of the Ventzke Scale. Correcting for the change in the specific rotation (-0.000184), the expansion of a glass tube (+0.000008), quartz wedge (-0.000130), and metal scale (-0.000018), the new weight was calculated to be 26.01+ g. It was thought advisable to ignore the small fraction and use the round number 26.00 as the normal weight, and the Commission officially so decided [14]. Owing to the absence of a more suitable term, and in order to divorce it as completely as possible from confusion with the Ventzke Scale, the new scale was referred to as the International Sugar Scale. The International Sugar Scale then was defined at the Paris meeting as follows: "The graduation of the saccharimeter shall be made at 20° C, 26.00 g of sucrose dissolved in water and the volume made up to 100 metric cc and polarized in a 200-mm tube. All weighings are to be made in air with brass weights, the completion of the volume and the polarization are to be made at 20° C. This will determine, the 100° point."

The advantages of the new scale were at once appreciated. It has been adopted by the National Bureau of Standards, the United States Treasury Department, the Physikalisch-Technische Reichsanstalt, the Institut für Zucker-Industrie and also by the makers of saccharimeters. (1) HERZFELD-SCHÖNROCK VERSION. Following this meeting of the Commission, Herzfeld [15] and Schönrock [16] (1901-04), on the basis of the above definition of the International Sugar Scale, standardized a number of quartz control plates on the saccharimeter and then measured their optical rotation for sodium light. They found, as the average of 10 plates, that a quartz plate which read 100° on the quartz-wedge saccharimeter with white light, filtered through bichromate, read 34.657° on a circular-scale polariscope for sodium light. This value, 34.657, became known as the Herzfeld-Schönrock conversion factor. By the use of this factor, optical rotations of quartz plates determined with sodium light could be converted into saccharimeter degrees and the standardization of saccharimeters effected without resorting to the use of a pure sucrose solution, which is always difficult to prepare. This version of the International Sugar Scale-namely the one which for all practical purposes had its 100° point set by the rotation in the saccharimeter of a quartz control plate of such thickness that its rotation for sodium light was 34.657— has frequently been referred to as the Herzfeld-Schönrock scale. This scale was the practical formulation of the International Sugar Scale as defined at the meeting in 1900 of the Commission and remained in practically world-wide use for many years.

(2) BATES-JACKSON VERSION.-At the meeting of the International Commission for Uniform Methods of Sugar Analysis in 1912 in New York, Bates reported [17] that work at the National Bureau of Standards indicated that the Herzfeld-Schönrock scale was not quite correct. A committee was appointed to investigate the question and report on it at the next meeting. The war intervened and the scheduled meeting was not held.

In 1916 Bates and Jackson [18] published their work on the redetermination of the 100° point of the saccharimeter, wherein it was shown that a normal solution of pure sucrose read only 99.895° on the Herzfeld-Schönrock scale, and consequently the 100° point should be where the 99.895° point then was, and that the corresponding quartz control plate read 34.620 for sodium light and 40.690 for mercury green. Because there seemed little likelihood, due to international

conditions, that the Commission would again meet for some time to come, the values found by Bates and Jackson were officially adopted by the National Bureau of Standards and the United States Treasury Department without waiting for the reconvening of the Commission, and were used in all of their subsequent work. Their lead was followed by makers of saccharimeters and by others generally throughout the sugar world. This version of the International Sugar Scale became widely known as the Bates-Jackson scale. The publication of this work stimulated great activity in the field, and although its validity was at first questioned in certain quarters, yet later, as more and more data were accumulated by world-wide investigators, it was found to be correct. In fact, when the Commission finally met in 1932 in Amsterdam [19], after a lapse of 20 years, it was found that the average of all the values determined by investigators of international prominence working in various parts of the world was exactly that found by Bates and Jackson and reported in 1916.

(3) AMSTERDAM VERSION (1932) [19].-At this meeting in 1932 the Commission adopted, under subject 1, the following resolutions: (a) It is recommended that this Commission adopt a standard scale for the saccharimeter and that this scale be known as the "International Sugar Scale." Rotations expressed in this scale shall be designated as degrees sugar (S).

