INDUSTRIAL A N D ENGINEERING CHEMISTRY
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The short oil rosin varnishes are less elastic and fail more rapidly than varnishes of the same length of oil, containing fossil or semifossil resins. The life of five 10-gallon rosin varnishes varies from 8 to 64 days, fall exposure, and gives a n average kauri reduction value of - 136, while three 10-gallon kauri resin varnishes lasted from 57 to 100 days in the fall test, and gave a n average kauri reduction value of -53. This, however, does not apply to blended varnishes, containing both fossil resins and rosin, nor to ester resin-tung oil varnishes. No further relationships of composition to durability can be found. Table IV shows wide variation in elasticity for varnishes containing similar percentages of oil. The diversity of materials used and the lack of uniformity in manufacturing these varnishes may be the explanation of this. The kauri reduction
Vol. 16, No. 7
values are in good agreement with the exposure data, as is shown in Table V. ACKNOWLEDGMEKT The writer wishes to thank the Educational Bureau of the Paint Manufacturers' Association of the United States (National Varnish Manufacturers cooperating) for assisting this work by donating funds for materials and for a n assistant. He wishes to express his appreciation to L. P. Nemzek, technical director of the Paint and Varnish Division, E. I. du Pont de Nemours & Company, and to L. V. Pulsifer, chief chemist, Valentine & Company, for their advice and interest in this investigation. A considerable part of the application of the varnishes and some of the physical testing was done by the writer's assistant, A. .N. Loudon.
Decomposition of Calcium Cyanamide on Storage' By K. D. Jacob, H. J. Krase, and J. M. Braham FIXED NITROGENRESEARCH LABORATORY, WASHINGTOK, D. C.
W h e n calcium cyanamide i s exposed to the atmosphere, it absorbs moisture and carbon dioxide. with the result that the nitrogen, which is originally present largely a s cyanamide nitrogen, i s partially changed to other forms. T h e extent of this decomposition i s dependent on conditions of storage a s to temperature, humidity, length of storage, and as to whether stored in bags or in bulk, and also a s to whether the calcium cyanamide has been hydrated and oiled. I n this paper are presented the resu!ts of a study on the nature and extent of the decomposition of calcium cyanamide under oarious storage conditions, o n quantities ranging f r o m a f e w kilograms to 450 metric tons. Some of the obseroations cover a period of 2.5 years. W h e n calcium cyanamide i s exposed in small lots ( af e w kilograms) to unusually seoere conditions of humidity and temperature for long periods, the cyanamide nitrogen is completely changed into other
forms, principally into dicyanodiamide and urea in the approximate proportions of 70 to 75 and 20 to 22 per cent, respectioely, of the total nitrogen. I n such a case, 7 to 8 per cent of the total nitrogen i s lost a s ammonia. Tests of this k i n d are to be regarded a s accelerated tests. for such seoere conditions are rarely, if ever, encountered in commercial storage. Untreated calcium cyanamide decomposes more rapidly than hydrated and oiled material. T h e decomposition of properly hydrated and oiled calcium cyanamide, stored in 45-kg. bigs over a period of 6 months, i s small under normal storage conditions a s to temperature and humidity. T h e decomposition of calcium cyanamide stored in bulk in such a manner that only a relatioely small surface is exposed to the atmosphere, a s in a silo, is almost negligible, the changes being confined largely to the top 20 cm.
HE important points with regard to the storage of calcium cyanamide are loss of nitrogen and nature and extent of the chemical changes occurring under various conditions. The conflicting and unsatisfactory data on the subject as given in the literature are due in part to the lack of adequate analytical methods and to the fact that, with a few exceptions, the experiments were made on only a few grams of material. The results of such experiments do not give accurate information on the storage of calcium cyanamide in commercial quantities. I n the course of the various investigations on calcium cyanamide a t this laboratory, numerous storage tests were carried out, under a variety of conditions, on quantities of material ranging from several hundred grams to 45.4 kg. (100 pounds) or more. In addition a study was made of the changes in calcium cyanamide stored in silos, a t U. S. Nitrate Plant No. 2 , Muscle Shoals, Ala., containing about 450 metric tons of material. The information obtained in these studies is presented in this paper.
