?JOY., 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 I I I I S T R Y TABLE I Weight of Dicyanodiamide Used
1111
D I C Y A N O D I A M I D E A N D M I X E D FERTILIZER MATERIALS-
mixture was analyzed, and t o our surprise it was found t h a t all t h e cyanamide had disappeared. Another fertilizer mixture was now prepared, its composition being identical with t h e previous one, and a t intervals over a period of two weeks samples were withdrawn and analyzed for cyanamide. T h e loss of cyanamide was very rapid, 60 per cent having disappeared in 24 hrs., and within I O days i t had practically all vanished. This a t once suggested a n investigation t o determine, first, t h e cause of this rapid disappearance of cyanamide, and, second, t h e products resulting from the transformation. A search through t h e literature showed t h a t while a vast amount of work has been done in reference t o the changes taking place when Cyanamid alone is added t o t h e soil or is kept in storage, a n d t h a t while studies have been made in regard t o t h e changes occurring in t h e soluble phosphates of mixed fertilizer containing Cyanamid, i t is a curious fact t h a t no one seems t o have paid any attention t o the changes which may occur in cyanamide when this extremely reactive substance is mixed with other fertilizer materials. The present paper reports some results of such an investigation.
A mixture was prepared consisting of acid phosphate
FACTORS CAUSING TRANSFORMATION OF CYANAMIDE
ammonium sulfate (4.2 g.), potassium sulfate (1.5 g.), and dried peat (4 g.). T o this were added 5 0 cc. of water containing 81.2 g. of dicyanodiamide. T h e mixture was treated with barium nitrate, barium hydroxide, etc., and t h e analysis carried o u t as described above for mixed fertilizers. T h e results of duplicate analyses were 81.5and 81.5 mg. of dicyanodiamide. A somewhat similar analysis has already been reported in one of t h e experiments under t h e heading of “microscopic appearance of the crystals.”
T h e fertilizer mixture which was prepared was composed of acid phosphate, ammonium sulfate, potassium sulfate, and Cyanamid (all being the usual commercial products), and dried peat. I n order t o ascertain which of these materials was instrumental in bringing about t h e rapid disappearance of cyanamide, mixtures containing Cyanamid and various combinations of these substances were prepared. Since it seemed probable t h a t the acid phosphate was involved in the reaction i t was used in each of t h e mixtures. T h e mixtures were: (I) acid phosphate and Cyanamid; ( 2 ) potassium sulfate, acid phosphate, and Cyanamid; (3) ammonium sulfate, acid phosphate, and Cyanamid; and (4) dried peat, acid phosphate, and Cyanamid. Samples from these mixtures were analyzed a t intervals. While all of t h e mixtures caused a slight decrease in cyanamide, only Mixture 4 showed a n y considerable decrease, t h e rate here being rapid and practically parallel t o t h a t of t h e original mixture. This suggested t h a t perhaps the dried peat was not so dry as the name would indicate, a n d a n analysis of this material showed t h a t i t did contain 36 per cent of moisture. The other materials were practically dry, although t h e acid phosphate contained a little moisture. I n a mixture containing acid phosphate, Cyanamid, and 8 per cent of water, the cyanamide decreased very rapidly, only 5 per cent of it remaining a t t h e end of 3 days. Several similar mixtures exhibited this same rapid decrease in cyanamide content. T o test t h e effect of moisture alone, moist quartz containing I O per cent of water was mixed with Cyanamid. Here, too, there was a decrease in cyanamide, resulting finally in its disappearance, but t h e rate was by no means so rapid as when moist acid phosphate was employed, t h e loss of cyanamide in t h e latter mixture during t h e first d a y being eight times as great as t h a t in t h e moist quartz mixture. On the other hand,
Wolume of Dicyanodiamide Solution
cc. 50 100 100 50 I00
50 25 50 25 30
Ma. 50.0 50.0 50.0 34.4 50.0 56.3 2.5 50.0 50.0 100.0
Weight of Dicyanodiamide Found
Ma. 49.9 49.3 49.8
35.5 49.2
56.4 2.3 49.4 48.9 93.6
DICYANODIAMIDE A N D CYANAMIDE-TO a solution containing I O O mg. of cyanamide (CNNH2) in 5 0 cc. there were added 41.8 mg. of pure dicyanodiamide. Two such solutions were analyzed. The analysis gave 41.9 mg. a n d 42.2 mg. dicyanodiamide. Similar analyses carried out with t h e cyanamide solution alone showed no dicyanodiamide. DICYANODIAMIDE AND UREA-A solution, containing 50 mg. of urea and 2 0 mg. of dicyanodiamide in 5 0 cc. s f water gave on analysis 19.5 mg. of dicyanodiamide. A solution of pure urea containing 4 mg. per cc. gave n o precipitate a t all with t h e reagents, a n d the same Tesult was secured with a urea solution containing I O O mg. per cc.
