INDUSTRIAL AND ENGINEERING CHEMISTRY
314
time is saved a t other points. The double precipitation removes sufficient impurities from the starch so that the usual preliminary extraction of the plant to remove sugars and the usual final treatment with clearing agents are unnecessary. This method gives lower results in all types of plants than other starch methods and is believed to give a more accurate value for the true starch present.
Summary The large variety of methods which exist for starch estimation bring out the fact that few of them are reliable even in limited cases, Neither acids nor diastatic enzymes are sufficiently specific for accurate results. The development of highly purified and specific enzymes may solve the problem. Methods based on other chemical and physical properties of starch, such as its solubility in salts and acids, and its insolubility in iodine and salt solutions, deserve closer study and no doubt many contributions will be made in the future along such lines.
Literature Cited Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 1930. Chinoy, J. J., Edwards, F. W., and Nanji, D. R., Analyst, 59, 673 (1934). Coe, M. R., J. Assoc. OficiaZ Agr. Chem., 9, 147 (1926). Collins, I. D., Science, 66, 430 (1927). Davis, W. A., and Daish, A. J., J . Agr. Sci., 5, 437 (1913). Davis, W. A., and Daish, A. J., Ibid., 6, 152 (1914). Denny, F. E., Contrib. Boyce Thompson Inst., 6, 129 (1934). Denny, E'. E., Ibid., 6 , 381 (1934). Denny, P. E., J. Assoc. OficiulAgr. Chem., 6 , 175 (1922). Eckart, H., Chem. Zelle Gewebe, 12, 243 (1925). Englis, D. T., Pfeifer, G. T., and Gabby, J. L., J . Am. Chem. SOC.,53, 1883 (1931). Fellenberg, Th. von, Mitt. Lebensm. Hyg.,7, 369 (1916). Ibid., 8, 55 (1917).
VOL. 7, NO. 5
Ibid., 19, 51 (1928). Fraps, G. S., J. Assoc. Oficial Agr. Chem., 15, 304 (1932). Freudenberg. K., J. SOC.Chem. Ind., 50, 288T (1931). Hall, E. H.;Ibid., 50, 4291' (1931). Haworth, W. N., Ibid., 53, 1059 (1934). Herd, C. W., and Kent-Jones, D. W., Ibid., 50, 15T (1931). Hill, A. C., Proc. C h m . SOC.,17, 45 (1901). Ibid., 17, 184 (1901). Hirst, E. L., Plant, M. M. T., and Wilkinson, M. D., J . Chem. SOC.,1932, 2375. Horton. E.. J . Am. Sci.. 11. 240 (1921). Jones, L,, J. Assic. Oficiul Agr. Chem ,'Xi, 582 (1932). Kaiser, A., Chem.-Ztg., 26, 180 (1902). Klinkenberg, G. A. van, 2. physiol. Chem., 212, 173 (1932). Kuhn, R., Ann., 443, 1 (1925). Lehmann, O., Plantu, 13, 575 (1931). Ling, A. R., J . Inst. Brewing, 28, 838 (1922). Ling, A. R., Nanji, D. R., and Harper, W. J., Ibid., 30, 838 (1924). Ling, A. R., and Nanji, D. R., J . C h m . SOC.,123, 2666 (1923). Ling, A. R., and Salt, F. E.,J . Inst. Brewing, 37, 595 (1931). Long, W. S., Trans. Kansas Acad. Sci., 28, 172 (1916). Nishimura, S., Chem. ZeZZe Gewebe, 12,202 (1925). Nordh, G., and Ohlsson, E., 2. physiol. Chem., 204, 89 (1932). Noyes, W. A,, Crawford, G., Jumper, C. H., Flory, E. L., and Arnold, R. B., J. A m . C h m . Soc., 26, 266 (1904). Ohlsson, E.,2.phyeiol. Chm., 189, 17 (1930). Rask, 0. S., J . Assoc. Oficial Agr. Chem., 10, 108 (1927). Ibid., 10, 473 (1927). Small, J. C., J . Am. Chem. Soc., 41, 107 (1919). Taylor, T. C., and Iddles, H , A,, IND.ENQ.CHEM,, 18, 713 (1926). Taylor, T. C., and Walton, R. P., J. Am. Chem. Soc., 51, 3431 (1929). Thomas, W., Ibid., 46, 1670 (1924). Waldeschmidt-Leitz, E., Reichel, M., and Purr, A., Naturwissenschujten, 20, 254 (1932). Walton, G. P., and Coe, M. R., J . Agr. Research, 23, 995 (1923). Weiss, H., 2.ges. Brauw., 45, 122 (1922). Widdowson, E. M., Biochem. J., 25, 863 (1931). RIWBIVE~D May 23, 1935. Presented before the Division of Agricultural and Food Chemistry at the 89th Meeting of the American Chemical Society, New York, N. Y., April 22 to 26, 1936.