failed to consider these points and erroneously concluded that *large quantities of nitrogen were lost from calcium cyanamide during storage. Corrected for changes in weight during storage, the results obtained by De Cillis,18* von Feilitzen,4 Kappen,14 Milo,21Burgess and Edwardes-Ker,26and Meyer and Gorkow33 show that the loss of nitrogen is dependent on humidity and temperature and on the length of storage. Even in almost completely decomposed samples the loss rarely exceeded 6 t o 7 per cent of the original total nitrogen. Very little loss was observed from samples stored in dry atmospheres and practically none from samples stored in closed containers. Prankez6could detect no loss of nitrogen from a pile of 41.9 metric tons (94,000 pounds) of calcium cyanamide stored for 7 months in a warehouse located a t Jacksonville, Fla , the floor being only a few feet above the St. Johns River. As to the literature concerning the chemical changes which calcium cyanamide undergoes on storage, the different investigators almost unanimously agree that, owing to the absorption of moisture and carbon dioxide, the nitrogen originally present as calcium cyanamide is transformed principally into dicyanodiamide and to a lesser degree into urea. Some other compounds are also reported t o be formed a t the same time in very small amounts. Perotti,2 as early as 1906, observed that dicyanodiamide was the principal nitrogen decomposition product of stored calcium cyanamide. Henschelz3later observed that considerable urea was formed under certain conditions. Hager and Kern28 found that when calcium cyanamide was treated with different quantities of water and stored in airtight containers the decreases in cyanamide and increases in dicyanodiamide were proportional to the amounts of water added. Miloz1states that in a 20-kg. bag of calcium cyanamide stored for 8 months in a
T
PREVI ous INVESTIGATIONS The early work on the subject was concerned chiefly with the loss of nitrogen from calcium cyanamide during storage. Calcium cyanamide readily absorbs moisture and carbon dioxide from the atmosphere, increasing in weight and decreasing in percentage of total nitrogen. Some of the earlier investigators 5
Received January 31, 1924.
* Numbers in text refer to bibliography a t end of article.
INDUSTRIAL A N D ENCINEERIiZ‘G CHEMISTRY
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dry warehouse under tropical conditions, 87 per cent of the total nitrogen was present as dicyanodiamide. Meyer and Gorkowaa observed that calcium cyanamide decomposed faster in damp than in dry atmospheres, also more rapidly in summer than in winter. A number of other investigations on the decomposition of calcium cyanamide in storage are reported in the literature. (See Bibliography.) However, most of the work was done with very small samples which, compared with the storage of quantities of commercial size, must necessarily be considered as greatly accelerated tests.
CHEMICAL REACTIONS INVOLVED
It hac been established that the decomposition of calcium cyanamide on storage is due principally to the action of water vapor. Carbon dioxide and temperature of storage also influence the rate of decomposition. Calcium Cyanamide is rapidly hydrolyzed by water, forming calcium acid cyanamide and finally free cyanamide.
+
2CaCNz 2H20--tCa(HCNz)z f Ca(0H)L Z Ca(HCPU’2)z ~ H z O Z = = Q H ~ C NCa(OH)2
+
+
(1) (2)
Reaction 2 is reversible to a slight extent. It has been well established that the formation of free cyanamide passes principally through the stages represented by Reactions 1 and 2, calcium acid cyanamide having only a temporary existence during the process of decomposition of calcium cyanamide in storage. However, other intermediate products may be formed. R/Iilo,*l for instance, states that basic calcium cyanamide and calcium cyanamide carbonate are formed. These compounds, however, are never present in more than very small quantities and have little or no bearing on the final decomposition products since they ultimately break up into free cyanamide, calcium hydroxide, and carbonate. The calcium hydroxide formed in Reactions 1and 2 and that originally present in hydrated calcium cyanamide readily absorb carbon dioxide from the atmosphere. Ca(OH)a
+ COz+CaCOa
+ HzO
(3)
The free cyanamide formed in Reaction 2 is hydrolyzed in part to urea. HzCNz
+ H%O-CO(NHz)2
(4)
The partial hydrolysis of free cyanamide to urea in an alkaline medium is to be expected, as shown by the recent experiments of Hetherington and Braham.35 I n completely decomposed calcium cyanamide only about 20 to 25 per cent of the total nitrogen is present as urea, the principal reaction being the polymerization of free cyanamide to dicyanodiamide. 2H2CN2+
(H~CNZ)~
(5)
It is statedzSthat amidodicyanic acid, melamine, ammeline, and ammonia are formed in small amounts during the decomposition of stored calcium cyanamide. These compounds, with exception of ammonia, are of little importance, since they are formed only in negligible quantities. Ammonia is probably the form in which any nitrogen lost during storage escapes. Lumps of decomposed calcium Cyanamide, when broken up, invariably give a decided odor of ammonia, which is probably due to the hydrolysis of urea. COCNHz)?
