March, 1925
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Determination of Mineral and Organic Ammonia in Fertilizers1 By F. B. Carpenter and H. L. Moxon VIRGINIA-CAROLINA CHEMICAL Co., FUCHMOND, VA.
OhlE of the states have recently enacted laws requiring fertilizer manufacturers to guarantee mineral and organic ammonia in addition to the usual statement of the minimum percentage of available phosphoric acid, ammonia, and potash. I n this classification nitrate of soda and sulfate of ammonia are considered as mineral and all other sources in general use as organic. The purpose of the law, as the writers understand it, is to inform the consumer of the percentage of ammonia actually derived from nitrate of soda and sulfate of ammonia. In carrying out the provisions of this law some difficulty has been encountered in getting results which correspond to those calculated from the formula used. The apparent discrepancies have resulted from two causes. First, many of the organic materials and base mixtures contain some ammonia in the form of ammonium salts. I n samples of acidulated fish and wet-mixed base recently examined approximately onethird of the ammonia was in the ammoniacal form. Process tankage and other organic sources also contain varying amounts. Second, the methods of the Association of Official Agricultural Chemists are not described in sufficient detail and are otherwise inaccurate for use with mixed fertilizers. An important omission is the failure to describe the style of connecting bulb tube used in distillation; this is of special importance in the zinc-iron method. These methods, which were originally intended for the determination of nitrogen in nitrates and ammonia salts, when applied to fertilizer have a tendency to convert some of the organic nitrogen into the ammoniacal form, and thus help to make the results of the so-called mineral nitrogen too high and the organic nitrogen correspondingly low. The purpose of this paper is to point out the causes of some of the inaccuracies in the methods in general use for the d e termination of the so-called mineral ammonia in mixed fertilizers. I n the Methods of Analysis of the A. 0. A. C. there are described one official method for the determination of ammoniacal nitrogen in fertilizers and two official methods for the determination of ammoniacal and nitric nitrogen. These are designated as the Magnesium Oxide, the Reduced Iron, and the Zinc-Iron Methods.2 The first of these has proved quite satisfactory, but under certain conditions the other two are not strictly accurate. The third method for use with nitrates, not yet included in the Official Methods, is the Devarda alloy m e t h ~ d which ,~ does not seem to have the same tendency toward high results as the other two nitrate methods and is in general the most satisfactory process tried. The magnesium oxide method should be employed in all cases where nitrates are not present. When the zinc-iron method is employed some of the organic nitrogen appears to be converted to the ammoniacal form and the results of mineral nitrogen are invariably high. The reduced iron method has the same tendency. In using this process it must be borne
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1 Presented before the Division of Fertilizer Chemistry at the 68th Meeting of the American Chemical Society, Ithaca, N. Y..September 8 to 13, 1924. * Assoc. Official Agr. Chem., Methods, Revised to November 1, 1919, p. 10. 8 J . Assoc. Oficial Agr. Chcm., 6, 451 (1922).
in mind that the digestion with dilute sulfuric acid has a tendency to oxidize the organic nitrogen and the treatment must be short; after boiling has commenced it should be continued for the prescribed 5 minutes with just enough heat to boil with the minimum amount of evaporation. The writers have found a reflex condenser useful in maintaining the volume of the sulfuric acid mixture. Although with proper precautions fairly good results may be obtained with this method, according to the writers' experience the Devarda alloy method is more satisfactory and safer to use when its determinations of both the nitric and ammoniacal nitrogen are required. One very important consideration in carrying out any of these processes is the style of bulb tube used to connect the distilling flask with the condenser. The only tube that has been found satisfactory under all conditions is the Davisson scrubber. With the ordinary types there is a tendency in the process of distillation for some of the alkali to find its way into the distillate. This seems to pass over in the spray caused by the action of the alkali on the reduced iron or other metal used. Table I-Comparative Analyses of Mineral Nitrogen by Different Methods-Stated as A m m o n i a Zinc-iron Reduced iron Devarda alloy Sample PerMgo cent Per cent Per cent Per dent Samales ronlain no nitrales
Samples contain nitrates 9.87 9.88 3.60 3.45 2.40 2.34 10 3.54 3.30 llb 2.52 2.38 a Theory 2.58 per cent. b Theory 2.26 per cent. 7 8 9
9.75 3.34 2.21 3.26 2.33
For the purpose of obtaining information concerning the relative merits of the different processes, comparative analyses have been made on several samples of fertilizer by the three official and the Devarda alloy methods, including different styles of connecting tubes. The results obtained are shown in the accompanying tables. I n all cases except where otherwise specified the Davisson scrubber was used in distillation. Table 11-Comparative Analyses by Zinc-Iron Method Using Differe n t C o n n e c t i n g Bulbs a n d Effect of T i m e o n Distillation Samples all contain nitrates TN-
DAVISSON MAGREDER CLARK DRICAL SCRUBBER BULB PLAINBULB BULB BULB 1.75 hours 2 . Y hours 1.5 hours 2.5 hours 1 . 5 hours 2.5 hours 2.5 hours No. Per cent Per cent Per cent Per cent Per cent Per cent Per cent 10.72 11.23 7 9.87 10.04 10.68 8 3.60 3.67 4.70 4.04 5.16 3.43 3.48 5.34 9 2.40 2.55 10 3.54 3.65 3.89 4.14 7.04 3.57 3.60 Distillation for first hour below boiling point. Note-Table I1 shows that the utmost care must be exercised in the distillation or the alkali will find its way through condenser causing high re-
sults. By increasing the rapidity of distillation varying results can be obtained with all the bulbs used with the exception of Davisson scrubber.
