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it has the decided advantage of introducing the least amount
LITERATURE CITED
of alkaline earth into the solution. The oil lye method has the advantage of requiring no precipitant. In a number of normal solutions prepared, 0.09 to 0.18 per cent of the total alkali was found to be present in the carbonate form, corresponding to 0.0048 to 0.0095 gram of actual sodium carbonate per 100 cc. Coles (2) obtained a 0.1 N solution of sodium hydroxide which gave no precipitate with barium hydroxide, by settling oil lye overnight and diluting a portion with freshly boiled water. Rising (18) prepared a similar 0.1 N solution by filtering oil lye and diluting with water which had been re-distilled over barium hydroxide, and found that the sodium carbonate content was about 0.0005 per cent.
(1) Clark, “The Determination of Hydrogen Ions,” p. 197, Wil-
ACKNOWLEDGMENT The authors wish to acknowledge the valuable help received from I. M. Kolthoff and C. L. Shao in the preparation of the manuscript.
(2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)
liams and Wilkins, 1928. Coles, J . Am. Chem. Soc., 30, 1192 (1908). Cornog, Ibid., 43, 2573-4 (1921). Han and Chu, IND.EN*. CHEM.,Anal. Ed., 3, 379 (1931). Jorissen and Filippo, 2. angew. Chem., 23, 726-7 (1910); Chem. Weekblad, 6, 145-9 (1909). Kolthoff, Pharm. Weekblad, 58, 1413-17 (1921); 2. anal. Chem., 61, 48-51 (1922). Kolthoff-Furman, “Volumetric Analysis,” Vol. 11, p. 77, Wiley, 1929. Lunge, 2. angew. Chem., 11, 169-71 (1897). McCoy and Smith, J . A m . Chem. Soc., 33, 468-73 (1911). Pregl, 2. anal. Chem., 67, 23-7 (1925). Rather, J . Am. Oflcial Agr. Chem., 1, 317-29 (1915). Rising, Svensk Farm. Tid.,16, 549-51; 566-8 (1913). Solvay Process Co., “Solvay Bulletin” No. A, sheet 8, 1925. Sorensen, Biochem. Z., 21, 186 (1909). Warder, J . Am. Chem. SOC.,3, 55 (1881). Wolf and Krause, Arch. Warmewirt., 10, 19-21 (1929).
RECEIVBD September 25, 1931. Presented before the annual convention of the Chinese Society of Science and Arts, Nanking, December 5 , 1930.
Composition of Vapors from Boiling Binary Solutions D. F. OTHMER,302 Seneca Parkway, Rochester, N. Y.
A
Vapor-composition curves, elevation of boiling The heating unit is formed by P R E V I O U S article (6) points of solutions, and related data on liquiditself before attachment to the described a m e t h o d and apparatus h a v i n g rest of the unit. It should be devapor systems necessary-for the design of engisigned to draw between and several advantages for the deneering equipment may be obtained conveniently 200 watts of power, Platinum termination of the composition of vapors arising from boiling and accurately with the apparatus and method and n i c h r o m e coils have been solutions of two volatile liquids. described. This work is a n imDrovement over used, and tungsten2would beuseSince this work was published, ful because of its low coefficient that previously published which lhas been used of thermal expansion which apthis system has been used by by several others also, in obtaining various data. proximatesthat of Pyrex,inmakthe writer and others in obt a i n i n g d a t a necessary for Several representative vapor-composition curves ing seals. Because of the high resistance of nichrome, a heater are given. severaltypes of engineering of this metal may be designed to problems, and various improvements have been made in the design of the glass apparatus. operate across an ordinary 110-volt circuit, but a platinumcoil unit should be designed to operate at a reduced voltage, APPARATUS USED The calculated length of wire is wound on a tube of Pyrex Figures 1 and 2 illustrate the apparatus’ used more recently previously pierced with two very small holes a t each end in studies of this nature. It is constructed of Pyrex glass, and of the length reserved for the coil. The ends of the wire it will be seen that, although several changes have been made, terminate in mercury wells attached to the sides for conthe same principles which governed the design previously used nection to the power supply. The lower end of the tube have been followed. An internal electric heater, incorporated carrying the heating coil is pierced with four holes about in the Kjeldahl flask which serves as the boiling pot, is the 5 mm. in diameter as close as possible to the inseal, so that largest single change, although the improved unit without no pocket is formed for liquid to remain undisturbed during the electric heater has been used as before, giving excellent the operation. OPERATION. When the flask is charged and current supresults with an external electric heater or a Bunsen flame. The unit is fabricated in one piece, being built around a plied, the bare wires lose their heat very readily to the surstandard Kjeldahl flask. This design is much simpler in rounding liquid. The vapor bubbles cause the boiling liquid construction, and offers several other advantages over the to rise around the coil, drawing fresh liquid down through the previous one which used a length of large-diameter glass tube, and through the holes a t the bottom. A cycle is made tubing. The methods and details of construction are ap: which ensures complete mixing throughout the liquid phase. parent by reference to the figures, and the changes from the Because of the very small bubbles formed in contact with the earlier model may be noted by comparison with the figure in fine wire, which is a t a temperature only slightly above the the previous article. If an external heat source is to be used boiling point of the solution, and the homogeneity of this rather than the internal one shown, the drain tube for sam- solution, this boiling is probably very nearly an “equilibrium ’ pling the boiling liquid is attached to the bottom of the flask at vaporization.” Vapor compositions have been determined from pressures a point opposite the inlet from the condensate reservoir, and supplied with a cock as before. 2 Tungsten wire may now be obtained from the Fansteel Co , Chicago, 1
The writer is prepared to supply directly orders for this apparatus.
