MONOSACCHAEIDS OR GLUCOSES. 91 



" The specific rotatory power of any substance is the amount of 

 rotation of the plane of polarized light in degrees of a circle, 

 produced by 1 gram of the substance dissolved in 1 c.c. of the 

 liquid, examined in a tube one decimeter in length. The specific 

 rotatory power of a substance is obtained by dividing the angular 

 rotation observed in the polarimeter (a) by the length of the tube 

 in decimeters (1) and by the number of grams in 1 c.c. of the 

 liquid (w). If a sodium flame is used as a source of light, the 

 specific rotation of the substance is that of light with wave- 

 lengths corresponding to the D line of the solar spectrum, and is 

 usually denoted by (a) d . Then the above statement may be ex- 

 pressed as follows : 



In this formula plus indicates that the substance is dextrorotatory, 

 and minus that the substance is levorotatory. If in this formula 

 the specific rotatory power of the substance under examination is 

 known, and we wish to find the value of (w), the weight of the 

 substance, then the formula becomes, 



In this formula a is the observed rotation, I the length of the tube 

 in decimeters, which is known, and (a) d the specific rotatory power, 

 which has been determined for all well-known optically active 

 substances ; w can easily, therefore, be calculated. The specific 

 rotatory powers of a few of the most important optically active 

 substances are as follows : 



Cane-sugar, (a) d = + 73.8 

 Milk-sugar " = + 59.3 

 Dextrin" " =+130.8 



Levulose (a) d = 106 



Egg-albumin " =- 33.5 

 Serum-albumin " = - 56 



Dextrose " = + 56 I Gelatin =-130." 



Other tests for the presence of dextrose are Pavy's modification 

 of Fehling's, Moore's, picric acid, and phenylhydrazin ; for the 

 methods of their use the reader is referred to special manuals on 

 chemistry and urine-analysis. 



Fermentations of Dextrose. Dextrose undergoes various fer- 

 mentations : (1) Alcoholic ; (2) Lactic ; and (3) Butyric. 



1. Alcoholic Fermentation. In alcoholic fermentation, under 

 the influence of yeast, the dextrose is decomposed and ethyl 

 alcohol and carbonic anhydrid are produced (C 6 H 12 O 6 = 2C 2 H 6 O -f 

 2CO 2 ).' This process is at the height of its activity when the 

 temperature is 25 C. ; when above 45 C. or below 5 C. it 

 ceases. When sugar is present in the solution to the extent of 

 more than 15 per cent, the process of fermentation will be 