(b) It is recommended that the polarization of the normal solution (26.000 g of pure sucrose dissolved in 100 ml, and polarized at 20° C in a 200-mm tube, using white light and the dichromate filter as defined by the Commission) be accepted as the basis of calibration of the 100° point on the International Sugar Scale. (c) It is recommended that the reading of the normal sugar solution on the Herzfeld-Schönrock Scale be accepted as 99.90° S.

(d) It is recommended that the following rotations shall hold for the normal quartz plate of the International Sugar Scale:

Normal Quartz Plate = 100° S 40.690° ±0.002 (λ=5461 A) at 20° C. 1° (λ=5461 A) = 2.4576° S.

Normal Quartz Plate = 100° S=34.620° ± 0.002 (λ=5892.5 A) at 20° C. 1° (λ=5892.5 A)=2.8885° S.

}(17) }(18)

(e) It is recommended that the Commission suggest that new saccharimeters be graduated in accordance with the International Sugar Scale and be inscribed by the manufacturers with the phrase, "International Sugar Scale." In the case of existing instruments graduated on the Herzfeld-Schönrock scale, it shall be permitted either to change the saccharimeter scale or to use a weight of 26.026 g in 100 ml.

(f) It is recommended that the method of purification of sucrose for use in fixing the 100° point on the saccharimeter scale, which was adopted at the Paris session of the Commission (in 1900), be subjected to further study.

(g) It is proposed that the recommendations (a) to (e) shall come into effect on September 1st, 1933.

At first reading it might appear that (b), (c), and (d) are three different definitions of the 100° point which might or might not be concordant. A little consideration, however, will show that (b) is a general restatement of the fundamental basis of the saccharimeter scale, while (c) is a recognition of the essential correctness of a particular numerical value which had been arrived at through the application of the general definitions of (b) to the then existing sugar scale. (c) thus transfers the general definition (b) to the actual physical instruments used for sugar testing and is the concrete physical expression, as determined by experiment, of the fundamental definition given in (b).

In (d) there is set up an equivalent secondary or working standard, based upon the numerical value in (c), whereby saccharimeter scales may be checked or standardized without recourse to the difficult procedure of preparing and using a normal solution of pure sucrose. In fact, having once determined the correct quartz control-plate equivalent (conversion factor), the original definition of the saccharimetric scale could be lost or discarded without affecting the graduation or standardization of saccharimeters. The 100° point could at any time be set or checked by the simple expedient of using a quartz control plate whose absolute rotation is 34.620° for sodium light or 40.690° for mercury light of wave length 5461 A. Since the values of such plates are not subject to change, they are far more convenient for the calibration and checking of saccharimeter scales than the normal solution of sucrose.

It is thus seen that (d) is the practical expression of (b) and (c) in terms of the absolute rotation of a quartz control plate and supplies the means whereby saccharimeter scales may be readily duplicated or checked.

(4) CORRECTION OF SACCHARIMETERS TO THE INTERNATIONAL SUGAR SCALE.-In Resolution 1(e) adopted by the International Commission for Uniform Methods of Sugar Analysis in 1932 in regard to the method of correcting saccharimeters to the new scale [19], two alternatives are provided: (1) “. . . it shall be permitted either to change the saccharimeter scale or" (2) "to use a weight of 26.026 g in 100 ml." The second alternative, namely changing the normal weight by a slight amount, is objectionable from the standpoint of introducing additional complications and is therefore to be discouraged.

The first alternative is much to be preferred, namely to change the saccharimeter scale. This does not mean that the existing scale must be removed and regraduated or replaced. It is sufficient to change the scale by the simple procedure of recalibrating it in terms of the desired scale by the use of standardized (International Sugar Scale) quartz control plates and applying the small scale corrections so obtained to all polarizations made in the subsequent use of the instrument. It is worthy of note that scale corrections resulting from inaccuracies in the wedges and other optical parts, including residual inaccuracies in the scale itself, may in many instances be nearly as large as the corrections referred to above and for accurate work must be taken into account either by the use of a calibration table or chart or by the use of a standard quartz control plate. No additional inconvenience is involved, therefore, if the corrections due to change of scale are included with those due to residual inaccuracies in the construction of the instrument.

3. ADDITIONAL CONSTANTS OF THE QUARTZ-WEDGE

SACCHARIMETER

(a) ROTATION RATIOS FOR QUARTZ AND SUCROSE SOLUTIONS

The ratios of the rotations in circular degrees of quartz and of sucrose solutions for two wave lengths have been determined as follows: [18]

(b) ABSOLUTE ROTATION OF NORMAL SUCROSE SOLUTION

The rotation of the normal sugar solution for λ=5461 A was found by direct measurement.

