A Study of Bunsen's Method A New Apparatus K. BRADDOCK-ROGERS AND K. A. KRIEGER The John Harrison Laboratory of Chemistry, University of Pennsylvania, Philadelphia, Pa.
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HE evolution method of Bunsen (3) has been the subject of numerous investigations for many years. These investigations have led to a better understanding of the mechanism of the method and a steady improvement of the apparatus. Sherer and Rumpf (17) in their analyses of the oxides of manganese asserted the dependability of Bunsen's method. Fleck (8) applied this method to the analysis of lead dioxide with the apparatus which is described by Fresenius (9). Four years later Ebell (5) reported that excess concentrated hydrochloric acid and lead dioxide produced some chlorine, E
IMPROVED BUNSENAPPARATUS but chiefly lead tetrachloride. His procedure was impractical. Topf (18) in his iodometric studies used the Bunsen apparatus so modified that carbon dioxide could be used to flush the system and prevent a suckback. His absorbers were Peligot tubes connected by rubber stoppers. UIIman (90) changed the apparatus so that the potassium iodide-iodine solution need not be transferred for titration. Marc (14) followed these experiments with an impractical apparatus. Finkener (7) was one of the first to cast doubt on the efficiency of this evolution method. He stated that too little oxygen was obtained in the analysis of the higher oxides when hydrochloric acid was used to decompose the sample, but that good results were obtained when the sample was decomposed by dilute sulfuric acid and potassium iodide
and by potassium bromide and hydrochloric acid. Farsoe (6) makes two departures in his experiments. First, he decomposed several oxidizing agents with 1 to 2 grams of potassiiim bromide, 20 cc. of concentrated sulfuric acid, and 80 cc, of water; second, he used an all-glass apparatus whose receiver had an inclined 10-bulb side arm as a trap. He claimed no reduction of the sulfuric acid, used carbon dioxide to ffush the system, but did not state whether the titration was made in the receiver. Beck (1) in his experiments on red lead titrated the liberated iodine with standard arsenite solution in the presence of sodium bicarbonate. Rupp ( I @ , in general agreement with Finkener, stated that the chlorine which passed over during the distillation was reduced to a slight extent to hydrogen chloride and that the use of hydrochloric acid was worse than hydrobromic acid, He used the apparatus of Jannasch (11). Jander and Beste (10) supported Rupp's views and stated that the interaction of steam and chlorine can be overcome by using a delivery tube less than 40 cm. long and a decomposition flask of 50 cc. capacity. Wagner (21) used an apparatus somewhat similar to that described in this paper in his investigation of potassium chlorate and found no evidence to support Rupp's views with either hydrochloric acid or hydrobromic acid. The apparatus described here was devised and used by BuckWalter and Wagner ($) in certain bromination experiments. It was a t the suggestion of Wagner that the authors applied this apparatus to Bunsen's method in the examination of the compounds which are reported. Le Blanc and Ebsrius ( l a ) , with an apparatus very similar to that of Farsoe (Zoc. cit.), report results on the oxides of lead in terms of oxygen. All the chemicals which were used in these experiments were Baker's c. P. Analyzed. POTASSIUM IODATE^ was dried at 105" C. and the amount required for a 0.1 N solution was weighed and dissolved with gentle shaking in cold water. The solution was made up to volume. POTASSIUM IODIDE, special crystals, iodate free, were dissolved in well-boiled water. The solution was prepared in small stock quantities and kept in the dark. SODIUM OXALATE was dried at 105" C. A stock solution was not used. HYDROBROMIC ACIDwas allowed to stand over red phos horus for 24 hours. It was filtered through asbestos into the Ask of an all-glass still and distilled. The constant boiling fraction was collected in dark glass bottles and stored in the dark. ARSENIC TRIOXIDE.The resublimed material was dried at 105" C. and the amount required weighed for a 0.1 N solution. It was dissolved in dilute sulfuric acid according to the method of Roark and McDonnell (16) and of Chapin (4). SODIUM THIOSULFATE SOLUTION was prepared by dissolving the salt in well-boiled water. The solution, approximately 0.095 N , was protected from light and carbon dioxide and frequently standardized. IODINE was sublimed from potassium iodide and resublimed. POTASSIUM PERMANQANATE~. The pure crystals were dissolved in well-boiled water. The solution was allowed to stand, filtered through asbestos, and preserved in the dark in dark bottIes. CARBON DIOXIDEwas generated from hydrochloric acid and pure calcite which had been placed in boiling water. STARCH.An 0.5 per cent solution of soluble starch was used. The solution was freshly made every few days. Blanks were continually run on the chemicals and the apparatus and in all cases they were found to be zero. The solid samples were weighed in one-gram weighing tubes.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
By placing the tube well on the inside of the neck of flask A (cf. sketch) in a horizontal position and slowly tilting it to the vertical position, the greater part of the sample dropped from the tube. The tube was then drop ed into flask A . Such a procedure prevented loss in transfer ofthe sample.
