Microanalytical Determination of Carbon and Hydrogen A Simplified Method JOSEPH B. NIEDERL AXD ROSLYN T. ROTH,Washington Square College, New York University, New York, N. Y. IWCE the introduction of organic microchemical methods
tion tube, Pregl’s (29) capillary tubes and rubber connections are eliminated. The combustion tube, g, is of quartz, 50 em. long, with B side arm (2.4) of capillary glass of the same dimensions as the arm of the bubble counter. It is filled with the Universal filling devised by Pregl (SO) and closed by a tight-fitting cork, removable for the introduction of the sample without disconnecting the oxygen stream. As constant-temperature device, h, for the lead superoxide, the improved mortar according to Verdin0 (S.4) is employed using p-cymene as the constant-boiling liquid. A copper APPARATUS rod, protruding from the mortar, heats the capillary conIn the simplified apparatus the use of air has been elimi- striction on the water absorption tube. The permanent nated from the combustion train and the gasometer is re- filling is heated by Flaschentrager’s (IS) electric furnace, and placed by the use of a reduction valve on the oxygen tank, a Bunsen burner serves as the movable burner. Pregl absorption tubes with a hollow ground-glass stopper a, and a Pregl precision stopcock (28). Traces of organic matter and hydrogen found in many sources of oxygen are and well-fitting copper wires suggested by Boetius (8) and eliminated by passing the gas through a preheater, b, devised modified by Whitman (27),to reduce the absorption of moisby Bock and Beaucourt (5) and modified by Whitman (S6). ture and carbon dioxide during weighing time, are used. It consists of two quartz tubes, one inside the other, the outer The water absorption tube, i , is filled with a coarse and fine one, which is filled with coarse copper oxide or platinum as- layer of anhydrone, previously treated with carbon dioxide, bestos, being 100 mm. long and 10 mm. in diameter. The with thick cotton plugs on each side of the layers. The carinner tube is 3 mm. in diameter, open a t the upper end and bon dioxide absorption tube, j, contains a IO-mm. layer of sealed to the outer tube a t the bottom, thence extending 40 anhydrone and is otherwise filled completely with ascarite. mm. downward, a ground-glass joint attaching it to the They are connected head to head, the water absorption tube spiral coil. The preheater is heated by an electric heating next to the combustion tube, with specially impregnated cap or by a Bunsen burner, and by cooling the oxygen in the seamless rubber tubing. The Boyle-Mariotte flask, I, is similar to Pregl’s .(SI) exspiral coil possible decomposition of the rubber connections cept for a stopcock on the gas inlet tube, as employed by is avoided. Lieb. A drier, k, filled with anhydrone, attaches it to the absorption tubes. A similar Mariotte flask is kept in the balance room, serving as an aspirator (27) to rinse the oxygen-filled absorption tubes with air while they are cooling t o balance room temperature. The air is purified b y passing it t h r o u g h a gas wash bottle containing sulfuric acid to remove organic matter, and a purifying tube containing ascarite and anhydrone is FIGURE1. COMBUSTION TRAIN c o n n e c t e d w i t h the wash bottle. a. Oxygen tank e. Bubble oounter i. Water-absorption tube The free end of the water absorption b. Preheater f. Drying tube j . Carbon dioxide-absorption tube tube is connected with the purifying c. Pressure regulator 8. Combustion tube k. Drier d. Asoarite tube h. Heating mortar 1. Mariotte flask train and the carbon dioxide absoration tube to the drier of the Mariotte The pressure regulator, c, is the usual one described by flask, so that the air flows in the same direction as the oxygen Pregl (28). The side-arm outlet is bent a t right angles di- during the combustion, bringing the temperature of the abrectly into an ascarite absorption tube, d, which also removes sorption tubes quickly down to balance room conditions. moisture, preventing dilution of the alkali in the bubble PROCEDURE counter. The bubble counter, e, and drying tube, d, are larger than 1. The capillary ends of the ascarite tube are cleaned with those used by Pregl (29). Having a total length of 150 mm. cotton, the copper wires inserted and the tube is wiped accordand a diameter of 12 mm,, the anhydrone filling needs re- ing to Pred’s directions, Placed on the rack for 10 minutes, transferred to the balance, and 5 minutes later weighed to 0.01 placement less often. BY connecting the capillary glass arm mg. It is reweighed after 5 minutes. The anhydrone tube is of the drying tube directly with the side arm of the combus- wiped and weighed in the same manner.
