June,
1915
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
SERIES1 SILVERIODIDE IODIN (per cent) IODOANTIPYRIN Gram 0.1498 0.2240
Gram 0.2000 0.3000 ANTIPYRIN Gram 0.2500 0.2500 0.2500 0.3000
Caffeine Antipyrin Gram Gram 0.2000 0.0500 0.0500 0.2000 0.2000 0.0500 0.2000 0.0500 0.0500 0.2000 0.0500 0.2000 0.0500 0.2000 0.0500 0.2000 0.0500 0.2000 0.0500 0.2500 0.0500 0.2500 0.0500 0.2500 0.0500 0.2500 0.0500 0.2500 0.0500 0.2500 0.2592 0.0648 0.2592 0.0648 0.1000 0.1000 0.2500 0.1667 0.1667 0.2500 0.1667 0.2500
Recovery 40.47 40.34
Theory 40.40 40.40
SERIES 2 SILVER IODIDE ANTIPYRINRECOVBRY Gram Gram Per cent 0.2496 99.84 0.3115 0.3111 0.2493 99.72 0.2503 100.12 0.3124 0.3731 0.2989 99.63 SERIES3 RECOVERY Residue Antipyrin “A” A d Caffeine Per Gram Gram Per cent Gram Gram cent 0.3836 0.2495 0.0499 99.8 0.1999 99.9 0.0507 101.4 0.3837 0.2490 0.1995 99.7 0.OSOl io012 0.3837 0.2494 0.1999 99.9 0.0512 102.4 0.3845 0.2492 0.1997 99.8 0.0514 102.8 0.2490 0.1995 99.7 0.3844 0.0499 99.8 0.3834 0.2494 0.1998 99.9 99.7 0.0506 101.2 0.3835 0.2489 0.1994 0.0497 99.4 0.3837 0.2500 0.2003 100.1 0.0514 102.8 0,3839 0.2486 0.1994 99.7 0.0503 100.6 0.3107 99.5 0.4658 0.2489 0.0502 100.4 0.3118 0.2498 99.9 0.4672 0.0513 102.6 0.3120 0.2500 100.0 0.4686 0.0509 101.8 0.4674 0.3114 0.2495 99.8 0.0493 98.6 0.4657 0.3116 0.2497 99.9 99.6 0.0498 0.4661 0.3115 0.2496 99.8 0.0649 100.2 0.3237 0.2593 100.0 0.4976 0.0648 100.0 0.4976 0.3236 0.2593 100.0 99.8 0.0998 0.2654 0.1238 0.0992 99.2 0.1666 99.9 0.5864 0.3138 0.2514 100.5 0.1648 0.3124 0.2503 100.1 98.8 0.5824 0.1677 100.6 99.5 0.5831 0.3107 0.2489
ence of which in t h e composite residue “A” would naturally vitiate t h e analytical findings. T h e application of iodin in small portions appears t o favor t h e production of a purer iodoantipyrin t h a n is t h e ease when this reagent is all added a t one time, as evidenced by t h e color of t h e caffeine-antipyrin residue. I n order t o free t h e latter from all contaminating v d a t i l e products under t h e conditions outlined in t h e method, particular attention should be given t o t h e actual working conditions of t h e drying oven,’ since incomplete or improper desiccation must necessarily lead t o widely divergent caffeine values, while heating a t temperatures materially higher t h a n I o j o is found t o exert a n unfavorable influence on t h e recovery of both caffeine a n d antipyrin. T h e color changes following t h e addition of strong nitric acid are quite characteristic, passing from colorless through deep red t o pale yellow in t h e course of 5 minutes’ boiling. I n view of this somewhat radical treatment t o which t h e caffeine is likewise subjected, any direct determination of this substance becomes impractical. The quantity of caffeine is therefore ascertained indirectly with a reasonable degree of accuracy by subtracting t h e weight of iodoantipyrin (calculated) from t h a t of t h e composite residue “A”. As aIready indicated, t h e determination of antipyrin is effected b y estimating t h e halogen contained in t h e iodo derivative a n d calculating t o t h e parent substance. Considerable experimentation was required before a suitable procedure could be found for t h e quantitative withdrawal of iodin from t h e pyrazolon complex. Treatment by Carius naturally gave very accurate returns b u t in point of facility was far from satisfactory. T h e well-known methods depending on t h e action on t h e one hand of alcoholic potash a n d on t h e other of metallic sodium a n d alcohol both failed completely in t h e object sought. Even direct I
CI. Lorin H. Bailey,
THISJOURNAL, 6 (1914). 585.
j21
a n d continued boiling with a n aqueous acid solution of silver nitrate gave little better results. Thus, in two determinations carried out under slightly varying conditions, only 35.28 a n d 3 7 . 8 2 per cent iodin could be recovered as silver iodide, t h e theory demanding 40.40 per cent. A very effective a n d convenient reagent was finally discovered in sulfur dioxide, which rather unexpectedly perhaps yet none t h e less completely removes t h e substituted iodin, as evidenced by numerous controls. EXPERIMENTAL
T h e d a t a given for Series I , 2 a n d 3 are representative of results obtained b y t h e authors in operations carried out substantially in accordance with the procedure outlined above. Experiments bearing directly on t h e behavior of caffeine a n d iodoantipyrin, when heated alone a n d in admixture a t 1 0 5 O a n d under conditions comparable with those followed in t h e regular method, indicate t h a t loss by volatilization is mainly chargeable t o caffeine, as will appear from a n examination of t h e following results. The several charges were first dissolved in 2 j cc. chloroform a,nd the solvent then blasted off a t a moderate heat prior t o treatment in t h e drying oven. WEIGHT AFTER HEATING ALONE Initial wt. 30 min. 30 min. 1 hr. Total loss Caffeine 0.1000 0 0993 0.0990 0.0980 0.0020 Iodoantipyrin 0.4000 0 4005 0.4003 0.4001 CafIodoanWEIGHTSAFTER Total IN ADMIXTURE loss feine tipyrin SUCCESSIVE HEATINGS 0.0500 0.4000 0.4494 0.4491 0.4478 0.4464 0.4454 0.4431 0.0069 0.1000 0.4000 0.4995 0.4992 0.4981 0.4963 0.4951 0.4926 0.0074 0.2000 0.4000 0.5996 0.5991 0.5978 0.5963 0.5954 0.5922 0.0078
___
Iodin determinations in the three composite residues were made with the following results: IODOANTIPYRIN RESIDUE AgI Gram Gram Gram Per cent 0.4431 0.2989 0.3997 99.92 0.4926 0.2986 0.3993 99.82 0.5922 0.2985 0.3992 99.80 SYNTHETIC PRODUCTS LABORATORY, BUREAUOB CHEMISTRY DEPARTMENT OF AGRICULTURE, WASHINGTON
THE DETERMINATION OF NITRIC NITROGEN IN SOILS By E. R. ALLEN Received February 9, 1915
O B J E C T O F T H E RESEARCH-The determination O f nitric nitrogen has been t h e subject of a very large amount of experimentation, discussion a n d controversy. I n spite of t h e array af methods t h a t have been proposed, more or less uncertainty exists in t h e use of any one of t h e m , as is shown, for instance, by t h e following statements: ‘ ‘ N o single method appears t o be applicable t o t h e determination of nitrogen in nitrates in all classes of water, sewages a n d sewage effluents, a n d there is no method which is not subject t o considerable error;”l a n d , “ T h e accurate determination of nitric acid in combination presents great difficulties, a n d can be made only by indirect means; t h e methods here given are sufficient for most purposes. T’ery few of t h e m can be said t o be simple, but it is t o be feared t h a t no simple process can ever be obtained for t h e determination of nitric acid in many of its combinations.”2 1 “Standard Methods of Water Analysis,” Amer. Pub. Health Assoc , p. 23 (1912). 2 Sutton. “Volumetric Analysis.” 10th Ed., p. 271 (1910).
