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b u t little variation, it may be convenient t o prepare curves t o obviate t h e necessity of calculating specific gravities and heating values. For example, if t h e natural gas usually contains less t h a n z per cent nitrogen, three curves might be drawn t o show t h e relationship between specific gravity (or heating value as t h e case may be) and t h e value of m-one curve for zero per cent nitrogen, one for I per cent, and one for z per cent. In this way, if t h e proper scale be chosen, t h e specific gravity or heating value may be expeditiously and accurately obtained from t h e curves without calculations. SUM MARY
I - T ~ o modifications of t h e apparatus for t h e analysis of natural gas are described: one a n indicator for complete combustion of t h e sample, and the other t h e substitution of Pyrex glass for the glass ordinarily employed in t h e combustion pipette. 2-The calculation of results of natural gas combustions according t o t h e theoretical equations is discussed. A statement of t h e average number of carbon atoms per molecule of paraffin hydrocarbon and t h e percentage of paraffin hydrocarbon in t h e natural gas is recommended as being more logical t h a n a statement of the percentages of two hydrocarbons forming a mixture equivalent, as regards combustion data, t o t h e one actually burned. 3-Tables of correction factors have been prepared for use in correcting results obtained by t h e theoretical equations for differences in t h e molecular volumes of t h e gases considered. A simple method of applying these corrections has been worked out and illustrated. 4-The necessity for accuracy in t h e measurement of gas volumes is shown by means of various simple calculations. ;-The calculation of specific gravity and heating value is discussed from t h e point of view of t h e theoretical and actual values. 6-A printed form is suggested which may be found useful in recording and computing results. UNITED NATURAL GAS
COMPANY
014 C I T Y , P I ; N V b Y L V . 4 N I A
THE DETERMINATION OF TOTAL NITROGEN INCLUDING NITRIC NITROGEN By I3. S. DAVISSON A N D J. T. PARSONS Received September 3, 1918 INTRODUCTION
T h e development of methods of nitrogen determination suitable for t h e attack of soil biological problems has been t h e subject of extended study in this laboratory.’ Soil biological investigations, approached from t h e physiological and biochemical viewpoint, require chemical methods of nitrogen determination of extreme accuracy and reliability, applicable t o amounts of nitrogen ranging from I t o 2; mg. contained in 2 5 0 cc. of soil extract or physiological solution. Naturally, 1 T h e general problem of refinement of nitrogen methods was outlined and begun by Dr. E. R. Allen, who has had general direction of the work and has assisted in the preparation of this manuscript. Papers which have appeared on this general project are: THISJOURNAL, 7 (1915), 521; J . Am. Ckem. SOC.,38 (1916), 1683; TIIISJOURNAL, 8 (1916), 896; I b i d . , 10 (1918), 600.
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methods for t h e determination of total nitrogen, including nitric nitrogen, are required. This particular problem has been t h e subject of a very considerable amount of discussion and experimentation, especially among chemists concerned with t h e analysis of fertilizers. The somewhat extensive referce work by t h e Association of Official Agricultural Chemists has resulted in t h e more or less arbitrary adoption of certain methods which are designated as official. T h e fact t h a t t h e methods have received such designation does not necessarily remove serious objections, b u t recognizes them as probably t h e most reliable of t h e existing methods for such determinations. Although t h e standards of accuracy have not been as high1 a s those in this laboratory, a satisfactory method has not been formulated. The existing uncertainty of t h e procedures in vogue is revealed, for instance, by recent callings2 for a trustworthy method for the determination of total nitrogen including nitric nitrogen. It was imperative, therefore, t h a t this problem be attacked with t h e aim of t h e development of a method capable of a high degree of accuracy. H I S T0 R I C A L