Normal sugar solution=100° sugar=40.763°.

(21)

Since the rotation ratio for the normal solution for λ=5892.5 A and λ=5461 A is shown by eq 20 to be 0.84922, the rotation of the normal solution for λ=5892.5 A is

Normal sugar solution=100° sugar=34.617°.

(22)

(c) ROTATORY DISPERSION CURVES OF QUARTZ AND NORMAL SUCROSE SOLUTION

The difference between the rotations of the normal quartz plate and the normal solution for λ=5892.5 A is shown to be 0.003° and for λ=5461_A_0.073°. The values indicate that the rotatory dispersion curves of plate and solution cross at about λ=5850 A. The reading of the normal solution on the true saccharimeter scale with the source λ=5892.5 A has been calculated to be 99.99°S.

(d) ROTATION DIFFERENCE, IN SUGAR DEGREES, FOR NORMAL SUCROSE SOLUTION BETWEEN λ=5461 A AND λ=5892.5 A

The difference in rotation in sugar degrees, for the normal solution on the saccharimeter, for the sources X=5461 A and λ=5892.5 A, was calculated from the absolute rotations, with the following result:

Saccharimeter reading (λ=5461 A)-saccharimeter reading

(λ=5892.5 A)=0.192S.

(23)

An independent experimental determination was made of this difference and the value 0.18, obtained.

(e) THICKNESS OF THE NORMAL QUARTZ PLATE

Inasmuch as the value of the conversion factor, i. e., the rotation of the normal quartz plate, is found to be 34.620° for λ=5892.5 A and 40.690° for X=5461 A, the old value of 1.5958 mm for the thickness of the normal plate is no longer applicable. Gumlich [20], as the result of a painstaking investigation, found the rotation of 1 mm of quartz for X=5892.5 A (the light traveling parallel to the optic axis) to be 21.7182° ±0.0005 at 20° C. Recently Lowry [21, 22] has made a number of measurements on the rotation of quartz and finds at 20° C 21.7283° per mm for (λ=5892.5 A) and 25.5371° per mm for λ=5461 A. The values of the thickness of the normal plate calculated from the above data are given in table 4. The argeement between the second and third values in column 4 is very satisfactory in view of the fact that two independent values of the rotation per millimeter are used. The agreement between Gumlich's and Lowry's values for sodium light is not satisfactory.

Of all the polarimetric constants relating to the sugars, none has received the thorough study by numerous investigators that has been given to the specific rotation of sucrose and its variations with concentration. The formulas of Tollens [23] and of Nasini and Villavecchia [24] giving the values at different concentrations have been generally accepted as the most accurate. Landolt [25] combined the two, giving [a]3892.5 A 66.435+0.00870c-0.000235c2(c=0 to 65), where c is the number of grams per 100 ml of solution. This equation gives a specific rotation of 66.502° for 26.016 g per 100 ml (vacuo).

120

From a critical survey of the work involving the specific rotation. of sucrose, performed by prominent investigators in various parts of the world, it appears that the most likely value for this constant is very close to 66.53° for 26 g of sucrose in 100 ml of solution and for sodium light (weighings in air with brass wts.).

In the light of this work Landolt's formula has been adjusted to give 66.53° at 20° C for 26.016 g per 100 ml (weighed in vacuo). The adjusted equation follows:

20
[a]3892.5 = 66.462°+0.00870c-0.000235c2

(24).

This equation gives [a] = 66.53° for 26.016 g of sucrose in 100 ml of solution and 66.54° for 16.280 g in 100 ml.

Bates and Jackson [18] in their investigation on the constants of the quartz-wedge saccharimeter made a determination of the specific rotation for two wave lengths. They found that the rotation of the normal solution for λ=5892.5 A is 34.617°, and for λ=5461 A is 40.763°. Since this solution contains 26.016 g of sugar (weighed in vacuo) in 100 ml at 20° C,

Dextrose may be determined upon the saccharimeter, the readings being directly in percent dextrose, provided the correct normal weight for this sugar is used. This saccharimetric constant, namely the weight of dextrose, which when dissolved in 100 ml of solution and