quantity into a thin-walled pipette of about 1-ml capacity, and cool to room temperature in running water. Wipe the outside of the pipette, allow the possibly diluted sirup in the point to escape, and make a refractometric measurement of the solids content of the cooled sirup. Repeat this procedure from time to time until a reading is obtained corresponding to 64.5-percent solids (n20-1.4521), or to such other value as, in the experience of the analyst, will give a filtered sirup of 65.0-percent solids. Filter the sirup through a filter which will allow the 100 ml to pass within 5 minutes and adjust the filtrate to 65.0±0.5percent solids (refractometric) by thorough mixing with the appropriate quantity of water. (2) SUGAR AND OTHER SOLID AND SEMISOLID PRODUCTS TENTA TIVE. For moisture and solids determination.-Grind in a mortar, if necessary, and mix thoroughly. For other determinations. Prepare a sirup by dissolving approximately 100 g of the sample in 150 ml of hot water, boil until the temperature approaches 104° C and complete the preparation of the resulting sirup as directed under (1), commencing at "draw a small amount into a thin-walled pipette." (b) MOISTURE OR SOLIDS (1) MAPLE SUGAR.-Proceed as directed under (b), p. 262. (2) MAPLE SIRUP, MAPLE CREAM, ETC.-Proceed as directed under (c), p. 262, using a sample prepared as directed under (a) (1) p. 235. The determination may be made by means of the refractometer, as directed on page 258. (c) ASH Proceed as directed on page 264. (d) POLARIZATION (1) DIRECT POLARIZATION.-Proceed as directed on page 157. (2) INVERT POLARIZATION. At 20° C.-Proceed as directed on page 155 or 157, after clarification with a minimum amount of basic lead acetate and the removal of the excess lead in the filtrate by anhydrous sodium carbonate. At 87° C.-Polarize the solution obtained under (d) (1), at 87° C in a 200-mm tube. (e) SUCROSE-POLARIMETRIC METHOD Calculate from the results of (d) (1) and (d) (2), using the appropriate formula, page 156 or page 158. (f) SUCROSE CHEMICAL METHOD By reducing sugars before and after inversion.-Determine the reducing sugars (clarification having been effected with neutral lead acetate, never with basic lead acetate) as directed on page 170, and calculate them to invert sugar from table 78, p. 564. Invert the solution as directed under (1), p. 156, exactly neutralize the acid, and again. determine the reducing sugars, but calculate them to invert sugar from the table referred to above, using the invert column alone. Deduct the percentage of invert sugar obtained before inversion from that obtained after inversion and multiply the difference by 0.95 to obtain the percntage of sucrose. The solutions should be diluted in both determinations so that not more than 240 mg of invert sugar is present in the aliquot taken for reduction. It is important that all lead be removed from the solution with anhydrous powdered potassium oxalate or Na2CO3 before reduction. (g) REDUCING SUGARS AS INVERT SUGAR (1) BEFORE INVERSION.-Proceed, as directed under 2 (a) (2), p. 170, on aliquots of the solution used for direct polarization, (d) (1), p. 236. (2) AFTER INVERSION.-Proceed, as directed under (1), on aliquots of the solution used for invert polarization, (d) (2), p. 236. (h) COMMERCIAL GLUCOSE [8] (1) SUBSTANCES CONTAINING LITTLE OR NO INVERT SUGAR. Commercial glucose cannot be determined accurately owing to the varying quantities of dextrin, maltose, and dextrose present in the product. However, in sirups in which the quantity of invert sugas is so small as not to affect appreciably the result, commercial glucose may be estimated approximately by the following formula: G=percentage of commercial glucose solids, S percentage of cane sugar. Express the results in terms of commercial glucose solids polarizing +211° S. (This result may be recalculated in terms of commercial glucose of any Baumé reading desired.) (2) SUBSTANCES CONTAINING INVERT SUGAR.-Prepare an inverted half-normal solution of the substance as directed on page 156; cool the solution after inversion, make neutral to phenolphthalein with NaOH solution, slightly acidify with HCl (1+5) and treat with 5 to 10 ml of alumina cream before making up to the mark. Filter, and polarize at 87° C in a 200-mm jacketed tube. Multiply the reading by 200 and divide by the factor 196 to obtain the quantity of commercial glucose solids polarizing +211° V. (This result may be recalculated in terms of commercial glucose of any Baumé reading desired.) (i) LEAD NUMBER (1) CANADIAN LEAD NUMBER [9] (FOWLER MODIFICATION). Reagent Standard basic lead acetate solution.