(12 g.),
THE CHANGES TAKING PLACE IN CYANAMID WHEN MIXED WITH FERTILIZER MATERIALS By Rolla N. Harger INVESTIGATIONS, BUREAU OF PLANT INDUSTRY, DEPARTMENT OF AGRICULTURE,WASHINGTON,D. C. Received July 28, 1920
S O 1 4 PERTILITY
u s.
I n a n a t t e m p t to analyze a n aqueous extract of a mixed fertilizer for cyanamide by t h e method of Perotti,2 i t was found t h a t t h e presence of phosphates interfered, since they, too, formed a precipitate with t h e silver nitrate upon making t h e solution alkaline with ammonium hydroxide. The difficulty was overcome by precipitating t h e phosphates by means of barium hydroxide and analyzing t h e filtrate. Although t h e manufacturer stated t h a t t h e fertilizer contained considerable quantities of cyanamide, not even a trace was found. T o test t h e accuracy of t h e method a mixed fertilizer was prepared containing a known weight of calcium cyanamide (Cyanamid) whose cyanamide content was known. The accurate results obtained upon analysis showed t h a t the method was applicable. Some days later a second sample of this 1 Presented a t the 60th Meeting of the American Chemical Society, Chicago, Ill., September 6 to 10, 1920. 2 Rend. SOC. chim. i t d , 1904, 192.
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Cyanamid when mixed with practically dry acid phosphate remained unchanged even after 2 or 3 mo. This rapid disappearance of cyanamide must therefore be caused by t h e presence of acid phosphate a n d a small amount of moisture. This conclusion was further confirmed b y experiments with complete mixed fertilizer, since only those samples in which these conditions existed (i. e . , acid phosphate and 5 t o I O per cent of moisture) showed any considerable decrease in cyanamide. CHEMICAL CHANGES INVOLVED
Upon complete evaporation of a sample from one of the mixed fertilizers, t h e cyanamide of which had entirely disappeared? there was left a quantity of long needles, which were identified as dicyanodiamide by the method described in t h e preceding paper, A quantitative determination of dicyanodiamide, made upon another sample of this fertilizer, showed t h a t 90 per cent of the cyanamide originally present had been transformed into dicyanodiamide. The mixture had now stood 30 days. At t h e end of I O O days it was again analyzed, and t h e results showed t h a t t h e dicyanodiamide content was practically unchanged. Another mixture of Cyanamid and acid phosphate, containing about I O per cent of moisture, was next prepared, and the changes taking place in cyanamide and dicyanodiamide content were followed h y making simultaneous analyses for these two substances at intervals. Since t h e chemical change occurring in t h e formation of dicyanodiamide from cyanamide is simply t h e union of two molecules of cyanamide t o form a molecule of dicyanodiamide, according t o t h e equation ”2
zCNNH2
HN
I I
C
H-N-CN there is no alteration in weight, and if this reaction is t h e only one involved t h e weight of dicyanodiamide produced should equal t h a t of t h e cyanamide lost; or, stated differently, t h e combined weights of cyanamide and dicyanodiamide should remain constant. This study served t o confirm what was apparent from t h e results already secured: namely, t h a t in t h e disappearance of cyanamide t h e principal chemical change was t h e formation of dicyanodiamide, and t h a t under t h e conditions employed this was a t all times practically quantitative. A similar study conducted with two complete mixed fertilizers yielded practically t h e same results, although toward t h e end of t h e period t h e amount of dicyanodiamide in t h e mixture did not so closely approximate t h e quantity of cyanamide which had disappeared, t h e final yield of dicyanodiamide representing only about 6 j per cent of t h e loss in cyanamide. Whether this result was due t o a parallel reaction which produced some other compound from t h e cyanamide-possibly urea-or whether part of t h e dicyanodiamide formed was subsequently decomposed into other compounds, has not yet been aetermined. When Cyanamid and moist acid phosphate (6 t o J O per cent HzO) were mixed, with or without other
12,
No.