I t is neither necessary nor desirable t o give a review of all t h e work dealing with t h e problem of determining total nitrogen including nitric nitrogen. T h e large amount of literature upon t h e subject, dealing as it does almost entirely with investigations whose aim was mediocre accuracy, shows t h a t even as measured by such a standard t h e various methods have not as yet reached a point where they yield uniformly satisfactory results. Two general types of procedure are employed for determining total nitrogen including nitric nitrogen. These two forms of nitrogen are determined together as ammonia b y reducing t h e nitric nitrogen previous t o t h e Kjeldahl digestions, or they are determined separately, in which case t h e nitric and ammonia nitrogen are leached from t h e sample and determined together after t h e reduction of t h e nitric nitrogen. The residue from t h e leaching is then Kjeldahlized for t h e remaining nitrogen. This latter t y p e of procedure might be used where t h e organic nitrogen exists in t h e insoluble form b u t is frequently not applicable t o biological studies. Soon after t h e introduction of the Kjeldahl method i t was observed t h a t t h e nitrates were not completely converted t o ammonia by t h e original procedure. Advantage was then taken of t h e fact t h a t t h e quite readily formed nitrophenols were more easily reduced t h a n t h e inorganic nitro compounds, and salicylic acid or phenol was added t o t h e sulfuric acid sample t o furnish conditions for t h e nitration of a phenol. T h e resulting nitrophenol was then reduced, with t h e aid of a reducing agent, t o an aminophenol which was subsequently completely hydrolyzed i n t h e boiling alkaline solution with the liberation ol ammonia. THE GUKXING-JODLBAUER NODIFICATION3 Of the With the exception of the work of Rhtscherlich and associates Lipman, A m . Fevtzlisev, i l l ] 41 (1914), 33, Breckenridge, THIS JOURNAL, 9 (1917), 1054. 8 Olsen, “Quantitative Chemical Analysis,” 5th E d , 1916,p 288 1
2
Apr., 1919
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
Kjeldahl method consists in treating t h e sample with 30 cc. of sulfuric acid containing 2 g. of salicylic acid, t h e solution being kept cool and shaken. Two grams of zinc dust are t h e n added and after 2 hrs. t h e solution is heated gently a t first a n d t h e digestion completed after t h e addition of I O g. of potassium sulfate. F O R S T E R ' S MODIFICATION-Having failed t o obtain complete recovery of t h e nitric nitrogen by t h e Gunning- Jodlbauer modification, Forster used sodium thiosulfate as t h e reducing agent. According t o his recommendation' t h e sample is treated with a mixture of 30 cc. sulfuric acid, I g. salicylic acid, and I t o z g. of sodium thiosulfate, a n d t h e solutions heated slowly a t first a n d finally digested. THE
ULSCW MODIFICATION
OF
KJELDAHL'S
XETHOD~
consists in t h e reduction of t h e nitric nitrogen b y means of hydrogen evolved from t h e action of sulfuric acid ( I . 3 j sp. gr.) and 2 t o 3 g. of reduced iron. The sample is treated with t h e acid and iron, allowed t o stand until t h e violence of t h e reaction ceases and then digested after adding potassium sulfate and more sulfuric acid. I n t h e analysis of fertilizers t h e nitric nitrogen is usually leached from t h e sample and determined separately by t h e Ulsch reduction method. The residue is then Kjeldahlized for t h e organic nitrogen. Wint;on3 used t h e Gunning- Jodlbauer modification arid found t h a t more consistent results were obtained when t h e mixture of acids a n d sample was allowed 'to stand 2 hrs. previous t o t h e addition of t h e zinc dust. After t h e addition of t h e zinc dust, t h e mixture was heated slowly and digested for 2 hrs., and t h e digestion completed after adding I O g. of potassium sulfate. Sherman4 compared Winton's procedure with t h e procedures where t h e solution stood only a short time before adding t h e zinc, a.nd t h e use of sodium thiosulfate for reducing t h e nitrates. He concluded t h a t Winton's modification gives bekter results t h a n either of t h e other procedures. Sherman thinks t h e long digestion before adding t h e zinc is advisable, especially if much chloride is present, and t h a t even t h e n t h e method is hardly dependable. Duggar a n d Davis6 employed Forster's modification fcr determining total nitrogen including nitric nitrogen in culture solution used in studying nitrogen fixation. They found t h a t only b y using 3 g . sodium thiosulfate a n d allowing I O t o 1 5 min. after apparent decomposition had taken place before digestion was completed, could complete recovery be obtained. I t should be stated, however, t h a t the official method calls6 for t h e use of 5 g. of sodium thiosulfate, which is even more t h a n the amount employed b y Duggar a n d Davis. Schenke' recommends t h e Ulsch-Kjeldahl method for determining total nitrogen. After reducing 1 Olsen, "Quantitative Chemical Analysis," 5th Ed., 1916, p. 288. 2 Z . anal. Chem., 30 (18911, 175-182, after Street i n Division of Chemistry, U. S. D e p t . of Agr., Bull. 35, p. 88. 3 Conn. Agr. Expt. Sta., B d l . 112 (1892), 4. 4 J . A m . C h e m . Soc., 17 (1895), 567. 6 Annals of Missouri Botanical Garden, 3 (1916), 413. 6 U. E;. Dept. of Agr., Bureau of Chemistry, Bull. 107 (1908), 8 (Rewised). 9 C h o n . Ztg., 17 (1893).
