130 C. U. C. P. ALUMNI JOURNAL August, 1918 



We therefore turned to the idea of vacuum evaporation at ordinary tempera- 

 ture and obtained satisfactory results by this method. We placed a small, weighed 

 sample in a flat container (Petrie dish) with a suction desiccator containing con- 

 centrated sulphuric acid as a dehydrator. We pumped out the air by use of a 

 water suction pump, and allowed the desiccator to remain in exhausted condition 

 for 24 hours, after which we removed the Petrie dish and weighed it. This was 

 repeated each day until the dish no longer lost weight, after which the residue 

 was calculated as glycerin. On samples of aqueous solutions of glycerin, we ob- 

 tained the following figures: 



Residue, 



2.090 gm. 



1.575 gm. 

 1.050 gm. 

 0.525 gm. 



In the case of mixture of rhubarb and soda, we evaporated in vacuo a meas- 

 ured quantity and thus obtained a residue consisting of glycerin, rhubarb extrac- 

 tive and sodium bicarbonate. The ash obtained from this residue calculated as 

 bicarbonate, was subtracted from the residue, the difference being glycerin and the 

 scarcely appreciable amount of rhubarb extractive. 



Our figures thus obtained are given below: 



Sample of mixture of rhubarb and soda contained 41.912 Gm. of glycerin, 

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



Theoretical 

 weight 

 glycerin 

 present. 



2.0956 gm. 

 2.0956 gm. 

 2.0956 gm. 



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 

 weight 

 glycerin 

 present. 



1.0478 gm. 

 1.0478 gm. 

 1.0478 gm. 



It will be seen that the figures thus obtained for glycerin were not uniform, 

 due undoubtedly to the fact that the ash did not consist wholly of sodium carbon- 

 ate. We therefore tried the expedient of converting the bicarbonate in the mixture 

 of rhubarb and soda into chloride by addition of the proper amount of concen- 

 trated hydrochloric acid and obtained the satisfactory results given below : 



Sample of mixture of rhubarb and soda contained 41.912 Gm. of glycerin 

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



Theoretical 



weight 



glycerin 



present. 



2.0956 gm. 

 2.0956 gm. 

 2.0956 gm. 

 2.0956 gm. 