Determination of Alkalies in Feldspars A Modified Hydrofluoric Acid Method E. W, KOENIG, Consolidated Feldspar Corporation, Erwin, Tenn.
M
UCH time and effort have been expended upon investigations of the possibility of replacing the timehonored J. Lawrence Smith (8) method for the disintegration of silicates, preliminary to the determination of the alkali metals, sodium and potassium, by a more expeditious procedure. Because of the ease of initial decomposition of the silicate sample by means of hydrofluoric acid, possible modifications of the original Berzelius (1) method-in the direction of the elimination of the undesirable conversion of sulfate to chloride by means of barium chloride-have long intrigued the analytical chemist. Low (6) and later Krishnayya (4) modified some portions of the method but did not successfully eliminate the particularly objectionable sulfate-chloride conversion. Scholes (7) described an excellent modification which eliminated most of the undesirable features of the original method and yet took full advantage of the hydrofluoric acid disintegration. The method gave results of good accuracy and precision with a considerable reduction in the amount of time necessary for analysis. Unfortunately, the procedure required a prohibitive amount of direct supervision and has. therefore never become popular for routine determinations. The method devised by Knowles and Redmond (S), wherein
the alkali metals are isolated as mixed chlorides after removal of aluminum and calcium as quinolate and oxalate, respectively, is productire of excellent results. The only objectionable feature of the method is the fact that, in materials with as high a percentage of aluminum as feldspar, the removaI of this component with 8-hydroxyquinoline is extremely burdensome unless a relatively small sample-0.1 to 0.2 gram-is used. The use of a small eample does not appreciably affect the accuracy of the total chloride determination, if reasonable attention is paid to the details of the method. However, the ultimate separation of the sodium and the potassium, when working with small samples, is uncertain by most of the gravimetric methods now available, unless an unreasonable amount of time is expended in their recovery. This is true regardless of the method of separation-perchlorate, chloroplatinate, or triple acetate-because of the solubility factors affecting one or the other of the alkali salts, depending on the method chosen for the separation. After a thorough investigation of each of the foregoing methods, a further modification of the Berzelius method was evolved. Volatilization of silica as tetrafluoride is unnecessary if complete removal can be accomplished by other means. This eliminates the necessity for the introduction of sulfuric
SEPTEMBER 15, 1935
ANALYTICAL EDITION
acid and its subsequent questionable removal with barium chloride. Hostetter (2) has shown that aluminum, iron, and magnesium can be precipitated as hydroxides by the addition of calcium oxide, which will also precipitate the fluorine as calcium fluoride. The silica can also be quantitatively removed as silicofluoride. Removal of calcium is accomplished by means of ammonium carbonate and ammonium oxalate and the alkali carbonates are converted to chlorides with hydrochloric acid. Table I indicates the accuracy of the method when compared with the J. Lawrence Smith procedure which was used as standard throughout this investigation.
TABLEI. ACCURACY OF METHOD Sample
J. Lawrence Smith
Modified Procedure
Gram‘“
Gram
70 99 M4072 M4084 B749 B763 National Bureau of
0.1220 0.1222 0.1042 0.1040 0,0825 0.0825 0.1087 0.1087 0.1128 0.1126 0.1077 0.1077 Standards certifioate value.
Error Qram
+0.0002 -0.0002 10.0000 10.0000 -0.0003 10.0000
KO unusual apparatus or reagents are required, though a good supply of platinum ware in the form of medium-capacity dishes is effective in reducing analytical time to a minimum when a large number of determinations are necessary. Reagents Hydrofluoric acid, 48 per cent. A commercial c. P . reagent was used. Calcium oxide. The ignition product of a specially purified reagent calcium carbonate was used. (Early in the investigation, erratic results for total alkali chlorides were encountered. They were traced to the calcium carbonate used, which was found to contain a considerable amount of sodium.) The reagent is purified by the method suggested by Schaal (6): A quantity of the reagent is repeatedly digested with fresh quantities of distilled water, the salt being finally dried and ignited to the oxide. A small correction, the extent of which can be found through analysis and which should not exceed 0.5 mg. when working with 0.5-gram samples, is to be deducted from the value obtained for total chlorides. This represents the amount of sodium, as chloride, which has escaped extraction during the purification process. Ammonium carbonate. One hundred grams of a c. P. reagent are dissolved in 80 ml. of ammonium hydroxide (sp. gr. 0.9) and diluted to 500 ml. Ammonium oxalate. A saturated solution of a calcium-free reagent is used.