I J
fertilizer materials, a rise in temperature of 2 0 ’ t o -30’ C. was always observed, and the mixture set t o a hard mass upon standing. When analyzed immediately there was no loss of cyanamide. The acid phosphate possessed but slight acidity, I O g. of this material requiring 2 7 . 5 cc. of 0.1N alkali t o t i t r a t e t o t h e neutral point with methyl red; yet when I g. of Cyanamid, which required 1 6 9 cc. of 0.1 N sulfuric acid t o reach the same end-point, was added t o I O g. of moist acid phoshhate, t h e resulting mixture, when added t o water, was always acid t o litmus. A n alkaline mixture could be obtained only b y adding a considerably larger quantity of Cyanamid. This can only mean a n interaction between t h e acid phosphate and Cyanamid. de Nolinari and Ligotl and later Brackett2 showed t h a t when Cyanamid and acid phosphate were mixed there resulted a “reversion” of t h e phosphate, i. e., t h e introduction of more calcium into t h e acid phosphate molecule t o form insoluble phosphates. When these facts are considered together, they indicate t h e probable course of t h e reaction which results in t h e rapid loss of cyanamide. The calcium cyanamide and acid phosphate first react t o form dicalcium or tricalcium phosphate and free cyanamide: zCa:?JCN f CaH4(PO& --t 2CaHP04 CNNHz Ca:NCN 2CaHPOq ---+ Cas(P04)ef CNNHz and t h e free cyanamide t h u s produced is rapidly transformed into dicyanodiamide and other products. Up t o this point in t h e investigation, t h e fertilizer mixtures contained less t h a n I part of Cyanamid t o I O parts of acid phosphate. I n a mixture of moist acid phosphate and Cyanamid, containing 2 5 per cent of Cyanamid, there was also a rapid conversion t o dicyanodiamide (practically quantitative), but only about 60 per cent of t h e cyanamide was thus transformed, and after this point was reached very little further change resulted. It is evident, therefore, t h a t there is a limit t o t h e quantity of cyanamide which a given quantity of moist acid phosphate will transform. Reference has already been made t o the fact t h a t t h e mixing of Cyanamid with moist quartz caused a disappearance of cyanamide. It was found t h a t most of t h e cyanamide was changed into dicyanodiamide. T h a t this change would t a k e place was somewhat t o b e expected, since Perottia and Hager and Kern4 have shown t h a t when Cyanamid containing moisture was stored for several months a Iarge portion of t h e cyanamide was converted into dicyanodiamide. Finally, analyses were made of six samples of mixed fertilizer, containing varying amounts of Cyanamid, which had been prepared for certain 1 9 2 0 field tests carried out b y t h e Division.6 Four weeks had elapse& since t h e fertilizers had been mixed. Each sample was found t o contain a large quantity of dicyanodiamide, t h e
+
+
J . soc agr. Brabant et Hainant, 64 (1909), 161. (1913), 933. a Atti acad. Lincei, [SI 16 (1906). I, 48. 4 Z.angew, Chem., 29 (1916), 221. 5 Prepared for field tests in experimental work being conducted b y Dr. 0.Schreiner, Dr. J. J. Skinner, and Mr. B E. Brown, of Soil Fertility Investigations. The mixtures were prepared according t o the usual fertilizer practice, no modifications being introduced, with a view of studying any changes in the cyanamide content. 1
* THISJOURNAL, 6
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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
1920
amounts of this compound ranging from 11.4 t o 33.4 Ibs. per. ton of the fertilizer mixtures.
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25
I
E X P E R I M E N T A L DETAILS
MATERIALS E M P L O Y E D . Acid Phosphate-This was the usual type of fertilizer material, containing 1 6 per cent of available P~05. Ammo.nium Sui-fate-The crude material of commerce, containing z j per cent of "3. Potassium Sul.fate-The salt commonly used in fertilizer, containing 50 per cent of KzO. Cyanamid-This was technical calcium cyanamide, a hydrated material which was about a year old a n d contained 2 1 per cent of cyanamide and 2.3 per cent of dicyanodiamide. In two of t h e experiments, there was used a more recently purchased hydrated Cyanamid which contained 29.4 per cent of cyanamide and no dicyanodiamide. M E T H O D S OF ANALYSIS-A 20 g. sample (in mixtures containing more t h a n 6 per cent of Cyanamid, a I O g. sample was used) of t h e fertilizer mixture was stirred with 50 cc. of water. T o this were added I O O cc. of a saturated solution of barium nitrate and then a solution of barium hydroxide until t h e mixture was slightly alkaline t o litmus. T h e barium hydroxide was added to precipitate phosphates, b u t when ammonium sulfate was present this would have produced large amounts of ammonium hydroxide, which would convert some of the cyanamide t o dicyanodiamide. T h e barium nitrate wits therefore a d d e d t o prevent this ammonia formation. T h e mixture was agitated vigorously for 3 0 min with a mechanical stirrer, then transferred to a 500 cc. graduated flask, made up t o t h e mark, thoroughly mixed, and filtered. Two zoo cc. portions were measured out, a n d one was analyzed for cyanamide and t h e other for dicyanodiamide. To determine cyanamide t h e method of Perotti, as modified b y Brioux,' was employed, t h e precipitate of silver cyanamide being dissolved in dilute nitric acid and titrated against 0. I N ammonium thiocyanate solution. For t h e determination of dicyanodiamide t h e method described in t h e preceding paper was used. CHANGES I N CYANAMIDE CONTENT OF A MIXED FERTILIZER
Fertilizer Mixture A contained: Grams Acid phosphate 100 Potassium sulfa 12 Ammonium sulfate.. . . . . . . . . . . . . 42 Cyanamid. Dried peat.. 36
....... .......