+ HzO---tCOz + 2NH8
(6)
Freshly prepared calcium cyanamide contains about 5 per cent of its total nitrogen in forms other than cyanamide nitrogen. This nitrogen is insoluble in water but is decomposed to a certain extent by dilute acids, with the formation of ammonia. The state of combination of this water-insoluble nitrogen is not definitely known, but it is thought to be present as metallic nitrides of more or less complex compositions.
.685
ANALYTICAL METHODS Total nitrogen was determined by the Gunning method.“ Caro’s methodbwas used for the determination of cyanamide and Brioux’s modification6of Caro’s method for dicyanodiamide. The latter method does not give accurate results for dicyanodiamide in the presence of amidodicyanic acid or when more than about 25 per cent of the total nitrogen is present as urea. At the time this investigation was undertaken, however, it was probably the most reliable of the many proposed methods, and the experimental data indicate that interference from the sources previously mentioned was not particularly serious under the conditions of the experiments. Urea was determined by the urease method“ and ammonia by aerating a weighed sample with sodium carbonatechloride solution in the apparatus devised by Matthews.d Calcium was determined by dissolving a weighed sample in hydrochloric acid, precipitating as the oxalate, filtering, and titrating the sulfuric acid solution of the oxalate with standard permanganate. I n all cases the actual determinations of total water were made by the Penfield tube method.e The gases evolved were passed through granular lead chromate and over a copper gauze, in order to oxidize ammonia and reduce any oxides of nitrogen present, and the water weighed directly. Carbon dioxide was determined by treating a weighed sample with acid, absorbing the carbon dioxide evolved in standard barium hydroxide solution, and titrating the excess barium hydroxide with oxalic acid, using phenolphthalein as an indicator.
EXPERIMEKTAL EFFECT O F STOR.4GE CONDITIONS ON THE RATEO F DECOMPOSITIOK O F H Y D R s T E D AND OILED CALCIUM CYAWAMIDECommercial calcium cyanamide is usually treated with 6 to 7 per cent of water and about 3 per cent of oil, and the material so treated is referred to in this paper as “maximum hydrated and oiled” calcium cyanamide. This quantity of water is sufficient to destroy any carbide that may be present in the freshly prepared material and to hydrate the calcium oxide. It serves the twofold purpose of eliminating the possible generation of acetylene and the consequent fire hazard, and reducing the bursting of bags resulting from the hydration of the calcium oxide during storage. Hydrated calcium cyanamide is an extremely fine, dusty powder, very disagreeable to handle, and it is primarily for this reason that the oil is added, although the presence of oil also retards somewhat the rate of decomposition of the material in storage. The addition of water and oil in these proportions reduces the total nitrogen content of the material from about 21.5 per cent to about 19.5 per cent. For storage or shipment in bulk, hydration of the calcium oxide is not so important, but it is necessary that all easily decomposable carbides be destroyed. The addition of about 3 per cent of water suffices for this purpose, oil being added to facilitate handling. For the purposes of this paper, calcium cyanamide treated in this manner is designated as “minimum hydrated and oiled.” I n order to determine the effect of storage conditions on the rate of decomposition of minimum and of maximum hydrated and oiled calcium cyanamide, 2.3-kg. (£) bags of each material were stored at a constant temperature of 30” C. and humidity of 70 per cent, and also in a well-ventilated, unheated storage room a t atmospheric temperature and humidity. In the latter case the average temperature was Assoc. Official Agr. Chem , Methods, 1921, p. 7. Pranke, “Cyanamid,” 1913, p. 20. The Chemical Publishing Co., Easton, Pa. Fox and Geldard, THISJOURNAL, 15, 743 (1923). J . A g r . S c i , 10, 72 (1920). e Penfield, A m . J . Sci , [31 48, 31 (1894). a
Vol. 16, N o . 7
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686
