I N D UETRIAL A N D ENGINEERING CHEMISTRY
November, 1923
in certain ioni~ati’onexperiments. It suggests that possibly a n increase in voltage increases the fraction of energy which can be made t o do chemical work, but that some other influence, such as concentration, or possibly an intermediate step of slow velocity, limits the production for the larger yields. Small variations in the velocity of the air through the arc do not affect the yield within the experimental range studied. When the velocity is high enough to render the arc unstable the yield decreases appreciably. At very low velocities it is to be expected that the yield would decrease. Cramp and Hoyle4 in an exhaustive study of the arc found that increasing the velocity of air through the arc increased the yield of nitrogen peroxide per ampere up to a maximum and then decreased it. It is important to point out, however, that their results were not on the basis of yield per given 4
J . Inst. Elec. Eng., 43, 319 (1909).
1175
energy input, but on the basis of yield for a given current. Haber and Platou5 found that increasing the velocity of air from approximately 0.5 liter per minute to 2 liters per minute increased the yield of nitric acid about one-third. Interrupting the arc so as to sweep out the gases from an extinguished arc does not give increased yields. This fact shows that after the current is shut off the kinetic energy of the molecules is not decreased instantaneously to a condition (temperature) at which the nitric oxide is stable. Spark discharges give less nitrogen peroxide per kilowatthour than arcs. The use of condensers is disadvantageous. No increase in yield results from previously ozonizing the air. Pure nitrogen peroxide may be readily obtained from air on a small scale with the use of silica gel in connection with an electric arc. 6
Z.Elektrochem., 16, 802 (1910).
J
Determination of Nitrate Nitrogen’ I n the Presence of Cyanamide and Some of Its Derivatives By Kenneth D. Jacob FIXEDNITROGEN RESEARCH LABORATORY, WASHINGTON, D. C.
IN
Cyanamide and certain of its derioatioes interfere in the deteralloy, gave in all cases reCONNECTION with investigations on the sults that were from 10 to mination of nitrates by reduction with Deoarda’s alloy. Cyanamide, dicyanodiamide, and guanylurea are quantitatioely 20 per cent above the theorate of nitrification of commercial calcium cyan%removed by precipitation with siloer sulfate. Urea, if present, ~ + c a l . This fact had preis conoerted into ammonia by the action of urease and the nitrogen viousb’ been observed by mide2 and Some of its derivcontained in the urease extract remooed with silver sulfate. C o d e 6 in the course of atives in the Soil an accurate After elimination of the interfering compounds the nitrate is nitrification experiments method for the determinawith cyanamide and dicytion Of nitrate nitroRen in determined by the Deoarda alloy method. the presence of these comanodiamide. ”he high reThese analytical methods were used at this laboratory in conpounds is desired. Of the nection with a series of soil nitrification studies on cyanamide, s d t s for nitrates, in the numerous methods Prodicyanodiamide, guanylurea, and urea, and have gioen entirely Presehce of cyanamide and consistent and satisfactory results on seoeral hundred separate its derivatives, are due to posed for the estimation of nitrate nitrogen, alone or analyses. the gradual decomposition in the presence of other of the latter compounds in forms of nitrogen, those hot alkaline solution with a based upon colorimetric or reduction procedures have as a slow evolution of ammonia, part of which appears as nitrate rule proved the most satisfactory. Colorimetric methods in the final analysis. I n order to obtain accurate results the give accurate results when the quantity of nitrate present interfering nitrogen must be removed before proceeding with is comparatively small, their relative accuracy decreasing as the nitrate determination. the amount of nitrate increases. It is also often difficult For the removal of cyanamide, dicyanodiamide, and guato obtain a colorless solution of the nitrate, especially with nylurea, an adaptation of Caro’s method, as improved by soils containing considerable organic matter and soluble Brioux,6 for the determination of combined cyanamide and salts. Of the reduction methods that using Devarda’s alloy dicyanodiamide was used. Brioux’s method involves the in dilute sodium hydroxide solution has under ordinary con- precipitation of these compounds from a water solution with ditions given consistent and accurate results in the hands silver nitrate and potassium hydroxide. This procedure of different investigators, as shown by the excellent work suggested a means of freeing the solution of cyanamide and of Allen3 and of D a v i ~ s o n . ~While the method gives satis- dicyanodiamide, but silver nitrate could not be used as a factory results in the presence of considerable soil organic precipitant because it introduced additional nitrate nitrogen. matter, it is unreliable in the presence of cyanamide and By using 100 cc. of a saturated solution of silver sulfate many of its transformation products. Modifications of the (containing about 0.75 gram Ag&04) the interfering nitrogen Allen method which eliminate these interfering substances from a solution containing as much as 50 mg. of cyanamide, are here presented. dicyanodiamide, or guanylurea sulfate is satisfactorily rePreliminary experiments on the recovery of added nitrate moved. The interference due to the presence of urea is nitrogen from mixtures containing cyanamide, urea, dicyano- also reduced, but is not completely removed by this prodiamide, or guanylurea sulfate, by reduction with Devarda’s cedure. Urea may be completely hydrolyzed’ to ammonia and IReceived June 18, 1923.
