(4) COOLING SLABS. Water-cooled slabs for standard plaques. As constructed according to the drawing, figure 96, two circular plates of aluminum are drawn down at their peripheries to form short skirts which can be placed edge to edge to form the water chamber. These are notched in such a way that when so placed, a pair of circular openings can be formed for the insertion of the inlet and outlet nipples. Within the chamber, with its inlet nipple protruding through one of the openings, is placed a flat spiral coil of aluminum tubing in contact with both plates and having its open discharge end at the center of the assembly. The outlet nipple is inserted in the other hole. The coil is tack- or spot-welded to one of the plates at a sufficient number of points to assure its remaining in place, and the joints between the skirts, as also between the nipples and the skirts, are carefully welded.

Plan view and side elevation. The latter is quarter-sectioned to illustrate the construction described in the text.

The faces marked fare to be carefully polished and they must not be marred in use. Alternatively (but with some disadvantages), the slab may be constructed of copper, with brazing or silver soldering in place of welding.

(This slab may be constructed in any other manner which achieves approximately the same result and cools the candy evenly by a flow of water directed to absorb the heat most rapidly at the center of the plaque, where the temperature is highest.)

In service, the slab should be level. Water should enter the coil at a temperature of 25° C and should flow at a rate of about 5 liters per minute into the center of the water chamber, thence through the spiral path between contiguous turns of the coil to waste through the outlet nipple.

Quenching plate.-For the prompt cooling of the superheated bottom of the beaker (to prevent charring of the residual sirup, which fouls the glass and complicates the washing), provide a square piece of 4-inch aluminum or sheet copper measuring 12 to 14 inches square. Aluminum is preferable to copper because of its lighter weight.

(d) HEATING CYCLE

The heating cycle of any candy sugar test includes the cooling interval (during which the material is restored to room temperature) as well as the cooking interval, which itself includes three main

regimes, or phases, of heating, as indicated by the temperature gradients of the cooking interval presented in figure 97. These three phases comprise (1) The bringing of the mixture to the boiling point (accomplished under two regimes in the NBS method (2) the concentration (usually under cover) to proximate saturation at the current temperature, and (3) the further concentration of the sirup under continuously increasing supersaturation to the terminal temperature. From what is said below of the utility and reliability of the candy test, it is evident that the most advantageous 12 duration to select for each of these intervals is that which differentiates the samples most precisely and most reliably in respect to their stability properties. The same thing is true of the terminal temperatures. If the heat effect is carried beyond an established optimum in either respect, the separation becomes blurred.

(4) with boiling of the sirup in the open beaker

FIGURE 97.-Temperature gradients developed during the 20-minute cooking interval of a simple barley-sugar test conducted according to National Bureau of Standards procedure, using a 600-ml glass beaker on the stove assembly illustrated in figure 95. Two regimes of heating prevail in the first (or preboiling) phase of this procedure. The resulting four regimes of heating: (1) with (1) DURATION OF THE COOKING stirring of the uncovered sirup, (2) without INTERVAL.-In all standard procestirring of the covered sirup prior to boiling, (3) with boiling of the sirup under cover, and dures conforming with these general are set off by the three abrupt flexures of the methods of candy testing, the correct temperature curve (a) at 70° C, where stirring cooking interval is assumed to be is terminated; (b) at the transition from quiescent heating to vigorous ebullition of the sirup; that which results when the test is and (c) at 120° C, where the sirup is uncovered. conducted in apparatus which has been carefully standardized and the heating device adjusted with reference samples of pure sucrose (p. 385) in the basic simple barleysugar test, as directed on page 372. As long as the specified adjustment of the apparatus is maintained the correct cooking interval will be yielded in any standard test on a sample of any appropriate composition, although the actual time elapsing between 30° C (86° F) and the terminal boiling temperature may be not quite the 20 minutes 20 seconds, required under reference conditions.

From this it follows that if the mean duration of the cooking interval in a minimum of four standard simple barley-sugar tests on an

"unknown" sample of commercial sugar should deviate from the mean duration observed in calibration with the prototype sample by very much in excess of 20 seconds, such deviation from the mean could be regarded as a characteristic property of the commercial sample.