.........
................... -
T h e materials were ground together in a mortar until they would pass through a zo-mesh sieve, and further mixed on a large piece of glazed paper. The mixture was analyzed immediately for cyanamide, and TABLE I-CHANGES IN CYANAMIDE CONTENTOF A COMPLETEMIXED FERTILIZER (MIXTUREA) TIME Mg. Cyanamide Days per G. Cyanamid Used Immediately after mixing 220.0 1 3 4 6 13
1
Ann. chim. a n a l , iS (1910), 341.
95.5 75.6 46.2 41.1 23.1
(b)
(a)
Grams Acid phosphate., , , , 90 Cyanamid.. 10
Grams
. . ..
..... ..
Acid phosphate.. Ammonium sulfate.. Cyanamid..
............
.........
45 18 5.5
(4
(C)
....... 45 ..... 6 .............. 5
Acid phosphate.. . . . . . 45 Dried peat.. . . . . . . . . . 18 Cyanamid.. 5.5
Acid phosphate.. Potassium sulfate.. Cyanamid
.........
The results of analyses are given in Table 11. TABLE ;I-CHANGES IN CYANAMIDE CONTENTOR VARIOUSMIXTURES OF CYANAMID" AND ACID PHOSPHATE WITH OTHER FERTWZER MATERIALS Mg. Cyanamide TIME er G. Cyanamid UsedDays (b) . (4 (dl 210 201 Immediately after mixing 202 196 180 152 192 ... 1 164 94 2
-(8
4 5 9
. .. .. .. .. .. a2 ..... . .139 ...... 120 ... 190 ...
E F F E C T OF MOISTURE CONTENT OF FERTILIZER MATERIALS
Moisture in t h e materials was determined by drying for 2 0 hrs. a t 100' C. Ha0 Per cent
Ammonium sulfate., . . . . . . . . . . 0 . 4 Potassium sulfate. . . . . . . . . . . . . 0 . 1 8 Dried peat. .................. 3 6 . 0 Acid phosphate.. 2.7
.............
I n t h e experiments described above t h e acid phosphate probably contained slightly more t h a n 2 . 7 per cent of moisture since some weeks elapsed before t h e moisture content was determined, a n d during this time i t had been stored in a paper bag exposed t o the drying action of t h e air. A t t h e time t h e experiments were performed t h e acid phosphate had already been considerably air-dried,-,Lso it contained much less
T H E J O U R N A L 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 Vol.
1114
moisture t h a n fresh acid phosphate, the moisture content of the latter being 6 t o I O per cent. I-CHAXGES
I N CYANAMIDE CONTENT
CYANAMID AND M O I S T ACID
PHOSPHATE-Mixture
B
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No.
II
of water. The filtrate was strongly acid t o litmus. Upon titration against 0.I N sodium hydroxide, using methyl red as an indicator, 2 . 7 5 cc. of the alkali were required.
was prepared containing: Acid phosphate (2.7 per cent HzO), grams . . . . 82 Cyanamid, grams.. ....................... 10 Water, grams .............................. 8 Total moisture, per c e n t , . . . . . . . . . . . . . . . . . . . . 10.2
The water was added t o the acid phosphate and the material ground in t h e mortar until uniform, the resulting mixture appearing quite moist. The Cyanamid was now added and this mixture again made uniform b y grinding. Almost a t once all evidence of moisture disappeared, and a fine, dry powder resulted. During this change, t h e temperature rose from 24’ t o 45’ C. When the resulting mixture was added t o water i t showed a strongly acid reaction toward litmus. The mixture was analyzed for cyanamide immediately and a t intervals over a period of 6 days, the results ‘being given in Table 111. TABLE 111-CHANGESIN CYANAMIDE CONTENT OF AMID”
A MIXTURE OF “CYANMOIST ACID PHOSPHATE (MIXTUREB) Mg. of Cyanamide per G. of Cyanamid Used TIME 210 0 hrs. 97.6 5 hrs. 21.4 2 days 17.3 6 days
AND
CYANAMID AND
AIR-DRY
ACID
PHOSPHATE-Mixture
c
contained: Acid phosphate (2.7 per cent HzO), grams.. Cyanamid, g r a m s . .