* Hereafter referred to as
cyanamide.
8Tsrs JOURNAL, 7, 521 (1915). 4 I b i d . , 10, 600 (1918).
J . Agr. Sci., 9, 113 (1919). r A n n . sci. agron., 27, Pt. 1, 241 (1910). 7 Fox and Geldard, THISJOUENAL, IG, 743 (1923). 6
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 15, No. 11
carbon dioxide within a very short time by the action of the described by Davisson,*the bulb, condenser tube, and adapter enzyme urease present in jack-bean flour. This procedure being made of Pyrex glass and thus eliminating danger of is effective in removing the interfering urea, since the am- alkali from the glass parts. monia formed can be easily removed by distillation before All the results have been corrected for the blank on redetermining the nitrate. However, the extract of jack-bean agents, and, in the case of soil extracts, the nitrate nitrogen flour itself contains nitrogen compounds which, on boiling present in the soil. The soil used was a Susquehanna loam with dilute sodium hydroxide, slowly evolve ammonia. The that had been under cultivation as a garden for about 15 extract from 170 mg. of jack-bean flour, analyzed for nitrate years, and contained a comparatively large quantity of nitrogen by Allen’s3 method, showed 0.39 mg. of nitrogen organic nitrogen. appearing as ammonia and 0.62 mg. as nitrate. The interI n order to determine to what extent cyanamide, dicyanofering nitrogen from the jack-bean flour extract is almost diamide, urea, and guanylurea interfere in the usual method completely removed by precipitation with silver sulfate and for determining nitrates by reduction with Devarda’s alloy, potassium hydroxide, as shown later. two sets of analyses were made, one using these compounds in water solution, and the other in the presence of soil exANALYTICAL METHODS tract. In the first case, quantities of the nitrogen comI N ABSENCE OF INTERFERIKG COM- pounds, each equivalent to 20.88 mg. of nitrogen, were 1. NITRATENITROGEN POUNDS-This method is essentially that devised by Allen. weighed into separate Kjeldahl flasks, 350 cc. of distilled A suitable aliquot of the solution containing the nitrate is water added, and the usual nitrate determination was carried measured into an 800-cc. Kjeldahl flask, 5 cc. of 20 per cent out. For the analyses in the presence of soil extract, quansodium hydroxide are added, and the total volume is made tities of the compounds, each equivalent to 20.88 mg. of up to 350 cc. The flask is connected to a distilling apparatus, nitrogen, were mixed with separate portions of 100 grams fitted with an efficient type of scrubber bulb, and boiled until of air-dried soil and each sample was immediately extracted 300 cc. of distillate collect in the receiver. This removes all with 500 cc. of water. Aliquots equivalent to 8.35 mg. of ammonia, either free or combined. To the 50 cc. of solution added nitrogen were analyzed for nitrates by the procedure remaining in the flask are added 200 cc. of water and 1.5 to applicable in the absence of interfering compounds. 2 grams of nitrogen-free Devarda’s alloy (about 60 mesh). The flask is immediately connected with the distilling appa- TABLEI-INTERFERENCE OR CYANAMIDE DICYANODIAMIDE UREA AND IN DETERMINATION OF N I T ~ A T E NITROGEN B; RRDU’CTION ratus, and 200 cc. are distilled into a known quantity of 0.1 GUANYLUREA WITH DEVARDA’S ALLOY or 0.05 N sulfuric acid, in the course of about 1 hour. The Added Organic Nitrogen Appearing as Nitrate Nitrogen NITROGEN --Aa-----Bbnitrogen, as ammonia, found by titrating the excess sulfuric COMPOUND Mg. Mg. Per cent Per cent acid with 0.05 N sodium hydroxide, using methyl red BS an Cyanamide 4.39 21.02 1.86 22,27 4.23 20.26 1.51 18.08 indicator, represents the nitrate present in the original aliquot. Dicyanodiamide 3.76 18.01 1.42 17.00 The Kjeldahl flasks should be free from all traces of De3.51 16.81 1.51 18.08 2.23 10.68 0.64 7.66 varda’s alloy or zinc before distilling off the original am- Urea 2.15 10.29 0.65 7.78 monia; otherwise some af the nitrate may be reduced and Guanyliirea 3.01 14.41 0.38 4.55 sulfate 2.90 13.88 0.38 4.55 thus fail to appear in the final nitrate determination. a In pure solution. Added organic nitrogen = 20.88 mg. 