The results given in Table I are partially presented in graphic form in Fig. I. I n all cases, except Expt. 6, the analytical results have been corrected for increases in weight of the bags during storage. The decrease in total nitrogen in Expt. 6 was probably due to the absorption of a small quantity of water, as the container was not perfectly airtight. loo The results given in Table I show that temperature and I / / / / / / I / I 1 1 1 humidity have a pronounced effect upon the rate of decomposition of hydrated and oiled calcium cyanamide in storage. Two and three-tenths kilogram samples of hydrated and oiled calcium cyanamide stored a t a constant temperature of 30" C. and relative humidity of 70 per cent were almost completely decomposed within one year, with approximately 70 per cent of the total nitrogen in the form of dicyanodiamide and 21 per cent as urea. In samples of a similar size stored at atmospheric temperature and humidity, average of 15" C. and 73 per cent, respectively, for the same period, only about 10 to 14 per cent of the total nitrogen was present as dicyanodiamide and 8 to 9 per cent as urea, despite the fact that a fresh surface was exposed to the action of atmospheric moisture and carbon dioxide a t three different periods. The rate of decomposition was not only dependent upon the temperature and humidity of storage, but also upon the size of the Durdfion o f Expermen,' -Months sample, as shown by the results of Expts. 4 and 5 . There was no significant difference in the rates of decomposition At each period of analysis the entire contents of the 2.3-kg. of the same quantities of minimum and of maximum hydrated bags were thoroughly mixed in order to obtain a uniform and oiled calcium cyanamide, although the former decomposed sample. Thus a fresh surface was exposed to the action of slightly faster under severe storage conditions and the latter moisture and carbon dioxide a t each period of sampling and under atmospheric conditions. Variations in the increase in therefore decomposition proceeded at a faster rate than if weight of, and absorption of carbon dioxide and water by, the bags had remained undisthrbed. The 45.4-kg. bag was the two materials under similar storage conditions were partly sampled by introducing a sampling tube of the type commonly due to the difference in the quantity of water originally added. used for fertilizers and withdrawing portions of a suitable Loss of nitrogen was greatest, about 6 to 7 per cent of the size, except a t the end of the storage period when the entire original total nitrogen, in the samples stored a t 30" C. and contents of the bag were thoroughly mixed before samples 70 per cent humidity. A strong odor of ammonia was for analysis were taken. noticed when these samples were analyzed a t the end of one year. No appreciable decomposition occurred in maximum TABLE I-EFFECT OF STORAGE CONDITIONS ON THE RATE OF DECOMPOSITIONhydrated and oiled calcium cyanamide stored in closed OF MINIMUM HYDRATED AND OILEIDCALCIUM CYANAMIDE containers for 6 months. EFFECTOF WATERON CALCIUMCYAXAMIDE STOREDIN CLOSEDCONTAINERS AT CONSTANT TEMPERATr;RES'-The calcium cyanamide used in these experiments originally contained 7.3 per cent water combined as calcium hydroxide, although none of the nitrogen originally present as calcium E x p f . 1. 2.3-kg. (5-pound) bag stored at 30° C . and 70 per cent humidity cyanamide had been converted into dicyanodiamide or urea. 0 19.71 92.2 0.5 1.8 0.41~ ... 9.67 Samples of several hundred grams each of this material were 2.74 6:93 2.1 5.7 88.7 1 19.35 1:83 7.96 18.67 26.63 10.2 29.1 58.3 3 18.58 5.73 18.35 25.97 44.32 agitated in a small mixing machine and properly sprayed with 17.9 63.5 12.9 6 18.64 5.43 35.63 24.26 59.89 sufficient water to bring the total free and combined water 21.1 69.9 7.4 12 18.29 7.20 Expt. 2 . 2.3-kg. bag stored at atmospheric temperature and humidity content up to the figures indicated in Table 11. The hydrated 1.91 4.91 6.82 samples were immediately stored in water-tight iron cans in 0.0 0.2 93.4 1 19.17 2.74 4.57 7.71 12.28 2.7 3.9 89.1 3 19.01 3.60 8.33 7.85 16.18 4.1 4.2 84.8 6 19.24 2.38 thermostats maintained a t 15" and 30" C. 15" C. and the relative humidity 73 per cent as recorded by a Friez hygro-thermograph. A 45.4-kg. (100-pound) bag of maximum hydrated and oiled calcium cyanamide was also stored at atmospheric temperature and humidity and 22.7 kg. (50 pounds) of the same material were stored in a closed container.