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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
I n our investigations on t h e physiology of t h e process of nitrification in soils, we have been conf r o n t e d a t t h e outset with t h e uncertainty of t h e methods, a n d t h e paucity of information regarding t h e probable errors of t h e same. I n reading t h e literature quite extensively we have been impressed b y t h e non-uniformity of methods employed b y physiologists; a n d i n m a n y cases i t is impossible t o decide how m a n y of t h e differences reported are due t o differences in physiology a n d how many t o analytical errors. Another source of error contributing t o t h e confusion of t h e existing d a t a on t h e nitric nitrogen problem is t h a t i t is not certain t h a t t h e prevailing methods of extracting t h e soil actually recover all t h e nitric nitrogen. T h e object of t h e present research mill be, however, t o develop a method suitable for t h e s t u d y of t h e physiology of nitrification. A second paper will be devoted t o t h e separation of ammonia, nitric a n d organic nitrogen, a n d a t h i r d t o t h e extraction of nitric nitrogen from soils. REQUIREMENTS T O BE MET-A method t o meet t h e requirements of t h e physiological s t u d y of nitrification should be applicable t o a m o u n t s of nitrate nitrogen varying from 0.1 t o 25.0 mg. contained i n each case i n 2 5 0 cc. of soil extract-therefore, i n t h e presence of organic matter. T h e error should be of t h e order of magnitude of z per cent or less. One-hundred-gram portions of soils are convenient a m o u n t s with which t o work in nitrification studies. If this a m o u n t is extracted with five times i t s weight of water, for instance, a n d a n aliquot, usually 2 5 0 cc., t a k e n for analysis, t h e n with samples containing 2 , 100, a n d 500 p a r t s nitric nitrogen per million of soil, a n d intermediate values, as m a y be met i n nitrification studies, a n error of z per cent would require a n analytical procedure, t h e probable error of which would be * o . o o z , + O . I O , a n d + o . j of a milligram for t h e a m o u n t s named. T h e method should also permit t h e determination of ammonia nitrogen i n t h e same sample. HISTORICAL-REDUCTIOX
METHODS
A review of all t h e literature on methods of nitric nitrogen determination would be scarcely possible or desirable. It is obvious t h a t reduction methods -provided t h e y proceed rapidly a n d quantitativelyare t h e most desirable since nitrogen is more easily a n d more accurately measured as ammonia t h a n in a n y other form: small amounts m a y be accurately determined colorimetrically, while larger amounts m a y be very satisfactorily determined b y titration. However, t h e fact t h a t reduction methods have b y n o means been adopted t o t h e exclusion of other procedures indicates t h a t t h e y do not give unifoimly reliable results. Indeed m a n y instances are recorded in t h e literature i n which chemists have failed t o agree on reduction procedures. T h e careful a n d thorough work of Mitscherlich a n d Herzl clears up much in this connection: t h e y conclude t h a t most reduction methods are burdened with errors; t h a t , however, reduction with Devarda’s alloy does give quantita1
Landw. Jahrb., 88 (1909), 279-318.
Vol. 7 , No. 6
tive results, a n d t h a t b y proper refinement of t h e distillation apparatus a n d of t h e titrimetric procedures a very high degree of accuracy m a y be a t tained. T H E D E V A R D A M E T H O D ’ consists of reducing nitric nitrogen in strongly alkaline’ solution with a finely divided alloy composed of jo per cent copper, 4 5 per cent aluminum, a n d 5 per cent zinc. I t is t h e only method, so far as we are aware, t h a t has escaped serious criticism in t h e literature. While i t s s u p e r i o r i t y over other methods has been questioned b y some, we have not found a case in which t h e reliability of the method i t s e l j has been questioned. According t o W. S. Allen,* i t gives reliable results, a n d Cahena regards i t as satisfactory a n d vastly superior t o Pozzi-Escot’s4 method. After trying different reduction methods Valmari5 concluded t h a t a finely powdered copper-aluminum alloy, t o which a small a m o u n t of zinc h a d been added t o produce brittleness-to which class, therefore, Devarda’s alloy belongs-is t h e best reducing agent for nitric nitrogen. Mitscherlich a n d Herze conducted a n extended investigation on t h e perfection of a n accurate Kjeldahl method which would include all forms of nitrogen, i n course of which t h e y studied, among other sources of error, t h e question of t h e reduction of nitric nitrogen. Using phenolsulfonic acid a n d zinc dust, sodium hydroxide a n d zinc-iron dust, Jodlbauer’s method, a n d Forster’s method, t h e y were unable t o obtain t h e theoretical a m o u n t of ammonia from nitrate. Because t h e y were unable t o recover t h e deficiency of nitrogen b y digesting t h e residues, according t o Kjeldahl, for total nitrogen, a n d because t h e use of larger a m o u n t s of reducing materials did n o t lessen t h e losses, t h e y concluded t h a t t h e “ n i trogen loss is not t o be attributed t o a n unfinished a n d , therefore, incomplete reduction b u t is much more likely due t o t h e f a c t t h a t gaseous nitrogen is evolved during t h e procedure. This loss can be avoided only through other reduction media. AS such a one we have chosen Devarda’s alloy.”’ Besides pointing out t h a t t h e Devarda procedure is t h e best for effecting reduction of nitric nitrogen, Mitscherlich a n d Herz, a n d also Valmari, proposed modifications of t h e original procedure. THE MITSCHERLICH-DEVARDA H E T H O D differs f r o m t h e original Devarda method in t h e a p p a r a t u s used, which effectively prevents t h e carrying over of alkaline spray into t h e receiver a n d still retains t h e advantage of ease of transfer of t h e ammonia from distilling flask into receiver, while avoiding t h e error due t o t h e solubility of t h e alkali of a glass distillation t u b e a n d t o t h e slight absorbing action on ammonia of block-tin condenser tubes. Using this 1 Zeit. anal. Chem., 33 (1894). 113; Treadwell-Hall, “Analytical Chemistry,” 3rd Ed., Vol. 11, p. 454 (1913). 2 Orig. Comm. V I I I , I n t . Cong. App. Chem., Vol. I , p 19-31, New York (1913). 3 Analyst, 36 (1910), 307. 1 Reduction with aluminum-mercury couple. 8 “Unter. ii. d. Lljsbarkeit u. Zersetzbarkeit d. Stickstoff im Boden.” Dissertation, Helsingfors. 1012, p. 43. 6 L O G . cit. 7 LOC.c i f . . p. 317.
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
a p p a r a t u s Mitschlerich a n d Herz obtained excellent results. F r o m I O determinations on each of four known amounts of nitrogen t h e y obtained these resu1ts:l NO.
