222 GLUCOSES, SACCHAROSES, ETC. 



constant of the carbohydrate in question must be known. The 

 results are generally calculated from the equation 



0=4 



where C is the weight of the substance (ejq)ressed in grams) con- 

 tained in a, litre of solution, A the rotation-constant of the 

 substance to be estimated, a the observed rotation, and L the 

 length of the column of solution in millimetres. If the concen- 

 tration of the solution h^^ an influence on the optical activity, 

 thenjp, the weight of substance in grams in 100 cc. of the solution, 

 must also be taken into account. ^ The same must be done for 

 the temperature when that exerts any influence on the rotatory 

 power (invert-sugar) (cf. § 199). 



Suppose for instance a solution of grape-sugar in a tube 0*1 

 metre long to have shpwn a rotatory power +3°, then (using 

 ToUens and Grote's constant), 



C = 1883'2xTfTr 



For a solution of levulose with rotatory power - 3°, 



C! = 943-4x^^ 



For a solution of cane-sugar with rotatory power -1-3° (using 



Wild's constant), 



C = 1505-6 Xt§^ 



In the first instance the solution would contain 56*496 gram$ 

 of dextrose per litre ; in the second, 28-302 grams of levulose in 

 tlie third, 45 "168 grams of cane-sugar. See also § 210. 



§ 209. Estimation of two Sugars. — Two sugars present in solution 

 together may be accurately estimated, provided that the fotatory 

 power of each is known, and the other conditions in § 208 are 

 fulfilled. This is frequently the case -with solutions of dextrose 

 and levulose. Neubauer^ then recommends observing the rotatory 

 power, and estimating the sugar with FehHog's solution. If the 

 latter indicates 15 per cent, of sugar, then if levulose alone were 

 present, the rotatory power (by sodium-light, in a tube 1 metre 



' See Hesse, Aijnal. d. Chem. un'd Fharm. clxxvi. 95, 1875, and Tollens, 

 Ber. d. d. chem. Ges. xi. 1800. 

 » Ber. d. d. chem. Ges. x. 827, 1877. 