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t h e nitric nitrogen he uses sulfuric acid containing phosphorus pentoxide, some cupric oxide, and completes t h e digestion. He claims higher results are obtained b y this method t h a n by t h e use of phenol and zinc. The report1 upon t h e Ulsch method for reducing nitrates shows t h a t t h e method tends t o give low results in t h e hands of different chemists. Buhlert and Fickendey2 found t h a t t h e method gives low results for nitric nitrogen when much soluble humus substance is present. Mitscherlich and her^,^ working in t h e field of soils and plant nutrition, found t h a t none of t h e methods in vogue for determining nitric nitrogen would give reliable results. They were unable t o obtain theoretical results b y t h e use of phenolsulfonic acid a n d zinc dust, sodium hydroxide a n d zinc-iron dust, or by Jodlbauer's or Forster's method. Since t h e y were unable t o recover this deficiency b y digesting t h e residues according t o Kjeldahl for total nitrogen or by t h e use of larger amounts of reducing substances, they concluded t h a t t h e loss was due t o t h e evolution of gaseous nitrogen. They chose Devarda's procedure which effects t h e reduction in an alkaline solution b y means of a zinc-copper-aluminum alloy, a n d as t h e result of a careful and extended study perfected a method4 for determining total nitrogen including nitric nitrogen. Their procedure is as follows: A weighed amount of soil, j t o I O g., and 2 0 0 cc. of water, or a definite volume of nitrogen-containing solution (up to 800 cc.) are brought into a I liter Kjeldahl flask and 3 g. of Devarda's alloy added. The flask is closed with a 2-hole rubber stopper carrying a funnel and a still head terminating in a delivery tube which reaches to the bottom of a joo cc. Kjeldahl flask containing 60 cc. of HSO, diluted with 20 cc. of water. The nitrate solution is made strongly alkaline by adding j o cc. of concentrated sodium hydroxide, the funnel closed, the flask carefully heated, and the solution distilled as far as possible. The ammonia nitrogen from the sample and that from the reduction of the nitrates is absorbed by the strong acid. When the distillation is complete, the flame is removed and the acid allowed to suck back into the flask containing the alkali. The flask is again heated and the steam used t o wash out the flask which contained the strong acid. The condensed water is allowed t o suck back and the process repeated. The contents of the flask are then digested until the solution becomes clear and bluish green. All the nitrogen of tHe sample exists now as ammonium sulfate as in the regular Kjeldahl digestion. The melt is diluted with a definite volume of water and dissolved by careful warming. I n determining total nitrogen of soils, only a n aliquot is used for distillation in order that a small amount of the salt may be present in the distilling flask. The distillation is made by adding alkali and scrubbing the steam through water containing a pinch of magnesium oxide and one of magnesium sulfate before passing into the standard acid, no condenser being used.
Extremely accurate results were obtained. I n deed these workers concluded t h a t as a result of their work it was possible t o determine t h e total nitrogen in dilute solutions with a n accuracy of * O . O I mg. 1
Convention of Assoc. Official Agr. Chemists, Bull. 35 (1892), 73 and
2
L a n d w . Viers.-Sta., 63 (1909), 239. Landw Jahvb., 38 (1909), 279. I b i d , 38 (1909), 279, 533.