CUBIC CENTIMETERS
Average 24.335 I I1 12.15 6.095 I11 2.44 IV
Probable error t0.070 t0.044 *0.025
+0.021
N / 5 0 &SO4 MILLIGRAXS NITROGEN True T r u e Probable Deviation from value value error true value -0.018 6.84 *0.02 24.40 -0.014 3.42 t 0 . 0 1 2 12.20 -0.001 1.71 t0.007 6.10 -0.000 0.68 t 0 . 0 0 6 2.44
T h e y conclude: “these results show better t h a n a n y words t h a t i n our hands t h e reduction of t h e nitrate nitrogen is complete, a n d t h a t t h e error of this analysis has not become greater t h a n t h a t of t h e a m m o n i a distillation.’’ T h e source of t h e nitrate nitrogen i n these analyses was potassium nitrate which gave t h e theoretical amount of potassium sulfate. Mitscherlich a n d Herz conclude their paper b y saying, “from t h e preceding work i t is worthy of note t h a t hitherto performed nitrate nitrogen analyses are burdened with very great errors, because great losses occur i n t h e reduction processes.2 T H E VALMARI-DEVARDA M E T H O D possesses t h e distinctive feature t h a t reduction is carried out in dilute alkaline solution, whereas strolzg alkali is required b y t h e original directions of Devarda. According t o Valmari, t h e reaction of a copper-aluminum-zinc alloy is electrolytic, innumerable small cells being formed with aluminum as anode a n d copper as cathode. T h e potential difference is, however, not enough t o decompose water at room temperature. Boiling produces a n evolution of hydrogen, a n d this evolution is much increased if t h e conductivity of t h e water is increased b y t h e presence of neutral electrolytes, a n d a very low concentration of alkali-even t h a t imparted t o t h e solution b y magnesium oxidehastens t h e actions sufficiently t o reduce nitrate rapidly a n d quantitatively t o ammonia. T h e nitrogen of a nitrate solution m a y be distilled off with magnesium oxide a n d a finely divided copper-aluminum-zinc alloy i n a go-minute distillation period, just a s if i t were a solution of a n ammonium salt. Valmari found t h a t in solutions high in organic m a t t e r t h e reaction is retarded so t h a t t h e evolution of hydrogen is not sufficient t o effect quantitative reduction. Satisfactory results are obtained b y t h e addition of j cc. of t h e sodium hydroxide solution used in Kjeldahl determinations, which makes t h e solution about N / I O in N a O H . Valmari also recommends t h e altering of t h e composition of Devarda’s alloy, pointing out t h a t t h e percentage of aluminum should be higher, b u t t h a t t h e brittleness of t h e mixture sets a certain limit. t h a t must not be overstepped. T h e proportions of 60 per cent aluminum, 37 per cent copper, a n d 3 per cent zinc give a n alloy still capable of being pulverized. T H E A L U M I N U N R E D U C T I O N M E T H O D , which has been used with varying success i n water analysis, has recently been recommended b y Burgess for t h e determination of nitrates in soil extracts.8 T h e procedure used is described on p. 5 2 5 . T h e fact t h a t 1
LOG.cit.. p. 289.
9
LOC.c i f . , p. 318.
a University ( 19 13).
of California Publications in Agr. Sci., Vol. I, No. 4
523
the somewhat extravagant conclusions are drawn t h a t “ t h e aluminum reduction method for t h e tietermination of nitrates in soils yields t h e most accurate results of all methods now commonly in vogue,” a n d t h a t “ t h e presence of extraordinarily large a m o u n t s of soluble organic materials (soluble h u m u s and dextrose) have little effect on t h e method,” a n d also t h e fact t h a t t h e Associate Referee of t h e Association of Official Agricultural Chemists on nitrogenous materials in soils’ recommends t h e adoption of t h i s as a n official method, caused us t o include some tests of i t in this work. DIscussIor-Although t h e power of Devarda’s alloy t o reduce nitric nitrogen t o ammonia quickly a n d quantitatively is apparently agreed upon, t h e original Devarda method possesses t w o sources of error: ( I ) Owing t o t h e rapid evolution of hydrogen, some fine alkaline spray is likely t o be carried over into t h e receiver, necessitating t h e redistillation of t h e receiver contents over N g O . ( 2 ) I n solutions high in organic matter-as are frequently encountered in soil extracts-the action of t h e strong alkali on t h e organic matter is so marked t h a t a sharp separation of t h e nitric from t h e organic nitrogen is not possible. T h e Mitscherlich-Devarda method eliminates t h e first of these errors a n d retains t h e second,l while t h e T‘almari-Devarda procedure reduces both, b u t , except in t h e case of reduction in 11gO solutions, when there is no danger of spray going over, completely eliminates neither. T h e aluminum reduction method also used a much more dilute alkaline solution for reduction t h a n t h a t employed in t h e hIitscherlichDevarda method. However, neither Valmari nor Burgess gave t h e extended attention t o t h e refinement of t h e methods t h e y recommended t h a t Nitscherlich a n d Herz gave t o theirs. Before, therefore, these methods employing more dilute alkaline solutions could be accepted t h e y h a d t o be as rigidly examined as t h e hlitscherlich-Devarda method h a d been. If a method applicable i n t h e presence of organic matter, in which t h e reduction is carried o u t in w e a k l y alkaline solutions could be developed t o a point where its probable error was of t h e order of magnitude obtained b y Mitscherlich a n d Herz, i t would surpass a n y t h a t has yet appeared, a n d we could hope t o later perfect t h e separation of t h e nitric from t h e organic nitrogen a n d t h u s a t t a i n our original object. The comparison of t h e reduction procedures used in t h e aluminum reduction, Mitscherlich-Devarda, a n d Valmari-Devarda methods, t h e determination of conditions affecting quantitative reduction, a n d t h e determination of t h e probable error of t h e method furnishes t h e basis of t h e experimental p a r t of this work. E X P E R I M E N TA L CHOICE
OF INDICATOR
FOR
THE T I T R A T I O N O F AM-
MoxIA-Since a reduction method for nitric nitrogen involves t h e titrimetric determination of a m 1 The Amerrcan Fertdizer, 4 1 (1914), 33. 2 It should be stated, however, t h a t Mitscherlich and Herz were not concerned with t h e separation of organic and nitric nitrogen b u t only in t h e question of complete reduction, so t h a t their method for total nitrogen would certainly include all nitric nitrogen.
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monia, a n indicator suitable for t h e titration of weak bases h a d t o be chosen. Preliminary tests convinced us t h a t methyl red, #-dimethyl-amino-azobenzene-0-carboxylic acid,* is easily t h e best indic a t o r t h a t has yet appeared for t h e titration of weak bases as ammonia. It is possible t o t i t r a t e with ease N / s o solutions of ammonia against strong acids, provided no C02 is present. We have observed also t h a t t h e end point is more distinct if t h e solution t o be titrated is cooled t o 10-15' C. This is doubtless 'due t o cutting down of hydrolysis of t h e a m monia salt of t h e complex organic acid indicator a t this temperature. T h e end point is more certain t h a n with either Congo red or alizarin red, a n d vastly more distinct t h a n with methyl orange, lacmoid, or cochineal. Another advantage is t h a t its color change takes place at a lower concentration of hydrogen a s ion t h a n does t h a t of methyl orange. According t o Tizard2 t h e visible color change, red t o yellow, t a k e s place between IO-'.^ a n d IO-^, while A. A . Noyes3 reports t h a t t h e transition color of methyl = IO-^ as compared red is most marked a t (H') with ( H f ) = IO-^ for methyl orange. Througho u t this work we have adhered t o t h e first faint appearance of brown-free from pink-in t h e pale lemonyellow alkaline solution as our end point. PREPARATION
O F MATERIALS
A K D SOLUTIOSS:
TIT-
STANDARDS-Tentha n d fiftieth-normal solutions of sulfuric acid a n d of sodium hydroxide were prepared free from CO1, a n d were standardized b y t h e sodium carbonate method which hlitscherlich a n d hIeeres4 found t h e most accurate. Fiftycc. burettes5 provided with three-way stopcocks, connected with t h e reservoir bottle, essentially as recommended b y Treadwell,6 were used. The white topped titrating shelf was directly in f r o n t of a south window, a n d t h e entering light was diffused by passage through a sheet of white paper, T h e method of reading t h e burettes was t h a t specified b y t h e Bureau of Standards.7 When portions of t h e solutions h a d stood i n t h e burettes 2 4 hours or more t h e y were discarded. Temperature corrections were made when necessary. A X A L Y T I C A L STANDARDS-The sources of nitric a n d a m m o n i a nitrogen used in t h e testing of methods reported in this paper were solutions of nitric acid a n d of ammonium hydroxide. These were prepared from carefully neutralized,s ammonia-free water a n d C. P. "03 or NHIOH. T h e y were accurately standardized against t h e titrimetric standards b y series of titrations. RIYETRIC
1 R u p p a n d Loose, B e y . d. chem. Ces., 4 1 (1908), 3905; see also Treadwell-Hall, "Analytical Chemistry," Vol. 11, p. 543, 3rd E d . (1913). This indicator can now he purchased from Merck & Co. J . Chem. SOC.Tuans.. 97 (1910), 2477-90. 3 J . A m . Chem. SOC.,32 (19101, 824. 4 Landzv. Jahrbiicheu, 39 (19101, 345. 3 All burettes used in this work were made according t o t h e specifications of t h e U. S. Bureau of Standards, b u t did not hear t h e control stamp. Calibration curves b y means of a 2 cc. Ostwald pipette showed, however, t h a t the limits of error did not exceed the tolerances permitted by the Bureau of Standards Czrc. 9 (1913), 16. 6 Treadwell-Hall, "Analytical Chemistry." Vol. 11. 3rd Ed., p. 5 5 6 (1910). 7 LOG. cif., p. 17. 8 T h e term "neutral water" a s used in this paper refers t o water neutral to the indicator used, i . e., to methyl red. Strictly neutral water, i . e . , i n which (H') = 10-7, would of course be alkaline t o methyl red.
