6. On the instant a temperature of precisely 176.7° C (350° F) is indicated, remove the beaker from the stove, simultaneously noting the time (as by the stopping of the timer device), and dump its contents all at once onto the center of the cooling slab. This operation should be performed in such a manner as to form a nearly circular plaque. When the stream breaks, turn the beaker to an angle of about 45° and allow the sirup to drain into the center of the plaque for 10 2 seconds. Lift the beaker with a turn which brings the threads of sirup into its mouth, and set it upon a quenching sheet of 1⁄4-inch aluminum or copper to prevent charring of the adhering sirup in the bottom of the beaker. Cover the beaker with the dried watch glass now taken from the oven and, when cooled to room temperature, weigh the whole assembly. 7. Five minutes after the pouring of the candy, strip the plaque from the water-cooled slab and place it in a desiccator or dry-air closet until it has cooled to room temperature. When the plaque is cool, proceed as indicated under b (2), below. (b) OBSERVATIONS FOR THE INTERPRETATION OF RESULTS (1) FOAM NUMBER.-When a layer of sudsy foam accumulates upon the surface of the sirup as it approaches the transition interval, the apparent volume of the mixture probably will expand suddenly at initial boiling [2, 4]. To obtain a roughly quantitative statement of the phenomenon, proceed as follows: Observe the number of seconds elapsing from the instant the rapid expansion begins until the moment the foam subsides to its minimum volume, and record the result as "duration of foaming." Observe also the distance in centimeters from the surface level of the quiescent, nonfoaming sirup to the highest level reached by the general surface of the foam on expansion, convert the result to percentage of increase in volume, and record the number as the "volume of foam." The product of these two numbers is the "foam number" [4, 6]. Space is available in the beakers for the accommodation of but little more than a doubling of the apparent volume of the sirup with the specified size of sample. If the expansion much exceeds this value, at the standard rate of heating, it may result in the overflowing and loss of a portion of the sirup, with consequent fouling of the stove and burner. If this misfortune threatens, reduce the rate of heating; do not disturb the flame but hold the vessel by hand at a greater distance above the flame, or hold it intermittently over the flame until all danger of loss is past. Do not include any prolongation of the heating which is involved in the quelling of foam as a part of the cooking interval. (2) EXAMINATION OF THE PLAQUE.--Notice the general appearance of the candy, especially with respect to color, transparency, inclusion of bubbles and specks, etc., and state the results in qualitative form. Weight of the plaque.-When the plaque has cooled to room temperature, weigh it with a precision of ±0.05 g. Projected area of the plaque.-Measure the projected area of the plaque, preferably by following the periphery of the disk itself with the stylus of a planimeter specially designed for such purposes. If this means is not feasible, first trace the outline of the plaque upon paper and later measure the area enclosed by the tracing. Express the results in square centimeters. Slump or specific area of the plaque.-Divide the number representing the projected area by the number of grams in the weight of the plaque, and record the quotient as the "slump", or specific area, expressed as square centimeters per gram. The numerical value of this quotient, under uniform conditions of testing, increases with increasing weakness of the sugar [13]. Mean thickness of the plaque.-Measure the thickness of the plaque at a minimum of 20 random points distributed evenly over the plaque, preferably by means of a dial-type thickness gage. In lieu of this, pieces of the plaque may be measured with an ordinary micrometer. The plaque is thicker the stronger the sugar from which it was prepared (with uniform conditions of testing) [13]. Color measurement of the solid candy.-Estimate the transmission of light of 560 mμ wave length (or of three or more wave lengths, if preferred) at several clear points on the plaque or at clear points on several pieces. Compute the transmissions for layers of exactly 5 mm thickness. To minimize surface reflections, observe the pieces while freshly immersed in a water-clear, slightly supersaturated sirup of pure sucrose contained in a wide, open-top colorimeter cell of about 1-cm length (on the optical axis). Employ any suitable instrument (chap. XIX), and correct the results for any perceptible absorption of light by the immersion sirup [13]. Yield and overweight of the candy.