2. MODIFICATION FOR NITRATE NITROGENIN PRESb I n t h e presence of soi! extract. Added organic nitrogen = 8.35 mg. ENCE OF CYANAMIDE, DICYANODIAMIDE, AND GUAHYLUREAT o a measured sample containing these forms of nitrogen Although the results given in Table I are not entirely are added 100 cc. of a saturated solution of silver sulfate and comparable because of the varying quantities of organic 10 cc. of a 15 per cent solution of potassium hydroxide. compounds used in the two cases, they show that, even in The precipitate is allowed to stand for about 1 hour, with the presence of comparatively small quantities of cyanfrequent stirring, and is then filtered directly into an 800-cc. amide and some of its derivatives, an appreciable portion Kjeldahl flask, The precipitate is washed six times with of the organic nitrogen appears in the final analysis as nitrate. 10-cc. portions of water, 5 cc. of 20 per cent sodium hydroxide I n order to determine the efficiency of the method for the are added to the flask, and the total volume is made u p t o removal of interfering nitrogen due to the presence of cyanabout 350 cc. After distilling off the ammonia the nitrate amide, dicyanodiamide, and guanylurea, quantities of these nitrogen is determined as in the preceding method. Urea compounds, each equivalent to 20.88 mg. of nitrogen, were is only partly removed by this procedure. thoroughly nlixed with 100-gram portions of air-dried soil, Blank determinations should be run on all samples of silver and the whole was immediately extracted with 500 cc. of sulfate, as this compound, unless especially purified, usually water. Aliquots equivalent to 8.35 mg. of added nitrogen contains an appreciable quantity of nitrate. were treated as described under (2) of “Analytical Methods,” 3. MODIFICATION FOR NITRATE NITROGENIN PRES- with the following results: ENCE OF UREA-A neutral aliquot of the original solution The interfering cyanamide, dicyanodiamide, and guanylcontaining urea, nitrate, and ather forms of nitrogen is urea nitrogen can be removed practically to within the limits treated with 10 cc. of a neutral 2 per cent extract of jack- of experimental error by precipitation with silver sulfate bean flour and allowed to stand for 1 hour. At the end and potassium hydroxide. The interference caused by the of this time the enzyme urease will have converted the urea presence of urea is reduced by this procedure, but its removal present into carbon dioxide and ammonia. In order to free is not complete. the solution of the nitrogen added in the jack-bean extract, In order to determine the efficiency of the method for the it is treated with silver sulfate and potassium hydroxide removal of interfering urea nitrogen, soil extracts containing solutions as in the previous procedure, and the nitrate nitro- urea were prepared in the same manner as those used in gen is determined as usual, after first distilling off the am- obtaining the results given in Table 11. Aliquots equivalent monia. Cyanamide, dicyanodiamide, and guanylurea are to 8.35 mg. of urea nitrogen were analyzed by the method also removed by this procedure. previously described for the removal of urea nitrogen. The average results given in Tables I1 and I11 compare EXPERIMENTAL RESULTS very favorably with respect to the removal of the added forms In obtaining the data the distillations were carried out on S T H I S JOURNAL, 11, 465 (1919). an ordinary Kjeldahl rack, using the scrubber distilling bulb
INDUSTRIAL A N D ENGINEERING CHEMIXTRY
November, 1923
1177
111-EFFICIENCYO F METHOD FOR REMOVAL OF INTERFERISG UREA TABLE11-EFFICIENCYOF METHOD FOR REMOVAL OF CYANAMIDE, DICYANO- TABLE NITROGEN DIAMIDE, AND GUANYLUREA (Added urea nitrogen = 8.35 mg.) (Added organic nitrogen = 8.35 Mg.) Added Organic Nitrogen Appearing Added Urea Nitrogen Appearing as Nitrate Nitrogen as Nitrate Nitrogen Mg. Per cent NITROGMN COMPOUND Mg. Per cent 0.092 0.031 0.37 0.045 Cyanamide
Av. Dicyanodiamide
Av. Guanylurea sulfate
Av. Urea Av.
0.023 0.057 0.031 0.035 0,023 0.031 0.031 0.040 0.031 0.065 0.098 0.040 0.048 0.063 0,452 0.528 0.490
0.27 0.68 0.37 0.42 0.27 0.37 0.37 0.47 0.37 0.78 1.17 0.47 0.57 0.75 5.41 6.32 5.86
0.019 0.019 0,027
Av.
