Photoelectric Determination of the Color of Corn Sirup BARRETT L. SCALLET, Anheuser-Busch, Znc., S t . Louis, M o . EA4SUREMENTof the color of corn sirup present,s certain difficulties not ordinarily encountered with other materials. The paleness of the colors involved necessitates the use of a long column of sample; the extremely high viscosity of the sirup necessitates the use of a sample container which can be filled and cleaned easily. For routine daily color measurements many sample tubes are required; a clean dry tube is needed for each sample, as the tubes cannot be emptied and rinsed with a portion of the next sample. I n this laboratory approximately 35 color measurement,s are made each day, and it is important that the sample tubes be inexpensive.
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Cylindrical tubes of Kimble glass (1.25inches in outer diameter, 5 inches long, open a t one end, and having a molded flat bottom) have been used satisfactorily in aLumetron Model 402E photoelectric colorimeter. For this purpose the instrument is set up so that
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A4typical light absorption curve for corn sirup is given in Figure 1 (curve obtained with t,he Coleman Universal spectrophotometer) ; maximum absorpt,ion is a t 380 mp. I n adapting the Lumetron instrument to the present use, it was found that a 420 nip filter (consisting of a 6-mm. thickness of Corning No. 5113 blue glass) and a 4.75-inch column of sirup gave the most
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COLOR OF CORN SIRUP
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it stands on what, would normally be the right. end. I n this position of the instrument the sample compartment is vert,ical and can accommodat,e the 5-inch tube. (The Photovolt Corp. now manufactures Lumetron Model 450 t o accommodate vertical tubes. This instrument has lower sensitivity than Model 402E but would probably give satisfact,ory results.) The photocell at' the bottom of the compartment is protected by a glass sheet inch thick; tubes are centered in a holder consisting of a fiberboard slab 0.125 inch thick with a 1.25-inch hole cut in it. The holder is wedged into the compartment just above the glass sheet. Transmit,tance values are read in the normal way.
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Color in Lovibond Units -Sum
Figure 2.
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Curve Relating Transmittance and Color of Corn Sirup
convenient spread of readings on the transmittance scale. A 380 mp filter increased the sensitivity of the measurements, but crowded the readings into the lower portion of the scale. It was desired to retain both the standard sample length of about 5 inches and the Lovibond color standards previously in use in the industry. X series of samples of corn sirup of various colors was therefore matched visually against Lovibond slides (series 510 yellow, series 200 red) in a split-field comparator, then read in the Lumetron. Results are plotted in Figure 2. Although the points do not fall on a straight line, this may indicate merely that the Lovibond units are not proportional to density. The curve is a convenient means of translating transmittance readings into Lovibond values. Results are reported in Lovibond units.
P DISCUSSION
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The method is rapid. Results are adequat,ely accurat,e for refinery control if precautions are observed. All sample tubes should be cleaned carefully and checked against a standard tube before being put into service. The standard t,ube is arbitrarily set a t lOOy, transmittance when filled with distilled water, and only those tubes showing between 98 and 1027, transmittance should be used. Tubes with more nearly flat bottoms are available, but are considerably more expensive. They should be used when exact measurements are required. The sample should be poured very carefully into the tube to prevent trapping air bubbles in the sirup, as these lead t,o falsely low t.ransmittance readings. If any bubbles are present the tube should be allowed to stand in a warm place until the bubbles come t o the top and can be scraped off Tyith a spat'ula. The level of corn sirup in the tube should be adjusted, if necessary,
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Wave Length, mp
Figure 1.
-4bsorption C u r i e for Corn Sirup
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ANALYTICAL CHEMISTRY
so that the sirup is just 0.25 inch from the top, This will prevent any lens effect of the meniscus from interfering with the reading. After the level has been adjusted, the tube should be checked visually to make sure that the surface is flat. This can be done by looking down through the full length of the sample at the bottom of the tube, which should appear as a smaller circle inside the mouth of the tube. If the bottom cannot be seen through
the mouth of the tube or is distorted, the surface is not flat and must be scraped. The glass sheet protecting the photocell must be cleaned carefully and the bottoms of the sample tubes must be kept clean to prevent partial blocking of the photocell. This method has been used daily for the past two years with emellent results on sirups in the RaumE range 20 t o 41.
A Text-book of Practical Organic Chemistry Including Qualitative Organic Analysis. Arthur 1. Vogel. xxiii f 1012 pages. Longmans, Green and Co., 55 Fifth .4ve., New York 3, N. Y., 1048. Price $10.50.
methods of manulactuie, which could not be adequately treated in one volume and still do justice to the other material covered. Considerable, although by no means complete information is given on such compounds as cyanamide, dicyandiamide, guanidines, andmelamine, which even 10 years ago were practically rare chemicals but are now produced in considerable quantity. As in the first edition the chemistry of the cyanides, cyanates, thiocyanates, and their complexes has been treated extensively and brought up t o date. This portion of the book is outstanding and references to the scientific literature are extensive and complete. The analytical section has been expanded to include the newer organic compounds. The author points out in the introduction that “several of the methods when used for the first time require manipulatory practice, however skilled the hands.” This is especially true of the newer organic compounds. No one active in the field of cyanogen compounds can afford to be L. J. CHRISTMAXS without the book.
