106 FOODS AND POOD ADULTERANTS. 



ratio of (a) tt to (a)j is 1 : 1.130G, the above numbers become for Biot ()= 

 53.27, for Berthelot (a) D =52.47, and Hoppe-Seyler (</.),,=51.48. Hesse 1 

 observed the rotatiou namber to be () 1) =52.6<" when the solution con- 

 tained 12 grams per lOOcc. and the temperature was 15 C. On the other 

 hand, when the concentration is only 2 grams per lOOcc. the number 

 assigned is () =53.63. It appears from this that the specific rotation 

 power of a solution of milk sugar diminishes with the increase of its 

 concentration, and this view is adopted by Landolt, Tollens, and 

 Schmidt. 



The following general formula 2 is used to correct the reading of the 

 polariscope for concentration of solution : 



(a) D =54.54 .5575c + .05475c 2 .001774c 3 , 



in which c = number grams sugar in lOOcc. solution. These observa- 

 tions are contradicted by the work of Schmoeger, 3 who, in an elaborate 

 series of experiments, using instruments of different construction and 

 observing all necessary precautions, found the rotation number of lac- 

 tose sensibly constant for all degrees of concentration up to the satura- 

 tion point. In thirty-two series of investigations, in which the degree 

 of concentration gradually increases from c=2.35.'>4 to 0=36.0776, and 

 in which a constant temperature of 20 C. was maintained, the variations 

 IL the numbers obtained were always within the limits of error of ob- 

 servation. The mean of all these numbers fixes the value of (a) n at 52.; 3. 



According to Schmoeger variations in temperature have far more to 

 do with changes in rotatory power than differences of concentration. 

 The value of (a) falls as the temperature rises. Under 20 C. the dis- 

 turbing influence of temperature is greater than above 20 C. At the 

 latter degree () varies inversely about .075 for each 1 C. change of tem- 

 perature. Pellet and Biard, 4 as a result of their observations, fix the 

 rotatory power of milk sugar at 56.94 for (ft)j [d. (a), =52.12)]. 



After a careful review of the methods used in the above resume and 

 the numbers determined by them, I am inclined to accept the mean ob- 

 tained by Schrnoeger as the one entitled to the greatest credit. It also 

 has the advantage of being almost the mean of all the various num- 

 bers which have been assigned as the specific rotating power of lactose, 

 viz : 



Poggiale 54.20 



Erdmann 51.50 



Biot 53.27 



Berthelot 52:47 



Hoppe-Seyler 51. 48 



Hesso 52.67 



Hesse 53.63 



Schmoeger 52. 53 



Pellet and Biard . . 52. 12 



Mean.. 52.65 



Bull, do 1'Assoc. des Chimistes vol. L 



l Anal. Chem. n. Pharm., vol. 170, p. 98. 



2 Tncker, Sugar Analysis, p. 91. p. 171 et, seq. 



3 Ber. chem. Gessell., vol. 12, p. 1922 cf wq. 



