T\HE 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
352
mately j o cc. portions of 4 per cent boric acid and tit r a t e d with standard sulfuric acid, using bromophenol blue as a n indicator. This indicator was selected in preference t o any of t h e others because when used under t h e conditions described for observing the endpoint, t h e disappearance of t h e purple color (which could also be observed through a screen as in hydrogenion determinations) is sharper and more distinct t h a n either of t h e others and has t h e added advantage t h a t itris not necessary t o keep a color standard for comparison. The soils were digested in 40 cc. of concentrated sulfuric acid containing I g. of salicylic acid in each 2 5 cc. The soil is allowed t o digest half an hour a t room temperature, then 0.5 g. of iron or zinc dust is added, and after standing half an hour longer j g. of Lipman's sulfate mixture1 is added and the digestion, completed over t h e flame. After digestion, when the solution has cooled sufficiently, distilled water is added a n d t h e liquid contents of t h e flask transferred t o anothgr Kjeldahl flask and t h e residue well washed with distilled water which is also transferred t o the second flask. The water added should not be much over 175 cc. One hundred cc. of saturated caustic soda and some mossy zinc are then added a n d t h e solution distilled into boric acid and t h e distillate titrated t h e same as t h e distillate from crops. Following the procedures outlined, first with t h e reagents employed for crops and for soils, and later with crops and soils, the figures shown in Table I1 were obtained. TABLE$ 11-NITROGEN FOUND IN CROPS AND SOILS
SUBSTANCE Reagents for Crops..
Weipht G.
.....
Flask
No. 1 2 3
Reagents for Soils..
......
4 1 2 3
Corn F o d d e r . .
.........
1
&orn F o d d e r . . . . . . . . . . . 2
4 1 2 3 1
Wheat Grain..
........
1
Wheat Grain..
........
2 3 1 2 3
2
1
Sweet Clover..
.........
1
Sweet Clover..
........
2
Soil No. 1..
...........
1
2 3
1
2 3
10
........... 10
Soil No. 2..
3 2
1 2 3 1
2 3
Titration Corrected for Indicator cc.
0.10 0.10 0.10 0.10
0.40 0.40 0.30 0.30 5.80 5.60 5.65 11.50 11.50 11.50 22.35 22.30 22.30 44.60 44.60 44.45 28.35 28.60 28.6057.00 57.00 57.10 4.05 4.00
4.IO 4.55 4.40 4.50
Less Check cc.
... ... ... ...
... ... ... ...
5.70 5.50 5.55 11.40 11.40 11.40 22.25 22.20 22.20 44.50 44.50 44.35 28.25 28.50 28.50 56.90 56.90 57.00 3.70 3.65 3.75 4.20 4.05 4.15
Average cc.
0.10
0.35 5.58 11.40 22.22 44.45 28.42 56.93 3.70 4.13
I n tests with an ammonium sulfate solution i t was found t h a t when 50 cc. of 4 per cent boric acid solution were used 95 mg. of nitrogen as ammonia could be recovered with accuracy. This result was obtained without the use of glycerin which Adler recommends. 1
R z S O I ,20 parts; FeSOa, 2 parts; CuSO+ 1 part.
Vol.
12,
No, 4
SUMMARY
Winkler's modification of the Kjeldahl method in which he proposed the use of boric instead of sulfuric acid in t h e receiving flask is found t o be as accurate as when the latter reagent is employed. Ninety-five mg. of nitrogen as ammonia can be recovered in the distillate when j o cc. of 4 per cent boric acid is used. Bromophenol blue is a better indicator t h a n those used by the other investigators. The method has the following advantages: I-It does away with t h e occasional errors t h a t arise from slight mistakes in measuring t h e sulfuric acid into t h e receiving flask. 2-As t h e boric acid solution.need be measured only approximately, much time can be saved, a n d a n unskilled helper can measure i t into the receiving flasks. 3-By proper adjustment of t h e strength of t h e standard aci'd and the weights of t h e samples taken the percentage of nitrogen can be read directlyfrom the burette. 4-It is necessary t o prepare accurately only one standard solution, i. e . , t h e sulfuric acid for titrating. A W I D AND ACCURATE METHOD FOR DETERMINING NITROGEN IN NITRATE OF SODA BY THE MODIFIED DEVARDA METHOD AND THE USE OF THE DAVISSON SCRUBBER BULB1 By C. A. Butt INTERNATIONAL AGRICULTURAL CORPORATION, ATLANTA,GA.
