V O L U M E 19, NO. 1 1
882 and a relatively longer period of extraction (approximately 2 hours). The results in Table I11 are 1.2y0above the calculated values, but agree closely n-ith those obtained by the regular ether extraction method as shown in Table IV. The value of the recovery factor, R, may be readily determined by following the procedure outlined in this report. The recovery factor should be redetermined for each new formulation of e powder.
to J. B. R-eaver, director of the Chemical Engineering Laborat o w , for advice and guidance. LITERATURE CITED
Am. SOC.Testing Materials, Tentative Recommended Practices
E50-46T (1946). Becker, W.W., IKD.ESG. CHEM.,ASAL. ED.,5, 152 (1933). Davis, T. L., “Chemistry of Powder and Explosives,” pp. 271-3, Kern York, John Wiley & Sons, 1943. Moran, R. F., ISD.EKG.CHEM.,ANAL.ED.,15, 361 (1943). Pitman, J. R., J . SOC.Chem. Ind., 19,982 (1900). Sutton, “Systematic Handbook of Volumetric Analysis,” p. 263, Philadelphia, P. Blakiston’s Son & Co., 1935. Waugh, T. D., Harbottle, G., and Noyes, R. M., ISD. ENG. CHEM., AKAL.ED.,18, 636-7 (1946).
ACKNOWLEDGMENT
The experimental work in this article was done in the Chemical Engineering Laboratory of the Badger Ordnance Works, operated by the Hercules Powder Company. The author is indebted
RECEIVED October 10, 1945.
Loss of Nitrate Nitrogen Caused by Chlorides Method f o r Determining Total Nitrogen PHILIP RIcG. SHUEY, Savannah, Ga. The Kjeldahl method is likely to give significantly low results when chlorides and nitrates are present in relati\ely large amounts unless the nitrogen content of the gases etolted before addition of the reducing agent is determined and added to the nitrogen obtained in the usual Kjeldahl procedure. The Deiarda method should be used when chlorides and nitrates are high and in the absence of cyanamide, urea, or organic material.
S
EVERAL methods for the determination of total nitrogen are
widely accepted as standard procedure. For the most part these are modifications of the well-known Kjeldahl method, involving digestion of the sample with concentrated sulfuric acid. With mixtures containing organic nitrogen-bearing materials the Kjeldahl-Gunning-Arnold ( 1 ) method, which involves digestion with concentrated sulfuric acid in the presence of a suitable catalyst, is in common use. en as organic I n mixtures containing nitrate nitrogen a nitrogen the sample is treated with concentrated sulfuric acid containing salicylic acid, and the nitro compound is reduced with sodium thiosulfate or zinc, as in the modified Kjeldahl method ( 3 ) . If nitrate nitrogen or nitrate nitrogen and ammonia nitrogen are the only forms present, the Devarda (4) method may be employed. This involves distillation of the sample in dilute sodium hydroxide solution with Devarda alloy, whereby both nitrate and nitrite nitrogen are simultaneously reduced t o ammonia and distilled along with any ammonia nitrogen which may have been present originally. This is an accurate and rapid method that is not affected by the presence of chlorides. I n the author’s laboratory, where mixed*fertilizer samples are continually analyzed, mixtures containing nitrates frequently show low values for total nitrogen. Investigation revealed’that this was repeatedly the case in mixtures containing both nitrate nitrogen and chlorides. Many fertilizers contain so little nitrate nitrogen that losses by the usual modified Kjeldahl procedure are of little importance ; however, for certain fertilizers relatively high in nitrate nitrogen the losses for nitrogen may reach significant proportions. Certain experimental work was undertaken to establish the validity of these observations and t o develop a method whereby nitrogen losses may be recovered. Although the work done in this laboratory pointed towards the recovery of nitrogen from certain fertilizer mixtures, the procedure recommended should find application in analytical laboratories where nitrogen determinations are made on materials other than those found in the fertilizer industry.
Table I.
.