88. 3 4
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Comparative results' on a garden soil showed this method t o give results I O ,4 per cent higher t h a n t h e Kjeldahl-Jodlbauer, and 7 . 5 per cent higher t h a n t h e Forster method. T h e authors attributed this t o t h e fact t h a t they could determine quantitatively t h e nitrate nitrpgen, which was apparently not completely possible up t o this time. It has recently been shown in this laboratory2 t h a t t h e quantitative reduction of nitrates can be accomplished b y t h e use of a small amount of Devarda's alloy in N / I O alkaline solutions. One gram of alloy is sufficient t o reduce 2 5 mg. of nitric nitrogen in 2 5 0 cc. of solution and t h e reduction is complete in I O min. alter t h e solution begins boiling. T h e method yielded results for nitric nitrogen essentially as accurate as those reported by Mitscherlich and Herz for total nitrogen including nitric nitrogen. DISCUSSION
Although t h e Gunning-Jodlbauer and Forster modifications have long been in use for reducing t h e nitric nitrogen previous t o t h e Kjeldahl digestion, there exists considerable disagreement as t o t h e accuracy of t h e results obtained b y these procedures. The methods do not give concordant results in t h e hands of different chemists, a fact which compels one t o question their accuracy. The most probable sources of error are t h e loss of gaseous nitrogen and t h e lack of complete reduction of the nitric nitrogen. It is important t h a t all t h e nitric nitrogen enter into t h e nitrophenol combination before reduction is made. The proper conditions for quantitative nitration of a phenol cannot be produced in dilute aqueous solutions and methods dependent on such a reaction are inherently liable t o error when applied t o these conditions. As concerns t h e Ulsch method, i t has been and still is widely used, yet more or less uncertainty exists as t o t h e accuracy of t h e procedure. The method has been found t o give unreliable results in the presence of any considerable amount of organic matter, a condition which is constantly encountered in biological studies. T h e work in this laboratory on nitric nitrogen and t h e work of Mitscherlich and Herz on total nitrogen, including t h e nitric form, present an appreciably higher degree of accuracy t h a n is characteristic of t h e other work mentioned above. T h e combination, therefore, of t h e features of the method of this laboratory for nitric nitrogen with those of t h e method of Mitscherlich and Herz for total nitrogen including nitrates appeared promising, and constitutes t h e main part of t h e work reportedinthis paper. A brief study of t h e Gunning-Jodlbauer, t h e Forster, and t h e Ulsch modifications of the Kjeldahl method was also included.
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sists of a glass condenser made of Pyrex glass tubing and water cooled. The steam is scrubbed through a magnesium oxide solution previous t o condensation, thus removing all danger of alkali being carried into t h e receiver. The receivers were 2 5 0 cc. Pyrex Erlenmeyer flasks. The condensers were cooled for 2 5 min. after distillation started and then drained a n d t h e distillation continued for I O min. By using this procedure t h e volume of t h e receiving flask was kept below 1 5 0 cc. S T A N D A R D soLuTIoNs-The materials and methods of preparation are t h e same as those used in former work.' S O L U T I O N S HIGH I N O R G A N I C MATTER-These SOlUtions were prepared from urea and asparagine and from a mixture of soil and manure extracts. T h e latter solution waf treated with dextrose, and after becoming nitrate-free i t was sterilized by a few drops of chloroform and preserved in a glass-stoppered bottle. These solutions were carefully standardized by a series of Kjeldahl determinations. BLANK DETERMINATIONS-Many chemicals, especially sodium hydroxide and sulfuric acid, carry some nitrogen which necessitates t h e use of blanks in total nitrogen determinations. A large number of blanks were run upon t h e reagents and an average taken for t h e correction t o be made. All d a t a reported have had such corrections made where necessary. K J E L D A H L DIGEsTIoivs-Several procedures are in vogue for Kjeldahl digestions, and while it is apparent t h a t reliable results are obtained by more t h a n one procedure, it is equally apparent t h a t the best procedure has not yet been established. I n this work, 20 t o 3 5 cc. of sulfuric acid, 0 .5 g. cupric oxide and 5 g. of potassium sulfate were used and t h e digestions continued for about one hour after the solution became clear. Where Devarda's alloy was used, no additional copper was used. G U N N I N G - J O D L B A U E R A N D FORSTER MODIFICATIONS-
The procedure followed in both cases was t h e same as t h a t recommended as official. A pure solution of sodium nitrate was measured into a 500 cc. Kjeldahl flask and diluted t o 2 0 0 C C . ~ I n t h e case of t h e former modification, t h e sulfuric and salicylic acid mixture was added and t h e reduction made with 2 g. of zinc dust, and t h e digestion then carried out slowly until t h e solution became clear. I n t h e case of t h e second modification, 5 g. of crystallized sodium thiosulfate were used together with I g. of salicylic acid and 3 0 cc. of sulfuric acid. The d a t a are reported in Table I. TABLEI Gunning-Jodlbauer 1 3 . 7 0 mg. Found Ma.