The apparatus was all glass with well-ground joints on which no lubricant was used. By moistening the joint with water and giving it a slight twist a perfect seal can be made. The volume of the decomposition flask, A , was 65 to 75 ml.; the receiver, B, 500 ml.; the trap, T , 25 ml. The tube, C, extended to within 2 mm. of the bottom of A , and tube K , to within 3 mm. of the bottom of B. It is advisable to place the receiver, B, in a beaker partly filled with cold water and to place a piece of asbestos between the beaker and the burner which is under A , In the potassium iodide-sodium thiosulfate experiments the receiver contained 4.0 grams of potassium iodide in 160 ml. of water; the trap, 1.0 gram of potassium iodide in 20 ml. of water. I n the arsenite-iodine experiments 35 to 40 ml. of standard arsenite solution were run into the receiver and diluted to 160 ml., and 5 to 6 ml. of the same solution, diluted to 20 ml., were run into the trap. The total volume of the arsenite solution was very carefully noted. Since the arsenite solution was acid, an excess of sodium bicarbonate was added just before the analysis was started. The use of arsenious acid and iodine in Bunsen’s method was used by Treadwell and Christie (19) and later recommended by Lunge (IS)on the grounds of expense. When the proper solutions had been placed in flasks B and T , and the sample had been introduced in A , the delivery tube of a carbon dioxide generator was attached to the funnel, C, and the apparatus was flushed with the gas. (This first flushing was optional.) The proper acid was added through C, and a slow steady stream of carbon dioxide was led through the system. The contents of A were gently boiled until one-third to one-half its volume had distilled over. The flame was removed and the apparatus allowed to cool somewhat and then disconnected a t D. Repeated tests at the exit of the trap for escaping halogen were always negative, The inlet tube and the trap are in one piece and fit into the receiver a t the ground joint, E. The joint is just opened and the carbon dioxide delivery tube is attached at F and the contents of the trap are washed into the receiver with neither loss nor contact with air. The flushing of the trap with distilled water is accomplished in the same way. The solution in the receiver is ready to titrate in an atmosphere of carbon dioxide.
EXPERIMENT 1 The efficiency of the apparatus and the general procedure are shown against two sets of standard solutions-potassium iodate and potassium permanganate, and arsenious acid and potassium permanganate. The potassium permanganate was standardized against sodium oxalate according to the familiar method of McBride. The sodium thiosulfate was standardized against potassium iodate. Into the decomposition flask was run from a carefully calibrated pipet (25 ml. capacity) the potassium permanganate, which was decomposed with 8 to 10 ml. of concentrated hydrochloric acid. The liberated iodine was titrated with the standard sodium thiosulfate and from these titrations the normality of the permanganate was calculated. This result agreed with the sodium oxalate standardization. A similar experiment was conducted with standard arsenious acid and potassium permanganate. Both hydrochloric acid and hydrobromic acid were used and the excess arsenite solution was titrated with standard iodine solution. These results agreed with the sodium oxalate standardization.