12
18.80
Expt. 3.
4.62
77.6
10.0
7.9
13.58
7.31
20.89
2.3-kg. (5-pound) bag stored at 30' C . and 70 per cent humidity
...
0
18.44 92.2 1.0 0.8 ' 0.670 18.13 1:iS 90.0 2.2 1.Q 2.63 2.95 5.38 3 17.60 4.55 66.4 21.1 10.2 6.76 12.92 19.68 6 17.30 6.18 18.1 65.2 19.1 16.89 15.96 32.85 12 17.44 5.42 10.0 68.2 20.9 34.15 17.90 52.05 Exdt. 4. 2.3-kg. . bag . stored at atmospheric temperalure and humidity 1.89 1.73 3.62 0.0 1.3 1 18.39 0.27 91'.8 4.6 5.46 3.15 8.61 1.2 90.8 3 18.09 1.S9 4.2 8.68 3.68 12.36 14.1 79.6 6 18.20 1.30 12 17.086 7.37 78.7 13.5 8.6 12.95 3.62 16.57 Expt. 5 . 45.4-kg. (100-pound) bag stored at atmospheric temperature and
1
.
.
I
humidity
18.23 1.24 18.42 0.11 18.90b 18.07 2:Ol
1 3 6
12
Expt. 6 .
4' 6
18.19 18.23
....
92.1 92.8 90.7 82.7
2.5 1.0 1.5 5.5
0.12 0.20 0.10 4.50
0.88 3.57 6.48 5.13
1.00 3.77 6.58 9.63
22.7 kg. ( 5 0 pounds) stored in closed container
92.3 92.7
Con present at start of test. b Probably in error.
o
0.2 0.5 1.7 8.1 0.8 0.0
0.8 1.3
.. ..
.. ..
.. 1 .
TABLE 11-EFFECT OF WATERON CALCIUM CYANAMIDE STORED I N CLOSED AT 1 5 O AND 30° C. CONTAINERS --TEMPERATURE 30° C.-----TEMPERATURE 15" C.----. Per cent Total Per cent Total Nitrogen as Total Nitrogen Dicyanoas Total Dicyano- HsO in HzO in diarnSample Time CyanamdiamSample Time Cyanamide ide Per cent Days ide ide Per cent Days 1 92.3 0.7 1 94 2 0.0 10.7 19.3 14
33 6
1
14
92 4 94.1 93 2
1.0 0.0 0.0
17.7 29.8
5 1 5 1 5
,929 88.5 77.4 81.5 43.4
0 6 5.6 15 8 12.7 52.4
The results given in Table I1 show that the rate of decomposition of calcium cyanamide is dependent upon both the temperature of storage and the amount of water added to the material. At 15" C. conversion of cyanamide to dicyanodiamf Results obtained by E. B. Vliet and W. E. Kuentzel at this laboratory in experiments on the hydration of calcium cyanamide.
