169 



Summarizing the average results, we find that the refractometer dry 

 substance is higher than the true. 



Per Cent. 



The difference in case of maple syrup 0.50 



The difference in case of cane syrup 0.29 



The difference in case of honeys 1 .45 



The difference in case of glucose 0.27 



The difference in case of cane molasses 0.79 



The difference in case of beet molasses 1.08 



The difference in case of beet molasses (half) 0.36 



With the exception of the honeys and possibly cane molasses, also 

 beet molasses undiluted, the differences are well within the error of deter- 

 mination of water by actual drying. By half dilution, the beet molasses 

 is brought within the limits, and where dilution with sugar solution tried 

 this difference would be cut down considerably. Cane molasses, showing 

 0.79%. might be considered within the limits, as a true moisture content 

 on this material is a difficult task. Honeys are. then, the only ones whose 

 difference is large, but it is hoped that with the work now being carried 

 on. the reason for this difference will be obtained and a method for pro- 

 cedure be established for this grade of substance. However, there is one 

 thing to be said in regard to the refractometer. that it is possible to ob- 

 tain duplicate results that are identical, and different investigators should 

 obtain identical results, which is a condition that does not exist with the 

 other methods for dry substance determination in use now. The refracto- 

 meter method has the advantage of being quick and not losing accuracy 

 by speed, and then only small portions are necessary for a determination. 

 The method of making a dry substance determination is substantially 

 this: The instrument (Fig. 1) is placed so that the light falls on the mir- 

 ror (R) and this is turned on its axis to reflect the light up through the 

 prism (B) and (A). The source of light can be daylight, but a better 

 one is a 32 or higher candle power lamp. The tubular (D) is connected 

 by rubber robing to the source of water supply of constant temperature 

 and the other tubular (E) has a rubber overflow connection. The ther- 

 mometer is placed in its socket. The optical parts of the instrument are 

 turned forward on the stand (a). By turning the catch (V) the prism 

 B is swung open on (C) from prism (A) and a few drops of the solution 

 to be examined is placed on the prism (A). Enough of the solution should 

 be added so that on closing the prism (B) on (Ai a part of the liquid is 

 forced out. The optical parts are brought bade into their original place. 