Vol. 7 , NO. 6
AMMONIA-FREE WATER-The regular laboratory-distilled water was treated with bromine water till t h e t i n t was distinctly yellowish, allowed t o s t a n d at least four hours, transferred t o a 5-liter Jena balloon flask, sufficient alkali added t o destroy t h e color, distilled through a n ordinary glass condenser, a n d stored in glass stoppered bottles. Of course, water so prepared reacted slightly alkaline. Whenever used in titrimetric operations i t was carefully neutralized beforehand with N/jo H2S04. When COz-free water was desired, t h e receiver was protected with a sodalime tube. This water was used in all operations reported in this paper. T. Baker's c. P. AMMONIA-FREE UAGNESIA-J. magnesium oxide was heated in a n electric furnace one hour or more a t a temperature of 7 0 0 t o 800' C. S O I L E X T R A C T S HIGH IPU- O R G A N I C M A T T E R B U T F R E E N I T R I C NITROGEN-one kilogram of air-dried greenhouse soil, which h a d been heavily manured for several years a n d h a d recently received a liberal application of barnyard manure, was well shaken with t w o liters of water containing 2 0 g. of dextrose a n d allowed t o s t a n d over night. I t t h e n showed not t h e slightest trace of nitrate by t h e diphenylamine test. Three hundred a n d fifty cc. gave, on distillation with magnesium oxide, 0.32 a n d 0.37 mg. of a m monium nitrogen a n d after Kjeldahl digestion 2 . 2 7 mg. of organic nitrogen. T h e solution was very highly colored, appearing decidedly reddish in t h e deeper layers. I t represents a n extreme, though not a n impossible case. I t s reducing power was tested b y titration with Fehling's solution. Ten cc. portions of t h e extract reduced 8.66, 8.48 a n d 8 . j 6 cc. of Fehling's solution. A L u MI N U xc OPP E R-ZIK c A L L o Y-T h e regular De varda alloy ( C u 5 0 : ,41 4 j : Zn j ) was used a n d not t h a t recommended b y Valmari. T h e Devarda alloy is purchasable on t h e market a n d met t h e requirements of our work. J . T. Baker's product was used, which was found t o be absolutely free from nitrogen. A product purchased from another dealer contained, oddly enough, a n appreciable amount of nitrogen. T h e J. T. Baker product was obtained i n t h e f o r m of a powder, much of which would not pass a 20 mesh sieve. Before use i t was all pulverized t o pass a 60 mesh sieve. DIPHENYLAMINE REAGENT-In a n investigation of this sort i t is, of course, necessary t o have a means of determining qualitatively minute amounts of nitric nitrogen. T h e diphenylamine-sulfuric acid method as modified b y K i t h e r s a n d R a y ' meets this requirement. We followed their directions except' t h a t as a rule t h e solutions were tested a t room temperature instead of at 40'. B y actual tests t h e reagent we used gave, under these conditions, a faint b u t distinct reaction in a solution containing I p a r t of nitric nitrogen in ~ 5 , 0 0 0 , o o o . T h e responses t o this reaction are classified in t h e accompanying tables as strong, faint, a n d none. INDICATOR soLuTIoK-Two-hundredths of a gram (0.02) of methyl red, i. e., t h e free acid, was disFROM
1
J . A m . Chem. SOC.,33 (1911). 708
J u n e 191j
T H E J O U R N A L OF IYDlTSTRIAL A N D ENGINEERING CHEMISTRY
solved i n IOO cc. redistilled alcohol.’ Four drops of this solution were used per titration. C H O I C E O F R E D C C T I O X PROCEDURE-Three methods were tested for their applicability t o our conditions: I-THE A L U M I N U M R E D U C T I O N METHOD-The procedure was t h a t employed b y Burgess,2 except t h a t one-half t h e a m o u n t of soil extract, containing only 12. j mg. nitric nitrogen was used. T h e soil extracts plus 2 5 cc. -V/28 H N O s a n d z cc. of j o per cent N a O H were concentrated t o a b o u t 4 0 cc. b y gentle boiling. T h e volume of t h e reducing solutions was 6-70 cc. I t was observed t h a t t h e action on t h e aluminum was much slower in t h e presence of organic m a t t e r t h a n in t h e checks. I n t h e l a t t e r t h e aluminum strips completely dissolved over night, while in t h e former t h e y h a d been b u t slightly attacked, a n d were coated with a t h i n gelatinous layer of organic m a t t e r . I n obtaining t h e d a t a of Table I these strips were left in t h e flasks during distillation in Nos. 2 c a n d d , a n d 3c a n d d , while in t h e cases of Nos. 2a a n d b? 3 a a n d b , a n d all of Set 1l t h e y were washed off a n d discarded TABLE I-RECOVERYOF 12.5 MG. OF NITRIC NITROGEN
BY THE ALUMINUM
REDUCTION METHOD Set N o . hrs. PhZNH No. Material reduction Mg. N found reaction(a) 1 C h e c k . . . . . . . . . . . . . . . 16 a t 20-22’ C . a 12.26 Faint b 12.29 None c 11.95 None d 12.32 Faint 2 Soil e x t r a c t . . . . . . . . . . . 16 a t 20-22’ C. a 8.11 b 8.25 c 12.60 Strong d ,.50 , 3 Soil extract, clarified a 3.81 with l i m e . , , , , , , . , , , 16 a t 20-22’ C.
’I
4
Soil extract, clarified withlime. . . . . . . . . . .
d 40 hrs. a t 2 0 - 2 2 O
”
8.10 12.+5~ 3 -
I‘.
