This form of instrument is adjusted to the Ventzke scale, which, for the purposes of this report, is defined to be such that 1 deg. of the scale is the one hundredth part of the rotation produced in the plane of polarization of white light in a column 200 mm. long by a standard solution of chemically pure sucrose at 17.5 deg.  C. The standard solution of sucrose in distilled water being such as to contain, at 17.5 deg.  C. in 100 c.c., 26.048 grms. of sucrose.

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

The definition should properly be supplemented with a statement of the equivalent circular rotation in degrees, minutes, and seconds that would be produced by the standard solution of sugar used to read 100 deg. on the scale.  This constant is now a matter of investigation, and it is thought best not to give any of the hitherto accepted values.  When this is established, it is recommended that it be incorporated in a revision of the regulations of the internal revenue relative to sugar, in order to make still more definite and exact the official definition of the Ventzke scale.

The instruments should be adjusted by means of control quartz plates, three different plates being used for complete adjustment, one reading approximately 100 deg. on the scale, one 90 deg., and one 80 deg..

These control quartz plates should have their exact values ascertained in terms of the Ventzke scale by the office of weights and measures by comparison with the standard quartz plates in possession of that office, in strict accordance with the foregoing definition, and should also be accompanied by tables giving their values for temperatures from 10 deg. to 35 deg..

(b.) Weights.—­The weights used should be of solid brass, and should be standardized by the office of weights and measures.

(c.) Flask.—­The flasks used should be of such a capacity as to contain at 17.5 deg.  C. 100.06 cubic centimeters, when filled in such a manner that the lowest point of the meniscus of the surface of the liquid just touches the graduation mark.  The flasks will be standardized to contain this volume in order that the results shall conform to the scale recommended for adoption without numerical reduction of the weighings to vacuo.  They should be calibrated by the office of weights and measures.

(d.) Tubes.—­The tubes used should be of brass or glass, 200 and 100 millimeters in length, and should be measured by the office of weights and measures.

(e.) Balances.—­The balances used should be sensitive to at least one milligramme.

II.—­SKILLED OBSERVERS.

The commission recommends that the work of polarizing sugars be placed in the hands of chemists, or at least of persons who are familiar with the use of the polariscope and have some knowledge of the theory of its construction and of chemical manipulations.  To this end we would suggest that applicants for positions where such work is to be done should be obliged to undergo a competitive examination in order to test their fitness for the work that is to be required of them.