... 90
........................ 10 Total moisture, per cent.. . . . . . . . . . . . . . . . . . . . 2 . 2
a n d was mixed as i n t h e preceding experiment. Immediately after mixing i t contained 223 mg. of cyanamide per gram of Cyanamid, and after standing 18 days it ,was found t o contain 194 mg. per gram of Cyanamid used. CYANAMID A N D MOIST QUARTZ-A mixture, D , containing Quartz (ground t o 200 mesh), grams., . . . . . . . . 90 Water, grams .............................. 10 Cyanamid, grams, ......................... 11.1 Total moisture, per cent.. . . . . . . . . . . . . . . . . . . . 9
was prepared and analyzed as in the previous experiments. There was no rise in temperature when t h e mixture was prepared, and i t remained moist, clinging together like moist sand when the jar containing i t was rotated. After a day an odor of ammonia was given off. At the end of 2 wks. it was somewhat more dry, but the particles still clung together, and it was by no means the dry powder described in t h e experiment with moist acid phosphate. Table I V gives the results of analyses of this material. TABLE IV-CHANGES AMID”
IN
CYANAMIDE CONTENT OF
AND
TIME: 0 . hrs.
24 hrs. 2 days 9 days
MIXTUREOF “CYANMOIST Q U A R T Z (MIXTURED) Mg. of Cyanamide per G. of Cyanamid Used 213.6 185.8 131.25 31.5 A
The results for Mixtures B, C, and D are shown graphically in Fig. 2 . A V A I L A B L E ACID I N A C I D PHOSPHATE-one gram Of acid phosphate was extracted for 0 . j hr. with 500 cc.
“0
/
2
.
3 v DAY.
5
6
7
8
9
I N C Y A N A M I D E C O N T E N T O F “ C Y A N A M I D ” WHEN MIXED AIR-DRYACID PHOSPHATE, MOISTACID PHOSPBATE, AND MOISTQUARTZ
F I G . 2-CHANGES
WITH
A V A I L A B L E A L K A L I I N CYANAMID-one gram Of t h e Cyanamid was stirred vigorously with joo cc. of water for 30 min., and filtered. The filtrate, which was strongly alkaline t o litmus, required 169 cc. of 0.1N sulfuric acid for neutralization with methyl red as indicator. DICYANODIAMIDE
CONTENT
OF
THE
MIXTURES-
Twenty grams of Mixture B were stirred for 30 min. with 2 0 0 cc. of absolute acetone, and filtered. The acetone extract was evaporated t o dryness, leaving a quantity of long needles mixed with some ‘dark material. Recrystallization of the residue from water gave colorless needles, melting at 2 0 j O, whose melting point was unchanged when mixed with dicyanodiamide. A solution of these crystals gave yellow crystals of silver picrate monocyanoguanidine (m. p. 230’) upon treatment with picric acid and silver nitrate (Fig. I , preceding paper). A quantitative determination of dicyanodiamide in Mixture B gave 179 mg. of dicyanodiamide per gram of Cyanamid, .at the end of 4 wks. At the end of I j wks., the mixture contained 193.5 mg. of dicyanodiamide per gram of Cyanamid used. Mixture C contained but 7.9 mg. of dicyanodiamide per gram of Cyanamid, Mixture D at the end of 9 days contained 1 7 1 . 2 mg. of dicyanodiamide per gram of Cyanamid used. A quantitative conversion of t h e cyanamide t o dicyanodiamide would have required t h e appearance of 230 mg. of dicyanodiamide per gram of Cyanamid used. 11-SIMULTANEOUS
CHANGES I N CYANAMIDE AND
DICYANODIAMIDE CONTENT CYANAMID AND MOIST ACID
PHOSPHATE-The
follow-
ing Mixture E was prepared:
...
184 Acid phosphate (2.7 per cent HtO), grams.. Water, grams .............................. 16 Cyanamid, grams. ......................... 22.2 Total moisture per cent.. ................... 1 0 . 2
Analyses for cyanamide and dicyanodiamide were made immediately, and a t intervals over a period of 8 days. The results are shown in Table V and Fig. 3.
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T A B L Ev - s l M U L T . % N C O L ~ S CII.\SGES I N CYASAYIDE A S D DICY.4SODlAM1DE IS A 1IiXTL‘RUOF “ c Y I N . % M I D ” . \ S D 1 f O I S T h C 1 D PHVSPIIATB