. . . . . . .. .. .. .. .. ....
MODIFICATION. . .. NITRICNITROGEN TAKEN.
Forster's
1 3 . 7 0 mg.
Found Ma.
EXPERIMENTAL
DISTILLING APPARATUS'-The apparatus finally adopted more or less provisionally in this work conLandm. Jahvb., 8.3 (1909), 533. THISJOURNAL, 7 (1919, 521. In the rather extended work which has been carried out in this laboratory on nitrogen methods numerous difficulties have been encountered 1
2
a
with different distillation devices. The development of the proper type of distillation procedure and apparatus is a quite complicated matter and will be discussed in a later paper.
AVERAGE DEVIATION FROM ACTUAL VALUE
A: ii
9.30 -3.96
THIS JOURNAL, 10 (1918), 600. were made to a volume of 200 cc. because that volume of soil extract is generally employed. 1
* The solutions
Apr., 1919
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
T h e figures reported here are representative of a great amount of d a t a obtained with these two procedures. T h e errors are very high but a careful purification of chemicals and checking of conditions did not yield different results. Since theoretical results could not be obtained upon pure solutions with these methods, no experiments were conducted with solutions high in organic matter. When sodium thiosulfate was used it was found t h a t some nitrates were not reduced, but with zinc dust t h e nitrates had disappeared, as shown by qualitative tests. Since t h e nitric nitrogen could not be recovered by the Kjeldahl digestion there must have been a loss of gaseous nitrogen. THE ULSCH MODIFICATION-The procedure recommended as official was used in studying this modification T h e acid solution in which t h e reduction was made was about 1.35 sp. gr. in all cases. Three grams of iron, reduced by hydrogen, were used, and after standing 30 min. the solutions were heated t o boiling for 5 min. Traps were used t o prevent spattering. With pure solutions t h e method may give almost theoretical results, b u t with solutions containing organic matter t h e results are invariably lower t h a n t h e theoretical. I n t h e manure and soil extract with added nitric nitrogen t h e results are much lower t h a n those where t h e urea a p d asparagine were used. The d a t a in Table I1 suffice t o show t h e hehavior of t h e method. While t h e results reported for pure solution are quite satisfactory, many were obtained which were far from t h e theoretical value.
309
tower. T h e apparatus used is shown in Fig. I . T h e tower can be easily made in the laboratory or i t can be made by dealers a t very little cost. The tower should be about 1 l / 4 t o 1'/2 in. in diameter and 14 in. long. A contains the nitrate solution, B is a 6 in. column of glass balls or broken glass rods about '/4 in. in length, and C is a small perforated plate which may be porcelain or made from rubber gasket material. The tower is easily washed after t h e reduction is complete.
-0
TABLE11-THB ULSCHMODIFICATION Urea and Asparagine Organic nitrogen. 17.51 mg. Nitric nitrogen.. 17.92 mg. 10.96 mg. , 17.92 mg. 28.47 mg. Total nitrogen. Found Found Mg. Mg.
SOWITION U S E D . . . . . . . . . . . . . . . . . . . .Pure
Solution
.. . . . .... .