1.2
10.16 ]Strong d 12.38 (a) T h e diphenylamine reactions reported in this a n d subsequent tables a r e t h e results of tests made on 1 cc. portions of t h e solutions after reduction. c
I t is believed t h a t t h e production of ammonia from organic m a t t e r entered somewhat into t h e determinations of Set 4. This action would, of course, be greater in t h e longer reduction periods. This would explain why No. 4a gave high values for nitrate a n d still b y t h e diphenylamine method showed considerable nitrate unreduced. T h e d a t a in Table I indicate t h a t t h e claims made for this method b y Burgess are too broad. Organic m a t t e r evidently does retard t h e reduction. I t should be noted here also t h a t t h e aluminum reduction method has been prescribed for t h e determination of nitric nitrogen in waters, “if t h e q u a n t i t y of organic nitrogen is less t h a n 0.1 p a r t in 1 0 0 , 0 0 0 . ~ T h e organic materials used b y Burgess, i. e . , soluble h u m u s a n d dextrose, d o n o t contain t h e t y p e of colloidal m a t t e r t h a t is encountered in extraction of soils containing decaying organic m a t t e r . Furthermore, i t is doubtful if a method which involves t h e transfer of a solution containing ammonia in t h e presence of a fixed alkali T h e directions given in Treadwell-Hall (Vol. 11, 3rd E d . , p. 543 (1913)) are t o dissolve 0.02 g. of free acid in 100 cc. of hot water. This recommendation is certainly incorrect, as t h e above a m o u n t of free acid will not dissolve in 100 cc. of water. The free acid is almost insoluble in water, its saturated solution a t t h e ordinary temperature being only a b o u t N/100,000, while its alkali salts are very soluble (Tizard, LOG.cit , 2485). University of California Publications in -4gr. Sci., Vol. I. No 4 (1913). Sutton’s “Volumetric Analysis,” 10th E d . . p 465 (1911)
525
will yield highly satisfactory results. At a n y r a t e t h e procedures described below involved less time a n d gave promise of greater accuracy. 2-THE VALMARI-DEVARDA M E T H O D Of reducing in t h e presence of MgO was first studied. T h e nitric nitrogen was introduced as ;V/’28 H K O o into Kjeldahl flasks, diluted t o 300 cc., a n d I g. hIgO a n d 3 mg. alloy added. T h e flask was t h e n connected with t h e regular Kjeldahl distilling rack, a n d distillation carried on for 30 minutes, rinsing o u t t h e condenser with steam a t t h e end of this period, as has been recommended b y Benedict.’ T h e results, given in Table 11, show t h a t t h e method gives promising results with TABLE11-REDUCTION A N D DISTILLATION OF
h’ITRIC ? i I T R O G E N I N THE PRESEKCE OF MAGN€SIUhf OXIDE 25 M o . NITROGEN TAKEN 5 MG. NITROGEN TAKEN Mg. N P h , N H Mg. N PhzNH No. found reaction No. found reaction l . . . . . . . . . . . . . 4.956 Faint 1 . . . . . . . . . . . . 23.21 F a i n t Z . . . . . . . . . . . . 4.962 F a i n t 2 . . . . . . . . . . . . 23.58 Faint 3 . . . . . . . . . . . . . 5.091 Faint 3 . . . . . . . . . . . . 2 3 . i 5 Faint 4 . . . . . . . . . . . . . 4.990 Faint 4 . . . . . . . . . . . . 22.85 F a i n t 3 .. . . . . . . . . . . . 5.013 Faint 5 . . . . . . . . . . . . 23.94 Faint AVERAGE.. . . . . 5.002 23.46
j mg. nitric nitrogen b u t fails in t h e presence of z j mg. Since Talmari obtained satisfactory results for 1 i . j mg. of nitric nitrogen i t was surprising t h a t our results were low for 2 5 mg. I t a t once occurred to us t h a t t h e alkalinity of t h e magnesia itself is not sufficient for rapid reduction of this a m o u n t of nitric nitrogen a n d expulsion of t h e ammonia, b u t t h a t t h e increased alkalinity resulting from t h e reduction of t h e alkali nitrate, used b y Valmari, might be sufficient t o produce quantitative results. I n obtaining t h e d a t a in Table I1 t h e nitric acid added was concerted into magnesium nitrate, which on reduction gave rise t o insoluble magnesium hydroxide, t h u s not increasing t h e alkalinity. T h e importance of this point was shown in t h e following experiment in which t h e 1 2 . j cc. N / 7 nitric acid added were just neutralized with LV/ I O alkali, t h e magnesium oxide a n d alloy t h e n added, a n d t h e reduction a n d distillation carried out a s b e fore. I n five determinations, 25.09, 24.81, 2 j . o j , 21.91 a n d 24.80 (av. 24.93) mg. nitrogen were recovered. These results show t h a t , while t h e alkalinity produced b y MgO alone is not sufficient t o effect quantitative reduction a n d distillation of a 25-mg. portion of nitric nitrogen i n a go-minute period, t h e alkalinity produced as a result of t h e reduction of a n alkali nitrate added t o t h a t produced b y MgO is sufficient t o effect t h e reduction in this time. I n all subsequent operations t h e s t a n d a r d nitric acid added mas neutralized with s t a n d a r d alkali, regardless of whether t h e reducing solution was made alkaline with hIgO or N a O H . T h e behavior of t h e method in t h e presence of organic m a t t e r was next studied: 300 cc. of t h e soil extract high in organic m a t t e r were measured into Kjeldahl flasks, t h e n I O cc. of a previously analyzed potassium nitrate solution ( 3 . 9 6 mg. nitric nitrogen) a n d j cc. of a n analyzed ammonium sulfate solution (4.98 mg. ammonia nitrogen) were added. One g r a m of magnesium oxide was added, t h e ammonia distilled off (30 minutes), a n d flask a n d contents 1 J. A m . Chem. Soc., 22 (1900), 259. This procedure was used in aU distillations reported in this paper, which were performed with t h e regular Kjeldahl distilling apparatus.
526
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
cooled; t h e water distilled off was replaced with a m monia-free water, 3 grams Devarda’s alloy were added a n d t h e reduction a n d distillation proceeded with. T h e analyses gave 5.05 a n d 5 . 1 6 mg. ammonium nitrogen, a n d 0 . 3 2 a n d 0 . 3 6 mg. nitric nitrogen. After reduction t h e solutions gave intense diphenylamine reactions. T h e very low results for nitric nitrogen confirm Valmari’s s t a t e m e n t t h a t t h e method fails in t h e presence of large a m o u n t s of organic m a t t e r . Clarification of t h e extracts with lime a n d other precipitants, t h e addition of electrolytes, increasing t h e a m o u n t of magnesia, all effected some improvem e n t , b u t did n o t bring t h e method u p t o where i t could be recommended as a quantitative procedure. An additional difficulty with t h e magnesia method is t h e fact t h a t in t h e presence of organic m a t t e r t h e foaming was very b a d a n d could not be avoided by t h e addition of such substances a s paraffin or crude oil. T h e other procedure of t h e Valmari-Devarda method, i. e . , reduction in approximately N / I ON a O H was next tested in pure solutions a n d in t h e presence of organic m a t t e r . Two cc. of our Kjeldahl alkali (50 per cent) added t o 300 cc. of water produced a n alkalinity slightly above 0 . 1 normal ( I O cc. of this neutralized 1 1 . 9 2 cc. of N / I O HzS04). T h e procedure was t h e same a s used before except t h a t on account of foaming, even in pure solutions, distillation could be carried on less rapidly a n d 45 minutes were required t o distill over 10-12 j cc. T h e solutions high i n organic m a t t e r were boiled for 3 0 minutes after t h e addition of t h e alkali a n d s t a n d a r d nitric acid, in order t o expel ammonia. Since there is always danger of some of t h e fine alkaline spray, produced b y t h e rapid evolution of hydrogen, being carried over, t h e contents of t h e receivers were redistilled over magnesium oxide. In order t o show t h e magnitude of t h e error so introduced, t h e results of both distillations are reported. Twenty-five mg. of nitric nitrogen were added in all cases a s N / 2 8 ” 0 3 .
