JACKSON: ROTATION OF DEXTROSE 531 



would cause a rotation of 100°$ on the scale of the quartz-wedge 

 saccharimeter. If the latter is controlled by the conversion fac- 

 tors determined by Bates and Jackson, 2 namely, 34?620 for 

 X = 5892.5 A or 40?690 for X = 5461 A or by the rotation of 

 26.000 gm. of pure sucrose in 100 cc, the normal weight of dex- 

 trose is 32.231 gm., weighed in air with brass weights. If the 

 saccharimeter is calibrated by the Herzfeld-Schonrock factor, 

 34?657, which Bates and Jackson have shown to be in error, the 

 normal weight of dextrose is 32.264 gm. 



For solutions more dilute than normal the rotations deviate 

 from proportionality. It is, therefore, necessary to apply cor- 

 rections, to make the scale reading indicate the per cent of sub- 

 stance. These corrections are given in Table 1. 



TABLE 1 



Reading: 90°S 80°S 70°S 60°S 50°S 40°S 30°S 20°S 10°S 

 Correction: +0.20 +0.35 +0.46 +0.53 +0.55 +0.53 +0.46 +0.35 +0.20 



The rotation of the normal solution (32.231 gm.) for X = 5461 

 A is 40?898. Since the normal quartz plate rotates 40?690, it 

 is evident that there is a considerable divergence between the 

 rotary dispersion curves of dextrose and of quartz. Thus, when 

 the quartz-wedge saccharimeter is set for a photometric match, 

 the field is slightly heterochromatic and the degree of repro- 

 ducibility of the setting is necessarily less than that of sucrose, 

 whose dispersion curve coincides more closely with that of quartz. 

 This difficulty is only overcome by an increased number of set- 

 tings and by some preliminary experience on the part of the 

 observer. 



The specific rotation, which is a function of the concentration 

 of dextrose, corresponds to the formula 



W 2 M6°i a = 62.032 + 0.04257 c 



where c is grams of anhydrous dextrose weighed in vacuo and 

 contained in 100 cc. of solution, or to the formula 



MS a = 62 - 032 + 0.04220 p + 0.0001897 p 2 

 where p is per cent dextrose by weight in vacuo. 



2 Journ. Wash. Acad., 6: 25. 1916; Bull. Bur. Standards, 13: 67. 1916. 



