purity," "gravity purity," and "refractive purity," when the percentage of sucrose is used as the numerator of eq 131, and solids by drying, by Brix spindle, or by refractometer, respectively, as the denominator. If the polarization is used as the numerator, terms are qualified by the expression "polarization.”

2. REFERENCES

the

[1] S. J. Osborne, Methods of Analysis, p. 214 (The Great Western Sugar Co., Denver, Colo. 1920).

[2] E. W. Rice, Facts About Sugar 22, 1066 (1927).

[3] G. L. Spencer and G. P. Meade, Cane Sugar Handbook, p. 494-551 (John Wiley & Sons, Inc., New York, N. Y., 1929).

[4] Noel Deerr, Cane Sugar, p. 492 (Norman Rodger, London, 1921).

XXVII. PACKING OF SUCROSE [1, 2, 3]

1. INTRODUCTION

The volume occupied by a given weight of sugar is a matter of importance, both in relation to the operation of the centrifugal station and the bagging of the sugar. It is the sum of the volumes of the actual crystals and of the voids between them, and depends on their size and shape as well as on the way in which they are packed together. A study of the physical factors involved in the packing of sugar has been made by Drinnen [1]. His results are also valuable in that they indicate the way to an improved technique, which is desirable for further study of the problem.

2. CRYSTAL DIMENSION

Sugar crystals were classified into various fractions in accordance with their size, using a set of standard Tyler sieves. The dimensions of the sieved fractions were estimated under the microscope by an eyepiece micrometer. Since the smallest dimension largely determines the sieve in which the crystal remains, this dimension should be the reference size for crystal measurements, provided that the crystals do not depart very greatly from the cubical shape. In table 48 are shown the results from the examination of 50 crystals from each sieve fraction.

TABLE 48.-Crystal size as related to sieve mesh

3. VOLUME OF CRYSTALS AND VOIDS

Two methods were used for this determination, (a) displacing the volume of air in a known weight of the sugar by means of a liquid in which sugar is insoluble and measuring the volume, and (b) weighing a known volume of sugar and calculating the volume of the crystals from the weight and specific gravity of the sugar. The former appears

to be the more accurate method. Average percentage figures obtained are shown in table 49.

TABLE 49.-Volume of sucrose crystals and of interstitial voids as related to sieve mesh size

Grain counts were taken for the various fractions on oven-dried sugar, per gram from each fraction, as follows:

TABLE 50.-Weight of crystals in relation to average grain size (screen fractions)

This is a very difficult matter to estimate, and the findings of Pellet, summarized by Thieme [3], are given in table 51.

TABLE 51.-Relation between weight and surface area of crystals for various crystal sizes (screen fractions)

[1] L. Drinnen, Proc. Queensland Soc. Sugar Cane Tech., 9th Conference, 1938, p. 199-202.

[2] Technical Communication No. 7, Bureau of Sugar Experiment Stations, Brisbane, Australia, 1938.

[3] J. G. Thieme, Studies on Sugar Boiling, translated by O. W. Willcox, p. 26-27 (Facts About Sugar, New York, N. Y., 1928).

PART 3. PREPARATION AND PROPERTIES OF THE

SUGARS AND THEIR DERIVATIVES

XXVIII. OPTICAL ACTIVITY, CONFIGURATION, AND STRUCTURE IN THE SUGAR GROUP

1. CONSTITUTION OF THE SUGARS AND THEIR
INTERRELATIONSHIPS

At the dawn of history our aboriginal ancestors were familiar with honey and the sweet exudations of various trees and plants, but the chemistry of the sugars did not begin until the introduction of cane sugar into Europe [1]. With the expansion and development of Europe, the need was felt for a sugar-bearing plant which could be grown in a temperate climate. In the course of the search for a source of sugar, attention was directed to many closely related natural products. Thus, in 1792 Lowitz [2] found that starch on hydrolysis gives a sweet substance, now known as d-glucose or dextrose. Many other natural products were found which, on hydrolysis, gave closely related products. These substances, with few exceptions, contain carbon, hydrogen, and oxygen, in the proportions corresponding to a hydrate of carbon, and hence they were named "carbohydrates."