Vol. 7 , No. 6
of organic matter. T h e Valmari-Devarda method, reducing in approximately N / I O alkali, appears t o be t h e more reliable procedure a n d is evidently applicable in t h e presence of organic m a t t e r . 3-MITSCHERLICH-DEVARDA METHOD-The procedure proposed by Mitscherlich a n d Herz for t h e reduction of nitric nitrogen differs from t h e original Devarda method in t h a t a different distillation a p p a r a t u s is used. It differs from Valmari’s method in this particular a n d also in t h e fact t h a t strongly alkaline solutions are used f o r reduction a n d distillation. I t is shown below t h a t for reduction a dilute alkaline solution is preferable t o t h e concentrated one used b y Mitscherlich, although Mitscherlich has shown beyond a doubt t h a t his method gives reliable results. Furthermore, a s mentioned above, reduction in a strongly alkaline solution renders t h e separation of t h e nitric a n d organic nitrogen almost impossible. Of t h e procedures tested, then, reduction with Devarda’s alloy in dilute sodium hydroxide solution is t o be preferred. FACTORS AFFECTING R E D U C T I O N - T h e factors studied were: ( I ) Concentration of alkali; ( 2 ) a m o u n t of alloy; ( 3 ) time. Since MgO solutions are too weak t o effect quantitative reduction in t h e presence of organic m a t t e r a n d solutions N / I O in N a O H are sufficiently strong, a n d since i t is advantageous t o keep t h e concentration of t h e alkali t o . a minimum, determinations were made in solutions high in organic m a t t e r which had been made approximately N / 2 0 in N a O H . T h e conditions were otherwise t h e same as in t h e set of determinations reported above, in which N / I O N a O H in presence of high organic m a t t e r was studied. Only 6 . 7 8 a n d 1 1 . 0 3 mg. of nitrogen were recovered from t h e 2 5 mg. nitric nitrogen added, a n d t h e solutions after reduction gave intense reactions for nitrites with Griess’ reagent. Hence N / 2 0 N a O H is not sufficiently strong t o effect a rapid a n d complete reduction, while according t o Table The concenTABLE 111-REDUCTION OF 25 M G . NITRIC NITROGEN IN APPROXIMATELYI11 N / I O is sufficiently concentrated. N/10 SODIUMHYDROXIDE trations between N / I O a n d N / 2 o were not studied. I N PURESOLUTION W I T H HIGHORGANIC MATTER M g . N found Mg. N found T h e directions in t h e literature v a r y somewhat in First Second Ph2NH First Second PhZNH regard t o t h e a m o u n t of alloy required. S u t t o n l No. dist. dist. reaction No. dist. dist. reaction 1 . . . . . . 24.99 2 4 . 7 3 Faint 6.. . . . 24.98 2 5 . 0 6 None states t h a t j times t h e weight of t h e nitrate should 2 . . . . . . . . 2 5 . 0 2 2 4 . 9 0 Faint 7 . . . . . 24.91 2 4 . 9 0 None 3 . . . . . . . . 2 5 . 1 2 25.01 Faint 8... . . 24.39 24.73 None be used. Valmari uses I t o z grams, while Mitscherlich 4 . . . . . . . . 25.07 24.77 Faint 9 . . . . . 24.45 2 4 . 4 9 None 5 . . ...... 25.22 2 4 . 9 4 Faint a n d Herz obtained with 2 grams t h e nitrogen equivalent 10 . . . 24.65 2 4 . 6 3 None A v ...... 2 5 . 0 8 24.87 A v . . , , 24.68 2 4 . 7 6 of 2 3 . 4 8 cc. N / j o acid as against a t r u e value of 2 4 . 4 0 , Reduction is evidently more complete in t h e pres- while their results quoted above were obtained b y t h e ence of organic m a t t e r . T h e tendency of t h e results application of 3 g . ; i. e . , t h e a m o u n t of alloy which t o be lower under these conditions is no doubt due Valmari recommends, Mitscherlich a n d Herz found t o t h e slight reducing action of t h e organic m a t t e r insufficient. I n order t o obtain more information . during t h e preliminary distillation period. T h a t on this point t h e experiments as shown in Table I V there is less alkali carried over in Nos. 6-10 t h a n in were carried out. T h e reduction of 2 5 mg. nitric 1-5, is t o be a t t r i b u t e d t o t h e fact t h a t , on account of nitrogen was performed in t h e regular manner in 3 0 0 foaming, t h e solutions containing organic m a t t e r cc. portions of pure solutions.. were distilled more slowly. Nos. 2 2 , 2 3 a n d 34 are t h e values obtained after reT h e magnesia method of Valrnari appears t o be distillation over MgO, while t h e other d a t a were reliable if organic m a t t e r is absent. T h e fact, how- obtained from a single distillation. ever, t h a t t h e alkalinity of t h e magnesia itself is not T h e results in Table IV show t h a t t h e recommendasufficient t o effect complete reduction would suggest tion t o use a n a m o u n t of alloy equal t o five times t h e t h a t , although very rapid a n d convenient, t h e method weight of nitrate is unsound. T h e concentration h a d best n o t be indorsed too stongly a s yet. It is of t h e alkali is apparently of more importance t h a n 1 “Volumetric Analysis,” 10th Ed., p. 285 (1910). unreliable in t h e presence of a n y considerable a m o u n t
,
June, 1915
T H E J O C R N A L OF I*VDUSTRIAL A N D E*VGINEERING C H E M I S T R Y
t h e a m o u n t of nitrate. T h e d a t a also clear u p t h e contradictions i n t h e recommendations of Llitscherlich a n d Herz as compared with those of T‘almari. Two grams of alloy are insufficient in strong alkali, while this a m o u n t is sufficient in LIgO solutions TABLEIV-AMOUNT
O F ALLOY REQUIRED TO REDUCE25 M G . X I T R I C -&MOUNTS O F ALKALI h - l T R O G E N I N P R E S E N C E OF DIFFERENT
No 1 2
3
4
50
MgO X/10 alkali Strong alkali(a) Grams b l g S PhzNH hlg. N PhzNH M g P; P h z S H alloy found reac. No found reac. No. found reac. 21 u 19.0.: Strong 31 0 . 5 0 a 21.54 Strong b 22.34 Strong b 1 8 . 0 7 Strong 0 . 7 5 a 2 4 . 9 1 Strong 22 a 24.84 Faint 32 a 16:48 Strong b 24.62 Strong b 1 5 . 9 4 Strong b 2 3 . 3 8 Strong c 25.05 F a i n t ... L 23.42 Strong d 24.27 Strong d 24.56 Strong 23 a 24.78 F a i n t 33 a 2 i : 3 5 Strong 1 . 0 0 a 22.42 Strong b 23.45 Strong b 2 5 . 0 1 None b 22.02 Strong c 24.78 Faint f. 23.52 Strong d 24.81 None d 7 4 . 9 1 Strong . 2 . 0 0 a 25.00 F a i n t ... 34 a 24139 Faint b 25.00 F a i n t ,.. h 24.94 Faint ... c 2 5 , 1 5 Faint .., ... ... d 25.15 Faint ( a ) 2 5 cc. of 50 per cent NaOH in 300 cc. Mitscherlich and Herz used cc. of concentrated alkali per 200 cc.
a n d one g r a m is sufficient i n W / I O solutions. T h e superiority of N / I O N a O H solutions over more concentrated ones in t h e m a t t e r of t h e alloy used is a p parently due t o t h e fact t h a t in t h e former case practically all t h e hydrogen is evolved a t I O O O , while i n t h e l a t t e r case much of i t is evolved a t lower temperatures. T h e fact t h a t MgO solutions, i n which practically all t h e hydrogen is evolved a t I O O O , require more alloy t h a n solutions N / I O i n N a O H is perhaps d u e t o t h e fact t h a t in these extremely weak alkaline solutions more hydrogen is evolved from t h e larger surface of t h e larger a m o u n t of alloy. At a n y r a t e , i n view of t h e d a t a on N I I O K a O H a n d on strongly alkaline solutions, t h e former solutions were heated during t h e reduction as strongly as foaming would permit. T h e time required for quantitative reduction of z j mg. of nitric nitrogen was next determined. The 300 cc. of solution contained in a Kjeldahl flask was heated t o boiling in minimum time, which i n each case was 8 minutes. T h e boiling was continued for t h e lengths of t i m e indicated below, t h e seething solution quickly filtered with suction a n d t h e filtrate tested with diphenylamine. No.
.
Minutes boiled. . . . . PhzNH reaction.. . . .