A few remarks taken from the Preface will reveal the purpose and general contents. “Many of the new procedures and much of the specialized technique developed and employed in (the author’s) researches are incorporated. . .It is not expected that the student will employ even the major proportion of the operations described, but a knowledge of their existence is thought desirable for the advanced student. . . . , A short theoretical introduction precedes the detailed preparations. . . , .The textbook is intended to meet the requirements of the student throughout the whole of his training. . . . It will also provide an introduction to research methods in organic chemistry and, it is hoped, may serve as an intermediate reference book for practising chemists.” Here, with the notable exception of quantitative organic analysis, is a one-package presentation of laboratory work in organic chemistry on all levels. As a teaching instrument, however, it may not find wide use in our American schools, for it embraces much more material than can be presented in any ordinary laboratory course. Chapters I and I1 (230 pages) cover the “Theory of General Technique” and “Experimental Technique.” Preparations and reactions begin on page 231 (Chapter 11) and conclude on page 887 (end of Chapter X ) . Qualitative organic analysis merits only 66 pages (Chapter XI), although the previous chapters feature tables of physical properties and assorted diagnostic reactions useful for identification. The Appendix, entitled “Literature of Organic Chemistry,” includes information on preparation of palladium catalysts, periodir acid in qualitative organic analysis, etc. The index is ample. The preparations are very numerous and appear to be well chosen. In nearly every instance the detailed example is followed by a number of “cognate preparations.” Thus the directions for making n-butyl iodide by the phosphorus-iodine method are followed by brief instructions for making thirteen other iodides in the same general n-ay. In a few instances the recommended procedure is not the best available. For example, the preparation of dimethylethynylcarbinol (p. 454) employs the sodamide method rather than the sodium acetylide which gives better yields, is much less hazardous, and can be adapted to a larger scale. The paper is of good quality, the printing is excellent, and there are remarkably few typographical errors. . 4 regrettable feature is that citations to the original literature are not given, although there are numerous references to firms supplying special apparatus and chemicals. Vogel’stextbook n-ill prove a rich source of information for graduate students and other bench workers in organic chemistry. I t should be available in every library that claims to serve their needs. G. F. HENXIOX
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Cyanogen Compounds, Their Chemistry, Detection, and Estimation. H. E. Williams. 2nd ed. xvi -I- 443 pages. Longmans, Green and Co., 55 E‘ifth Ave., New York 3, N. Y., 1948. Price, $10.50. Since 1915 those engaged in the field of cyanogen compounds have turned to Williams when confronted with a problem. For some years the book was inadequate, but now the second edition has appeared in modified and greatly expanded form. The new edition has omitted
EdProceedings of the Society for Experimental Stress Analysis. ited by C. Lipson and W .AM.Murray.Vol. \’, No. 2. AddisonWesley Press, Ino., Cambridge 42, Mass. Price $6.
Methods in Medical Research “Methods in Medical Research,” a series of annual volumes devoted to methods and techniques, is to be published by the Year Book Publishers, Inc., Chicago, Ill. The Governing Board is coniposed of Irvine H. Page, A. C. Ivy, Colin >I RlacLeod, . Carl I’. Schmidt, Eugene .4.Stead, and David L. Thomson. Volume I, undw the editorship of Van R. Potter, Cniversity of Wisconsin, was available in May 1948,and succeeding books are due every January. Contents of Volume I include: “Assay of .Intibiotics,” by Henry Welch; “Circulation,” by Harold D. Green: “Selected Methods in Gastroenterologic Research,” by .4, C . Ivy; and ”C:ellular Respiration,” by S’an R. Potter.
Constant level Control for Water Baths SIR: The type of apparatus discusbed by Snell (g), was described by the writer in March 1912 (1). Although I used this apparatus in 1938, it is so simple and straightforward that I would be surprised to find that I was the first to utilize it. This communication is not t o claim priority but to point out two details that may be of interest. -4s will be seen from Figure 2 ( 1 )reproduced here, the simple siphon shown in Snell’s diagram is slightly modified (see B ) . Owing to the vacuum created at the top of the siphon. air bubbles tend to form there and break the siphon action. I, therefore, included an air trap in the form of an inverted funnel with two inlets at the bottom and an outlet at the top, the latter closed by a rubber tube and a clip. By