-Activate litharge by heating it to 650 to 670° C for 21⁄2 to 3 hours in a muffle. (The cooled product should be lemon color.) In a 500-ml Erlenmeyer flask provided with a return condenser, boil 80 g of normal Pb acetate crystals and 40 g of the freshly activated litharge with 250 g of water for 45 minutes. Cool, filter off any residue, and dilute with recently boiled water to a density of 1.25 at 20° C. Determination. Weigh the quantity of sirup containing 25 g of dry matter, transfer to a 100-ml flask, and make up to mark at 20° C, or use the solution in which the conductivity value has been determined 323414°-4217 (j). Pipette 20 ml into a large test tube, add 2 ml of the standard basic Pb acetate solution, cork, and allow to stand for 2 hours. Filter with suction on a 25-ml tared Gooch having an asbestos mat at least 3 mm thick. When nearly all the liquid has run through, fill the crucible with cold water. Repeat to a total of four washings, taking care to prevent formation of fissures in the precipitate by keeping it covered with water and avoiding too great suction. Dry at 100° C, weigh, and multiply the weight by 20. (2) WINTON LEAD NUMBER [10]. Reagent Standard basic lead acetate solution.-To a measured volume of the reagent prepared for determination of the Canadian lead number (1) add 4 volumes of water, and filter. A blank should be run with each set of determinations. Determination of lead in the blank.-Transfer 25 ml of the standard basic Pb acetate to a 100-ml flask, add a few drops of glacial acetic acid, and make up to the mark with water. Shake, and determine PbSo, in 10 ml of the solution, as directed below. The use of acetic acid is imperative in order to retain all Pb in solution when the reagent is diluted with water. Determination.-Transfer 25 g of the sample to a 100-ml flask by means of water. Add 25 ml of the standard basic Pb acetate solution and shake. Fill to the mark, shake, and allow to stand for at least. 3 hours before filtering. Pipette 10 ml of the clear filtrate into a 250-ml beaker, add 40 ml of water and 1 ml of H2SO4, shake, and add 100 ml of 95-percent alcohol, dry in a water oven, and ignite in a muffle or over a Bunsen burner, applying the heat gradually at first. and avoiding a reducing flame. Cool and weigh. Subtract the weight of PbSO, so found from the weight of PbSO, found in the blank, and multiply by the factor 27.33. The use of this factor gives the Pb number directly, without the various calculations otherwise required. (1) APPARATUS. (j) CONDUCTIVITY VALUE [11] Conductivity cell. Should be made of resistance glass with platinized Pt electrodes firmly fixed and adequately protected from displacement. These electrodes may be sealed in a vessel into which the solution under examination may be run and subsequently drawn off (Zerban type), or attached to a support so that they can be lowered into a cylinder (or a 100-ml beaker) containing the solution (dipping type). The cell must be provided with a thermometer graduated in tenths of a degree over the range 20° to 30° C, and the bulb must be placed in the immediate vicinity of the electrodes. The cell constant should be approximately 0.15. Galvanometer or a microphone hummer (or an induction coil) and a sensitive telephone receiver. Suitable source of current.-Dry or storage cells if a hummer or induction coil is used; 110-volt alternating current if a galvanometer is used. Resistances of 10 and 100 ohms. Should be fixed and accurate. Slide wire or Wheatstone bridge. Device for control of the temperature of the cell to within ±0.1° C.This may consist of a thermostat or a vessel into which water of suitable temperature may be run to adjust the cell contents to 25 ° C. (2) DETERMINATION OF THE CELL CONSTANT.-Prepare solutions. of 0.3728 and 0.7456 g of dry KCl in water, which offers a resistance of at least 25,000 ohms in the cell, and make them to the mark at 20° to 25° C in 500-ml volumetric flasks. Fill the cell with the more dilute (0.01 M) solution, adjust to 25° ±0.1° C, measure the electrical resistance, and multiply the number of ohms by 141.2. Rinse with the stronger (0.02 M) solution, fill the cell with the solution, measure its resistance at 25° C, and multiply by 276.1. Average the two results. (3) DETERMINATION.-Weigh out a quantity of sirup that contains 25 g of dry matter, transfer to a 100-ml volumetric flask with warm water of the same quality as that used in the determination of the cell constant, cool to 25° C, make to mark, and measure the resistance in the cell at 25° ±0.1° C. Divide the cell constant by the number of ohms found. (k) MALIC-ACID VALUE (COWLES) [12]-TENTATIVE Weigh 6.7 g of the sample into a 200-ml beaker; add 5 ml of water, then 2 ml of a 10-percent calcium acetate solution; and stir. Add, gradually and with constant stirring, 100 ml of 95-percent alcohol and agitate the solution until the precipitate settles, or let stand until the supernatant liquid is clear. Filter off the precipitate and wash with 75 ml of alcohol, 85 percent by volume. Dry the filter paper and ignite in a platinum dish. Add 10 ml of 0.1 N HCl, and warm gently until all of the lime dissolves. Cool, and titrate back with 0.1 N NaOH solution, using methyl orange indicator. The difference in milliliters divided by 10 represents the malic-acid value. of the sample. Previous to use, the reagents should be tested by a blank determination and any necessary corrections applied. 