Calibration and Salt Error of the Antimony Electrode Its Application in Soil Reaction Measurements NORMAN J. KING Agricultural Laboratory, Department of Agriculture and Stock, Brisbane, Queensland, Australia
T
H E urgent necessity for solution of antimony trioxide The calibralion of the antimony' electrode has an electrode of more uniin h y d r o f l u o r i c acid. Some been investigated with many series of buffer soluversal application than workers added antimony trioxtions. The buffer solutions of Clark and Lubs, the hydrogen and quinhydrone ide t o the system under examiand McIlvane, and the citrate mixtures of Sorenelectrodes has resultedduring the nation, whereas others relied on sen have been found unsuitable for this calibralast d e c a d e in investigations the oxide present in the metal to w i t h electrodes of the metalgive the requisite conditions. tion. metal oxide type. The only one The author used rods about The change in slope of the antimony electrode of these which has met with any 4 mm. in d i a m e t e r cast from curve as found by m a n y workers is explained, and success is the antimonious oxide the purest antimony obtainable, a new curve constructed in which the e. m. f. of electrode, which conforms more and Merck's G. R. a n t i m o n y the antimony electrode is a linear function of the or less with the theory as distrioxide. I n a g r e e m e n t with cussed by Kolthoff and Hartong. other workers it is found that p H f r o m p H 3.0 to 12.0. Among the earliest workers in more reproducible and a c c p t e The antimony electrode was applied to a wide this field were Uhl and Kestranek r e a d i n g s are obtained with a range of soils and the results were compared (2O), Kolthoff and Hartong (11), t a r n i s h e d electrode. After a and Rolthoff and Furman (IO), critically with the hydrogen-electrode figures. long p er i o d of work in buffer The salt error of the antimony electrode is defined all of whom utilized its propersolutions, however, the coating t i e s in acid-base t i t r a t i o n s . of a n t i m o n y trioxide becomes and a new curve constructed with buffer solutions More recently R o b e r t s and so heavy as to render the elecwhich are normal with respect to potassium F e n w i c k (16), S h u k o v and trode sluggish. It is then neceschloride. The same range of soils was measured A w s e j e w i t c h (lr), F r a n k e sary to clean and r e p o l i s h it with the antimony electrode in normal potassium and Willaman (4,Lava and with emery powder. After this chloride suspension and the results compared H e m e d e s (I%'), Harrison and treatment the electrode should V r i d h a c h a l a m (6),Best ( I ) , remain s t a n d i n g in water for with the hydrogen-electrode measurements. Itano (7),and others have used about three d a y s to o x i d i z e it in h v d r o a e n - i o n exDonent slightly; otherwise erratic podeterm&tio& in many forms and with varying technic. tentials will be obtained. The technic adopted was that In all cases a series of buffer solutions has been measured employed by Best (1). Measurements were made on a Camwith the hydrogen electrode and the resulting pH plotted bridge Instrument Company slide wire potentiometer against against the e. m. f. of an antimony oxide electrode when in a Veibel (2.2) half-cell. Quinhydrone for the standard was conjunction with a standard cell. The relation between the prepared according to the method of Valeur (21). A mirrorpotential of the antimony oxide electrode and the pH value type moving-coil galvanometer was used and all readings was found by most of the recent workers to be a straight line made in conjunction with a standard Weston cell with an from pH 1 to pH 12, but others [notably Best ( I ) , Oosting N. P. L. certificate. Hydrogen for the hydrogen electrode (14), and some of the earlier workers] have shown that a was generated from electrolytic zinc and Merck's G. R. sulfuric change of slope occurs a t varying acidities depending on the acid, and was purified according to Clark (5). The bubbling investigator. type of hydrogen electrode was used for the pH determinaOne of the purposes of the investigation in this laboratory tions. was to endeavor to elucidate the reason for the change in The various buffer