165 
RerractiveE Inpex as A Measure oF Dry SUBSTANCE IN 
SACCHARINE Propwcts.* 
By A. HucH 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° C. 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. Differences of as 
high as 0.5% have been noted, especially where the substance under exami- 
pation 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. 256) in 1884 and again in 1886 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. Tolman and Smith,’ using the heatable prism in- 
strument, such as is used today, and pictured later in this paper, found 
*Published by permission of the Secretary of Agriculture. 
lJour. Amer. Chem. Soe. (1906), 28, 1476. 