Manure and Soil Extract 2 . 1 8 mg. 10.96 mg. 13.14 mg. Found
-c FIG. I
THE D E V E L O P M E N T O F A N E W P R O C E D U R E
Since t h e above modifications gave little promise a n d since t h e combination of the method for nitric nitrogen developed in this laboratory with the Mitscherlich and Herz procedure appeared promising, this latter ptoblem was next taken up Reduction was therefore effected in N / I O alkali by means of I g. of Devarda's alloy instead of the 3 g. of alloy and strong alkali used by Mitscherlich and Herz. A t the outset, however, the difficulty of incomplete absorption was encountered using a n apparatus essentially the same as t h a t employed by Mitscherlich and Herz. The considerable volume of hydrogen evolved before t h e solution hoils sweeps out with i t some ammonia a n d this ammonia is difficult t o scrub from the mixture of air and hydrogen. An absorption tower readily overcame t h e difficulty, t h e hydrogen being completely scrubbed as it passed through the acid in the
Solutions high in organic matter show a tendency t o foam when reduction is made in a n alkaline solution. This trouble can be greatly overcome by using about 4 drops of ordinary lubricating oil, the oil being easily destroyed subsequently in t h e Kjeldahl digestion. Using the apparatus as described and the procedure outlined below, several determinations were made upon organic solutions with added nitric nitrogen. Determinations were not made upon pure solutions of nitrates, since i t had already been shown t h a t nitrates can be completely reduced in N / I ONaOH with I g. of Devarda's alloy.' T h e results are found in Table 111. This method has given concordant and trustworthy results. It has been applied t o a n organic solution which must be considered 'abnormal and it is there1 LOC.
cit.
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
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fore without doubt applicable t o all conditions arising in biological studies. TABLEI11 Urea and
. . . . . . . . . . . . . . . . . Asparagine
SOLUTIONU S E D . .
Soil and Manure Solutions Extract Organic.. . . . . . . . . . 17.51 mg. 2.18 mg. 2.18 mg. 3 . 1 2 mg. N I T R O ~ ETN A K E N N i t r i c . , . . . . . . . . . . I O . 96 mg. 10.96 mg. ( T o t a l . . . . . . . . . . . . . 28.47 mg. 13.14 mg 5 . 3 0 mg. Found Found Found hig. Mg. Mg. 28.43 13.14 5.29 28.45 13.19 5.29 13.19 5.35 13.05 5.28 13.21 5.36 13.21 5.29 13.20 5.24 13.15 5.20 5.28 13.09 5.28 13.15
1
Average.. .......................... 28.43 Average deviation from true value.. .... 0.047 Probable error. . . . . . . . . . . . . . . . . . . . . . 0.03 Probable error expressed in per cent. , 0.09
.
*+
13.15
+ 0.046
?c 0 . 0 3
0.25
5.30
* 0.035 0.03 0.56
Although t h e work of this laboratory is not concerned with t h e analysis of fertilizers, it was thought advisable t o determine whether t h e method is applicable t o such work. A fertilizer was prepared consisting of potassium sulfate, acid phosphate, with 2 . 5 1 5 per cent of nitrogen as dried blood and sodium nitrate. The sample used was 0 . 5 9 g. The analysis of this fertilizer is shown in Table I V and t h e results show t h a t t h e method is applicable t o such determinations. TABLS IV-ANALYSIS OF FDRTILIZER Nitrogen taken in dried blood.. . . . . . . . . . 12.22 mg. Nitrogen taken in sodium nitrate.. ...... 2.62 mg. True value.. Found Mg. 14.88 14.76 14.74 14.78 14.75
-
...............
-
14.84 mg.