solutions used were as follows: slope experienced in the use of this electrode, and also why the Clark and Lubs, H 3.0 to pH 10.0 same behavior of the electrode was not observed by all workSorensen's phospfate mixtures, pH 5.3 to pH 8.0 ers. The first step was to discover if possible from the literaMcIlvane's standards, pH 2.2 to pH 8.0 Kolthoff's buffers, pH 3.0 to pH 9.2 ture the type of buffer solutions used by each worker. Many Ringer's mixtures, pH 10.9 to pH 12.0 of the published articles stated the type used and from others Palitzsch's mixtures, pH 6.8 to pH 9.2 certain conclusions may be drawn. Clark and Lubs buffers Universal buffer solution, pH 3.0 to pH 11.0 were used by Best (I), Oosting (14), and also by Roberts and Fenwick (16). Lava and Hemedes (1.2) used potassium diAs mentioned previously, those investigators who have hydrogen phosphate-sodium hydroxide mixtures. Franke used stick antimony electrodes in Clark and Lubs buffers and Willaman (4) do not state the type used, but as their have obtained curves which change in slope a t some specific range is from pH 1 to 12 they obviously could not have been pH figure. The author constructed curves a t 16", 20", Clark and Lubs. Harrison and Vridhachalam (6) calibrated and 26" C., all hydrogen-electrode measurements being cartheir electrodes with Universal buffer solution. The majority ried out in duplicate and antimony electrode measurements of these investigators used rods of metallic antimony as elec- in triplicate. The curves obtained are of the same type as trodes, though Roberts and Fenwick (16) used crystals of those published by Best a t 14", Z O O , and 27" C. It is noticeantimony electrodeposited a t high current density from a able that in each case the relation between pH and e. m. f. 323
ANALYTICAL EDITION
324
420
353
650
BOO
E.M.L -Antimony Oxfde Electrode.
Vol. 5, No. 5
950
FIGURE1
FIGURE 2
is a straight line from p H 4.0 to about pH 7.0. A change in direction takes place between the latter figure and pH 8.0, from which point it is again a straight line to pH 10.0, though of different slope from the first part of the curve. Eleven points were determined between pH 6.8 and pH 8.5 and the change is found to begin a t the point where the boric acidpotassium chloride-sodium hydroxide buffers begin to operate. It had previously been pointed out, and was the experience of the author, that potassium chloride introduced a large salt error into antimony electrode determinations. It was decided as a matter of interest to eliminate potassium chloride from the series of buffers from pH 7.8 to 10.0 and to construct curves with the new solutions. Although the buffer value of the mixture would naturally be altered by this change, boric acid-sodium hydroxide mixtures are good buffers without the potassium chloride. The new determinations gave a line following on exactly from pH 7 6 where the potassium dihydrogen phosphate-sodium hydroxide buffers had left off. The cause of the change in slope was therefore shown (at least with the Clark and Lubs buffers) to be due to the potassium chloride in the final series of solutions. It has been known for some time that potassium chloride introduces a serious salt error, when pH determinations on soils are being made, though Uhl and Kestranek (90) stated that chlorides do not interfere in potentiometric titrations with the antimony electrode. It is therefore logical to assume that the calibration of an electrode for use in systems where appreciable concentrations of chlorides do not usually exist (e. g., soils) should be carried out in the absence of potassium chloride. The Clark and Lubs buffer solutions were then made up as before, except that all the solutions were made normal with respect to potassium chloride. A new curve was constructed a t 26” C. and was found to be a straight line from pH 4.0 to 10.0 and parallel to the line from which potassium chloride had been eliminated. The difference between the two curves was approximately 0.4 pH unit. This figure was then assumed to be the salt error of the antimony electrode with Clark and Lubs buffers. It remained to be proved whether a curve of similar slope was obtained with the other buffer solutions, and also whether the salt error was of the same magnitude.