111.
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April 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
a few centimeters of m e r c u r y above atmospheric down to low pressures comp a r a b l e to those employed industrially for vacuum d i s t i l l a t i o n . For pressures above the barometer, the vent is connected to the manometer of the constant-pressure c o n t r o 11e r previously described (4) and the operation is followed the same as at atmospheric pressure. For vacuum runs, the vent from the vapor jacket and the vent from the condensate reservoir are connected to a 12-liter P y r e x glass flask for a capacity effect, a vacuum pump, a n d a manometer. The vacuum connection to the vapor j a c k e t has a cock which i s c l o s e d when the system is purged of air. The manometer has an e l e c t r i c a l contact which breaks when the vacuum exceeds t h e s e t point and releases a solenoid operating a vacuum leak. As m e n t i o n e d FIGURE 1. APPARATUS FOR DETERa b o v e , t h e appaMINING VAPORCOMPOSITION ratus shown in Figure 1,but without the electrical heating unit sealed to the bottom of the flask, has been used with an external source of heat. This type of unit is simpler in construction and has all of the advantages of the other, except those due to the peculiar type of boiling which the internal electrical heater causes. The method of operation for determining 2,y curves is exactly the same as previously described, and the same advantages which were previously noted may be expected to an accentuated degree of the modified apparatus. TABLEI. RESULTSWITH APPARATUSOF USUALTYPESOF BINARYVAPORCOMPOSITION CURVES BENZENE-ACETICACID WATER-FORMIC ACID (%. BENZENE) (% WATER) Liquid Vapor Liquid Vapor Wt. % Wt. % Wt. % Wt. % 10 6.0 18.2 20 23.6 23.5 30 34.8 50.2 40 64.4 50 75.8 60 83.6 70 90.2 80 90 95.8
ACETICACID-ACETIC ANHYDRIDE (9' ACETICACID) Lfquid Vapor Wt. % Wt. % 10 23.2 42.3 20 30 66.5 40 65.2 72.4 50 60 78.6 70 84.1 80 89.7 90 95.0
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ADVANTAGES.The new apparatus has the following differences: 1. Sim ler in design and construction, a standard size flask substitute! for the large glass tubing. Smaller, more compact, less fragile. 2. Greater ease of insulating vapor jacket if desirable (2). 3. Free end on vapor tube leaving flask ground to wedge sha e. This allows insertion of the thermometer bulb directly in %e liquid if desired. The tip previously used is excellent for Dreventine miming where a countercurrent of liquid passes against a ?king va&r stream, but is not neceseary here. 4. Less vapor friction through condenser, important when low vacuum is used. 5. Deeper trap for condensate return, eliminating danger of boiling back.
There are these add i t ion a1 advantages if the electric internal heater is used: 1. More uniform boiling with extremely small vapor bubbles. 2. C o n s t a n t and thorough agitation of liquid. 3. Impossibility of s t a g n a n t liquid collecting near sample cock of flask. 4. Better control ensuring uniform rate of distillation. Constant-pressure control readily applied. 5. Smooth vacuum funs without bumping.
