ANALYTICAL EDITION
JANUARY 1.3, 1936
(2)
(3) (4)
(5) (6)
439 (1868); Fremy, E., Compt. rend., 83, 1136 (1876); Goday, S. R., Chimie & industrie, 32, 51; Mangin, L., Compt. rend., 109, 579 (1889); 110, 295 (1890); 111, 120 (1890); 113, 1069 (1891); 116, 653 (1893); Timberlake, H. G., Botan. Gaz., 30, 73 (1900); Treub, M., “Quelques recherches sur la r81e du noyau dans la division des cellules v6g6tales,” Amsterdam, 1878; Wood, F. M., Ann. Botany, 38, 273 (1924). Anderson, D. B., Am. J . Botany, 14, 187 (1927); Freudenberg, K., Zocher, H., and Dtirr, W., Ber., 62, 1814 (1929); Goday, S. R., Chimie & industrie, 32, 51; Griffioen, K., Rec. trav. botan. nderland., 1934, 31; Harlow, W. M., N. Y . State Coll. Forestry, Tech. P u b . 21 (1927); 24 (1928); 26 (1928); Am. J. Botany, 19, 729 (1932); Ritter, G. J., and Chidester, G. H., Paper Trade J., 87, 17, 131 (1928); Soarth, G. W., Gibbs, R. D., and Spier, J. D., Trans. R o y . SOC.Can., 23, 269 (1929). Bailey, A. ,J., J . Forestry, 33, 688 (1935). Bailey, A. J., Mikrochemie, in press. Bailey, A. J., Paper I n d . , 16, 480 (1934); Svensk Papers-Tidn., 37, 791 (1934). Bailey, A. J., Paper Trade J., 101, 3, 40 (1935).
55
(7) Carpenter, C. H., and Lewis, H. F., Ibid., 99, 3, 37 (1934); Freudenberg, K., J . Chem. Education, 9, 1171 (1932); Ritter, G. J., and Kurth, E. F., IND.ENG.CHEM.,25, 1250 (1933); Scarth, G. W., Gibbs, R. D., and Spier, J. D., Trans. Roy. SOC.Can., 23, 269 (1929). (8) Forsaith, C. C., N. Y . State Coll. Forestry, Tech. P u b . 18, 64 (1926). (9) Hggglund, E., Ber., 56, 1866 (1923). (10) Harlow, W. M., N. Y . State Coll. Forestry, Tech. P u b . 26 (1928); Ritter, G. J., IND.ENG.CHEM.,17, 1194 (1925); Soarth, G. W., Gibbs, R . D., and Spier, J. D., Trans. Roy. SOC. Can., 23, 269 (1929). (11) Harlow, W. M., and Wise, L. E., IND.ENG.C H ~ M 20, . , 720 (1928). (12) Klason,’P., Svsnsk Papers-Tidn., 35, 224 (1932). (13) Ludtke, M., Biochem. Z.,233, l(1931). (14) O’Dwyer, M. H., Biochem. J., 22, 381 (1928): Ritter, G. d., and Kurth, E. F., IND.ENG.CHEM.,25, 1250 (1933). (15) Ritter, G. J., and Fleck, L. C., Ibid., 18, 608 (1926). RECEIVED October 15, 1935.