junction with Sorensen’s buffers Ringer’s mixtures of disodium phosphate and sodium hydroxide were used to extend the curve to the region of high pH value, The range pH 10.9 to 12 connected up accurately with the Sorensen’s eurve both in aqueous and normal potassium chloride solut#ion. Kolthoff’s (.9) buffer solutions made up from succinic acid, borax, and potassium dihydrogen phosphate gave a good range of standards from pH 3.0 to 9.2. These behaved similarly to the previous buffers, giving straight parallel lines about 0.4 pH apart for the aqueous and potassium chloride solutions respectively. McIlvane’s standards consisting of disodium phosphate and citric acid were found to give entirely erroneous and very erratic results with the antimony electrode, particularly in the acid range of the buffer solutions. I t is assumed for want of a better explanation that complex antimonyl citrate compounds are formed analogous with the com ounds formed between antimony oxide and tartaric acid. KoltKoff and Furman (10) state that
Sorensen’s mixtures of primary and secondary phosphates have only a small range from pH 5.3 to 8.0. I t is of sufficient extent, however, to cover the critical stage-viz., pH 7.5 to 8.0. Here again the antimony electrode potential was a linear function of the pH value, and the buffers normal with respect to potassium chloride also gave a parallel straight line removed by approximately 0.4 pH from those in salt-free solution. In con-
FIGURE 3 potentiometric titration of tartaric acid with the antimony electrode is inaccurate and results in measurable quantities of antimony being in solution at the end of the titration. Sorensen’s citrate-sodium hydroxide mixtures after Walbum also gave very erratic values. Palitzsch’s borax-boric acid mixtures with a range from pH 6.8 to 9.2 gave a straight line of similar slope to the preceding ones.
It was considered that, for the calibration of an electrode of this type, where salt errors are likely to occur as a result of the introduction of some specific ion, it would be better to adopt a buffer series which contained similar compounds throughout its entire range. Such a series is given by the
September15,1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
Universal buffer mixture of Prideaux and Ward (16) which, on gradual neutralization with sodium hydroxide, would subject the electrode to changes of hydrogen-ion concentration ranging from pH 3 to 12. A series of such buffers, standardized with the hydrogen electrode and measured with the antimony electrode, were found to give a straight-line graph of similar slope to that given by the previous buffer solutions. When made up normal with respect to potassium chloride, however, a curve was obtained which is illustrated in Figure 3. It was noted when standardizing the more acid solutions of this series on the hydrogen electrode that a perceptible and steady drift was occurring towards a lower potential, which seemed to imply chemical reaction in the system with consequent increase in hydrogen-ion concentration. Whatever the explanation of this phenomenon, it appears that the Universal buffer solution is unsuitable for use in normal potassium chloride. The more alkaline portion of the curve is a straight line and removed by about 0.4 pH from the normal curve. Figures 1 and 2 show the curves obtained with the buffer solutions of Sorensen, Ringer, Palitzsch, and Kolthoff both in aqueous and normal potassium chloride solution. Since the completion of this work there has come to hand the paper by Britton and Robinson (2) on the potentiometric titration of Prideaux and Ward's Universal buffer mixture with the antimony electrode, and the calibration of their electrodes with that solution. The relation obtained by them is for all practical purposes a straight line, the slight flattening of the curve above pH 11.0 being possibly due to a dilution effect, as the readings were all carried out on the same solution while adding progressive amounts of 0.2 N sodium hydroxide. As all of the above buffers giving curves of the linear type were measured at 24' C., and as all agreed as to slope and deviation from the theoretical value, a single equation covers the entire series. In no case was a deviation of more than 2 TABLE I.
COMPARISON OF
325
millivolts from this curve noted with any buffer solution. The constants have been recalculated for purposes of comparison to apply to the chain Sb-/Sbe08, test solution/sat. KCl/N KCI solution, HgCl/Hg + the equation at 24' C. being E = 0.019 0.0575 pH or E - 0.019 pH =
+
0.0575
This equation attains more towards the theoretical value than that of other workers, the theoretical slope of which at 24' C. would be 58.9 millivolts per pH unit.
