August. 1918 C. U. C. P. ALUMNI JOURNAL 131 



Sample of mixture of rhubarb and soda contained 20.956 Gm. of glycerin 

 dehydrated by standing in vacuo and 3.5 Gm. of sodium bicarbonate in 100 mils. 



Theoretical 



StudN-ing the foregoing tables, it will be seen that the glycerin figures obtained 

 by the assay are satisfactorily uniform, the variation between the highest and low- 

 est result when preparation of full glycerin content was used, being only 0.35 per- 

 cent. On the other hand the figures obtained are about one percent higher than 

 the amount of glycerin actually present in the sample, a figure higher than that 

 represented by the extractive of the rhubarb. This variation, however, is less 

 than that obtained by us from other assay methods and is in favor of the seller of 

 the sample. 



Our present method of assay is as follows : 



Five mils of the mixture of rhubarb and soda are accurately weighed in a 

 Petrie dish and after the addition of enough concentrated hydrochloric acid to 

 convert the bicarbonate into chloride, it is then evaporated in a vacuum desiccator 

 containing sulphuric acid as dehydrating agent and a small dish containing soda 

 lime to absorb any excess of hydrochloric acid. After exhaustion of the container, 

 the mixture is allowed to stand twenty-four hours before weighing. It is similarly 

 treated each day until it ceases to lose weight. After thus obtaining the weight 

 of glycerin, sodium chloride and extractive contained in the sample, the residue is 

 ashed and the weight of the ash, sodium chloride, subtracted from the residue ob- 

 tained by evaporation gives the amount of glycerin and extractive present in the 

 sample. Of course, from the weight of sodium chloride, the amount of sodium 

 bicarbonate present in the original mixture can be obtained by molecular weight 

 calculations. 



It is obvious, if the glycerin in the mixture of rhubarb and soda is replaced 

 by some of the cheaper glycerin substitutes now on the market, the residue ob- 

 tained by evaporation would be something other than glycerin. As most glycerin 

 substitutes contain glucose or similar reducing carbohydrates, all samples of the 

 mixture of rhubarb and soda should be tested, prior to the glycerin assay, for re- 

 ducing sugars. This procedure is, however, subject to several difficulties. In the 

 first place, the extractive in mixture of rhubarb and soda contains substances of 

 reducing character. Our tests in this direction, however, show that the amount 

 L' small, two mils of Fehling's solution (representing o.oi gm. glucose) requiring 

 from twenty-one to 21.7 mils of the official mixture for complete reduction. 



On the other hand, a more serious difficulty comes from the tact that the 

 various suggested glycerin substitutes contain different forms of carbohydrates, 

 such as commercial glucose, straight or invert sugar. As these substances possess 

 different Fehling factors, and as different samples of commercial glucose give dif- 

 ferent reduction figures with Fehling's solution, this part of the problem is by no 

 means solved and we hope to do further work in this direction. In passing, how- 



