Optical Spectroscopic Determination of Boron Polarizing Attachments R. K. CALFEE AND J. S. MCHARGUE, University of Kentucky, Lexington, Ky.
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HE exact measurement of certain impurities, usually present in minute quantities in metals, tissues, and compounds, is often important in metallurgy and the nutrition of plants and animals. Chemical methods for the determination of minute quantities of the minor elements are often tedious, complicated, and, in many cases, entirely unreliable. The quantitative spectzoscopic methods as described by several i n v e s t i g a t o r s ( I , I,6,8,10, 11, 12) are ideally suited for this type of analysis, and are considered (5) more accurate than chemical methods. Spectrographic methods have been 0- --$4
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troscopic determination of boron, described by the authors in 1932 ( 7 ) , depends upon the absorption of certain lines of the boron spectrum by a standard solution of potassium permanganate. The boron is converted to methyl borate, volatilized with methyl alcohol, and burned in an atmosphere of oxygen before an absorptiop cell containingthe permanganate solution. The boron content of the alcohol solution is estimated from the normality of the potassium permanganate solution added t o the cell to obscure the bright lines of the boron spectrum. (This procedure has since been modified to check the absorption of the spectrum and to allow duplicate readings to be made on the same solutions. After absorption of the boron spectrum a solution of ferrous ammonium sulfate, standardized against the permanganate, is added to the solution in the cell. In properly conducted determinations the spectrum will be discernible upon the addition of 0.2 ml. or less. Duplicate readings are made by adding a definite quantity, usually 5 mI., and again absorbing the bright lines by additions of permanganate solution. A correction is made for the water added with the ferrous ammonium sulfate.) Recent improvements in this method, which allow determinations t o be made a t more efficient Iight intensities, include a tube for saturating natural gas with a solution of methyl borate in methyl alcohol, ignition in an oxygen blast. a standard boron spectrum for comparison, and polarizing accessories for measuring differences in light intensities.
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A New Procedure The optical system is shown in Figure 1. The transmission of light is represented by dotted lines. Light originating at burner 1 is plane-polarized by plate 2, and is reflected by a small mirror, 4,through the lower half of slit 5. Light originating at burner 3 passes over the mirror, 4, and through the upper half of slit 5 . Lenses 6, 8, and 10 invert the spectra and retain proper focus on the compound prism, 7. The analyzing plate, 9, is mounted on a movable scale. A standard boron solution is burned at 1 and the sample solution is burned at 3. Rotation of plate 9 changes the intensity of the spectrum originating from burner 1, leaving that from 3 unchanged, thus allowing the intensities of the two t o be matched and the unknown to be measured in terms of the known. A glass burner as shown in Figure 2 is used for exciting the spectrum. Connections with oxygen and gas are made at 1 and 2, respectively. The orifice at the lower end of tube 2 is necee-
applied successfully for the control of industrial proc2. XYGEN esses (4) in alloy analysis FIGURE BLAST'I BE and for the classification of For burning and saturatsteels, as well as test meth- ing natural gas with an solution of ods (13) and color meas- alcoholic methyl borate urements in textile fabrics (9). Spectroscopicmethods of analysis are also applicable to samples of biological material (3). Photographic methods of spectrum analysis have been developed to a much greater extent than optical methods. In many instances the wave lengths of lines most accurately measured are beyond the range of visible light. A permanent record of the 1 chemical constituents of matter can also be obtained by photographic methods. Most optical methods have been based upon systematic observation and dilution of a solution of some compound of an element until certain lines are no longer visible in the spectrum. Since the end point of such a method occurs under conditions of low instrument efficiency, a high A degree of accuracy is i m p o s s i b l e . A FIGURE 3. CONSTRUCTION DETAILSO F quantitative optical method for the spec-
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B POLARIZING
COLLIMATOR ATTACHMENT
to hold 2 ml. and is detachable to facilitate the changing of solutions. Constant gas pressures are maintained by the use of glass stopcocks. The construction of the collimator attachment is shown by diagram A , Figure 3. The clamps, 1 and 3, support the burners rigidly in position; they are accurately aligned and permanently attached. The polarizing plate is held in the cylinder, 2, by a brass spring. A slight degree of rotation is rovided for accurate adjustment of the zero point on the scale. $he mirror, 4,is permanently sealed in proper position. The slit, 5, is adjustable, as indicated, by means of a screw and spring. Attachment is made to the collimator tube, 6, of the spectroscope by means of a removable clamp. Diagram B, Figure 3, shows the worm and pinion, 4, provided for rotation of the polarizing Elate. Caps are bolted on for protection and support of wor ing parts. The attachment is constructed of brass.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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with dilute sulfuric acid and precipitate the halides with a solution of silver sulfate. Excessive quantities of sodium sulfate are then removed by dehydration with ethyl alcohol and filtration. The boron after removal of the alcohol is concentrated by solution and filtration or distillation with methyl alcohol. The use of phosphorus pentoxide is very effective in inducing esterification, particularly in the distillation of residues which require much water to transfer. The final solution of boron is made with methyl alcohol containing 5 per cent (by volume) of sulfuric acid. Usually 5 readings on 3 portions of the final solution are made and the average is taken as the actual boron content. Theformula p.p.ni. = R X Vo/W converts the scale reading to p. p. m. of boron in the moisture-free sample.