MEASUREMENTS OF AQUEOUS SOIL SUSPENSIONS The major portion of the hydrogen-ion work carried out'in this laboratory is in connection with soil reaction. As the application of the antimony electrode would proceed along these lines, it was decided to examine a number of soils varying widely in distribution and reaction to test fully the applicability of the electrode. The soils used are principally of Queensland origin, though a few from New Guinea and India have been included as a matter of interest. The pH determinations were made with the bubbling hydrogen electrode, and the technic used was similar to that for the buffer solutions. Readings were taken a t the half-minute period and in no case was a considerable drift experienced after this time. Soils in the alkaline range were free of appreciable amounts of carbonates. Difficulty was experienced in obtaining soils of pH greater than 8.5 with sufficiently low calcium carbonate to obviate disturbance of the carbonate equilibrium. Certain soils were therefore leached free of lime with 0.05 N hydrochloric acid, treated with sodium hydroxide, and the excess removed by washing with alcohol. Although not natural
l" VALUES OBTAINED ON A RANGE OF SOILS BY HYDROGEN AND ANTIMONY ELECTRODES (pH value of aqueous and N KC1 suspensions
Sr- i/d
AQnHlons SUSPENBION N KC1 SUBPlNBION Hydrogen Antimony Difference Hydrogen Antimony Difference DESCRIPTION electrode electrode H - SbzOs electrode electrode H - SbrOa LOCALITY Texture Type .. 4.09 $0.10 3.00 2.94 +0.26 Beerwah Queenaland Sand Podsol 4.19 4.30 +0.03 3.62 3.67 -0.05 Beerwah Queensland Sand Podsql 4.33 5.48 -0.05 4.37 4.38 Samarai Papua Alluvium 5.43 -0f01 Sandy loam 4.30 4.34 5.70 $0.04 Scrubby Ck. Red loam 5.74 -0.04 Loam Queensland 6.12 4.38 4.46 -0.08 Red loam 6.12 0.00 Clay loam Eel Creek Queensland 6.20 4.53 4.54 -0.01 Cooran Queensland -0.06 Loam Podaol 6.14 6.36 4.76 4.80 -0.04 $0.04 Loam Callagrabah Queensland Red loam 6.40 6.52 5.07 5.10 -0.03 -0.03 Sandy loam Rabaul New Guinea Podsol 6.49 -0 0 A 4.94 4.94 6.54 Loam Cooran Queensland Podsol 6.50 0.00 5.19 5.18 6.49 Sandy loam Markhun Valley New Guinea Alluvium 6.54 $0.05 $0.01 6.72 4.76 4.86 Loam Wamuran Queens1and $0.03 Podsol 6.75 -0.10 6.80 4.90 5.06 Clay loam $0.08 -0.16 Eel Creek Queensland Red loam 6.88 6.98 5.40 5.46 Sand -0.08 Byrnestown Queensland -0.06 Podsol 6.90 6.95 5.27 5.26 -0.03 Loam Gympie Queenaland Red loam 6.92 $0.01 -0.n~ 6.98 4.84 4.94 Loam Scrubby Ck. Queensland -0.10 Red loam 6.95 7.10 4.55 4.68 -0.13 -0.10 Loam Cooran Queensland Podsol 7.00 5.55 5.58 -0.04 7.08 Loam Goomboorian Queenaland -0.03 Podsol 7.04 5.91 5.84 7.08 Loam Rabaul New Guinea Alluvium 7.14 +0.06 $0.07 7.30 5.80 5.84 Clayey sand Willowburn Queensland -0.04 Podaol 7.22 -0.08 Kin Kin Queensland 7.25 6.20 6.22 Loam -0.02 Immature 7.24 -0.01 Eumundi 7.32 5.46 5.58 Loam -0.12 Bueenaland Podsol 7.28 -0.04 Kilooy 7.39 5.68 5.70 Loam -0.02 -0.05 Queensland Podsol 7.34 7.36 5.70 5.64 Light clay Scrubby Ck. $0.03 Queensland Podsol 7.39 $0.06 Wamuran 7.36 5.68 5.72 Loam +0.04 Queenaland Red loam 7.40 -0.04 Conondale 7.50 5.97 5.96 Loam -0.02 Queensland Podsol 7.48 $0.01 Scrubby Ck. 7.48 5.09 5.08 Loam $0.05 Queensland Podsol 7.53 $0.01 Kilooy 7.78 5.97 5.94 Loam -0.04 Queena1and Podsol 7.74 $0.03 Kilooy 7.83 6.20 6.03 Loam -0.04 $0.17 dueeneland Podsol 7.79 Wamuran 7.74 6.28 6.16 Loam +0.08 Queeneland Podsol 7.82 +o. 12 Glastonbury 7.94 5.82 5.70 Clay +0.05 Queensland $0.12 Alluvium 7.99 6.98 Sandy loam Tiruppur India 8 12 7.12 -0.04 Podaol 8.08 +O. 14 6.78 Loam Pimpama Queensland 8.09 6.85 -0.07 4-0.07 Podsol 8.02 Obi Obi Loam 6.90 Queensland 8.26 6.95 +0.05 Podsol 8.20 -0.06 6.18 Clay loam Widgee 6.10 Queensland -0 03 8.28 Red loam 8.25 +0.08 Yarraman 8 50 7.63 Loam -0.07 Queensland Red loam 8.43 7.62 +0.01 Cunnamulla Queensland 8.58 7.76 Heavy clay +0.03 7.82 Alluvium 8.61 -0.06 Clay Coulstoun Laikes Queensland 8.62 7.69 7.63 +0.06 10.06 Cunnamulla Queensland 8.72 7.83 Heavy clay 7.81 $0.08 +0.02 -n nz Clermont Clay Queensland 8.86 7.80 7.76 +0.04 Blairmoor Clay Queensland 9.35 7.70 7.64 -0.08 +0.06 Blairmoor Clay Queensland 9.32 7.70 7.63 -0.03 +0.07 Cunningham Clay Queensland 9.41 8.39 8.33 -0.03 +0.06 Obi Obi Loam Queens1and 9.73 9.74 -0.10 10.56 -0.01 The majority of the red loams classified above were not developed from basic igneous rocks, but from the highly metamorphosed schists of the coastal range.