RESULTS Figures 3 to 5 show the r e s u l t s of three of the many curves plotted with this apparatus. They are all near normal a t m o s p h e r i c press u r e , 750 mm. and the results given in Table I are taken a t even liquid composition from curves drawn with a large n u m b e r of experimental points. The results are in weight p e r c e n t s of t h e more volatile liquid rather than the mole per cents more often FIGURE 2. DIAGRAM OF APPARATUS used in engineering calculations. All of the materials used in obtaining these data, including the formic acid, were purified from good original sources to a high degree by distillation methods in apparatus previously described (3). Very close boiling cuts were obtained for the experimental work. The three curves in Figures 3 to 5 illustrate the three usual types of binary vapor composition curves: the benzene-acetic acid mixture having a minimum constant-boiling mixture, the formic acid-water mixture having a maximum constant-boiling mixture, and the acetic acid-acetic anhydride mixture being normal in that it has no constant-boiling mixture.
T"
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ANALYTICAL EDITION
FIGURE3. BENZENEAND ACETICACID
FIGURE4. WATERAND FORMIC ACID
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% WATER IN LIQUID
I n the previous paper (2) the constant-boiling mixture of benzene and acetic acid was not noted, since i t is higher in benzene than any of the points plotted. The portion of the curve near the azeotropic point, which is a t 98.5 per cent benzene, has been carefully plotted on an enlarged scale. Formic acid forms with water one of the comparatively few binary mixtures having a constant-boiling or azeotropic mixture of maximum boiling point. Bergstrom ( I ) has plotted the vapor composition curve for mixtures of the liquid higher in water content than the azeotropic mixture, and his curve falls just below that drawn in the upper loop,
FIGURE5. ACETICACIDAND ACETIC ANHYDRIDE
The acetic acid-acetic anhydride curve is typical of a normal binary mixture having no constant-boiling or azeotropic mixtures. LITERATURE CITED (1) Hausbrand, “Principles and Practice of Industrial Distillation,” Wiley, 1928. (2) Othmer, IND.ENQ.CHEM.,20, 743 (1928). (3) Othmer, Ibid., 22, 322 (1930). (4)Othmer, Ihid.,Anal. Ed., 1,97 (1929). RECEIVED September.8, 1931.
Potash Analyses Study of Methods for Eliminating Errors in Determination of Potash in Fertilizer Mixtures High in Phosphoric Acid C. M. BIBLE,Mellon Institute of Industrial Research, University of Pittsburgh, Pittsburgh, Pa.
I
N RECENT years it has been recognized by many
analysts that fertilizer mixtures high in phosphoric acid present difficulties in the determination of the potash content. Since 1925 reports have been published by Kerr (6),Bible ( I ) , Fraps (S), Haigh (4), and Lockhart (6). Workers on the problem attribute potash losses to the formation and attack of metaphosphates on silica, either the silica dishes used during evaporation and ignition, or soluble silica that may sometimes be present in amounts sufficient to cause trouble, even though evaporation and ignition may be carried out in platinum. The first four chemists mentioned have tried to solve the trouble by some method of removing the phosphoric acid before the ignition step, whereas Lockhart minimizes the metaphosphate attack by carefully controlling the ignition temperature. Removal of the phosphoric acid by any of the suggested methods prevents most of the attack on the silica dishes. I n 1926 the writer determined quantitatively the losses in the weight of silica dishes resulting by use of the official LindoGladding method and a modified method ( I ) in which the phosphoric acid was removed with magnesium oxide. Six new dishes were obtained for the tests from a leading manufacturer of silica ware. Three dishes were used by the official Lindo-Gladding method and three by the modified method on regular factory mixtures until each dish had been used seven times. The three dishes used in the official method lost in
weight 0.0339, 0.0427, and 0.0444 gram. The three used in the modified method lost in weight only 2.7 per cent as much. Much of the silica dissolved or loosened from the silica dish appears as an impurity in the potassium chloroplatinate, even if the dissolved residue is filtered prior to the addition of chloroplatinic acid. By dissolving the potassium chloroplatinate from the crucible with hot water, one can frequently find much insoluble impurity. I n some cases the silica is sufficient to make filtration very difficult. The modified methods providing for removal of the phosphoric acid, on the other hand, give precipitates of potassium chloroplatinate completely soluble in water. The ignited residue likewise dissolves in water much more readily. Removal of the phosphoric acid prior to ignition prevents losses of potash due to formation of insoluble potassium phosphosilicates or of potassium metaphosphate, which is soluble with difficulty. Results obtained by the modified methods usually do not fall far short of the theoretical potash content. The only objection to the use of any of the methods providing for the removal of the phosphate is that there appears to be a greater loss of potash due to occlusion, because of the additional precipitate that results, and there appears to be no practical way of recovering the occluded potash. Although the modifications contribute to refinement of the method, still the full potash values cannot be obtained.