July, 1924
IhrD UXTRIAL AND ENGINEERING CHEiMIXTRY
ide and other compounds is very small in 14 days, even in the presence of as much as 33.6 per cent total water. On the other hand, the rate of decomposition a t 30" C. is dependent upon the amount of water present and is very rapid when the total water reaches 29.8 per cent. The results obtained a t 30" C. confirm the observations of Hager and Kern previously mentioned. The results as a whole possess some practical significance with regard to the agricultural use of calcium cyanamide, inasmuch as they indicate that accidental wetting of the material during the winter or early spring would probably not result in serious decomposition of the cyanamide provided tho temperature of storage did not greatly exceed 15" C. On the other hand, calcium cyanamide exposed to rain, or water other than that present in the atmosphere, during the summer should be applied to the soil as soon as possible in order to avoid formation of dicyanodiamide, which is generally considered as possessing no value for fertilizer purposes. Exposuro of calcium cyanamide to rain would, however, in either case cause serious caking, and prolonged exposure might result in loss of nitrogen due to the leaching of free cyanamide and calcium acid cyanamide. DECOMPOSITION OF BAGGED CYANAMIDE DURIKG LONG PERIODS OF STORAGE-FOr these experiments, bags containing approximately 45.4 kg. (100 pounds) of maximum and minimum hydrated and oiled calcium cyanamide were stored under differing conditions of temperature and humidity and then various portions of each bag analyzed. One bag of maximum hydrated and oiled calcium cyanamide was stored a t atmospheric temperature and humidity, the average of which was 15' C. and 70 per cent, respectively, as recorded by a Friez liygro-thermograph. Bags of maximum and minimum hydrated and oiled and untreated calcium cyanamide were also stored in a room maintained a t a constant temperature of 30" C.and a relative humidity of 70 per cent. I
Depth o f 8amp/es-Cm.
At the end of 12 months the bag stored a t atmospheric temperature and humidity was sampled and analyzed, with the results as given in Table 111. TABLE III--COMPOSITION
O F DIFFBRENT P O R T I O N S O F A 45.4-KG. BAG OF MAXIMUX HYDRATED AND OILED CAI,CIUM CYANAMIDE STORED FOR 12 M ~ N T HAT S ATMOSPHERICTEMPERATURE A N D HUMIDITY Total -PER CENT TOTAL NITROGEN ASNitrogen DicyanoSAMPLE TAKEN FROM Per cent Cyanamide diamide Urea S t a r t of experiment 18.44 92.2 1.0 0.8 Entire bag 16.48 82.7 8.1 5.5 Top of bag 15.58 19.5 69.1 8.0 Interior of bag 17,22 87.6 4.2 3.5 Calcium cyanamide treated with 7 per cent water and 2 5 per cent oil Average temperature during storage, 15' C. Relative humidity, 73 per cent
At the end of 14 months the bags stored a t 30" C. and 70 per cent humidity were analyzed. Samples were taken from the top of the bag, from the interior, and also a representative sample from the entire bag. As was to be expected, the top of the bag showed the greatest degree of decomposition, while the interior showed the least.
687
In general, it can be said that the maximum hydrated and oiled calcium cyanamide resists decomposition better than the minimum hydrated and oiled material, which in turn is somewhat more satisfactory than the untreated calcium cyanamide. The nitrogen lost from the bags approximates fairly well the figures given in Table I, Expts. 1 and 3, in which the loss was calculated from the increase in weight. Caking was quite serious in all samples stored a t 30" C. and 70 per cent humidity, but the maximum hydrated and oiled material appeared somewhat best in this respect. DECOMPOSITION OF UNTREATEDCALCIUMCYAXAMIDE IN SILOSFOR LONQPmIoDso--Information on the STORED changes occurring in calcium cyanamide when very large quantities are stored in bulk is particularly important. The only experiments reported in the literature concerning the storage of large quantities of calcium cyanamide in bulk are those carried out by P r ~ ~ n kinewhich , ~ ~ only the loss of nitrogen mas determined. The closing down of U. S. Nitrate Plant No. 2, Muscle Shoals, Ala., on February 9, 1919, afforded an