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a t New York University (1)in 1925, the interest in these procedures has widened considerably (21, SS), notably a t the University of Pittsburgh, Coal Research Institute, Pittsburgh, Merck’s Research Laboratory, Rockefeller Institute, College of Physicians and Surgeons, Columbia University, Loyola College, Baltimore, and elsewhere. A simplified method for the microdetermination of carbon and hydrogen is described below, incorporating numerous improvements.
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2. After removal of the copper wires, the absorption tubes are which char. Attempts have been made to replace the lead connected head to head by a rubber tubing 20 mm. long, another euperoxide by metallic copper or silver. Lindner suggests 15 mm. long being attached t o the anhydrone tube, the rubber tubings having been moistened previously with a trace of glycerol. air for the actual combustion and nitrogen for the transport The absorption tubes are then attached to the combustion train, gas, but even partial use of air would oxidize the copper and the anhydrone tube adjoining the latter, and the ascarite tube necessitate frequent renewals. Avery, Brackenbury, and next to the drier of the Mariotte flask, the side arm of which is Maclay (2) use a metal tube allowing the insertion of a copper always in a horizontal position. 3. The cork stopper of the combustion tube is removed, the coil for the combustion of substances containing nitrogen. substance quickly introduced t o within 50 mm. of the oxidation Niederl and Whitman (27) use nitrogen exclusively by mixing filling, and the tube immediately closed. Then the stopcock to the sample with copper oxide and employing a combustion the Mariotte flask is opened, tube filling similar to-the micro-Dumas: 4. As soon as the gas flow is normal (5 cc. er minute), a Investigations of the weighing errors small flame is applied 30 mm. from the sample, sl%vly increased until it envelops the combustion tube, and then gradually moved of absorption tube are summarized by toward the sample, observing whether the substance sublimes, Hernler (18) and include the observadistills, or decomposes, the distillate or sublimate slowly being tions of Schoorl (33,Friedrich (15), driven toward the heated oxidation filling. If it decomposes with Brunner ( I O ) , and Meixner and Krocker charring, it is heated strongly directly under the substance until (23). Blumer (4) and Flaschentrager no black residue remains. The combustion is carried out with 75 cc. of oxygen and should take about 15 minutes, after which it (12) constructed tubes with side-arm is repeated to burn off all traces of charring, requiring only about exits which could be closed by movable 5 minutes. glass stoppers. Mercury for a liquid 5. The gaseous products are washed out with 75 cc. of oxygen in 15 minutes, then the stopcock of the Mariotte flask is closed, seal was adopted by Kemmerer and the absorption tubes are detached and immediately attached t o Hallett (19) and improved by Cornthe air filter, and the entire train is connected t o the aspirator wall (11). Friedrich d e s c r i b e s two and washed with 50 cc. of air at the rate of 10 cc. per minute. kinds of mechanically self-sealing tubes By employing two sets of absorption tubes and utilizing the waiting time during the analysis, while washing out the gaseous (14). All these absorption devices have products, for wiping and weighing the second set, the time for an been found of little advantage, as the analysis may be reduced t o about 35 minutes. difficulty of h a n d l i n g (wiping) such tubes i n c r e a s e s , while on account of prevented temperature-pressure equaliDISCUSSION FIGURE2. PREzation no greater constancy is observHEATER The use of an extra combustion tube for a precombuster, able. a. Preheater tube as previously used, incurred the possibility of overheating b. Condenser At first m o i s t e n e d soda lime and the rubber connections a t the end, but this danger is elimi- calcium c h l o r i d e , as r e c o m m e n d e d nated by the preheater described above. by Pregl (B), were used in the absorption tubes which, Improvements in the Pregl pressure regulator and advice however, required refilling every six or seven analyses, and on the treatment of rubber tubing are given by Weygand ascarite, capable of absorbing up t o ten times as much (36). A new pressure meter is also described by Friedrich carbon dioxide, was substituted for the soda lime. But (14). A newer method of treating rubber tubing with strong when the tube was aspirated, it increased in weight about potassium hydroxide and steaming out has been found effec- 0.02 mg. for every 100 cc. of air or oxygen, equivalent to over tive (16). 