarization will be zero. A very extended experience with the instantaneous cold aqueous diffusion has shown that the results obtained thereby are quite as reliable as those given by hot alcoholic or aqueous digestion.