Conclusions
It is impossible to obtain satisfactory results with any of the methods tested, especially those for the determination of nitric nitrogen, without using a connecting bulb so constructed
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as to prevent the alkali in the distilling flask from being carried over mechanically into the distillate. The Davisson scrubber has been found satisfactory for this purpose. The zinc-iron method invariably gives results too high in mixed fertilizers containing organic matter. The reduced iron method has a tendency to give high re-
Vol. 17, No, 3
sults, but with proper precautions is much more satisfactory than the zinc-iron method. When nitrates are present the Devarda alloy method has proved more satisfactory than either of the official methods. I n all cases where nitrates are not present the magnesium oxide method should be employed.
The Determination of Dicyanodiamide' By C. D. Garby FIXED NITROGEN RESEARCHLABORATORY. WASHINGTON, D. C.
ICYANODIAMIDE is one of the important deriva- cyanodiamide and sufficiently insoluble. It was noted, tives of cyanamide. Interest in a suitable method for however, that guanylurea often formed precipitates more its determination is occasioned, not only by the in- readily than did dicyanodiamide, and that in some cases the creasing importance of dicyanodiamide for the syntheses of precipitation appeared to be quite complete. various chemicals, but also in connection with its occurrence The insoluble character of nickel guanylurea was observed in fertilizers containing calcium cyanamide in which it is by Grosman and S ~ h u c kand , ~ a method for the determinaobjectionable. tion of nickel based on this fact was developed by them and I n the work a t this laboratory there has been occasion to their co-workers. The reverse of this procedure-i. e., the determination of guanylurea by predetermine dicvanodiamide. not onlv in crude calcium cyanamide and in cipitation as a nickel salt-was Several methods for the determination of s u g g e s t e d by von Dafert and some of the simpler fertilizer mixdicyanodiamide, particularly in connection iLliklauzs as a method for the d e tures containing it, but also in mixwith the use of calcium cyanamide as a tures that have in some cases cont e r m i n a t i o n of dicyanodiamide. fertilizer, have been suggested, but have Their method, in brief, consisted tained urea, (dicyanobeen found unsuitable. After a careful in evaporating a nitric acid soludiamirjine), guanidine, biguanide, study of the various suggested methods the amidodicyanic acid, and melamine. thus of hydrolyzing tion the sample to the dryness dicyanotwice, nickel guanylurea method was developed. The quantitative determination of The method as described in this paper has diamide to guanylurea, and then dicyanodiamide in the presence Of been in use in the Fixed Nitrogen Research precipitating the latter compound these compounds is rendered particLaboratory for the past two years, and in from a solution of the residue b y 'larly because Of the 'lose all cases has given far better results than means of nickel nitrate in a strongly chemical relationship of many of any of the other methods. alkaline solution. The reactions them to dicyanodiamide. in these two steps of the procedure Several methods have been suggested for the determination of dicyanodiamide, particularly are expressed by the equations: in connection with the use of calcium cyanamide as a fertilizer. NHzC(NH)NHCN HOH HNOs + NH*C(NH)NHCOTheir unsuitability, even for relatively simple mixtures, has NHz.HNOs already been pointed out by Harger2 and others, and the 2C2HsN40.HNOsf Ni(NO& f 4NaOH + Ni(CZHjN10)2.2H20 4NaNOs 2H10 method devised by Harger has likewise been found to have serious limitation^.^ The more recent method for dicyano- These authors stated that the precipitation of nickel guanyldiamide suggested by Johnson' is subject to a very large urea was not affected by the presence of ammonium salts, number of corrections and is limited in its application. After guanidine salts, and urea, even when the latter was present a careful study of the various suggested methods, the de- in quantities ten times greater than that of dicyanodiamide, velopment of a more suitable and a more generally applic- but that cyanamide interfered on account of its conversion able method was undertaken. to guanylurea on hydrolysis. Their method was carefully investigated. Preliminary Experiments The method was first tried out on various sized samples Attempts were first made to devise a simple and direct of pure dicyanodiamide, following closely their procedure, method for the determination of dicyanodiamide, such as except that the precipitate of nickel guanylurea was weighed direct precipitation by a heavy metal. I n this connection directly, after drying, instead of being ignited to the oxide and solutions of salts of various metals-copper, gold, cadmium, then weighed. This modification was made since it was found thallium, antimony, bismuth, chromium, gadolinium, ura- that consistently high and somewhat variable results were nium, iron, cobalt, and nickel-were added to both acid and obtained if the precipitates were ignited to the oxide, owing alkaline solutions of dicyanodiamide and also to solutions probably to partial oxidation of the nickel oxide (NiO). of cyanamide, urea, guanylurea nitrate, guanidine nitrate, Satisfactory results were not obtained in any of the experiand amidodicyanic acid. Mannitol was used to prevent the ments; the precipitates in twenty-five determinations correprecipitation of metal hydroxides in alkaline solutions. No sponded to 91.0-97.2 per cent of the dicyanodiamide acprecipitates were obtained which were both specific for di- tually used. It is probable that by igniting the precipitate to the oxide von Dafert and Miklauz obtained results agree-
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Received September 24, 1924.
* THISJOURNAL, ia, 1107 (1920). a A m . FerfiZizcr. S4. 49 (1921): THISTOIJRNAL.. 14.. 143 (1922). . 4 THIS~ o u R N i t ,is, 533 i i g z i ) .
Bcr., 39, 3356 (1806). Z . landw. Versuchsw. Daulschosterr. 22, 1 (1919); J . Sac. Chem. I n d . , 88, 837 (1919); Chcm. Zcntr., 90, 109 (1919). 6
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