-The total yield, y, of the candy is the sum of the weight of the plaque and the weight of the candy adhering to the boiling-vessel, thermometer, and cover. The "overweight" in grams is the difference expressed by (y-wt of dry substance introduced), which, in all standard tests, is (y-250). It represents approximately the weight of the residual water retained by the candy, partly combined as water of hydrolysis, partly as solvent or solute in the supercooled solution. In standard tests it is expressed as a percentage of the sample weight simply by multiplying by the factor 0.4. Breaking of the plaque. The relative brittleness or toughness of the plaque can be estimated by breaking the plaque with a suitable impact device. Ordinarily, it is simply broken by hand. In either case, the pieces are placed promptly in a container, such as a glass-top mason jar which can be closed to protect the candy from the moisture of the atmosphere. If the candy is to be examined in aqueous solution, the container should be tared. (3) EXAMINATION OF THE CANDY IN AQUEOUS SOLUTION. From the net weight, w, of the candy stored in the container, and the yield of the candy per gram of the dry substance introduced, compute the weight of dry substance introduced (see above) equivalent to the contents of the container, as sw/y, where s represents the weight of dry substance in the sample (250.00 g in all standard tests). Add equilibrium water until the total weight of the contents is precisely double this quantity, i. e., 2sw/y. Cover the container securely and without the application of any heat, shake or rotate it, preferably by mechanical means, until the candy is completely dissolved. Use this stock solution for whatever tests or analyses are to be made on the aqueous solutions, keeping in mind the fact that 1 g of the original dry substance of the sample is represented by 2 g of the stock solution. (c) APPARATUS (1) BOILING-VESSELS.-Glass beakers, Griffin form, 600-ml capacity, of chemical resistant, low-expansion Pyrex or equal glass must be used as the boiling-vessels. Each beaker is to be provided with a notched watch-glass cover and with a quickly detachable combination handle and thermometer support with quick-opening spring-actuated clasp, as indicated in figure 90. For lightness and cleanliness, the handle and thermometer support are constructed mainly of aluminum. For uniformity of results, the thermometer bulb should be located precisely as indicated in the drawing, and the burner should be of precisely the form and arrangement indicated in figure 92. Since Consists of 600-ml chemical-resistant-glass beaker provided with a notched water-glass cover, thermometer, and handle set carrying the thermometer support with spring-actuated clasp. The aluminum handle set is clamped onto the beaker by means of the hinged hoop bands which are secured by closing the handle shell, Jackknifewise, over the straight protruding ends of the bands. It is retained at a fixed level on the beaker by the V-shaped wings which bear upon the sides of the lip of the beaker, and by the short hook which rests in the notch of the lip. variations in the thickness of the beaker bottoms cause relatively large variations in the duration of the cooking interval with any given adjustment of the burner and gas supply, beakers which are to be used interchangeably on a particular adjustment of the heating equipment should be carefully matched as to weight and as to heat transmission. A counterpoise, preferably adjustable, should be provided for the taring of each assembly. Since the handle sets are so easily removed, and should be removed while the glass parts are being washed, all weighings may be made without the handle sets. Thus consecutive tests can be run without loss of time by providing a sufficient number of matched beakers and thermometers with but two handle sets. (2) HEATING DEVICES. Standard device with flow manostat for gas heating.-This apparatus, which will be described in greater detail elsewhere, practically meters the gas to the burner jets at a steady rate of flow. The heat capacity of the burner and the associated parts is small; only a few minutes of operation is required to establish a state of steady output of heat to the boiling-vessel, provided that the calorific value of the gas is approximately constant. The apparatus is comprised of the following parts: Flow manostat.-The essential feature of the manostat, figure 91, is the balanced valve, V which floats in the orifices of the plates, OP, and is actuated by the float, F, which in turn is operated by changes in FIGURE 91.-Flow manostat for gas pressure regulation. The preferred form, as illustrated at A, has a double self-balancing valve which floats freely in the two gas orifices and does not close the openings completely at any level, as illustrated more clearly in the enlarged view C. A simpler form of regulator with a single, spring-balanced valve is illustrated in view B. the level of the hydrostatic liquid in response to changes in the pressure of the regulated gas stream. The floating valve is retained in the centered position in the orifices of the plates OP by the bearing plates B (as lettered in the enlarged view, C). The valve-and-float assembly is further stabilized by the ballast weight, B (refer to views A and B). The liquid tank J, the float chamber with the gas outlet O and the top closure S, may be made of glass, as indicated, for the convenience of visibility of the moving parts during the adjustment and operation of the manostat. However, a simpler construction has proved amply satisfactory in service. The pointer, P, (view B) is convenient with either the single or the double valve [13]. Gas from the service pipe enters at I, and the regulated gas streams for two or three burners is taken off at O. Since the regulation of pressure is dependent in part upon a steady outflow at O, which is to |