(2) DURATION OF THE COOLING INTERVAL.-Although the decomposition of the ingredients of a candy test is most rapid at the terminal boiling temperature, there seems to be less promise of a gain in differentiation of samples [10, 11] by either delay or prolongation of the cooling interval than in shortening it and making it more uniform. This fact sufficiently explains the specification of the water-cooled slab in standard tests [13].

(e) SAMPLES

(1) TYPES OF MATERIALS TESTED. This discussion of the National Bureau of Standards improved simple barley-sugar test is limited to its use (a) in the standardization of equipment for candy tests in general, which involves only reference samples of specially purified sucrose (see below); and (b) in the routine inspection of commercial white sugars, where ordinarily only samples of char-refined sugars (and direct-consumption sugars of comparable purity) will be involved. A discussion of the modifications of the basic procedure permitted for the setting up of other types of candy tests will be presented elsewhere [13].

(2) REFERENCE SAMPLES.-Reference samples for the purposes of candy-test procedure include two general classes of materials: (a) Specially purified lots of an individual chemical substance, such as sucrose, which, for practical purposes, are essentially reproducible. These may be designated primary or prototype samples, (b) materials such as commercial sucrose, dextrose, and corn sirup. As a class, these may vary considerably in composition.

For the most critical reference purposes, prototype sucrose prepared according to the method of Bates and Jackson [3] is specified. For the standardization of equipment (p. 381), grade A char-refined sugar generally serves for the reference sample which, although specially purified as a commercial product, really belongs to the second class of reference material.

(f) IMPROVEments of THE NATIONAL BUREAU OF STANDARDS METHOD OVER THE HOOKER PROCEDURE

For the reasons stated in the introduction, the National Bureau of Standards basic method for the simple barley-sugar test differs from the Hooker candy test in the following details:

The boiling vessel is a 600-ml chemical-resistant glass beaker with detachable thermometer support in place of a copper casserole with no thermometer support.

The weight of sample is 250.00 g of sugar on a dry basis, instead of 1⁄2 pound without reference to moisture content.

The water is added to make up to a total weight of 350.00 g, i. e., 100.00 g of total water, including the moisture in the sample, instead of 3 oz (87 or 89 ml) of water by volume. This involves a decrease of about 2 percent in the ratio of sugar to water.

The cooking interval starts at a standardized initial temperature of 30° C (86° F) instead of at a haphazard room temperature.

The duration of cooking is specified for reference conditions only instead of for each individual test, and the interval is changed from what amounts to 23 minutes 2 minutes to 20.00 minutes ±20 seconds (for the reference conditions) and to whatever interval of time results with reliably adjusted apparatus in the individual tests on the unknown samples.

The form and arrangement of the burner are definitely specified instead of being left to chance, and means are provided for attaining the precision required.

The boiling vessel is covered at the moment the temperature of the mixture reaches 70° C (158° F), with the sugar practically dissolved, before, instead of after, boiling has commenced.

The vessel is uncovered at the instant the sirup has attained a temperature of 120° C (248° F) instead of precisely 15 minutes after the heating was started 29.

Once the sugar is approximately all dissolved and a temperature of 70° C (158° F) is attained, the thermometer remains fixed in the clasp attached to the vessel throughout the remainder of the cooking interval, with its bulb located at a definite place in the sirup where it is least exposed to direct radiation from the vessel bottom immediately above the flame, and at a place where the sirup is least superheated and least subject to fluctuation of temperature. Hand stirring of the uncovered boiling sirup is omitted.30 No stirring rod is used at any time.

The plaques are formed on a water-jacketed metallic slab which is supplied with a steady current of water at a temperature of 25° C (77° F), instead of on a simple sheet of copper which varies in temperature. This augments the uniformity of heat exposure to which the different samples are subjected.

For the observation of certain variable properties of the samples, which were not comprehended in the original Hooker candy test, the National Bureau of Standards basic method provides special means. Especially notable among these properties are the varying tendencies of the samples to foam at the initial boiling, to "froth" later, to form colored compounds in the test, and to slump or spread and yield different specific areas in the formation of the plaque.