N in Sample Per cent 2.525 2.501 2.498 2.505 2.500
AVBRAGE. 1 4 . 7 8
__
2.505 DISCUSSION
While t h e Gunning- Jodlbauer and Forster modifications may give acceptable results when t h e sample consists of solid material, t h e d a t a reported in this paper show t h a t these procedures are not reliable for studies in biology where large volumes of solutions must be employed. The nitrates in dilute solutions will not all be converted into nitrophenol upon the addition of t h e sulfuric acid and salicylic acid mixture, and therefore unsatisfactory results will be obt ained. The Ulsch method of reducing t h e nitric nitrogen must be considered as not altogether reliable. A serious objection t o t h e method is making t h e reduction in a strongly acid solution by means of hydrogen evolved from a dissolving metal. There is danger of loss of gaseous nitrogen, and t h e formation of ferrous sulfate in t h e presence of nitrates is not desirable. The oxidation of some ferrous salts will certainly cause a loss of some nitrogen as nitric oxide. Furthermore, t h e results reported in this paper support t h e finding of Buhlert and Fickendey t h a t t h e method does not give reliable results in t h e presence of organic matter. The method proposed b y Mitscherlich and Herz, while satisfactory from t h e standpoint of accuracy,
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must be considered somewhat cumbersome in manipulation. The large amount of alkali used and t h e necessarily large amount of sulfuric acid, together with t h e 3 g. of alloy, produce such a large quantity of material in t h e flask t h a t t h e digestion can be carried on only with t h e greatest difficulty. The new procedure, therefore, which accomplishes t h e reduction in dilute alkali and thereby reduces t h e amount of alloy from 3 g. t o I g. and t h e amount of concentrated sulfuric acid from 60 cc. t o 3 0 cc., avoids t h e large amounts of solid material so troublesome in t h e digestion. Moreover, t h e employment of t h e absorbing tower insures complete absorption of t h e ammonia evolved during reduction. The method in its present form is easy of manipulation and t h e time necessary for a n analysis is much less t h a n t h a t required for the methods where salicylic acid is used. P R 0 C E D U R E R E C 0 M ME N D ED
I n t h e absorbing tower are placed 3 5 cc. of sulfuric acid consisting of 4 parts of acid and I part of water. The solution, 2 0 0 cc. of soil extract, or if t h e solution is smaller in volume i t should be diluted t o a t least I O O cc., is placed in a 5 0 0 cc. Kjeldahl flask and sufficient 50 per cent (the quantity of alkali t o be used should be determined) sodium hydroxide added t o make t h e solution N / I O in sodium hydroxide. T o t h e solution are added 4 drops of oil and I g. of Devarda's alloy (60 mesh, made free from ammonia by heating t o about 200' C. for 30 min.) and t h e flask connected with t h e tower. The solution is heated t o boiling in minimum time and, kept boiling gently for 2 0 min., during w h k h time t h e acid in t h e tower just about reaches t h e boiling temperature. The flame is now removed and t h e acid allowed t o suck back into t h e flask after which t h e solution is boiled for a few minutes and t h e flame removed. The tower is then washed with small quantities of distilled water and t h e water permitted t o suck back into t h e flask. Four washings with about 2 5 cc. each of water a r e sufficient t o remove all t h e ammonia from t h e t o w e r . The solution is now evaporated t o charring, j g. of potassium sulfate added and t h e digestion continued €or about I hr. after becoming bluish. After digestion is complete t h e ammonia is distilled after adding strong caustic soda carrying potassium or sodium sulfide. It is necessary t o add a relatively large excess of alkali t o t h e melt before distilling. Fertilizers carry considerable insoluble organic material which, when present during t h e reduction of t h e nitrates, causes foaming. This difficulty may b e overcome by placing t h e sample in a beaker, adding 50 cc. of water, heating t o boiling, and filtering through a small nitrogen-free filter paper into a 500 cc. Kjeldahl flask, a n d washing t h e residue and beaker several times with hot water. The nitrates are now in solution and are reduced as outlined above. After the reduction is complete and t h e water boiled o f f , t h e filter paper with t h e residue is added t o t h e flask together with 5 t o 7 g. potassium sulfate, t h e mass digested, and t h e ammonia determined in the usual manner.
Apr., = 9 = 9
T H E JOC'RiVAL O F 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 SUMMARY
I-The procedures designated as official for determining total nitrogen including nitric nitrogen are not suitable for studies in soil biology where large volumes of solution must be employed. 11-The presence of much organic matter interferes in t h e reduction by t h e Ulsch method. 111--The reduction of nitric nitrogen in an alkaline solution with Devarda's alloy removes any danger of loss of gaseous nitrogen. IV-The method which has been perfected effects t h e reduction in alkaline solution, t h u s avoiding loss of gaseous nitrogen; dilute alkali is used, and t h e amount of interfering substances in digestion t h u s largely avoided; and by means of a reliable absorbing device escape of ammonia is guarded against. I t possesses t h e added features of ease of manipulation a n d extreme accuracy of results.
