SCIENCE. 



393 



THE ROTATORY POWER OF COMMERCIAL 

 GLUCOSE AND GRAPE SUGAR. A METHOD 

 OF DETERMINING THE AMOUNT OF RE- 

 DUCING SUBSTANCE PRESENT BY THE 

 POLARISCOPE. 



By Prof. W. H. Wiley. 



From the Journal of the American Chemical Society, Vol.11. 



In " the trade " the name of grape sugar is applied 

 only to the solid product obtained from corn starch. On 

 the other hand, the term "glucose " is given to the thick 

 syrup made from the same material. 



I shall use these words in their commercial sense. 



INSTRUMENTS EMPLOYED. 



I used in the following investigations two polariscopes 

 made by Franz Schmidt and Haensch, Berlin. The 

 readings of these instruments, after correction tor dis- 

 placement, agreed well together. 



The one was the instrument ordinarily used, in which 

 the purple ray is employed, and the quartz half moons 

 give blue and red tints. 



Both of these instruments are graduated to read 100 

 divisions, each equal to one per cent sugar with a solu- 

 tion containing 26.048 grms. pure cane sugar in 100 c.c. 

 In addition to this scale the half shadow has another 

 which gives the actual angular rotation. 



This is especially convenient when the specific rotatory 

 power of a substance is to be determined. The angular 

 rotation, however, can be calculated for the former 

 instrument. 



For if we take the specific rotatory power of cane 

 sugar at 73. 8°, we have the following equation : 

 a X 100 



73-8 = 



is therefore 



scale 



2 X 26.048 3 

 Each division on the cane sugar 

 equal to o°.3845 angular measure. 



This quantity corresponds to the transition tint. It is 

 different for the- differently colored rays. In the half 

 shadow polariscope, an instrument particularly adapted 

 to persons afflicted with any degree of color-blindness, 

 the mono-chromatic light coming from the sodium-Bun- 

 sen lamp passes through a crystal of acid potassium 

 chromate. The ray thus produced is less rotatable than 

 the " transition tint." 



When the instrument gives 100 divisions on the sugar 

 scale, it shows an angular rotation of only 34^42' = 34°7. 

 Our division, therefore, of the sugar scale, is equal to 

 o°.347 angular measure. 



To determine the specific rotatory power of cane sugar 

 for the sodium-acid potassium chromate ray, we use the 

 following equation : 



Sp. rot. pr. = = 66«6. 



r 2 X 26.048 



To determine the specific rotatory power for any othei; 

 substance which has been determined for the transition 

 tint, we multiply by the factor 0.9024. 



Thus, if we take the specific rotatory power for any 

 other substance which has been determined for the 

 transition tint, we multiply by the factor 0.9024. 



Thus, if we take the specific rotatory power of dex- 

 trine for the transition tint at 139 , for the half shadow 

 tint it will be 139 X 0.9024 = I25°4. 



These data rest upon the accepted formula : 



w X X w 

 Here « = angular rotation. 



— specific rotatory power. 

 f = amount of substance 

 solution. 



(T = specific gravity of solution. 

 X = length of observation tube, 

 w = weight of substance in grms. 



MATERIAL. 



The glucose studied in the following examinations, 

 was made by the Peoria Grape Sugar Company. I am 

 under obligations to Mr. Allen, the superintendent, for 

 many favors in connection with my work. The grape 

 sugars were made in Buffalo. 



ROTATORY POWER. 



The average value of 8 for the "half shadow ray " is 

 nearly 85 . For the purple ray it is nearly 94 . It 

 however varies extremely in different samples. 



The following table will show the range of these var- 

 iations. 



Table I. 



Showing variations of d in different specimens of glu- 

 cose and grape sugar, together with the specific grav- 

 ities of the same. 



No. 



e 



Sp. Gr. 



1 



91 5° 



1 .406 



2 



91-5° 



1.407 



3 



98.10 



1.440 



4 



79-93 



1-4*4 





75-47 



1. 414 



6 



83-97 



1. 417 





82-75 



1 .416 



1::::::::: 



86.41 



I-4IS 



9 



84.11 



1. 416 



10 



87.19 



1. 417 



No. 



13 

 14 

 15 

 16 



17 

 10 



19 



e 



Sp. Gi. 



89.36 



1 .416 



87-73 



1 .422 



89-77 



1-4*7 



70.84 



1-463 



69.40 



1-463 



87.67 



1.412 



109.99 



1.427 



93-17 



1 -431 



89-75 



1.409 



9I-3I 



1. 421 



From a study of this table it is seen that within small 

 limits 9 is independent of the specific gravity of the solu- 

 tion. Nos. 14 and 1 5 were grape sugar, and the specific 

 gravity is much higher here than in the glucose, while 

 the value of is much less. 



Where the increase in density, however, is considera- 

 ble, as in 3 and 17, there is also a marked increase in the 

 value of 0, although this increase is not proportional to 

 the increment of specific gravity. In masses of homog- 

 eneous nature and structure we should expect a priori 

 that would always be proportional to the density of the 

 body, t, e., to the amount of optically active matter in a 

 unit number of grammes. 



It is thus seen without further argument that commer- 

 cial glucoses are not optically homogeneous, even when 

 made in the same factory and by processes which do 

 not sensibly vary. 



A further study of these optical reactions convinced 

 me that the rotatory power of commercial glucose in- 

 creased as the percentage of reducing substance dimin- 

 ished. 



The following table shows the value of 9 and the cor- 

 responding percentage of reducing matter as obtained by 

 Fehling's solution. 



Table II. 



No. 



e 



I % Glucose. 



in one grm. of the 



1 91-50 



2 9 T -5° 



3 98 . 10 



4 79-93 



5 75-47 



6 83.97 



7 82.75 



8 86.41 



9 84.11 



10 89.19 



53.20 

 52.36 

 54.60 



6173 

 62.50 



59-35 

 61 .40 

 58.80 



58.55 

 55-6o 



No. 



13- 

 14- 



15- 

 16. 



17- 

 18. 

 19- 



89.63 



87 -73 

 89.77 

 70.84 

 69.40 

 87.67 

 109.99 

 93 17 

 89-75 

 20 91.31 



% Glucose. 



53 



5o 



56 



49 



52 



36 



69 



93 



69 



jo 



56 



34 



39 



22 



57 



14 



54 



37 



56 



Si 



It will be seen by the above table that as the per cent 