SPECTROSCOPIC ANALYSESFOR BORON TABLEI. COMPARATIVE IS PLANT MATERIAL Sample Carrot (leaves) Carrot (tuber) Sweet potato Tomato (fruit) Tomato (fruit Tomato (fruit) Tomato (vines) Tomato (vines) Cabbage Lettuce
VOL. 9, KO. 6
Storage of Carbon Dioxide from Dry Ice for Dumas Determinations W. H. HAMILL AND J. A. ALICINO Fordham University, New York, N. Y.
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RY ICE is a conveaient source of pure carbon dioxide and
the following method of storage makes it readily available for Dumas nitrogen determinations with less effort and in purer form than is ordinarily possible with double Kipp generators.
Boron Permanganate Polariaation method method P. p . m. P. p. m. 7.4 5 2 9 a
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The equipment and procedure described have been in use for about 6 months. Analyses compare very favorably with values obtained by the previously published method ( 7 ) . Individual readings are much closer to the average, smaller samples are permissible, and the analytical procedure is much shorter. Data on a few samples of plant material analyzed by both methods are given in Table I. Summary Polarizing attachments and an oxygen-methane blast burner for the spectroscopic determination of boron are described. Natural gas saturated with methyl borate in methyl alcohol is ignited in an oxygen blast to excite the spectrum. A standard solution on ignition and polarization produces a reference spectrum in juxtaposition to the spectrum of the sample. The degrees of rotation of the analyzing plate are read on a scale in terms of parts per million of boron in the solution upon matching the intensities of the spectra. Recommendations are given for the treatment of samples containing halides and large amounts of sodium salts. Samples containing from 1 to 600 p. p. m. of boron have been analyzed. Literature Cited (1) Breckpot and Mevis, Ann. soc. sci. Bruzelles, B54, 99-119 (1934). (2) Brode and Steed, IND. EXG.CHEAL,Anal. Ed., 6, 157-9 (1934). (3) Drea, W. F.,S,Nutrition, 8, 229-34 (1934). (4) Dreblow and Harvey, IND. ESG. CHEM.,25, 823-5 (1933). (5) Duffendack, 0. S., Wolfe, R. A., and Smith, R. W., Ibid., Anal. Ed., 5, 228-9 (1933). ( 6 ) Kreamer, W., 2. anal. Chem., 97, 89-93 (1934).
(7) McHargue, J. S., and Calfee, R. IC., IND.EKQ.C H E M Anal. ., Ed., 4, 385-94 (1932). (8) Nitchie, C. E., Ibid., 1, 1-7 (1929). (9) Nutting R. D., Teztile Research, 5, 391-400 (1935). (10) Schubert. H.. and Cruse. Z. vhwsilc. Chem., A172. 143-55 (1935). Smith, D. M:, S. Inst. Metah, 55,417-25 (1934). Triche, Henry, Compt. rend., 199, 419-21 (1934). Waldbauer and Gantz, IND.ENG.CHEM.,Anal. Ed., 5, 311-13 (1933). RECEIVED February 25, 1937. Contribution from the Department of Chemistry of the Kentucky Agricultural Experiment Station. The invstigation reported in this paper is in connection with a project of the Kentucky Agricultural Experiment Station and is published by permission of the director.
FIQURE I Two carboys are mounted in a rack (Figure l), connected as shown, and the lower one is filled with water. Carbon dioxide from any convenient source, which need not be pure, is introduced through b and bubbled through the water until it is free of dissolved air. A flask containing a few chunks of dry ice is then connected at a and the water is forced from A to B, displaced air escaping through d. A carbon dioxide Kipp generator, which requires no precautions in filling, is connected at c and serves to maintain an atmosphere of carbon dioxide above the water in B. During operation the combustion tube is connected at a.
The time required to recharge a 40-liter (10-gallon) carboy is about 15 minutes. Over a period of months, since first setting up the apparatus, the blank has been 0.010 cc. within 10 per cent and has not changed either upon refilling or standing. Of this residual gas only 0.003 cc. is due to impurity in the carbon dioxide (1000 bubbles), the rest apparently being expelled during combustion from the combustion tube and filling. Because of the pressure under which the gas is stored, it has been found that one minute suffices for flushing out the combustion tube. RECEIYED May 19, 1937.