ANALYTICAL EDITION
326
soils, these sufficed to test the antimony electrode a t a higher p H than was otherwise possible. All determinations were carried out in triplicate, and replicates always agreed to within 1 millivolt. Antimony oxide was added to the system and the antimony electrode allowed to stand in the soil suspension. The details of technic were similar to those used in the previous buffer solution work. 110
l l l l l / I
FIGURE4. CORRELATION OF PH VALUES DETERMINED BY THE HYDROGEN AND ANTIMONY OXIDE ELECTRODE IN NORMAL POTASSIUM CHLORIDE SUSPENSION
The results obtained are shown in Table I. The pH varied from 4.09 to 10.56 with the antimony electrode and the results are considered to be highly satisfactory. The average difference between hydrogen and antimony electrodes for 43 soils is less than 0.05 pH unit, the average positive deviation being 0.057 and the average negative deviation 0.049 p H unit. The maximum errors are $0.10 and -0.10. Similar results are recorded by Snyder (I@, who used Franke and Willaman’s equation.
STIRRED AND UNSTIRRED SUSPENSIONS The above results were recorded with a stationary electrode, The technic of investigators has varied considerably. Kolthoff and Furman state that agitation is necessary; Franke and Willaman and Britton and Robinson used mechanical stirrers; Roberts and Fenwick kept their solution flowing over antimony crystals; Snyder used both a rocking electrode and a stationary one; Best, and Harrison and Vridhachalam worked with unstirred suspensions ; and Oosting used both stirred and unstirred soil suspensions. It is the conclusion of the author that either method is applicable, provided that the calibration of the electrode is carried out with the same technic. For instance, Snyder obtained better results with the rocking electrode, but he was using an equation evolved by Franke and Willaman on stirred buffer solutions. The principal advantage of the stationary method is that determinations can be made in test tubes in the same way as for quinhydrone, and that the method is suitable for field determinations with a portable potentiometer of the type recommended by Itano (8) or Harrison and Vridhachalam. VALUEOF ANTIMONY ELECTRODE IN SOIL REACTION MEASUREMENTS I n agricultural and research laboratories where large numbers of soils are handled daily, and in soil survey operations where reaction is an important factor in classification, a rapid method of pH determination becomes of primary importance. The time required for attainment of equilibrium with the hydrogen electrode, particularly with the Crowther electrode, usually outweighs the advantages accruing from
Vol. 5, No. 5
increased accuracy of the determination. Biilman’s quinhydrone electrode has therefore been adopted in most laboratories for routine work, and is eminently satisfactory with most soil types. With the growth of soil reaction work throughout the world the limitations of this electrode became apparent. Soils with a pH greater than 8.0 disturbed the quinone-hydroquinone equilibrium as a result of the acid nature of quinhydrone, and gave erroneous values. It was also pointed out as early as 1929 by McGeorge (IS)that certain Hawaiian soils known to contain appreciable quantities of manganese dioxide gave higher pH values with the quinhydrone than with the hydrogen electrode. Heintze and Crowther (6)explain this as a reduction of the manganese dioxide by hydroquinone, the resulting manganese hydroxide raising the p H of the soil suspension. Similar discrepancies have been noted with many of the basaltic red loams of Queensland, and as this soil type constitutes a fair percentage of the coastal agricultural areas, manganiferous soils attain considerable importance in daily routine work. It was with the object of applying the antimony electrode to these soils and the strongly alkaline soils of the more arid districts that the above work was carried out. ANTIMONY ELECTRODE IN N KC1 SUSPENSIONS OF SOILS For some years this laboratory has recorded reaction measurements of soils in both aqueous and normal potassium chloride suspensions, as recently urged by the committee on soil reaction measurements for the International Society of Soil Science (19). The value of this latter figure is being gradually acknowledged by soil authorities. p H values in normal potassium chloride appear to be less influenced by changes in biological and meteorological conditions and thus