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NORMALITY OF POTASSIUM PERMANGANATE AsaOrIz 5 ml. HBr 15 ml. HPO 0.09366 0.09366 0.09362 0.09362 0.09364
SODIUY OXALATE KI-NanSzOa SODIUM OXALATE10 ml. HC1 0.09378 0.09380 0.09370 0.09370 0.09380 0.09373 0.09370 0.09365 0.09376 0.09381 0.09370 0.09362 0.09384 ..... Av. 0.09378 0.09379 0.09370 0.09366
.....
... .
EXPERIMENT 2 In the decomposition of the oxides of lead, concentrated hydrochloric acid must be avoided. Lead tetrachloride (PbCL) is readily formed from chlorine and lead chloride (PbC12) in the presence of concentrated hydrochloric acid and this compound is hard to break up under the conditions of this experiment. Therefore the concentration of the acid must not be too high. Any strength acid under 7.5 N was perfectly safe. KI-NapSzOaa
AszOs-1~~ KI-NnaSzOab (expressed as per cent PbOa) 34.12 34.15 34.21 34.26 34.12 34.15 34.12 34.16 34.13 34.15 34.12 34.25 34.13 34.23 34.19 34.13
RED LEAD
Av.
34.21 34.18 34.15 34.29 34.29 34.25 34.23 34.23
LEWD DIOXIDE
(expressed as per cent PbOn)
88.90 88.84 88.84 88.92 88.88 88.84
...
b
Av. 88.87 88.83 88.96 Decomposed by 20 to 25 ml. 6 N HC1. Decomposed by 5 ml. HBr (sp. gr. 148) 4-16 ml. HzO.
EXPERIMENT 3 The analysis of the mineral pyrolusite presented nothing unusual. The sample which was taken for analysis was brought to constant weight by drying the sample in the weighing tubes a t 105’ C. KI-NskhOaa PYROLUSITE
86.69 86.50 86.65 86.74 86.74 86.70
...
(expressed
a8
KI-NasSzOd per cent MnOn) 88.57 86.61 86.64 86.60 86.66 86.74 86.78
Av. 86.67 86.62 a Decomposed by 15 ml. 6 N HCl. b Decomposed by 5 ml. HBr (sp. gr. 1.48) 15 ml. HnO.
CONCLUSIONS The Bunsen method applied to the decomposition and analysis of potassium permanganate, red lead, lead dioxide, and pyrolusite, is dependable and accurate. Hydrobromic acid and hydrochloric acid are of equal value for the decomposition of the substances reported. The arsenious acid and the sodium thiosulfate methods of estimation are both dependable, but the latter is to be preferred because only one standard solution is required, as against two in the former. The apparatus which is described is easy to handle, requires a minimum of the operator’s t h e , and can be adapted to numerous evolution methods. It is also excellent in students’ hands.
ACKNOWLEDGMENT The authors wish to express to E. C. Wagner of this laboratory their sincere thanks and appreciation for his numer-
ANALYTICAL EDITION
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the course of this investigation on the apparatus which he designed.
OUR suggestions during
Vol. 5, No. 5
(10) Jander and Beste, 2.anorg. allgem. Chem., 133,46 (1924).
(11) Jannasch, “Praktischei Leitsaden ber Gewichtsanalyse,” 1897, n. 2x3 F
LITERATURE CITED Beck, Z. anal. Chem., 47, 465 (1908). Buokwalter and Wagner, E. C., J . Am. Chem. Soc., 52, 5241 (1930). Bunsen, Ann., 86, 265 (1853). Chapin, J . Am. Chem. Soc., 41,351 (1919). Ebell, Rep. anal. Chem., 141 (1886). Farsoe, 2.anal. Chem., 46,308 (1907). Finkener, Zbid., 43,656 (1904). Fleck, Pha~m.Zentralhalle, 22, 152 (abstr. Z . anal. Chem., 21, 444 (1882). Fresenius. “Quantitative Analysis,” 6th ed., Vol. 1, p. 476.
