165 



Refractive Index as a Measure of Dry Substance in 

 Saccharine Products.* 



By A. Hugh Bryan. 



Dry substance determinations are the most difficult determinations a 

 a chemist has to make, and again one of the most important. In sugar 

 materials, containing many organic substances and also inorganic salts, 

 various reactions and changes are going on when the sample is heated in 

 the course of making a dry substance determination. Varying degrees of 

 heat also tend to decompose these substances. Also, the length of time of 

 heating is a very important factor. The accepted method for sugar com- 

 pounds, where accurate results are desired, is the loss of weight at 70° 

 C. when heated in vacuum. It has been found at that temperature that 

 levulose shows little, if any, decomposition. Sugar chemists of Germany 

 modify that procedure by drying at 65° to 70° C. in the air until all vis- 

 ible water is gone, and then heat for from 2 to 4 hours at 105° G. in 

 vacuum, it being claimed that by first drying and then heating to 105° in 

 vacuum, no sugar is decomposed. It is a fact, however, that if one makes 

 two determinations of moisture on the same sample at different times. 

 it is more than likely that the results will not check. Di'fferences of as 

 high as 0.5% have been noted, especially where the substance under exami- 

 nation is high in reducing sugars. It can hardly be expected to obtain a 

 method for determining moisture accurately without a direct determination 

 of this by drying. Such a procedure takes time, and at its best, so far. 

 gives only approximate results. 



The refractometer was first tried in sugar work by Strohmer (Zeit 

 Ruben Zuckerind., Vol. 21. p. 250) in 1884 and again in 1SS6 by Muller 

 (Ibid. Vol. 37, p. 91). They showing that the index depended on the 

 concentration of solution. The latter investigator gave a table for esti- 

 mating the dry substance of beet juices from the refractive index. Again 

 in 1901, Stolle published a table for the above. All of these used the old 

 forms of instruments. Tohnan and Smith, 1 using the heatable prism in- 

 strument, such ns is used today, and pictured later in this paper, found 



*Puhlished by permission of the Secretary of Aerioulture. 

 '.lour. Amer. Chem. Soc. (1906), 28, 1476. 



