530 JACKSON: ROTATION OF DEXTROSE 



equivalent, and K the thermal capacity of the liquid per unit 

 volume. Thus the temperature rise depends solely on Ap and 

 K; it is independent of the shape, diameter, or length of the 

 tube, the viscosity of the liquid, or the rate of discharge. 



CHEMISTRY. — The saccharimetric normal weight and the spe- 

 cific rotation of dextrose. 1 Richard F. Jackson, Bureau of 

 Standards. (Communicated by S. W. Stratton.) 



Pure dextrose was prepared from starch conversion products 

 and from invert sugar solutions. After a preliminary purging 

 had removed a great portion of the adhering impurities, the sub- 

 stance was dissolved to form a 60 per cent solution in water and 

 the crystals allowed to form slowly during continuous agitation. 

 Two or three recrystallizations were sufficient to produce dex- 

 trose of high purity. A portion was subjected to a fractional 

 crystallization and another portion precipitated by ethyl alcohol. 

 The various purified samples showed essentially identical prop- 

 erties. 



Dextrose crystallizes from water solution with one molecule 

 of water of crystallization which it loses very readily at 60°C. 

 The residual moisture was removed by heating in a vacuum at 

 60°-80°C. for several hours. 



To prepare the solution for polarization, approximately the 

 quantity required was weighed and dried in a weighed volu- 

 metric flask, and the solution was made up to the graduation 

 mark of the flask at 20°C. From the data obtained the den- 

 sities of dextrose solutions were calculated and found to corre- 

 spond to the formula: 



D 20 o = 0.99840 + 0.003788 p + 0.00001412 p 2 where p is 



per cent anhydrous dextrose by weight in vacuo. The formula 

 is valid for values of p between 5 and 30. 



The solution was allowed to stand over night at room temper- 

 ature in order to destroy the mutarotation. 



Twelve independent measurements were made to determine 

 the weight of substance which, contained in 100 cc. of solution, 



1 To appear in detail as a Scientific Paper of the Bureau of Standards. 



