METHODS FOB DETERMINING SUGAR. 15 



air hubbies from remaining on its surface. The flask is then filled to 

 the mark with water, shaken, filtered, and polarized. The percentage 

 of sugar in the juice thus obtained is multiplied by a factor to obtain 

 the amount of sugar in the beet. This factor corrects for the marc 

 or solid portion of the beet. It is not, however, accurate to deter- 

 mine the marc by the usual method, namely, by washing away the 

 soluble portion of the beet, drying, and weighing, calculating the per 

 cent of solids, subtracting this from 100, and using the figure found 

 for the juice factor. With this procedure the results will be too high 

 for the reason that the marc contains water other than that holding 

 the sugar and no correction is made for it. The marc of beets varies 

 from 4 to 5.5 per cent, with an average of about 4.7 per cent. The 

 juice factor calculated from this figure would be about 95.3, but when 

 the colloidal water or water of marc is considered the figure is from 

 88 to 95, depending on the condition of the beets and the pressure 

 used. A factor as low as 82 may be obtained if the beets are badly 

 wilted from long standing in a dry climate, such as Colorado. This 

 factor may be determined for a given locality by selecting beets of 

 average condition and finding the per cent of sugar in the juice by 

 the indirect method just given; then on a small portion of the same 

 sample of beets determining the per cent of sugar in the beet by one 

 of the direct methods, and dividing the per cent of sugar in the beet 

 by the per cent of sugar in the juice. Such a factor is applicable to 

 beets of like condition. 



The indirect method is used somewhat extensively, for by its use 

 in addition to the percentage of sugar the purity of the juice (the per 

 cent of sugar in the solids of the juice), which is considered by some 

 to be an important factor in beet analysis, is obtained. This method 

 is advantageous in that large quantities of pulp, representing many 

 beets, can be used for pressing; therefore it is very easy to obtain an 

 average sample when the original quantity is large. The main objec- 

 tion to it is that it does not give the sugar in the beet direct, the use 

 of a factor being necessary. This average factor varies somewhat in 

 different localities, ranging from 91.5 to 93, and its use works to the 

 advantage of one sample and to the disadvantage of another. If not 

 much depends on the accuracy of the results, this method can be 

 used, but it can hardly be recommended when exactness is desired. 



ERRORS OF THE METHOD. 



Errors in the actual determination of the percentage of sugar creep 

 in from the following sources, but with beets of 15 or even 20 per 

 cent sugar content these errors may be within the error of reading or 

 tho limits of the sensibility of the instrument: 



(1) Use of the wrong normal weight. Most polariscopes that have 

 been purchased during the last five or six years are standardized for 