311
using 5 cc. of potassium hydroxide solution containing 2 g. potassium hydroxide and 0.8 g. pyro, t h a t 0.4 t o 3 . 4 per cent of carbon monoxide were given off. Calvert' found t h a t 2 t o 4 per cent carbon monoxide were produced when pyro acted upon oxygen. Weyl and Goth2 reached t h e conclusions t h a t t h e absorption was a t a, maximum when t h e soda was sufficient t o form t h e compound CsHs(ONa)s, b u t this is not t h e case when potash is used instead of soda. He recommended 0 . 2 5 g. pyro in I O cc. sodium hydroxide, sp. gr. 1.030. Weyl and Zeitler3 state t h a t t h e maxi-
DIVISIONOF SOIL TECHNOLOGY OHIO AGRICULTURAL EXPGRIMENT STATION OHIO WOOSTER,
e
SODIUM PYROGALLATE SOLUTIONAS AN ABSORBENT FOR OXYGEN1>2 By G. W. JONF,S
AND
M. H. MEIGHAN
I n this report are shown experiments made for t h e purpose of determining t h e feasibility of using sodium hydroxide t o replace t h e more expensive potassium hydroxide in pyrogallate solutions for t h e absorption of oxygen. I n view of t h e high price of potassium hydroxide, due t o t h e war, and t h e inability at times of obtaining it a t all, relief was sought b y using sodium hydroxide.
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A great amount of experimental work has been done b y different investigators along these lines. Of recent date, Shipley8 made exhaustive tests on sodium hydroxide as a substitute for potassium hydroxide and concludes t h a t it is as good or superior t o potassium hydroxide, t h a t no carbon monoxide is given off, a n d t h a t t h e rate of absorption is proportional t o t h e concentration of t h e pyro. Anderson4 criticizes t h e solutions recommended b y Shipley as being too viscous, and states t h a t expense saved in cost of material is more t h a n offset by t h e time lost for complete absorption and t h e extra amount of manipulation. LiebigO was one of t h e first t o make use of potassium pyrogallate for absorbing oxygen. He found from experiments t h a t I g. of pyro in ammoniacal solutions absorbed 0.38 g. of oxygen or 260 cc., and I g. pyro in a potassium hydroxide solution absorbed 189. T h e strength of t h e ammoniacal or potassium hydroxide solution is not stated. He also tested gallic and tannic acid as a n absorbent b u t found them very slow as compared t o pyro. Boussingault6 found when Published by permission of the Director, Bureau of Mines. Read at the 56th Meeting of the American Chemical Society, Septem ber 10 to 13, 1918. 8 J . A m . Chem. Soc., 38 (1916), 1687 4 THISJOURNAL, 7 (19151,587; 8 (1916). 999. 6 A n % , 17 (1851), 107. Comp:. rend., 57 (1863),883. 1
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FIG. 1 -RELATIVEABSORPTION OF LIQUIDS TESTING APPhR4TUS
mum absorplion was obtained with potassium hydroxide (of specific gravity 1.05, and t h a t 1.50 is too strong. Lewes4 states t h a t freshly made pyro solution must not be used, t h a t it should stand 24 hrs. After t h e solution had been used for some time carbon monoxide was given off. Clowes5 found t h a t carbon monoxide was given off unless there was excess of potassium hydroxide. He recommends a solution of 160 g. potasstum hydroxide a n d I O g. pyro in zoo cc. water. This solution will not give off carbon monoxide even when analyzing pure oxygen. Bertheloto states 1
Ann., 130 (1864), 248.
* Ber., 14 (1881), 2659.
* A n n . , 205 (lSSO),255. 4 J . SOC.Chem. Znd., 10 (1891), 407. 5 I b i d . , 15 (1896),742. 6
Compt. Tend., 126 (1898), 1066.