c
4
$60
z
I5a B 40
70
40
50
60
70
80
90
pH-Antlmonq Oxide Electrode.
LOO
FIGURE5. CORRELATIONOF PH VALUES DETERMINED BY THE HYDROGEN AND ANTIMONY OXIDE ELECTRODE IN AQUEOUSSUSPENSION measure a more permanent characteristic of the soil. Worsley ($8) discussed the effect of neutral salt solutions on Egyptian soils, and European authorities use the method widely in fertility studies. I n Queensland the potassium chloride figure has been known to explain lack of fertility on sugarcane lands when the pH of the aqueous suspension failed to throw any light on the matter. It is not often with normal soils that the pH in normal potassium chloride suspension is greater than 8.5, and therefore the p H of the suspension does not prohibit the use of the quinhydrone electrode. But it is the author’s experience that manganiferous soils “drift” more frequently in potassium chloride than in aqueous suspension. It became important therefore that the antimony electrode should be applicable in salt suspension, and consequently a study of the salt error of this electrode was considered necessary. I n the previous work of Best and King (unpublished)
September 15,1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
it was found that the e. m. f. of the antimony electrode in a normal potassium chloride suspension, if read off from the calibration curve, gave a figure approximately 0.4 pH unit higher than the same suspension with the hydrogen electrode. This error was fairly constant for a large number of soils, though larger variations were occasionally experienced. If this salt error were entirely due to a surface action on the electrode, it would be expected that the effect of normal potassium chloride on a buffer solution would be comparable with that on a soil suspension. It was decided to measure the variation in pH of a number of buffer solutions made up normal with respect to potassium chloride, and compare these with the pH of the buffers without potassium chloride. The results of this work are stated in the early part of this pasper. Every series of buffers shows a difference of approximately 0.4 pH unit between the aqueous and the normal potassium chloride buffer solutions. As this figure agrees closely with the salt error experienced in measuring soils, it was thought that this second curve could be utilized for giving the relation between e. m. f. and pH for the soils in normal potassium chloride suspension. The curve obtained for the buffers in normal potassium chloride was parallel to the original curve and removed from it by approximately 0.4 pH unit. The slope of the curve remains constant, the equation for potassium chloride suspensions reading E = 0.041 0.0575 pH or E - 0.041 pH =
+
0.0575
I n Figures 4 and 5 are shown the values for the hydrogen and antimony electrodes on the 43 soils plotted against each other, and also the theoretical line. Figure 4 refers to the aqueous suspensions and Figure 5 to the suspensions in normal potassium chloride. The same series of 43 soils measured previously in aqueous suspension were used for this work, and the latter columns of Table I show the results obtained. The average error as compared with the hydrogen electrode is 0.058 pH unit, which is slightly larger than the error in aqueous suspension. The average positive deviation is 0.06 pH and the average negative deviation is 0.055 pH unit. These figures are considered fairly satisfactory for agricultural advisory or soil survey work where the sampling error is likely to exceed the error of the determination. For such operations the antimony electrpde is strongly recommended. It is robust in construction and does not appear to be affected by (‘poisons” of the type which affect the hydrogen electrode. Its range of applicability is considerable and is only limited by the pH at which antimony trioxide is soluble in the system under examination. It is proved to be a fairly reliable indicator of hydrogen-ion concentration and is accurate enough for certain avenues of soil work where extreme precision is not required. It is ideally suited for field work, particularly in the form illustrated by Harrison and Vridhachalam (5).