0.040
TABLE IV-RECOVERYOF NITRATE NITROGEN IN PRESBNCE OF CYANAMIDE
AND SOMEOF ITS DERIVATIVES (Added nitrate nitrogen = 3.89 mg., added organic nitrogen = 8.35 mg.) ORGANIC NITROGEN Added Nitrate Nitrogen Recovered COMPOUND Mg. Per cent None 3.930 101.03
Av. Cyanamide
of orgmic nitrogen. In order to determine the efficiency of the procedures as regards the recovery of added nitrate nitrogen in the presence of the organic nitrogen compounds, soil extracts were prepared in the same manner as those previously used. Aliquots containing 3.89 mg. of added nitrate nitrogen in the form of potassium nitrate and 8.35 mg. of' added organic nitrogen were analyzed by one of the procedures dependent upon the nature of the organic nitrogen presenc.
Av. Dicyanodiamide
Av. Guanylurea sulfate Av. Urea Av.
3,920 3.925 3.894 3.928 3,955 3,898 3.919 3.932 3.974 3.879 3.960 3.936 3.896 3.852 3.874 3.886 3.877 3.919 3.894
100.77 100.90
101.08 102,16 99.71 101.80 101.19 100.16 99.02 99.59 99.89 99.66 100.74 100.10
Colloidal Copper Hydroxide as a Fungicide' By Henry D. Hooker, Jr. UNIVERSITY O F MISSOURI, COLUMBIA, Mo.
A
'r PRESENT there is no entirely satisfactory fungicide
available. The two most important ones are Bor. deaux and lime-sulfur, but both burn the foliage under certain climatic conditions, and neither is remarkable for its sticking or spreading properties. Bordeaux is difficult to prepare correctly and the ready-made mixtures on the market have not proved ideal. Lime-sulfur does not control some fungus diseases, such as apple blotch, and consequently fruit-growers must supplement lime-sulfur spraying by subsequent applications of Bordeaux where this disease is prevalent. Lime-sulfur is, moreover, a most disagreeable material to handle. It was thought that a colloidal copper compound would prove an ideal fungicide. If a material having a positive electrical charge could be prepared, it should have in colloidal isuspension the sticking and spreading qualities of lead arsenate. It was thought that the burning properties of Bordeaux might be eliminated by preparing an insoluble compound such as copper hydroxide in colloidal suspension because plant membranes are impermeable to colloids.
PREPARATION OF COPPER HYDROXIDE Colloidal copper hydroxide was prepared by using a modification of the method reported by Bradfield2 for the preparation of colloidal iron hydroxide, aluminium hydroxide, and silicic acid. A 10 per cent solution of sodium hydroxide was added to a solution of copper sulfate with constant stirring until the supernatant liquid lost its color. Copper hydroxide was thrown down as a pale blue precipitate. An excess of alkali leads to the formation of a deep blue precipitate which changes on standing to black copper oxide. 2
Received July 23, 1923. J. Am. Chem. Soc., 44, 965 (1922).
This must be avoided and it is better to leave some copper sulfate in solution than to attempt to reach an end point. The mixture so prepared contains sodium sulfate, a small amount of copper sulfate in solution, and a precipitate of insoluble copper hydroxide which holds, probably by adsorption, a considerable amount of copper sulfate. The preparation of colloidal copper hydroxide depends on the removal of the electrolytes-namely, the copper sulfate and sodium sulfate in solution and likewise a large part of the adsorbed copper sulfate. This was accomplished by agitation and repeated washing by sedimentation. Distilled water was used. When first thrown down by the addition of sodium hydroxide solution, a mixture was obtained that was far from homogeneous. This was pumped under pressure with a hand pump through a spray nozzle from one receptacle t o another, to break up the precipitate and render the mixture as homogeneous as possible. This procedure was repeated after every few washings. The mixture was transferred to a tall glass vessel and allowed to settle for 24 hours. The supernatant liquid was siphoned off, distilled water was added, and the whole was mixed thoroughly by vigorous stirring. After a dozen such washings by sedimentation practically all the free salt was removed. As long as the copper hydroxide was washed in relatively small volumes of water-50 parts of water by weight t o one of copper hydroxide-the supernatant liquid remained clear. After the free salt had been removed, the volume of wash water was increased to 200 parts of water by weight to 1 part of copper hydroxide, and the process of washing by sedimentation continued. After several washings the precipitate settled, leaving an opalescent, supernatant liquid. This contained a very small amount of copper hydroxide, which settled out after standing for