Nitrogen in Mix‘tures Containing Potassium Sulfate (Series A)
Sample 1A
2A 3A 4A
70
70
2 14
2 11 2 99 4 02 4 94 5 93 10 16
3 4 5 6 10
5h 6A
Kjeldahl Method
Theory
05 04 02 01 05
Devarda Method
Difference between Methods
70 2 3 4 5 6 10
13 08 03 05 07 10
70 0 0 0 0 0 0
02 09 01 11 14 06
EXPERIMENTAL
In the Kjeldahl method, modified to include nitrate nitrogen, reactions involving nitrate nitrogen are represented as follows (6, 8) :I
I.
Salicylic Acid-Sodium Thiosulfate Method
+ &SO4 (KH,),SOa + 2HNO3 + 2CsH4:O H , COOH = 2CsH,. OH .,NOz.COOH + salicylic acid nitrosalicylic acid
2NH4SO3 2HSO3
2HzO
+ + 6H2S03+ 6s 6HzS03+ 2CsH3.0H.SOz.COOH+ 2H20 = 6H2S04 + 2CsH3, OH. YH?.COOH aminosalicylic acid 6Sa2S203 6H2SOa= 6 S a z S 0 4
6s
+ 12HzSO4
11.
18SO2
+ 12H2O
Salicylic Acid-Zinc Dust Method
+ HZSO4 (SH,)zSO4 + 2HSO3 + 2C6H4.O H , COOH 2C6H3,O H . SOz. COOH + 2H2O 6Zn + 6H2S04= 6ZnSOa + 12H 2XH4S03
2HxO3
e
NOVEMBER 1947 12H
883
+ 2Ce.Ha. OH. XOz. COOH
2C6H3.0H.NHz.COOH
=
+ 27HzSOd
2CsH3,OH. ”2.
+
COOH 4H20
+
+
14coz (NH4)2S04 26S02 30H20
+
In the presence of chlorides, the nitric and hydrochloric acids formed by the action of sulfuric acid on the salts of these acids react to some extent to form nitrosyl chloride (NOCl). This compound appears to escape complete fixation by the salicylic acid and results in subsequent losses unless steps are taken to recover the nitrogen from the gases evolved during the initial standing or fixation period. Losses in nitrogen were observed about 35 years ago when lowgrade kainite, in which the chloride-potash ratio was particularly high, was largely used in fertilizer mixtures. The authpr has noted only one reference in the literature which appears to verify his observations. Chamot, Pratt, and Redfield ( 5 ) state that low nitrogen results are obtained in water high in chlorides by the phenol disulfonic acid method: “The lower results when a xater residue contains chlorides are partially due to mechanical loss and in part due to interaction of the hydrochloric and nitric acid liberated.” It is customary in the fertilizer industry to indicate the percentage of the three main plant food constituents by a series of code numbers. The percentage of total nitrogen (Tu’) occupies the first position, the percentage of available phosphoric acid (P205) the second, and the percentage of soluble potassium ( K 2 0 ) the third. Thus a 2-12-6 grade contains 2% nitrogen, 12Tc available phosphoric anhydride, and 6 7 potassium oxide.
Table 11. h-itrogen in Mixtures Containing Potassium Chloride (Series B) Sample
Theory
1B 2B 3B 4B
2.14 3.05 4.04 5.02 6.01 10.05
70
5B 6B
Kjeldshl Method
70 2.12 2.97 3.87 4.91 5.86 9.87
Devarda Method
Difference between Methods
70
%
2.14 3.08 4.07 5.05 6.11 10.15
0.02 0.11 0.20 0.14 0.25 0.28
I n this study twelve laboratory mixtures were very carefully prepared; Series A consisted of 2-12-6, 3-9-6, 4-8-6, 5-10-5, 6-8-6, and 10-0-10, in which commercial potassium sulfate containing only 4.207, potassium chloride was used, and Series B was composed of the corresponding grades in which commercial potassium chloride was employed. Sodium nitrate was the only source of nitrogen in all cases. Cyanamide, urea, and organic Gatter were purposely omitted from the experimental mixtures in order to compare results obtained by the modified Kjeldahl and Devarda methods. Results obtained by the two methods (Table I) showed no marked differences, although with but one exception slightly lower results were obtained by the Kjeldahl method. From Table I1 i t will be observed that with one exception appreciable differences occurred in all instances, results obtained by the Kjeldahl method were low in each case, and in general differences found by use of the two procedures became progressively greater as the quantity of nitrogen increased. A series of tests as then made to determine whether the nitrogen evolved during the initial standing period could be recovered and determined. After the sulfuric-salicylic acid mixture was added to weighed portions of samples of Series A and B, the evolved gases were aspirated through a dilute solution of sodium hydroxide, and the latter was then distilled using the Devarda alloy. The gases from samples in Series A, which contained potassium sulfate, were found to be free of nitrogen; but the gases in all
samples in Series B, containing potassium chloride, showed significant amounts of nitrogen (Table 111). With but one exception, when the nitrogen recovered from each sample is added to that obtained by the Kjeldahl method, results are closer to those obtained by the Devarda method directly. Qualitative tests on the caustic soda solutions through which the gases \yere scrubbed were positive for nitrate (9) and nitrite ( 2 ) nitrogen. A laboratory experimental mixture containing lOy0 nitrogen and lOy0 potash was prepared, using ammonium nitrate as the source of nitrogen and potassium chloride as the source of potassium. The mixture was analyzed for nitrogen by the modified Kjeldahl method, which gave a nitrogen figure of 0.457, less than the Devarda method. This amount was recovered in the evolved gases, using the above-described procedure.