The specifications are planned for systematic modifications in the less critical details to provide for the setting up of specialized procedures meeting the requirements of various types of candy tests not considered in the present discussion. The Hooker procedure was devised for a very limited field of service.

(g) UTILITY AND RELIABILITY OF THE CANDY TESTS

Barley-sugar tests and the associated observations offer one of the simplest and surest means of evaluating the quality of commercial

This specification obviates the possibility that the sirup may become considerably supersaturated while the vessel is still covered; thus it avoids danger of starting crystallization by the shock of uncovering the vessel. Moreover, when tests are operated on different cooking intervals (for which provision will be made in specialized procedures not covered in the present discussion), they are placed on a more nearly uniform basis in respect to the effects of uncovering when uncovering occurs at a uniform temperature instead of at a uniform time from the start of heating [4].

30 It was shown as long ago as 1913-14 that hand stirring of the boiling sirup is a productive source of variability in the results obtained by different operators of the Hooker procedure [4].

white sugars. The Hooker procedure has proved adequate for verifying the purification of the most highly refined commercial products and for detecting gross faults of purification in products of ordinary quality. Regardless of the classification of the product in trade, a lot of sugar which consistently yields excellent barley sugar in the Hooker test almost certainly will prove adequately refined for practically any manufacturing use. Conversely, a lot which repeatedly yields poor results in this test assuredly contains inexpedient quantities of impurities, either too little of certain favorable kinds or too much of the deleterious kinds. Since impurities of the latter class can impair the keeping qualities of the sugar as seriously as they affect its suitability for manufacturing uses, candy tests have a much broader field of usefulness than is comprised by the needs of the confectionery industry alone. For many years certain progressive producers of refined and direct-consumption sugars have used candy tests of various kinds as a guide to the improvement of their wares, and as a means of routine control in the daily maintenance of the particular quality standards which each producer has set for his output. All too frequently general consumers have overlooked the possibilities of the candy tests, not merely as a means of inspecting their purchases or as an instrument for comparing the different products offered, but also as a basis upon which specifications can be definitely established prior to purchase. Important disputes have arisen over the stability of sugar in storage, as well as in manufacturing operations, which might have been avoided through such specifications. Losses of sugar are suffered by producers themselves, as well as by handlers and consumers, in spoilage which could be forestalled through a more extensive use of candy tests.

In the sugar and confectionery industries, two phases of the effects of impurities upon the stability of sugar in candy tests commonly are distinguished as the inversion, or hydrolysis, of sucrose and the caramelization of the resulting mixture of sucrose, the products of hydrolysis and certain other substances which may be present. Caramelization is a phenomenon which comprises numerous complex reactions resulting in the formation of colored compounds and other substances which are deleterious to the quality of candy. 31 The types of reaction which occur, and the velocities of the reactions (hence the extent to which they progress during any individual test), are influenced by the particular regime of conditions which obtains during the operation of the test, not solely by the kinds and the amounts of impurities present. Therefore, the arbitrary schedule of heat expossure of the sample under arbitrary conditions of operation ought to be specified within sufficiently narrow limits of variability to assure that the resulting decomposition shall be practically proportional to the reciprocal of the stability of the material. The quality of the sample 32 finally is judged by an examination of the product of the test. While a visual examination of the plaque may serve the more inexact purposes

"Involved in both phases of the instability of the material are not only various decompositions and deg. radations of sucrose and the products of hydrolysis, but also reactions comprising several types of chemical synthesis, probably including reversions and polymerizations and possibly chemical combinations between glucose and amino acids or between glucose and proteins in certain instances. The reactions are so numerous and yet so generally interdependent and (with but slight alteration of conditions) so variable that their chemistry and kinetics never have been cleared up, even for a single case.

"Except those phases of the quality which are indicated by the appearance of the sirup while boiling. Differences of quality are distinguishable by this method in only a limited number of samples. (See "foam number", p. 373.)