321
(10) Kolthoff a n d F u r m a n , “Potentiometric Titrations,” W h y , 1926. (11) Kolthoff, I, M., a n d Hartong, B. D., Rec. trav. chim., 44, 113 (1925). (12) Lava, V. G., a n d Hemedes, E. D., Philippine Agr., 27, 337 (1928). (13) McGeorge, W. T., Soil Sci., 27, 83 (1929). (14) Oosting, W. A. J., Mededeel. Landbou. Wageningen, 1921, 3. (15) Prideaux, E. B. R., a n d Ward, A. T., J. Chem. Soc., 125, 426 (1924). (16) Roberts, E. J., a n d Fenwiok, F. J., J. Am. Chem. SOC.,50, 2125 f 1928). (17) S h L k o v a n d Awsejewitch, Z . Elelctrochem., 35,349 (1929). (18) Snyder, E. F., Soil Sci., 26, 107 (1928). (19) Soil Research, Soil Reaction Com., 2, 144 (1930). (20) Uhl, A., and Kestranek, W., Monatsh., 44, 29 (1923). (21) Valeur, A., Ann. chim. phys., 21, 547 (1900). (22) Veibel, S., J. Chem. SOC.,123, 2203 (1923). (23) Worsley, R. R. le G., Ministry Agr. Egupt, Bull. 83, 16 (1929). RECEIVED November 15, 1932.
A Multiple Steam Bath WARRENL. BEUSCHLEIN AND WILLIAMM. DEHN Chemistry Laboratory, University of Washington, Seattle, Wash.
I
N MOST laboratories use of hot-water funnels of the ordinary
type is attended with inconvenience, danger, and loss of materials. The depicted copper steam-tight bath has solved these difficulties. A 6-funnel type was installed in a hood and was found to be instantly available for processes of hot filtering, drying of solids, and evaporating of liquids, and a source of heat for mild or stronger digestions. The construction of the metal bath can be made extremely simple. Soldered joints are sufficiently strong for the covered container and 60” cones. Inlet steam and condensate outlets are made by attaching appropriate pipes to threaded locknuts soldered on to the bath. Where legs are desirable, short lengths of pipe can be screwed into additional locknuts STEAM I N L E T
2pI
LITERATURE CITED Best, R. J., J. Agr. Sci., 21,337 (1931). Britton, H . T., a n d Robinson, R. A , , J. Chem. Soc., 1931, 458. Clark, W. M., “Determination of Hydrogen Ions,” Williams & Wilkins, 1923. Franke, K . W., a n d Willaman, J. J., IND. EKG.CHEM.,20, 87
(1928). Harrison, W. H., a n d Vridhachalam, P. N., Mem. Dept. Agr.
India, 10, 157 (1929). Heintze, S . G., and Crowther, E. M., Trans. 2nd. Comm. I n -
tern. SOC.Soil Sci.. 19298. 102. I t a n o , A., Ber. Ohara. Inst. iand. Forseh. Japan, 4 , 2 7 3 (1929).
Ibid., 4, 19 (1929). Kolthoff, I. M., J. Biol. Chem., 63, 135 (1925).
FIGURE1
soldered on to the bottom of the container. The funnels may be centered or, if the bath is to be used also as a hot plate, they may be inserted asymmetrically. Single or double funnel baths can be used as portable laboratory equipment, depending upon the usual steam can for heat. RECEIVEDAugust 1, 1933.