(12) Le Blanc and Ebsrius, Z . anal. Chem., 89, 81 (1932). (13) Lunge, G., and Berl, E., “Chemeurisch-technische Untersuchungs methoden,” 7th ed., Vol. 1, p. 972. (14) Marc, Chem.-Ztg., 26,556 (1902). (15) Roark and McDonnell, J. IND.ENQ.CHEM.,8,327 (1916). (16) Rupp, 2.anal. Chem., 57, 226 (1918). (17) Sherer and Rumpf, Chem. News, 20,302 (1869). (18) Topf, 2. anal. Chem., 26,295 (1887). (19) Treadwell and Christie, 2.angew. Chem., 18, 1930 (1905). (20) Ullman, Chem.-Ztg., 18, 487 (1884). (21) Wagner, E. C., IND.ENQ.CHEM.,16,616 (1924). R ~ C E I YMay ~ D 16, 1933.
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Automatic Pressure Regulators for vacuum Distillation 11. Sulfuric Acid as a Manostat Fluid E. B. HERSHBERG AND E. H. HUNTRESS Research Laboratory of Organic Chemistry, Massachusetts Institute of Technology, Cambridge, Mass.
I
N A PREVIOUS communication (2) a simple portable
apparatus was described for the automatic control of reduced pressure during the vacuum distillation of organic compounds. I n connection with further more exacting work, however, it was desired to increase the precision of regulation. In order to do this the authors have designed a second simple control (Figures 1 and 2) in which the final pressure adjustment is effected by means of a thermionically controlled flutter valve, and in which concentrated sulfuric acid is substituted for mercury as the manostat liquid. This combination is approximately ten times as sensitive as the previous unit and permits a regulation of *0.015 mm. mercury at any pressure up to atmospheric.
THETHERMIONIC RELAY The manostat contacts actuate the g r i d c i r c u i t of a 71-A t y p e vacuum tube, which controls the operation of a 2000-ohm magnetic relay. The circuit is similar to that described in the previous paper, but operates in the opposite sequencethat is, closing of the grid circuit causes the plate current to flow and this in turn closes the relay. The latter lifts a rubber pad from a capillary inlet allowing air to leak into the system and establish the correct pressure. Needle valves of the c o n v e n t i o n a l design (Hoke No. 304) are employed for rough adjustment of the air inlets, leaving the final flutter control to be effected by the relay system.
THE MANOSTAT
The manostat shown in Figures 1 and 4 combines several desirable features. It operates throughout the entire range of pressure, uses a minimum of fluid, and presents but litble frictional resistance. The bulbs B and C (Figure 4) provide for a sudden change of Dressure. The diameter of B is such that most of the motion is confined to the right-hand arm A and by tilting alone a range of *2.5 mm. m e r c u r y may be secured. The manostat is constructed of Pyrex c h e m i c a1-r e si s t a n t glass with sealed-in platinum contacts F and G. External connection is made through mercury pools H and the center e l e c t r o d e is joined to a standard taper ground-glass joint I to facilitate cleaning and filling the manostat. The stopcock J is l u b r i c a t e d with v a s e l i n e only, rubber lubricants being more or less attacked by the acid. The manostat is sealed into the ground-steel joint with Picein or de Khotinsky cement. Flexible rubber connections are avoided and manostat s e t t i n g is f a c i l i t a t e d by p i v o t i n g on the ground steel joint K , which serves as an axis for rotation. The joint is of s t a i n l e s s steel ( A l l e g h e n y metal) both parts being cut a t the same lathe setting with about a 14’ taper and lightly ground together with 600-mesh s i l i c o n c a r b i d e . V a s e l i n e is used as l u b r i c a n t and the pressure of the a t m o s p h e r e o r c h e c k n u t s suffices to VIEW OF MANOSTAT FIGURE 1. FRONT