3. DETERMINATION OF SUGARS IN MILK PRODUCTS The estimation of lactose in fresh milk is, from the standpoint of sugar analysis, relatively simple, but the preparation of the sample for analysis involves procedures regarding which there is much dispute. The Association of Official Agricultural Chemists finds it satisfactory to clarify with copper sulfate in preparation for reducingsugar analysis or with mercuric nitrate for polariscopic analysis. On the other hand, the British Subcommittee on Milk Products recommends the use of zinc ferrocyanide, prepared in the presence of the sample, but permits the use of phosphotungstic acid. The volume of the precipitate is relatively large and must be calculated or determined. An important commodity is condensed milk sweetened with sucrose. Occasionally the sucrose is partially inverted by the action of enzymes or microorganisms, and in some instances further action of microorganisms converts the levulose so formed into a nonreducing levan. In some cases, other sugars may be added as sweetening agents. The analysis of such sugar mixtures becomes an intricate problem. Many of the methods for the sugar mixtures in milk products have been elaborated solely for the purposes of milk analysis, but appear to be capable of general application to other products. (a) DETERMINATION OF THE VOLUME OF THE PRECIPITATE If the percentages of fat and protein of a milk product are known, the volume of the clarification precipitate can be calculated with fair approximation by the method of the British Subcommittee on Milk Products [13]. The volume of the protein precipitate varies with the nature of the precipitant. For phosphotungstic acid clarification the specific volume of fat is 1.08 and for protein, 0.74. The volume then is fat 1.08+protein 0.74, to which is added a further empirical correction of 1.5 ml. For the zinc ferrocyanide method the volume of precipitate is about double that for the phosphotungstic acid precipitate. The volume of precipitate is then fat X1.08+protein 1.55. The British subcommittee, however, recommends actual determination of the volume of the precipitate for each sample [13]. (1) Weigh 100 g of milk into a 200-ml flask. Add precipitating reagents, make up to the mark at 20° C, filter, and polarize at 20° C. Reading A. (2) Weigh 100 g of the same milk and 16.8 g of sucrose into a 200-ml flask, dissolve the sugar, add precipitating reagents, make up to the mark at 20° C, filter, and polarize at 20° C. Reading =B. (3) Weigh 140 g of the same milk into a 200-ml flask and add seven-fifths of the previous quantities of precipitating reagents. Make up to the mark at 20° C, and filter. Take 70 ml of the filtrate, make up to 100 ml, and polarize at 20° C. Reading C. (4) Measure 70 ml of the filtrate from (3) into a 100-ml flask, add 8.4 g of sucrose, dissolve, make up to the mark at 20° C, and polariez at 20° C. Reading D. The correction for volume of precipitate for 100 g of milk 2001 D-C = milliliters. (1) OPTICAL METHOD. (b) LACTOSE IN MILK [14] Reagents. (a) Acid mercuric nitrate solution.-Dissolve mercury in twice its weight of concentrated nitric acid and dilute with an equal volume of water. (b) Mercuric iodide solution.-Dissolve 33.2 g of KI and 13.5 g of HgCl, in 200 ml of glacial acetic acid and 640 ml of water. Determination.-Determine the specific gravity (20°/20°) of the milk and place in a flask graduated at 102.6 ml, the volume of milk indicated in table 31. Add 1 ml of solution (a) or 30 ml of solution (b), fill to the mark, shake frequently for at least 15 minutes, filter through a dry filter, and polarize. The volumes in the table are those of a double-normal weight of lactose (32.9 g per 100 ml); hence, if a 200-ml tube is used, divide the saccharimeter reading by 2 to obtain the percentage of lactose in the sample. (2) CHEMICAL METHOD.-Dilute 25 g of the sample with 400 ml of water in a 500-ml volumetric flask and add 10 ml of CuSO, solution (Soxhlet solution 1) and about 7.5 ml of a KOH solution of such strength that 1 volume is just sufficient to precipitate completely the copper as hydroxide from I volume of the copper sulfate solution. (Instead, 8.8 ml of 0.5 N NaOH solution may be used). After the addition of the alkali solution, the mixture must still have an acid reaction and con |