Table 111. Nitrogen Recovered by Devarda ;\lethod Sample Kitrogen, 92 1B 2B 3B 4B 5B 6B
0 12 0 . i6 0.12 0.08 0.13 0.27
METHOD FOR DETERMINATION OF TOTAL NITROGEN IN HIGH NITRATE-CH LORIDE MIXTURES
After the sample is weighed for the regular determination and transferred to t,he Kjeldahl flask, t.he flask is connected with a t\yo-hole stopper, and through one hole is inserted a thistle tube extending approximately 6.25 em. (2.5 inches) from tmhesurface of the liquid in the flask. The flask is also fitted with another tube, or a regular nitrogen connecting bulb, which is connected by means of pressure tubing wit’h a Drechsel high-form gasabsorbing bottle of 200-ml. capacity containing 150 ml. of water to Lvhich have been added 6 ml. of caustic soda o,f 50% strength. The Drechsel bottle is then attached to the suction line and the pressure turned on a t the rate of approximately 0.5 liter of air per minute, whereby the evolved gases are drawn from the flask into the caustic soda. -4fter 45 minutes t’he caustic soda solution containing the evolved nitrogen is transferred to another Kjeldahl flask and after the Drechsel bottle has been rinsed with 150 ml. of distilled water, approximately 3 grams of Devarda metal are added and the distillation is carried out as usual. The result obtained, added to the result found after reducing, digesting, and didlling from the original flask according t,o the modified Kjeldahl method, will give the total nitrogen present.
Note. An article by Dyer and Hamence ( 7 ) was called to the author’s attention after the present, paper had been written. Their method is likewise a combination of the Devarda and Kjeldahl methods, but no salicylic acid is used and reduction of the nitrates is effected first by addition of Devarda’s alloy and sodium hydroxide. Then, on heating, the ammonia evolved is trapped in a U-tube with bulbs, which is attached to the flask. When the evolution of ammonia has ceased, the ammonium sulfate formed is washed back into the flask. After’cooling, concentrated sulfuric acid is added, the water is boiled off, and the procedure is from this point conducted according to the Kjeldahl method in the absence of nitrates. LITERATURE CITED (1) Am. Pub. Health Assoc., “Standard Methods for Examination of Water and Sewage,” p. 133, 1937. (2) Assoc. Official Agr. Chem., Official and Tentative Methods of .4nalysis, 2.28, p. 27, 1945. (3) I b i d . , 2.27 and 2.28, pp, 27, 28. (4) Ibid., 2.31, p. 28. (5) Chamot, Pratt, and Redfield, J . Am. Chem. SOC.,33, 388-81 (191 1).
(6) Clark, K. G., private communication. (7) Dyer, Bernard, and Hamence, Hubert, Analyst, 63, 866-9 (1938). (8) Mahin, E. G., ”Quantitative Analysis,” p. 518, New York,
McGraw-Hill Book Co., 1919. (9) Snell, F. D., and Biffen, F. M., “Commercial Methods of Analysis,” 1st ed., p. 109, Kew York, McGraw-Hill Book Co., 1944. RECEIVED September 17, 1946