The carbohydrates comprise the sugars and the polysaccharides. The polysaccharides are compounds which, by hydrolysis, yield sugars. The sugars are classified as simple sugars or monosaccharides, and compound sugars comprising the disaccharides, trisaccharides, and tetrasaccharides. The simple sugars are classified further as trioses, tetroses, pentoses, methylpentoses, hexoses, heptoses, etc., according to the number of carbon atoms in the sugar molecule. The hexoses, pentoses, and methylpentoses occur in many plant products and play important roles in many biological processes. The two most important simple sugars are dextrose and levulose.

Few organic compounds have been studied as intensively as the hexoses, and in particular, dextrose. This substance was known in ancient times as grape sugar, but was not isolated from starch until 1792. It was found in diabetic urine in 1815 by Chevreul [3], and in cellulose in 1819 by Braconnot [4]. Crystalline dextrose, however, did not find wide use until a successful method for the production of the hard refined crystalline sugar was devised at the National Bureau of Standards [5]. This method in its essential principles was applied commercially, and many millions of pounds of white crystalline dextrose are now produced annually.

During the latter half of the nineteenth century many organic chemists devoted their attention to the study of dextrose. In 1843 Dumas [6] ascertained that dextrose has the empirical formula CH2O, and in 1870 Baeyer [7] advanced the structural formula

CH,(OH).CH(OH).CH(OH).CH(OH).CH(OH).CHO.

This formula was supported by subsequent molecular-weight determinations [8] and by the following chemical reactions: (1) The sugar yields, on oxidation with bromine water or nitric acid, a monocarboxylic acid (gluconic) which contains the same number of carbon atoms as the parent sugar [9],

CH2OH(CHOH),CHO+Br2+H2O→CH2OH(CHOH),COOH+2H Br

(gluconic acid)

This proves that the aldehyde or potential aldehyde group lies at one end of the carbon chain. (2) On reduction with sodium amalgam, the sugar yields a hexahydric alcohol [10] (sorbitol),

CH2OH(CHOH),CHO+H,→CH2OH(CHOH),CH,OH.

(sorbitol)

(3) Reduction of the sugar with hydriodic acid gives normal hexyl iodide, which proves that the carbon atoms are combined in a straight chain. (4) The sugar combines with hydrogen cyanide to give a nitrile, which, after saponification and reduction with hydriodic acid, yields a normal heptanoic acid,

H

CH2OH(CHOH),CHO+HCN→CH2OH (CHOH),C—CN→CH,(CH2),COOH

он

(normal heptanoic acid)

This confirms the straight-chain formula and shows the presence of an aldehyde or potential aldehyde group [11]. (5) The sugar yields pentaacetyl and other derivatives, indicating the presence of five hydroxyl groups. (6) Treatment with phenylhydrazine gives glucose phenylhydrazone,

CH2(OH).CH(OH).CH(OH).CH(OH).CH(OH).CH=N-NHC,H,

and prolonged action gives glucosazone,

H

CH,OH.CH(OH).CH(OH).CH(OH).CC=NNHCH..

N–NHCH

The formation of hydrazones is typical of carbonyl compounds, and the formation of osazones is peculiar to alpha hydroxy aldehydes and ketones. Although these properties support the polyhydroxy aldehydic formula, other properties which will be considered later show that the aldehyde modification is only one of the several tautomeric forms which are characteristic of the sugars. Indeed, the crystalline sugars contain lactol ring structures, and even in solution the quantity of the free aldehyde modification is extremely small.

While the chemistry of dextrose was being developed, a number of other sugars were being investigated. Some of these resemble dextrose in that on oxidation they give acids containing the same number of carbon atoms, whereas others give acids containing fewer carbon atoms. The most important of the latter group is d-fructose