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that for equal concentrations, all sugars have about the same index of re- 
fraction. Main’ published tables of water content from refractive index 
in 1907, and called attention to the accuracy of this method, as compared 
with the true dry substance. Since that time the literature has been full 
of articles on this method of determining the dry substance. 
All authors, with but few exceptions, claim much for this method as a 
quick one and yielding comparable results. They all agree that the re- 
sults so obtained are nearer the true dry substance than by obtaining the 
dry substance from the specific gravity. The substances dissolved along 
with the sugar seemingly have a closer refractive index to sugar than 
specifie gravity. 
Working on syrups of various origins, I obtained the following aver- 
age figures... The method for true dry substance was loss of weight in 
vacuum at 70° C. The table of Prinsen Geerligs, and also his corrections 
for temperature were used. These are given later in this paper. 
IN CASE OF MAPLE SYRUP. 
Thirteen samples were examined. In only one case was the refracto- 
meter dry substance higher than the true, and in all others the true dry 
substance was higher. This difference ranged from 0.20% to 1.54% with 
an average of 0.50%. 
WITH CANE SYRUP. 
Ten samples were examined. In three cases the refractometer dry 
substance was higher than the true by 0.16%, 0.34%, 0.62%. The other 
cases range from 0.24% to 0.93%, or an average difference on the whole 
of 0.29%. 
HONEYS. 
Twenty-four samples were examined. In 2 cases the refractometer 
dry substance was higher than the true by 0.21% and 0.91%. In all the 
rest it was lower by from 1.15% to 2.52%, with an average of 1.45%. 
This is the greatest difference noted. One of three causes or all may ac- 
count for this large difference. (1) The actual dry substance may not be 
right, viz., this product may not give up all of its water at 70° in vacuum, 
or, (2) the dextrin of the honey may change the refractive index of the 
lfnter. Sugar J. (1907), 9, 481. 
2Norr. See Jour. Amer. Chem. Soc. (1908), 30, 1443, for a previous paper on this subject 
by the author. 