There is among chemists with whom I have come in touch, and especiaIly among those engaged in the fertilizer industry, a very strong conviction t h a t the usual methods for t h e determination of nitric nitrogen, as in the analysis of nitrate of soda, are far from satisfactory for routine work and none too accurate in the hands of the average analyst. Procedures used in t h e average fertilizer works laboratory should of necessity be both rapid a n d accurate; moreover, it is very desirable t h a t constant attention be not required. The modified Kjeldahl-Gunning method, which had been used in our laboratory for several years, produced fairly satisfactory results, provided considerable time were given t o complete the solution and reduction of the nitrate in the salicylic acid mixture. I n addition to this time-consuming procedure, agreeing duplicate determinations have been very difficult t o obtain, unless the sample be dried and ground very fine. Naturally, therefore, our attention was turned t o other direct methods. The Devarda method, as refined in late years by W. S. Allen2 and also E. R. Allen,3 appeared the most promising, as both investigators obtained almost theoretical results. The method recommended by W. S. Allen, while very accurate, necessitated the use of the modified Knorre apparatus which was rather elaborate and more complicated as to operation than seemed desirable. The procedure outlined by E. R. Allen for nitric nitrogen in soil extracts, which he designated as the Volmari-MitscherlichDevarda method, seemed more suitable in that the reduction and distillation were effected in a very dilute alkali solution which permits the reaction to proceed quietly, a distinct ad1 Presented before t h e Fertilizer Division a t t h e 58th Meeting of t h e American Chemical Society, Philadelphia, Pa., September 4, 1919. 8th Intnn. Congr. A g g L Chem., 1 (1912), 19.
THISJOURNAL, 7 (1915), 521.
Apr., 1920
.
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
vantage over other methods in which strong alkali solutions are used. E. R. Allen found that one gram of 60-mesh alloy was suficient to reduce 2 5 mg. nitric nitrogen in 300 cc. of approximately 0.I N NaOH, reduction and distillation being completed in 40 min., using the modified Mitscherlich apparatus in which the water cooling is dispensed with and the ammonia absorbed by passing the steam through a scrubber into the receiving flask. By using the E. R. Allen method in this laboratory in connection with the regular Kjeldahl rack without a scrubber, favorable results were obtained, provided the reaction was allowed to proceed with gentle heat for several hours and the distillation then completed over a low flame. Even then at times we found that the alkali mist would be carried into the tube of the condenser, thereby rendering blank tests variable. None of these procedures, therefore, seemed simple or rapid enough until the Davissonl type of scrubber came to our notice. This scrubber bulb is built similarly to and may be substituted for the Hopkins connecting bulb where the necessity arises for a scrubber for the ammonia vapors: Davisson found that the entrained alkali can be satisfactorily removed when the vapors are scrubbed through water previous to condensation. According to his statement, the first steam which passes into the scrubber condenses on the surface of the bulb and flows down about the small bulb and there acts as a scrubbing solution for the remaining vapors. This solution is neutral or slightly alkaline, and the long period of steam distillation removes all the ammonia. When using this scrubber in connection with the modified Devarda method, it was found in this laboratory that since the alkali mist passed into the condenser tube before any condensation occurred in the bulb it was necessary to draw about 2 0 cc. of water by suction into the scrubber before beginning the distillation. A large number of the solutions left in the scrubber a t the end of the distillation period have been tested with Nessler’s reagent. Out of a total of more than 30 solutions, only z have shown the reaction for ammonia and they showed only a very faint coloring. Likewise a large number have been tested by the phenolsulfonic acid method,e and in no case were nitrates found. To determine whether or not any alkali passes the scrubber, ammonia-free water and sodium hydroxide were used in blank tests on three separate occasions, and the distillate titrated, one drop of 0.1N sulfuric acid being sufficient in all cases to produce a distinct color change with methyl red indicator. This confirms Davisson’s statement that thorough scrubbing of the vapors is accomplished. T h e method used in this work is based on the findings of W. s. Allen, who recommended using 3 g. of Devarda’s alloy t o I g. of nitrate of soda, and t h e findings of E. R. Allen, who verified Volmari’s conclusions t h a t approximately 0 . I N sodium hydroxide solutions are sufficiently concentrated for the reduction a n d distillation, a n d t h a t strongly alkaline solutions cause the reaction t o be so violent t h a t care must be continually exercised t o prevent a loss of the determination. The Devarda’s alloy used i n this work was obtained from J. T. Baker, and upon testing was found t o be ammonia-free. A fineness test on t h e original sample showed: IOO per cent passing Io-mesh sieve, 76 per cent passing zo-mesh sieve, 19 per cent passing 60-mesh sieve. 1 THISJOURNAL,
11 (1919), 465. Chemical Analysis,” 1917, p. 539.
