Chap. XXX.] USE OF SACCHARIMETER. 415 



The feeblest rotation will thus be exhibited, and the 

 extent to which the analyser must be turned to 

 restore the former tint, indicates the extent of the 

 rotation. If, then, the original tint has been obtained, 

 the tube containing the solution to be examined is put 

 in its place, when the slightest change in the colour 

 indicates a rotation of the plane. In Soleil's 

 saccharimeter the amount of rotation is estimated 

 not by turning the analyser, but by a compensating 

 arrangement placed between the solution tube and the 

 analyser. The compensator consists of a single quartz 

 plate rotating to the right, and then of a quartz plate 

 rotating to the left. The latter is, however, made of 

 two wedges, sliding on one another, the sharp end of 

 one being over the blunt end of the other. By a 

 screw the wedges may be moved from one another, 

 the practical effect of which is to diminish the 

 thickness of the quartz plate which they compose, or 

 they may be moved towards one another, which 

 increases the thickness of the plate. Thus, if the 

 solution of sugar has rotated the plane of polarisation 

 to the right, by turning the screw a sufficient thick- 

 ness of the quartz plate rotating to the left is 

 interposed to compensate for the rotation to the right 

 of the sugar. The thickness of the quartz plate 

 interposed is read off on a scale, and the rotation of a 

 quartz plate of a definite thickness being known, the 

 measure of the rotation effected by the sugar solution 

 is determined. 



Use of the saceharinieter in medicine. 

 The instrument may be used for estimating the 

 amount of sugar present in diabetic urine. The 

 urine is first clarified by heating with acetate of lead, 

 and then filtered. The field of the saccharimeter 

 being all of the same colour, the tube filled with the 

 diabetic urine is put in its place, when the two sides of 

 the field will at once appear of a different colour by 