I
I1
0 Strong
2.5 Strong
I11 5.0 Faint
IV 10.0 Faint
T h e d a t a show t h a t reduction h a d proceeded sufficiently a t t h e e n d of five minutes. O p t i m u m conditions for quantitative reduction are, therefore, N / I O N a O H a n d one g r a m of alloy, t h e t i m e required for t h e expulsion of t h e ammonia being ample t o allow quantitative reduction. C H O I C E O F D I S T I L L A T I O X APPARATUS-The almost endless number of devices t h a t have been proposed f o r t h e distillation a n d quantitative determination of ammonia m a y be divided into t w o general classes, I n t h e first of these t h e condenser, usually block tin, is cooled with water, a n d i n t h e second t h e water cooling is dispensed with, a n d t h e ammonia is transferred a n d absorbed b y passing t h e steam directly into t h e s t a n d a r d acid of t h e receiver. Those of t h e first t y p e are preferable for t h e carrying o u t of routine determinations in large numbers where a convenient a m o u n t of nitrogen m a y be t a k e n for analysis, while those of t h e second t y p e are better suited for refined
527
procedures on small a m o u n t s of nitrogen. Obviously t h e n a device of t h e second class is t o be preferred for use i n determinations of nitric nitrogen in soils in which t h e a m o u n t s of nitrogen dealt with are very limited indeed a n d in which every possibility of refinement must be t a k e n advantage of. T h e most desirable a p p a r a t u s of this second class is evidently t h a t of hlitscherlich.’ T h e Pannertz2 modification of t h e original Devarda, a n d t h a t more recently devised by VC’. S. Allen3 are both inferior t o ?rIitschcrlich’s apparatus, because ( I ) t h e scrubbing of t h e vapors is less complete, a n d ( 2 ) t h e solubility of t h e alkali contained in t h e glass distillation t u b e s vitiates titrations with N/ jo solutions. JTe, therefore, adopted for subsequent4 work t h e a p p a r a t u s shown in Fig. I , which is essentially t h a t of llitscherlich. a n d which constitutes Mitscherlich’s modification of t h e original Devarda method. X few slight modifications have been made in t h e apparatus. T h e Hugerschoff distillation bulb used b y Mitscherlich is replaced b y t h e Hopkins t u b e B; t h e 2 5 0 cc. Kjeldahl scrubbing flask is replaced b y t h e zoo cc. round-bottomed ring-necked Jena I
/I
‘
Fig.2
flask D; a n d t h e delivery ends of t h e distillation t u b e s C a n d E are provided with slight bulb-like enlnrgements perforated with I m m . holes. This last improvement n o t only insures better scrubbing in flask D a n d better absorption in flask F , b u t b y producing more even ebullition reduces t h e danger of spattering. Flask F is a 300-cc. seasoned Jena Erlenmeyer. Alitscherlich a n d Herz call special attention t o t h e necessity of t h e distillation t u b e E being made of quartz. Trials with such substances as Jena glass, borate silica Jena glass, a n d porcelain, failed t o give satisfactory results. Only when quartz was used were t h e probable error of distillation a n d titration kept sufficiently low. Since Mitscherlich a n d Herz report 366 d e t e r m i n a t i o n ~ ~conducted t o ascertain t h e suitability of substances other t h a n quartz a n d failed t o get a satisfactorily low probable error of Jahr., 38 (1909), 280. Treadwell-Hall, “Analytical Chemistry,” Vol. 11, 3rd Ed., p. 454 (1913). 3 Orig. Comm. 8 t h I n t . Cong App C h e m , Vol. I , pp. 19-31, New York (1912). 4 All distillations u p t o this point had been carried o u t with the ordinary Kjeldahl distilling rack. 6 Landw. Jahrb., 38 (1909), 302. 1 Landw.
2
528
T H E J O U R N A L OF I N D U S T R I A L A N D ENGIAVEERING C H E M I S T R Y
t h e blank distillation with a n y other material, we accepted their conclusions on this point without further experimentation.’ Approximately 40 cc. of water are placed in flask D, together with a pinch of magnesium oxide a n d one of magnesium sulfate. T h e former facilitates t h e expulsion of ammonia, although Mitscherlich a n d Herz found i t unnecessary,2 while, when magnesium sulfate is present a n d s p r a y containing sodium h y droxide is carried over from flask A t o D,t h e hydroxyl ions are a t once precipitated as magnesium hydroxi’de, a n d t h e probability of alkali being carried i n t o flask F is reduced. T h e time required t o completely reduce t h e nitric nitrogen a n d drive it quantitatively i n t o flask F was determined on 25-mg. portions of nitric nitrogen, which were reduced with I g. alloy in N / I O N a O H . T h e reduction a n d distillation were carried on for varying periods. T h e distillation was controlled so as t o avoid a n y danger from loss due t o spattering from flask F . Extraneous heat was not applied t o flask D . No. Minutes reduction and distillation. Milligram nitrogen recovered.. .
. . . . .. .. . . ..,
I 20
24.38
I1 30 24.74
I11 40 25 .OS
IV 40 25 .05
The above d a t a show incomplete recovery in a 2 0 min. period, doubtful in 30 min., while satisfactory results are obtained in 4 0 minutes’ reduction a n d distillation. A period of 4 0 minutes was, therefore, adopted for all subsequent work. Blank reductions a n d distillations, using N-free reagents, showed very small amounts of acid neutralized. I n t e n runs t h e average was equal t o 0.09 ’cc. of N / j o H2SOa, with maximum a n d minimum values of 0.18 a n d 0 . 0 1 cc., respectively. This shows t h a t no appreciable a m o u n t of spray is carried over nor alkali dissolved out of t h e glass p a r t s of t h e apparatus. P R O B A B L E E R R O R O F T H E METHOD-NO description o r development of a method is complete without some consideration of t h e accuracy attainable with i t , which property of a method is best expressed as its probable error calculated by t h e method of least squares. T h e choice of a method for a particular line of investigations is made somewhat a t random unless there is some knowledge a t hand relative t o t h e accuracy attainable with t h e different methods applicable. We have, therefore, devoted some attention t o t h e m a t t e r of probable errors, a n d , although our values are calculated f r o m only I O determinations, t h e y serve t o shorn- t h e order of magnitude of t h e error of t h e results yielded b y t h e method. T h e probable error of t h e complete method was determined in pure solutions on 5- a n d nj-mg. portions of nitric nitrogen, using N / I O alkali in t h e reducing solution, I gram alloy, a n d distilling for 40 minutes in t h e Xitscherlich apparatus. These probable errors are certainly t o be regarded a s quite small. T h a t obtained with N / j o solutions is of practically t h e same magnitude a s t h a t reported b y llitscherlich a n d Herz who used N / j o solutions 1
The tubes which we used were obtained from Hanovia Chemical
Co., Newark, N. J., and were made according to specifications shown in Fig. 2, at a cost of $7.80 each. Thin-walled tubes can he purchased at a
much lower cost, but because of their fragility are not to be recommended. * Landw. Jahrb., 38 (1909), 306.
V O ~7. , NO.6
altogether. Since t h e reduction is effected in weakly alkaline solutions a n d will proceed quantitatively in t h e presence of high organic m a t t e r , t h e method TABLE V-PROBABLE
ERROR OF
cc. N/50
No.
.
l . . . .. 2...... 3 ...... 4..,...
Has04
17.76 17.76 17.76 17.67 s... 17.83 6 . . . . . . 17.73 7 17.77 8. 17.70 9 . . . . . . 17.70 1 0 . . . . . . 17.67 A v . . . . . 17.735 Theoretical value. . , , , , . . , Probable error.. . . , . . . . . . Deviation from theoretical value, . . . . , , . . . . . , . , . .
..
... ..... I . .
NITRIC NITROGEN DETERMINATION
Mg.
nitroaen 4.976 4.976 4.976 4.951 4.996 4.968 4.979 4.960 4.960 4.951 4.969 5.000 10.009 -0.031
cc.&SO4 N/10
nitroeen Mg.
