* Equilibrium rotation.

TABLE 150.-Corrections to be applied to saccharimetric readings of levulose solutions when a constant normal weight is used

[Normal weight at 20° C 18.407 g; normal weight at 25° C = 19.003 gm]

1 In order to avoid constant repetition of the negative sign, the polarizations of levulose are considered positive. The positive signs in the above table indicate that the negative polarizations of levulose are to be increased to higher negative values.

XXXVII. APPENDIX 2.-RÉSUMÉ OF THE WORK OF THE INTERNATIONAL COMMISSION FOR UNIFORM METHODS OF SUGAR ANALYSIS

ALEXANDER HERZFELD, chairman; F. G. WIECHMANN, American Secretary

FIRST SESSION [1] HAMBURG, GERMANY, JUNE 12, 1897

1. Kinds of quartz plates to be selected. At the start, only quartz plates of high polarizing value shall be tested; later, however, such also as will cover the entire scale range of saccharimeters.

2. Method of examination of quartz plates.-Their examination is to be conducted in the same manner as has been done heretofore by the Commission of Trades Chemists under guidance of the Society of the Beet Sugar Industry of the German Empire, with the participation of the Imperial Normal Testing Bureau and the Physical Technical Reichsanstalt.

3. Temperature to be adopted as the normal temperature for polarization.—For the examination of quartz plates 20° C is to be chosen as the normal temperature, and the metric liter is to be adopted. The normal weight to be adopted is hence to be 26.00 g, where 26.048 g is the normal weight valid for Mohr's liter at the temperature 17.5° C.

4. Additional methods and means suggested in order to decrease differences in polarization work. In consideration of the well-known difficulties in sampling bagged sugar, sampling each bag does not offer sufficient advantages to justify a departure, in the interests of trade, from the customary method of sampling 20 bags in every 100 bags.

5. Desirability of an endeavor to introduce uniformity of analytical methods for beet-sugar work in all countries concerned.—Such an endeavor shall be made. For the computation of sugars, analyses shall be admissible only of such chemists as shall have pledged themselves to execute the analysis of sugar in accordance with the methods prescribed by the International Commission.

6. The determination of invert sugar.-The determination of invert sugar is to be made only in solutions which have been clarified with lead solution and from which the lead has then been removed. If volumetric determinations are made, the amount of reduction due to the chemically pure sucrose must be deducted.

SECOND SESSION [2] VIENNA, AUSTRIA, JULY 31, 1898

1. Results of the international examination of quartz plates. In general, such examinations proved satisfactory. Certain discrepancies were undoubtedly due to the fact that the examinations had not always been made at 20° C, as prescribed. Reference was made to the observations of Herzfeld, Wiechmann, and Wiley that pressures, due to varying temperatures affecting their mountings, exercise an influence on the rotation values of fixedly mounted quartz plates and quartz wedges. Whereas the quartz plates heretofore used-owing to the fact of their being firmly held in their mountings-are apt to be strained when their temperature is raised, and whereas such strains cause irregularities in the polarizing values of these plates, it was resolved that the investigation above referred to should be repeated, making use of other quartz plates not subject to the defect mentioned. On the motion of Messrs. Dupont and Jobin it was resolved to employ plates the rotation values of which shall cover the entire scale of the saccharimeter, one levorotatory and four dextro-rotatory plates, the thickness of which is at the same time to be given, so that the plates shall remain serviceable when the normal weights shall be changed.

In determining the value of the plates there shall be employed not only the normal temperature of 20° C but, on the motion of Messrs. Wiley and Wiechmann, also of 30° C, in order to take into due account the condition of warmer countries. In employing apparatus with quartz-wedge compensation the changes shall be studied which the saccharimeter itself suffers in consequence of variations of temperature. As source of light there shall be employed only yellow sodium light or light sufficiently purified by ray filters.

Upon the motion of Dr. Hermann, of Hamburg, it was furthermore agreed to emphasize specifically in the protocol that the commission had thus far made no such changes in the normal weight for polariscopes which could influence the results of polarization in the least. This had been mentioned already in the protocol of the Hamburg session of June 12, 1897.