* Scott, “Standard Methods of
3 53
T o determine the effect of t h e degree of fineness on t h e results a few determinations were carried o u t using in one determination 3 g. of alloy remaining on 20 mesh and in the duplicate 3 g. of t h e alloy passing zo mesh with the following results: Test Number 1
Alloy Remaining on 20 Mesh Per cent
Alloy Passing 20 Mesh Per cent Ammonia Found Ammonia Found 19.97 19.96 19.96 19.98 ................. 18.85 18.82 18.81 18.81
........................ ........................
2 3...... 4
........................
These results indicate t h a t an alloy passing a IOmesh sieve is sufficiently fine under t h e conditions of t h e method to be outlined. T h e time required for complete reduction and distillation was also studied. Tests were made, distilling 15, 30, 45, and 60 min. T h e results follow: Minutes Distilling Per cent a m m o n i a found..
......
15 16.21
30 18 49
45 18.99
60 19.03
T o the contents of the flasks containing t h e condensate from an additional 15 min. distillation, one drop of 0.1N sulfuric acid gave a distinct color change with methyl red indicator. This shows t h a t one hour’s reduction a n d distillation is sufficient for a practically complete recovery of the nitrogen. METHOD O F ANALYSIS
T h e method i n detail recommended for the analysis
of nitrate of soda is as follows: PREPARATION OF SAMPLE-The sample should be p u t through a Io-mesh sieve a n d mixed thoroughly. This we have found to be sufficiently fine t o obtain good duplicate checks. Out of a total of 2 3 samples analyzed since adopting this procedure, duplicate determinations have shown t h e following agreements: 3 5 per cent within 0.0; per cent “3, 78 per cent within 0.10 per cent, and all within 0.1j per cent. D E T A I L S O F MANIPULATION-weigh 17.034 g. a n d transfer to a 5 0 0 cc. volumetric flask (calibrated t o correspond with t h e pipette t o be used) a n d a d d 300 cc. of water. Warm t o dissolve, cool, and make up t o mark. After mixing thoroughly, pipette 2 5 cc., corresponding t o 0.8517 g. of sample, into a Kjeldahl flask of 500 t o 650 cc. capacity. Add 300 cc. of water, 3 g. Devarda’s alloy ( 7 5 per cent of which will pass 20-mesh sieve), 3 t o j cc. 4 5 ’ B6. sodium hydroxide, and connect a t once with t h e Kjeldahl distilling apparatus fitted with the Davisson scrubber i n t o which has been drawn 2 0 t o 30 cc. of water. Conduct. distillation of t h e ammonia synchronously with t h e reduction, regulating t h e boiling so t h a t 175 t o 2 0 0 cc. of distillate is collected in about one hour. When distillation is about half completed, i t is recommended t h a t part of the solution in the scrubber be sucked back into the distilling flask, allowing IO--20 cc. t o remain in the bulb, this being accomplished by removing the flame or holding t h e flask out of place a moment while still connected. This removes the danger of the liquid splashing into t h e condenser tube, and by reducing the volume in t h e bulb facilitates t h e passing of t h e last traces of ammonia into t h e receiving flask.
3 54
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Twenty-one cc. of 0 . j N sulfuric acid are used in which t o absorb t h e ammonia and t h e titration is carried out as in t h e regular Kjeldahl method, using methyl red indicator. Cc. 0.5 N acid required = per cent ammonia A C C U R A C Y OE METHOD-0.5 N sulfuric acid used in t h e following work was carefully standardized by t h e sodium carbonate method.' This solution in a series of tests averaged within 0.03 per cent of t h e theoretical ammonia equivalent of specially prepared and dried ammonium sulfate when ammonia in t h e salt was determined by t h e above method. 0 . 2 5 N sodium hydroxide was prepared by titration against t h e 0.5 N H2S04 using methyl red indicator. A check sample of sodium nitrate was prepared from C. P. sodium carbonate and nitric acid, free from chlorides and sulfates, recrystallized and dried a t 150' C. Upon analysis this salt showed the following: 0 . 0 8 per cent H80 .................................. NaCl ................................ KNOa. ............ NazSOa. ...................... .. FezOa ................................ AlzOs. ................................
.................... ....................