17.80 17.79 17.83 17.81 17.73 17.79 17.78 17.81 17.76 17.82 17.79
24.94 24.92 24.98 24.95 24.84 24.92 24.91 24.95 24.88 24.97 24.93 25.00 AO.028
----
-0.01
is t o be regarded as having attained t h e aim of this work, and, it is believed, can later be perfected t o a point where it will meet t h e requirements of a physiological s t u d y of nitrification. DISCUSSIOX
CONSIDERATIONS-A few additional points deserve attention in regard t o t h e above results. Apparently too much has been claimed for t h e aluminum reduction method. Aside from t h e objection t o it t h a t i t involves transfer of alkaline solutions containing ammonia, it is certainly more sensitive t o some forms of organic m a t t e r t h a n is t h e reduction with Devarda’s in solutions N / I O or stronger in N a O H . Reduction in solutions made alkaline with MgO has much t o commend i t , since t h e error due t o carrying over of s p r a y is avoided, in pure solutions a t least; i t is very rapid, since t h e a m o u n t of hydrogen evolved is too small t o produce foaming, a n d , therefore, t h e reduction a n d distillation may be performed in 30 minutes. -4 very large a m o u n t of effort was spent in this work in a n a t t e m p t t o obtain a reliable a n d accurate method b y t h e reduction in t h e presence of MgO, a n d distillation with a n ordinary Kjeldahl rack, a method which would be extremely simple a n d rapid. T h e quest was finally abandoned, however, partly because t h e reduction in presence of MgO is of doubtful value a n d p a r t l y because t h e Kjeldahl rack itself is less suited for refined work t h a n t h e a p p a r a t u s proposed b y Mitscherlich a n d Herz. Of course, t h e MgO reduction might be employed in ordinary soil extracts a n d t h e N/IOsolutions in those high in organic m a t t e r , a s originally recommended b y Valmari, yet t h e fact t h a t solutions N/20 in N a O H are unreliable for t h e reduction in t h e presence of high organic m a t t e r indicates t h a t a very low a m o u n t Qf organic matter would prevent quantitative reduction of nitric nitrogen in M g O solutions which are less t h a n N / I O O O ,a n d justifies, in our judgment, t h e rejection of this procedure €or t h e determination of nitric nitrogen in soil extracts, where varying a n d uncertain a m o u n t s of organic m a t t e r are always present. Solutions approximately N / I O in N a O H are apparently t h e lowest alkalinity t h a t can be safely used in reductions with Devarda’s alloy in soil extracts. It is superior t o reduction in t h e more concentrated solutions n o t only i n t h e points mentioned above b u t because there is less danger of t h e flask contents GENERAL
June, 1 9 1 5
T H E J O C R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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boiling over as a result of violent action, a n d such method, is t h e most accurate a n d reliable t h a t has devices as a water bath’ under t h e generating flasks yet appeared for t h e determination of nitric nitrogen m a y be dispensed with. Using N/IO solutions for re- in soil extracts. LABORATORY O F S O I L BIOLOGY, duction a n d t h e hIitscherlich apparatus, extremely acOHIOAGRICULTURAL EXPERIMENT STATION,WOOSTER curate results are obtained quite easily. P R O C E D U R E RECOVNEKDED-The procedure finally recommended for t h e determination of nitric nitro- THE LOSS OF NITROGEN AND ORGANIC MATTER IN CULTIVATED KANSAS SOILS AND THE EFFECT gen in soil extracts, which is t o be designated as t h e OF THIS LOSS ON THE CROP-PRODUC1‘ a1mari - L’lit s che r 1i ch - De v ar d a method, a n d which ING POWER OF THE SOIL1 is regarded as t h e most reliable t h a t has yet appeared, B y C 0. SWANSOX in t h a t it combines t h e strong a n d eliminates t h e Received January 22, 1915 weak features of each, is as follows: F o r t y cc. of T h e decrease in t h e crop-producing power of t h e water. a small pinch of magnesia a n d one of mag- soil is a fact familiar t o all students of agricultural nesium sulfate are added t o flask D of t h e Mitscher- problems. T h e larger productiveness of virgin soils lich a p p a r a t u s (Fig. I). Twenty-five cc. of stand- as compared with t h e productiveness of these same ard acid a n d 6 0 cc. of neutral redistilled mater are soils after they have been under cultivation for several placed in flask F . T w o hundred a n d fifty or 3 0 0 cc. decades is well known by t h e men who broke u p t h e of aqueous soil extract are placed in a joo cc. Kjel- virgin prairie sod a n d have continued t o cultivate dah1 flask, 3 cc. of 5 0 per cent sodium hydroxide t h a t soil for half a lifetime or more. If we make a a d d e d , t h e mouth of t h e flask closed with a small s t u d y of t h e figures compiled b y t h e State Board of funnel t o prevent spattering, a n d t h e contents of Agriculture for t h e forty-year period, 1872-1911,we t h e flask boiled for 3 0 minutes. T h e mater which shall find t h a t t h e leading crops show a n average dehas boiled off is replaced, a n d , after cooling, I g. of crease i n crop production. I n Brown County t h e Dei-arda’s alloy ( 6 0 mesh), a n d a small piece of paraffin average corn production for t h e first twenty-year are added a n d t h e flask connected with t h e a p p a r a t u s ; period, 1872-1891, was 36 bu., a n d for t h e second reduction a n d distillation are carried on for 40 minutes. twenty-year period, 1892-1911, was 3 0 bu. Riley T h e receiver contents are t h e n cooled, 4 drops of 0.02 C o u n t y produced a n average of 3 3 b u . in t h e first per cent solution of methyl red added, t h e excess acid period, a n d z j bu. in t h e second. I n Sedgwick County, is nearly neutralized, t h e liquid boiled t o expel COS, t h e first period shows a n average of 3 2 bu., a n d t h e choled t o 1 0 - 1 j o a n d t h e titration completed. second 2 1 bu. “ M o r e live s t o c k ” is mentioned b y some people as t h e panacea for this soil. If t h a t b y S U M MARY I--A heduction method is considered t o be prefer- itself were t h e cure, t h e n a typical live stock county, able for t h e determination of nitric nitrogen in soil where more grain is fed t h a n raised, should not show extracts. Of such procedures only t h e modified this decrease in crop production. Butler is such a Devarda a n d aluminum reduction methods gave county. I n t h e period between 1872 a n d 1891, t h e average corn production was 3 2 bu. per acre, a n d in promise of meeting our requirements. 11-Reduction with Devarda’s alloy in hIgO solu- t h e second period, 1892-1911,t h e average was 2 6 bu. tions. a n d t h e aluminum reduction method, did It is not necessary t o give more figures t o prove this not give reliahle results in t h e presence of high or- fact. Any one who makes a s t u d y of t h e figures compiled b y t h e State Board of Agriculture will find ganic matter. 111-Reduction with Devarda’s alloy in strongly t h a t there is a n average decrease in crop production alkaline solutions renders separation of t h e organic a n d t h a t this is t r u e in Butler, Greenwood a n d Chase, a n d nitric forms of nitrogen almost impossible, re- typical live stock counties, as well as Brown, Sedgwick a n d Russell, where t h e t y p e is called grain farmipg. quires a larger a m o u n t of alloy t h a n does reduction Seeds adapted t o climate and soil is a n important in solutions S I O in S a O H , a n d t h e reaction is so violent t h a t care must be continually exercised t o factor in crop production. Seed improvement m a y not have made all t h e progress promoters of agriculprevent a loss of t h e determination. IT-Reduction with Devarda’s alloy in solutions t u r e desire, b u t t h a t t h e seed used b y farmers in genAT I O in N a O H gave reliable results in t h e presence eral is more a d a p t e d t o t h e climate a n d soil t h a n t h e of high organic m a t t e r . I t requires a small a m o u n t seed used t h i r t y or forty years ago no student of agriof alloy. t h e reaction proceeds quietly, a n d t h e action culture will deny. Instruments of tillage have also of such dilute alkaline solutions on organic m a t t e r is been improved. T h e better t h e soil is cultivated, very slight. Reduction in solutions N , / 2 0 in NaOH other things being equal, t h e greater its crop-prois unreliable in t h e presence of high organic matter. ducing power. I n spite of these two factors which \’-The Mitscherlich a p p a r a t u s is superior t o t h e should have increased t h e a\-erage crop production other distillation devices for t h e manipulation of t h e per acre, we have a decrease. T h e Chemical Department of t h e Agricultural ExDe var d a method . T71-The method proposed, which combines t h e periment Station has made a chemical analysis of about 2 5 0 samples of Kansas soil t a k e n from thirteen desirable features of t h e Valmari-Devarda a n d of t h e Mitscherlich-Devarda procedures, a n d which is different counties. These samples are analyzed for t o be designated as t h e Valmari-Mitscherlich-Devarda total nitrogen, phosphorus, potassium, calcium, or1
r s e d by W. S . Allen, LOG.c i l .
1
Read before the Kansas Academy of Science, December 2 2 , 1914