Procedure Transfer 0.5 gram of the -150-mesh sample (previously dried a t 110” C.) to a 75-ml. platinum dish (a dish of the Payne type is particularly suitable) and moisten with water. Add an excess (10 ml. is sufficient) of hydrofluoric acid and evaporate the solution to dryness on the water bath. Take up the residue with water (complete solution is unnecessary) and transfer to a 100-ml. beaker, to which approximately 2.5 grams of purified calcium oxide have been added. Police and rinse the dish, adding the washings to the beaker. Stir, and after boiling briskly for 5 minutes, filter through a retentive paper, catching
315
the filtrate in a 300-ml. porcelain casserole or platinum dish. Police the beaker and add the rinsings to the filter. Wash the precipitated hydroxides and fluorides several times with boiling water and discard the residue. Add 25 ml. of ammonium carbonate solution to the filtrate and evaporate to dryness. Take up in a minimum of water, add 15 ml. of the ammonium carbonate solution, and allow to digest for 15 minutes. Filter throu h a retentive paper, catching the filtrate in a 100-ml. beaker. %ash the residue sparingly with cold water and discard. Treat the filtrate with 4 drops of ammonium oxalate and digest, while uncovered, a t a temperature just below the boiling point for 1 hour. The solution is now reduced in volume to about 50 ml. Filter through a tight paper, catching the filtrate in an untared platinum dish, and wash the residue well, but sparingly, with a 1 per cent solution of ammonium oxalate. Discard the residue and after treatment with an excess of hydrochloric acid (to convert carbonates to chlorides), evaporate the filtrate to dryness on the water bath. The ammonium salts are completely volatilized at a low temperature (below dull redness) and the salts just melted. Dissolve the residue in a minimum of water and filter through a small paper, catching the filtrate in a tared platinum dish. Wash the residue sparingly with cold water and discard. Add a few drops of hydrochloric acid to the filtrate to convert any alkali carbonates to chlorides and repeat the evaporation. Just melt the salts over a very low flame and desiccate over an active desiccant. Weigh rapidly (alkali chlorides are relatively hygroscopic) and record as total alkali chlorides. Reserve the residue for the determination of sodium and potassium. The nonvolatile matter removed by filtration after the first volatilization of the ammonium salts is of no great consequence, amounting to only 0.7 mg. (*0.4 mg.). In any but the most exacting analysis this step in the procedure can be eliminated entirely by weighing the total alkali chlorides plus nonvolatile matter and correcting for the latter.
Summary A further modification of the Berzelius method for the disintegration of a silicate, preliminary to the isolation of the alkali metals as chlorides, has been successfully employed in the analysis of feldspar. Replacement of the J. Lawrence Smith procedure by the modified method entails no sacrifice in analytical accuracy and reduces the time required for a n analysis. Reagent costs have been reduced and a more economical use of equipment has been attained. Possibilities of the application of the method to the analysis of other ceramic materials and products are encouraging, though they have not been investigated.
Literature Cited (1) Berzelius, J. J., Pogg. Ann., 1, 169 (1924). (2) Hostetter, J. C., J. IND.ENQ.CHBM.,6, 392 (1914). (3) Knowles, H. B., and Redmond, J. C., J . Am. Ceram. Soo,, 18 (a), 106-12 (1935). (4) Krishnayya, H. V., Chem. News, 107, 100 (1913). (5) Low, A. H., Ibid., 67, 185 (1893). (6) Sohaal, R., J. Am. Ceram. Soc., 13 (2), 113-25 (1930). (7) Soholes, S. R.,Ibid., 15 (3), 342-3 (1932). (8) Smith, J. L., Am. Chemist, 1, 404 (1871); Am. J. Sci., [31 1, 269 (1871). RECEIVED May 27, 1935.
Microchemistry in Industry AT THE Symposium on Recent Advances in Microanalysis, presented at the New York meeting of the AMERICAN CHEMICAL SOCIETY in April, 1935, under the chairmanship of Beverly L. Clarke, Frank Schneider, of Rutgers University, spoke briefly on “Microchemistry in Industry.” He reported the results of a survey made to discover the extent to which micromethods were being used in industrial laboratories in this country. A sur-
prising number of concerns were found to be making use of the principles of microchemistry to some extent. He pointed out that a closer cooperation between teachers of microchemistry and industrial laboratories would increase this number, and would reduce the number of cases where micromethods are tried and abandoned owing to faulty understanding of fundamental principles. He. proposed the organization of a microchemical society.
