Circular of the National Bureau of Standards

For the purposes of this treatise, the subject matter presented has been divided into five parts. The first of these covers a mathematical treatment of the physical phenomena and a description and discussion of the physical equipment, such as polarimeters, saccharimeters, and accessory apparatus utilized in the study and applications of polarized light.

The development of polarimetric equipment is discussed from the historical standpoint, but emphasis has been placed upon recent developments. This phase of the subject is followed by a general discussion and evaluation of the numerous methods for the analysis and study of raw and refined sugars and sugar products. Special emphasis has been made upon recent contributions and applications of physical science to chemical analysis, including electrical conductivity, colorimetry, refractometry, densimetry, hydrogen-ion concentration, turbidity and viscosity. The latter subject includes the Bureau's recent contributions and important new data on the subject.

The methods of preparation and properties of the sugars and their derivatives are given in considerable detail. In this connection a detailed study of the literature has been made and the most dependable methods of preparation of the more important sugars and their derivatives are given.

A section of general information relating to such subjects as special tests by the Bureau, issuing of standard samples, certificates and statements, test fees, etc., is included.

One hundred and fifty numerical tables are given, which provide a working basis for experimental and analytical purposes. The data given in certain of these tables have not heretofore been available. In table 148, "Optical Rotation and Melting Point of Certain Sugars and Their Derivatives," the data given are the result of a careful examination of a vast literature. There are also included the United States Customs Regulations and a digest of the Proceedings of the International Commission for Uniform Methods of Sugar Analysis.

PART 1. POLARIZED LIGHT, POLARIMETERS, SACCHARIMETERS, AND ACCESSORY APPARATUS

I. INTRODUCTION

Since the organization of the National Bureau of Standards in 1901 there has been submitted for test a great variety of polariscopic apparatus typifying the designs and methods of construction adopted by American and European manufacturers. The Bureau is equipped with examples of the standard apparatus of the leading polariscope builders, as well as special apparatus for work requiring the highest attainable precision. For most of the apparatus sent to the Burcau for test no intimation is given as to the degree of accuracy to be certified. In these cases it is the practice to report the tests to such precision as the Bureau's previous experience with the type of appa

ratus involved has shown it to merit. On the other hand, a precision is frequently requested which is greater than the apparatus justifies. In general, two grades or standards of accuracy have been found adequate in standardizing polariscopic apparatus. The first grade is for work requiring the highest commercial accuracy. The second grade is for all scientific work except special research in which the precision of the supplementary data entering into the ultimate results justifies still higher accuracy in the polarimetric data. In the latter case the Bureau will cooperate with investigators in providing not only for tests of the highest precision but also, on request, in furnishing any information at its disposal in reference to methods of measurement and the design and construction of special apparatus. It also is the desire of the Bureau to cooperate with manufacturers, scientists, and others in bringing about more satisfactory conditions relative to the weights, measures, measuring instruments, and physical constants used in polariscopic work, and to place at the disposal of those interested such information relative to these subjects as may be in the Bureau's possession.

II. POLARIZED LIGHT

1. NATURE OF POLARIZED LIGHT

According to the modern wave theory, light is an electromagnetic disturbance that travels as trains of waves oscillating transversely to the direction of propagation. The associated electric and magnetic forces are, therefore, not only perpendicular to each other but also to the direction of advance. Moreover, the oscillations consist, in general, not only of very nearly periodic variations in the magnitudes of the forces but also of more or less periodic changes in the directions of the force vectors about the propagational axis. The variations in magnitude for the two associated forces are generally so simply related that, although they are 90° out of phase, it is customary in most problems related to polarimetry to consider only the variations in one force. Since the electric force is commonly identified with the light vector, its variations are those usually discussed in such problems.

Although the variations in magnitude and direction of this vector are oscillatory in character, they would undoubtedly seem to possess only the slightest indication of their intrinsic periodicity if it were possible actually to see them as they occur in any beam of polychromatic light. Moreover, the amplitude and period continually vary even if the light is practically monochromatic; also even if the component in any direction perpendicular to the propagational axis is segregated in order to eliminate the directional variation in the unresolved oscillation. In comparison to the rapidity of the primary oscillation, however, the variations in amplitude and period develop slowly. For the sake of simplicity, it is customary, therefore, to consider that both amplitude and period are constant for time intervals that arc very great compared to the period. In many cases, this makes it possible to treat the complex oscillations of light as very simple forms of periodic motion.

Of the possible oscillatory forms of periodic motion in a wave-like disturbance such as light, the simplest to visualize and the easiest to analyze are the rectilinear, circular, and elliptical. Obviously, the last of these is the most general of the three, since in a broad sense it

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Circular of the National Bureau of Standards, Issue 440