Methods of Wine Analysis J
C. H. MCCHARLES
S
AND
G. A. PITMAN, Cresta Blanca Wine Co., Livermore, Calif.
AMPLING is more of a problem than one might suspect in an apparently homogeneous liquid such as wine. Air coming in contact with dry wine under certain conditions causes the formation of volatile organic acids. As this may occur a t the top of a tank, the difference between the volatile acid content of the top and the bottom of a tank may amount to as much as 0.020 per cent. One tank was found to contain a t the bottom, 0.108 per cent; middle, 0.125 per cent; and top, 0.148 per cent of volatile acid. To secure a truly accurate sample, the entire tank should be thoroughly agitated; satisfactory results can usually be obtained by mixing samples from the top, middle, and bottom of the tank. For routine tests, a sample from the center of the tank will suffice. ALCOHOL.Alcohol is usually determined in California wineries with the ebullioscope, but with the increasing number of chemists entering the wineries, the use of hydrometers and pycnometers is increasing. Some laboratories are increasing the accuracy of their ebullioscopes by determining the boiling point of wine distillates, but most plants still test the wine without this precaution. In the case of sweet wines, a dilution is sometimes made to reduce the effect of sugar on the boiling temperature. A limit of accuracy of 0.1 per cent is considered desirable. Accurate alcohol spindles are now available a t a reasonable figure and can be used in as little as 100 cc. A convenient method used in some plants is to distill 100 cc. of wine plus 50 to 75 cc. of water into a 100-cc. volumetric flask, and determine the alcohol on the distillate with a spindle. The residue in the boiling flask can be washed into a 100-cc. volumetric flask and the solids or “dry extract” roughly determined with a Balling hydrometer. This dealcoholized residue may be saved for the subsequent determination of reducing sugar and tannin. VOLATILE ACIDS. This term is used to describe those substances removable from wine by steam distillation and possessing an acid reaction to phenolphthalein. I n the United States volatile acids are calculated as acetic acid. With the recent introduction of new limits on volatile acids, this test becomes vitally important and greater accuracy in its determination is desired than previously, a limit of 0.005 per cent being frequently requested.
Slight variations of the official method (1) are in general use; usually a 10-cc. sample is steam-distilled until 50 to 100 cc. of distillate are collected, titrated, and calculated as acetic acids. At present the various regulatory agencies, following the official method of the Association of Official Agricultural Chemists, do not make allowance for the fact that any sulfur dioxide in the wine is distilled and measured as a volatile acid. Certain types of wines (Haut Sauterne and Chdteau Yquem) need up to 0.035per cent of sulfur dioxide to prevent fermentation in the bottle. When titrated as a volatile acid, 0.035 per cent of sulfur dioxide is equivalent to 0.066 per cent of acetic acid. The limit on a white wine is 0.110 per cent of volatile acid as acetic; 0.110 - 0.066 = 0.044 per cent of normal volatile acid, which might be taken as the limit for these types of wines. Such a limit excludes with certainty any wines over a year old. TOTAL ACIDS. This is the term used to describe the total titratable acidity in wine. It includes both volatile and fixed acids and is calculated as tartaric acid. The determination of total acidity in white wine presents little difficulty when phenolphthalein is used as an inside indicator ( I ) , but the intense red color of red wine makes the use of phenolphthalein as an inside indicator difficult unless diluted with 50 to 150 volumes of boiling distilled water. Some chemists use a mixture of 1 per cent phenolphthalein powder in powdered potassium sulfate as an outside indicator. For rough work many chemists use the change in color of the natural anthocyanin pigment of the grape as an indicator. Absolute accuracy is not as important in this determination as some others. REDUCING SUGARS.Reducing sugars are frequently determined by the Lane and Eynon method (S),which measures the amount of unused cupric ion after the wine has been boiled with a known amount of Fehling’s solution. The official or Munson and Walker (6) method is not very popular among the wineries, because it is slow and requires an analytical balance. The Shaffer and Hartmann (8) method, a volumetric iodometric method, is being used in many plants where a high degree of accuracy is desired, and is popular in the various fruit industries in California. An accuracy of 0.010 or 0.020 per cent is desirable in the reducing sugar test.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
METALS. Iron and other metals are to be avoided in wine because they form a recurring cloud and render the wine difficult to stabilize. The limits for iron and tin, the two worst metals in wine ( 7 ) , are about 2 to 5 p. p. m. The method of Leavell and Ellis (4)is being used for the determination of iron with apparent satisfaction by several plants. SULFURDIOXIDE. Sulfur dioxide in wine is best determined by the bicarbonate-hydrochloric acid (8) method such as is in general use in the dried fruit industry. Satisfactory results may be obtained using a 32- or 50-cc. sample, distilling into iodine, and titrating with thiosulfate. The federal limit on sulfur dioxide in wines is 0.035 per cent and an accuracy of 0.005 per cent may be expected of the analyses. TAXXIN.Tannin in wines is usually considered of insufficient importance to warrant analysis. However, where desired, the official method (Z?), using indigo-carmine as an
VOL. 8, NO. 1
indicator and titrating with standard permanganate, is followed.
