416 PHYSIOLOGICAL PHYSICS. [Chap. xxx. 



the rotation clue to the sugar. The screw of the 

 compensator is now turned till the uniform hue is 

 restored, and the extent to which the compensator has 

 been moved is read off on the scale. It has been 

 found that with Soleil's instrument a displacement of 

 100 divisions of the scale is effected by a solution of 

 sugar containing 225'6 grains of sugar in a litre. Each 

 division of the scale, therefore, represents 2-256 

 grains of sugar. Suppose 10 divisions are indicated on 

 the scale when the original tint of the field is restored, 

 then 10 X 2 -256 = the quantity in grains of sugar 

 present in 1 litre of the urine. 



To put it generally, to determine x, the amount in 

 grammes of the substance in 1 cc. of the solution 

 employed, one requires to know r the rotatory power 

 of the substance, I the length in decimetres of the 

 column of solution in the tube, and a the angle 

 of rotation. Then 



a 



* - 7S7 ' 



