sucrose at 17.5° C., the standard solution of sucrose in distilled water being such as to contain, at 17.5° C., in 100 cubic centimeters 26.048 grams of sucrose. The density of this solution will be 1.10 at the given temperature.

In this definition the weights and volumes are to be considered as absolute, all weighings being referred to a

vacuum.

DIRECTIONS FOR THE POLARIZATION OF SUGAR.

ART. 1396. The following directions for the use of the polariscope in testing sugar are based upon the recommendations in a report made by a commission consisting of the chief chemist of the Department of Agriculture, the chemist of Internal Revenue, and the assistant in charge of the Office of Standard Weights and Measures, Coast and Geodetic Survey, and must be closely adhered to in all tests of sugar for classification.

ART. 1397. The instrument to be employed in the testing of imported sugars for the assessment of duty is known as the half-shadow apparatus of Schmidt & Haensch. It is shown in the accompanying illustration.

The tube N contains the illuminating system of lenses and is placed next to the lamp; the polarizing prism is at O, and the analyzing prism at H. The quartz wedge compensating system is contained in the portions of the tube marked F, E, G, and is controlled by the milled head M. The tube J carries a small telescope, through which the field of the instrument is viewed, and just above is the reading tube K, which is provided with a mirror and magnifying lens for reading the scale.

ART. 1398. The tube containing the sugar solution is shown in position in the trough between the two ends of the instrument. In using the instrument the lamp is placed at a distance of at least 200 millimeters from the polarizing end; the observer seats himself at the opposite end in such a manner as to bring his eye in line with the tube J. The telescope is moved in or out until the proper focus is secured to give a clearly defined image, when the field of the instrument will appear as a round, luminous disk, divided into halves by a vertical line passing through its center, and darker on one half of the disk than on the other when the compensating quartz wedge is displaced from the neutral position. If the observer, still looking through the telescope, will now grasp the milled head M and rotate it first one way and then the other, he will find