Literature Cited (1) Assoc. Official Agr. Chem., Official and Tentative Methods, 3rd ed., p. 140 (1931). (2) Ibid., p. 141. (3) Lane and Eynon, J. Assoc. Oficial Agr. Chem., 9, 35 (1926); 12, 38 (1929). ENQ. CHEM.,Anal. Ed., 6, 46 (1934). (4) Leavell and Ellis, IND. ( 5 ) Munson and Walker, J. A m . Chem. Soc., 28, 663 (1906); 29, 541 (1907). (6) Nichols and Reed, IND.EXG.CHEM.,Anal. Ed., 4, 79 (1932). (7) Searle, LaQue, and Dohrow, IND. ENG.CHEM.,26, 617 (1934). (8) Shaffer and Hartmann, J. Bid. Chem., 45, 349-90 (1921). RECEIVED August 29, 1935. Presented before the Diviaion of Agricultural and Food Chemistry, Symposium on the Chemietry and Technology of Wine, at the 90th Meeting of the Ameriran Chemical Society, San Francisco, Calif., August 19 to 23, 1935.
Micro-Dumas Generation of Carbon Dioxide WALTER S. IDE, Burroughs Wellcome and Company, U. S. A., Experimental Research Laboratories, Tuckahoe, N. Y.
W
HILE the use of the Kipp generator as a source of carbon dioxide is satisfactory, this is true only when two generators are coupled in series. A much simpler method is to generate the carbon dioxide from magnesite, contained in the closed end of the combustion tube. This method utilizes very little space, an item of consideration in most laboratories, and the cost of equipment is greatly reduced, the combustion tube and the microazotometer being all that is necessary in addition to the balance. Berl and Burkhardt (1) have described a semi-micromethod for the determination of nitrogen, using magnesite as the source of carbon dioxide and an average specimen of 30 to 40 mg. of substance. They use an azotometer with a graduated volume of 10 cc. (2). In the present method an ordinary microcombustion tube is used, one end being sealed off and rounded, making a tube approximately 40 cm. long. Magnesite is introduced into the closed end of the tube to a depth of about 3 cm. It is necessary to use Kahlbaum magnesite ( j d r anal.), the pea size being broken into smaller pieces. Following the magnesite in successive order are an asbestos wad of about 3 mm., 4 cm. of copper oxide, the specimen (3 to 4 mg.) mixed with copper oxide, copper oxide for about 5 cm., an asbestos wad, reduced copper spiral followed by asbestos, 5 cm. of copper oxide, and finally another asbestos wad, leaving about 5 cm. of the tube empty. Before the combustion of the specimen, the tube is swept free from air by heating the magnesite. The closed end is surrounded with wire gauze, to eliminate distortion, and heated with a strong flame, and at the same time the long burner is turned on. Bubbles with a diameter of
one-tenth division appear in from 4 to 5 minutes, and true microbubbles are obtained if heating is continued for another minute. When bubbles of one-tenth division appear in the azotometer the flame under the magnesite is turned down until the barely luminous flame just touches the gauze, so that the generation of carbon dioxide is nearly stopped. The combustion is carried out in the usual manner. The rate of decomposition of the compound can be controlled very accurately, as there is very little free space behind the specimen, and any change in the rate of decomposition is indicated immediately in the azotometer. When the specimen is completely decomposed and the burner under the specimen has reached the long burner, the flame under the magnesite is increased slowly until the nitrogen has been removed and the microbubbles appear in the azotometer. The writer uses two combustion tubes, one being filled while the other is in use. The decomposition of the specimen and sweeping of the gases take from 25 to 30 minutes, depending on the amount of nitrogen in the compound. The azotometer is read after 10 to 12 minutes. The total time from the beginning of sweeping until the final reading of the nitrogen volume should not exceed 50 minutes. From the volume of nitrogen collected, 2.2 per cent is deducted to give the net volume to be reduced to normal conditions. This value is determined by example, Kahlbaum analyzing a known compound-for hippuric acid-at the beginning and end of each series of analyses. This value has remained constant, and obviously represents a blanket correction, apart from temperature and pressure corrections. All the nitrogen values in the publications from this laboratory during the past three years have been determined by this procedure. The method was investigated a t the suggestion of J. S. Buck of this laboratory.
Literature Cited (1) Berl and Burkhardt, Ber., 59, 897 (1926). (2) Weygand, C., “Quantitative analytische Mikromethoden der organischen Chemie in vergleichende Darstellung,” p. GO, Leipzig, Akademische Verlagsgesellschaft, 1931. RECEIVED August 7, 1935.