0 . 0 2 per cent 0 . 6 2 per cent Trace Trace Trace Trace Trace Trace
Correcting for t h e KzO found and deducting from I O O per cent all t h e impurities t h e result is 99.80 per cent sodium nitrate. T h e theoretical ammonia, therefore, equals 20.00 per cent. Results which were obtained a t various times on t h i s check sample are as follows: Per cent Per cent Per cent Ammonia Ammonia Ammonia Found No. Found No. Found No. 9 . . . . . . . . 19.95 5 . . . . . . . . . 20.03 1. . . . . . . . . 19.99 l o . . . . . . . . 19.96 6 . . . . . . . . . 19.95 2 . . . . . . . . . 20.00 11 . . . . . . . . 19.99 7 . . . . . . . . . 19.96 3 . . . . . . . . . 19.99 12 19.99 8 . . . . . . . . . 19.98 4 . . . . . . . . . 20.04 Highest.. . . . . . . . . . . . . . . . . . . 20.04 Lowest.. . . . . . . . . . . . . . . . . . . . 19.95 Average.. . . . . . . . . . . . . . . . . . . 19.99
........
It will be noted the extremes show a variation of ~0.09per cent ammonia, equivalent t o 0.45 per cent sodium nitrate. Blank determination showed a n equivalent of 0.01 per cent ammonia, which was .deducted from all results. The effects of t h e presence of sodium chloride and .also sodium carbonate were then determined with .results as follows: rILLING BEFORR DIS'~ AMOUNTSADDEDTO ALIQUOTI N FLASK NaL!Oa NazCOA NaCl NaCl 0.04 g. 1 g. 0.04 g. 1 g. Added Added Added Added Per cent Per cent Per cent Per cent Ammonia Ammonia Ammonia Ammonia Found No. Found Found Found hTo. 19.92 6...... 20.02 19.94 1 . . . . . . . . 20.03 19.97 7 19.97 19.94 2 . . . . . . . 20.04 19.89 8...... 20.00 19.99 3 ........ 19.93 20.03 9...... 20.02 20.03 4 . . . . . . . . 20.00 19.99 l o . . . . . . 19.99 20.02 5 ........ 19.99 19.96 Av.. 20.00 19.98 Av.. . . . . 20.00
.......
....
1
Scott, LOC.cit., p. 503.
Vol.
12,
NO. 4
The foregoing figures indicate t h a t neither of these compounds in quantities of I g. or less has a n a p preciable effect on t h e results. I n order t o show whether or not t h e same degree of accuracy is attainable on commercial nitrate of soda, two samples were selected a t random from a lot arriving a t t h e laboratory, and each was run i n duplicate by three analysts. Following are their results: Sample 1 Per cent Ammonia Found
ANALYST 1 ........................
18.79 18.83
Sample 2 Per cent Ammonia Found 18.97 18.93
18.81 18.82 18.78
18.95 18.97 18.98
18.80 18.83 18.84
18,98 19.00 19.01
-
~
Average.. 2.
............
.......................
Average.. . . . . . . . . . . . . 3 ........................
___
0
__
Average . . . . . . . . . . . . . . 1 8 . 8 4
19.01
Upon making analyses on these two samples for all impurities and using t h e average ammonia figures for Sample I, 18.82 per cent, and Sample 2, 18.98 per cent, t h e following shows t h a t the method had yielded exceptionally accurate results: Sample 1 H s 0 . . . . . . . . . . . . . . . . . . . . . 3.08 Insoluble.. . . . . . . . . . . . . . . . 0 . 2 1 NaCl. . . . . . .
. _ ' 0.51
NaClOa.. . . . . . . . . . . . . . . . .
I-
......
A1203 Fen03 CaO. .................... M g O . . . . . . . .L.. . . . . . . . . .
Sample 2 2.74 0.26 0.33 0.56 0.05
0.94 0.10
0.09
0.09 0.18
0.07 0.10 0.04 0.06 2.55 92.57
KNO3.. . . . . . . . . . . . . . . . . . . 3.48 hTaNO3.. . . . . . . . . . . . . . . . . . 90.98
TOTA I................
0.51
__
-
99.98
99.93
Sample 1 NaNOs by modified Devarda method.. . . 93.92 NaNOa b y deducting from 100 per cent all impurities a n d correcting f o r the K?O found. . . . . . . . . . . . -93.93
Ssmple 2 94.72
94.78
SUMMARY
The modified Devarda method as outlined, used in connection with the regular Kjeldahl rack, fitted with t h e Davisson scrubber, i n addition t o being rapid, is capable of producing exceptionally accurate results and is suitable for routine work. Reduction and distillation may be completed in one hour. The presence of I g. of sodium chloride or sodium carbonate in t h e sample is shown t o have no a p preciable effect on t h e determination. Ten- t o twenty-mesh alloy is shown t o be sufficiently fine under t h e conditions of the method outlined. I n view of t h e excellent results obtained i t is hoped t h a t t h e fertilizer division will include this procedure or a modification of t h e same in any work t h a t may be carried out toward t h e improvement in our methods for nitrate of soda analysis.