0.04 mg. increase for 175 cc. of oxygen and 50 cc. of air used The original form of the bubble counter was replaced by a in an analysis and due to the difference in vapor pressure of few authors with a similarly functioning arrangement. Boe- calcium chloride and ascarite. According to Baxter and tius (6) uses a bubble counter having on each side a special Starkweather (3) a liter of air passed over calcium chloride and removable tube, one filled with ascarite, the other with sodium hydroxide contained residual water vapor of 0.36 phosphorus pentoxide-pumice stone mixture. and 0.16 mg., respectively, indicating that 100 cc. of air Pregl's combustion tube has been retained by most authors dried over fused calcium chloride would give up 0.02 mg. of except Flaschentriiger ( I $ ) , whereas Avery, Brackenbury, moisture on passing over ascarite. For this reason anhyand Maclay ( 2 ) suggest the use of copper and silver tubes drone, a more effqcientdehydrating agent, was used. with water-jacketed ends. Muller and Willenberg (24) simAccording to Willard and Smith ( S 7 ) , anhydrone is as plified the handling by devising a side-arm inlet for the com- efficient a drying agent as phosphorus pentoxide. It is neubustion tube. tral, porous, and stable towards heat up to 250' C. Its Boetius ( 6 ) ,Weygand (36),and Lindner ($2) tested exten- vapor pressure is 0.000 mm. a t 0' C. and it is capable of absively the materials used by Pregl for the filling of the com- sorbing water up to 30 per cent of its weight. Kirk and bustion tube. Boetius (7) shows in numerous experiments McCalla (80) reported using ascarite and anhydrone and a gradual lessening of the water content of the lead superoxide Boetius (9) ascarite and phosphorus pentoxide. A change in and Friedrich (16) finds that this substance gradually takes the absorption of the combustion products is described by up carbon dioxide and gives it off again in the combustion of Nederl and Meadow (26). The absorption of carbon dioxide substances containing nitrogen, halogen, and sulfur. Haas takes place in a filter tube and is gravimetrically determined and Rappaport (17) suggest cerium dioxide for copper oxide- as barium carbonate. In previous attempts to eliminate the use of air in the comlead chromate as filling, contending that the tube is better protected. Kirk and McCalla ($0) use catalytic manganic bustion, Muller and Willenberg (24) and later Kirk and oxide, and Friedrich (16) has devised a catalytic combustion McCalla ($0) weigh the absorption tubes filled with oxygen inmethod, permitting the easy removal of the lead superoxide, stead of air. Later experiments on absorption tubes which a platinum foil serving as the catalyst. Kiederl (65) calls are not self-sealing show that they cannot be brought to conattention to the danger of not having present sufficient oxy- stant weight when filled with oxygen, and self-sealing tubes, gen for the complete oxidation, when using this method. as mentioned before, do not allow for the equalization of In a succeeding article Friedrich (14) separates the thermal pressure and temperature of the contained oxygen or air to decomposition of the substance and the oxidation of the de- balance room conditions. Table I shows the decrease in composition products using the catalyst only for the last, but weight of the absorption tubes on standing, due to the reit seems that combustion would be difficult for substances placement of oxygen by air, comparing also the increase in
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weight when filled with air due to the absorption of moisture and carbon dioxide, with and without wires in the capillaries.
Vol. 6 , No. 4
(14) Friedrich, A., “Die Praxis der quantitativen organischen Mi(15) Friedrich, kroanalyse,” A.. Mikrochemie, p. 22, Franz Deuticke, 338 (1931,. Leipzig und Wien, 1933.
Friedrich, A., 2. angew. Chem., 36, 481 (1923). Haas, P., and Rappaport, E., Mikrochemie, 7, 327 (1929). Hernler, F., Zbid., Pregl Festschrift, 1929, p. 154. A~CARIT~P Kemmerer. G., and Hallett, F., IND. ENG.CHEM.,19, 173 (1927). Minutes Kirk, P., and McCalla, A., Mikrochemie, 12, 88 (1932). 15 45 90 15 46 90 Kirner, W. R., IND. ENO.CHEM., Anal. Ed., 5, 363 (1933). Filled with oxygen Lindncr, J., Ber., 60, 124 (1927); Ibid., 65, 1697 (1932). -76 -126 Without wires -47 -104 -168 -23 With wires -9 -41 -88 -13 -37 82 Meixner. A.. and Krocker. F.. Mikrochemie. 5. 