274 Prof. E. J. Mills and J. Hogarth. [Jan. 23, 



is 66°'256, which is to 73°'8 as 1 to 1-11386— a factor which differs 

 from the above experimental one by 0'45 per cent. 



All the specific rotations given by ns are corrected by this factor, 

 and are comparable with those in general nse. 



In all onr experiments the specific rotation is calculated by the 



formula [a] = — . Where [a]= specific rotation, a = the reading in 



degrees, V the volume of solution containing the weight p, and I = 

 the length of the column in decimeters (in the above experiments, 

 2). 



II. Determination of the Permanent Specific Rotation of Lactin. — The 

 lactin was purified by filtration through animal charcoal, and two or 

 three crystallizations, after which it left no sensible residue on ignition 

 in air. Five sets of readings were made : — 







(1.) Average of 5 readings. Specific rotation 52 '84 



(2-) „ „ 53 "23 



(3.) ,, ,, ,, ,, ,, 53 '37 



(4.) „ 3 „ „ „ 53-04 



(5.) ,, „ ., ,, ,, 53 '07 



The general mean of these numbers is 53°*12, which, multiplied by 

 the factor 1*11386, gives 59°"17 as the permanent specific rotation of 

 lactin. The number given by Berthelot* is 59 0, 3. In every experi- 

 ment, care was taken that the rotatory power of the solution had 

 become constant. Three different samples of lactin were employed. 

 Experiments (1), (2), and (3), were on sample I, (4) on sample II, 

 and (5) on sample III. As the samples were prepared at different 

 times, and by a method varying slightly each time, the very small 

 differences in the results show that the lactin contained little or no 

 impurity. 



III. Examination of the Law for the Change of Rotation in a freshly 

 prepared Solution of Lactin. — If the rotatory power of an aqueous 

 solution of lactin be examined at short intervals of time, it soon 

 becomes apparent that a change is taking place, the angle through 

 which the plane of polarization is rotated becoming gradually less. 

 The object of the following experiments is to quantify the phenomenon 

 in question. 



Tive grms. of lactin were dissolved as rapidly as possible (time 

 taken, 1 hour 15 minutes) in cold water, and the solution made up to 

 100 cub. centims. The polarimeter tube (2 decims. long) was filled 

 with the liquid, and a first observation taken 15 minutes after com- 

 plete solution, or 1^ hour after first contact. Succeeding readings 



* "Ann. Ch. Phys.," [3], liv, 82 ; lx, 98. 