121 (1927). Filled with air Miiller, E.,i n d Willenberg, H:, J . prakt. Chem.; 99, 34 (1919). Without wires 3 11 I9 $ 3 $ 6 $13 Niederl, J. B., 2. anal. Chem., 89, 62 (1932). With wires + 4 $ 2 $ 1 $ 4 8 $ 9 Niederl, J. B., and Moadow, J. R., Mikrochemie, 9, 350 (1931). Niederl, J. E., and Whitman, E., Zbid., 11, 287 (1932). LITERATURE CITED Pregl, F., and Fyleman, E., “Quantitative Organic Microanaly(1) Anonymous, Mikrochemie, 11, 483-7 (1932). sis,” 2nd ed., pp. 22, 40, 43, 56, Blakiston’s, Philadelphia, (2) Avery, S., Brackenbury, J., and Maclay, W., IND.ENG.C H ~ M . , 1930. Anal. Ed., 4, 23s (1932). (29) Zbid.,p. 25. (3) Baxter, G., and Starkweather, H., J . Am. Chem. Soc., 38, 2036 (30) Ihid., p. 30. (1916). (31) Ibid., p. 50. (4) Blumer, F., Rer., 50, 1710 (1917). (32) Schoorl, H., Chrm. WeekbZad, 16 (1919). (5) Bock, F., and Reaucourt, K . , Mikrochemie, 6, 133 (1918). (33) Spoerri, P.E . , J . Chem. Education, 10, 491 (1933). (6) Boetius, M., “’tjher die Fehlerquellen bei der mikro-analytischen (34) Verdino, A., Mikrochemie, 9, 123 (1931). Bestimmung des Kohlen- und Wasseratoffes nach der Methode (35) Weygand, C., “Quantitative analytische Mikromethoden der von Fritz Pregl,” p. 27, Verlag Chcmie, Berlin, 1931. organischen Chemie in vergleichender Darstellung,” p. 81, (7) Zbid., p. 59. Akademische Verlagegesellschaft. Leipzig, 1931. ( 8 ) Zbid., p. 100. (36) Whitman, B., Research Report, New York Univ., 1933. (9) Zbid., p. 82. (37) Willard, H., and Smith, J . A m . Chem. SOC.,44, 2038 (1916). (10) Brunner, K., see Pregl, F.. and Fyleman, E.,loo. cit., p. 46. (11) Cornwall, R. T. K., IND.ENQ.CHEW,Anal. Ed., 3, 4 (1931). Rncmrvin October 14, 1933. Part of a thesis presented by Roslyn T. Roth (12) FlaschentrRger, B., J . prukl. Chern., (2) 99, 34 (1919). t o the Faculty of the Qrsduate School of New York University in candidacy (13) Flaschentriiger, Mikrochemie, 9, 15 (1931). for the degree of master of science.
TABLE I. CHANGEIN WEIGHTOF ABSORPTION TUBES (Measured in 0.001 mg.) ANHYDRONl Minutes
-
+
+
+
+
(16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28)
Determination of Selenium and Arsenic by Distillation In Pyrites, Shales, Soils, and Agricultural Products W. 0. ROBINSON, H. C. DUDLEY, K. T. WILLIAMS,AND HORACEG. BYERS Bureau of Chemistry and Soils, Washington, D. C.
I
NVESTIGATION of an animal disturbance (known locally as alkali disease), which was traced to vegetation grown in certain soil areas, rendered urgent the development of a rapid and accurate method for the detection and estimation of selenium in both organic and inorganic materials. The methods outlined below are an extension and improvement of a distillation method described by Robinson (7) during the progress of the work. The principles of the distillation method are outlined by Noyes and Bray (6). Selenium can be separated from all the other elements except arsenic,and germanium by distillation with concentrated hydrobromic acid. The selenium must be in, or be converted into, the hexavalent condition before distillation in order to insure its distillation with the acid. I n most cases this conversion may be accomplished by the use of bromine. The excess of bromine distills a t a low temperature and the hydrobromic acid then reduces the selenium to the quadrivalent condition. In this form it readily distills along with hydrobromic acid. When a distillation method is applied to soils and other insoluble materials difficulties due to bumping and frothing may be encountered. Bumping may be greatly minimized by the introduction of short pieces of capillary tubing, sealed at one end. In the case of soils, at least, frothing is diminished or wholly prevented by the use of a sufficientexcess of bromine. In the distillate, selenium may be precipitated quantitatively by reduction by sulfur dioxide and hydroxylamine
hydrochloride. The selenium may be estimated either gravimetrically or by the colorimetric procedure of Cousen (2). In either case reprecipitation is essential to free the precipitate from sensible quantities of impurities. Arsenic is quantitatively distilled along with the selenium and may be determined in the fdtrate from the first selenium precipitation. If present in but small quantities it is best determined by one of the modifications (3, 9) of the cerulean blue molybdate method of Denigbs (4). In general, the procedures described below are very sensitive and may be used for any material with such modifications as may be necessary. The method as developed for soils is perhaps the most sensitive used in soil analysis. One part of selenium in ten million parts of soil may be easily detected and by use of the integration procedure described below, quantities as small as one part in a billion may be isolated. APPARATUS distilling apparatus is graphically described in Figure 1. The still is conveniently made of Pyrex glass and rubber connections must be avoided. Measuring flasks and Nessler jars of 25 cc. capacity are also required. REAGENTS All reagents should be free from selenium. Blank determinations should be made on all reagents.
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