opportunity to study the rate of decomposition and the penetration of moisture and carbon dioxide into calcium cyanamide in silos a t the plant. The silos are constructed of concrete, are 4.9 meters (16 feet) square, and each has a capacity of 421 cubic meters (14,885 cubic feet) or about 450 metric tons. They are covered by large, loose-fitting iron doors. Nine silos are contained in a large building, which is well ventilated by numerous windows. The calcium cyanamide was delivered direct from the mill room to the silos by a series of bucket elevators and screw conveyors, so that it was exposed to the air only during its passage from the mill room. The experiments were carried out on silo No. 9. The plan of the investigation was to take samples of the calcium cyanamide at 5-cm. (2-inch) intervals to a total depth of 45 cm. (18 inches), and by frequent sampling to obtain data on the rate of decomposition of the material a t the different depths. Accurate sampling of the material a t the different depths presented a difficulty, which was finally overcome in a satisfactory manner by the use of a thin iron tube, 45 cm. long and 5 cm. inside diameter, with slots cut into the side 5 cm. apart to allow the insertion of thin slide gates which divided the tube into 5-cm. sections. In taking the samples a point was selected on the surface which had not been disturbed by previous sampling and the tube was carefully inserted in such a manner that calcium cyanamide came up into the inside of the tube t o the same level as the surface of the material on the outside. When the tube had been properly filled it was carefully lifted out and the slide gates inserted, the 5-cm. sections being removed separately and placed in airtight containers for analysis. Analyses were made a t seven different periods during 30.5 months' storage, but the results given in Table IV for the storage periods of 11.5and 21.5 months are sufficient to show the general trend of the decomposition of calcium cyanamide stored in bulk. The results are partially presented in graphic form in Fig. 11. Examination of the data in Table I V will show that formation of dicyanodiamide was quite serious in the first 10 cm. of the material after 11.5 months, but in the samples taken a t a depth of 15 to 20 cm., after 21.5 months, only 2.4 per cent of the total nitrogen was present as dicyanodiamide, and even These experiments were planned and started by J. F. Carle, formerly chief chemist, t l . S. Nitrate Plant No. 2, who carried on the investigation from February 9, 1919, t o March 6, 1920. A description of the work and a portion of the analytical data are given in an unpublished report by Mr. Carle on "The Behavior of Calcium Cyanamide during Storage a t U. S . Nitrate Plant No. 2." The investigation was continued by this laboratory until September 1, 1921.
INDUSXRIAL A N D ENGINEERING CHEMISTRY
688
after 30.5 months (results not given in table) this figure was only 8.3 per cent. The formation of dicyanodiamide was always accompanied by production of urea in smaller quantities, the sum of the two corresponding approximately to the decrease in cyanamide. The results as a whole show that the decomposition of calcium cyanamide, stored in bulk for a period of about 2.5 years, is confined almost entirely to the first 15 cm. of exposed material. TABLE IV-COMPOSITION OF UNTREATED CALCIUMCYANAMIDE STORED IN SILOSAT U. S. NITRATS PLANT No. 2. MUSCLE SHOALS. ALA. Depth of Total PERCENT TOTAL NITROGEN AS Total
CyanDicyanoHzO coz amide diamide Urea Per ceqt Per cent I-Analysis after 11.5 months’ storagea 14.50 42.3 39.7 12.1 12.91 15.49 0-5 17.61 2.16 71.6 17.9 12.60 6.8 5-10 19.00 95.1 2.1 8.76 1.18 0.4 10-15 19.34 95.8 0.5 7.70 0.0 1.14 15-20 19.60 94.6 0.5 7.30 1.01 0.0 20-26 19.75 94.1 5.61 0.93 0.0 0.0 25-30 19.90 94.2 4.28 0.77 0.0 30-35 0.0 2.96 94.1 0.74 20,40 0.0 0.0 35-40 94.7 1.27 0.70 20.96 0.0 0.0 40-45 2-Analyses after 21.5 months‘ storageb 11.69 68.9 21.6 12.55 27.68 0-5 5.5 61.7 17.03 13.02 20.9 19.39 12.8 5-10 27.5 1.57 61.0 16.60 6.8 16.12 10-15 18.19 2.5 89.5 .9,62 2.4 0.80 15-20 8.28 0.78 20-25 18.67 1.4 92.1 1.4 7.40 93.7 0.5 0.8 0.68 18.89 25-30 0.55 18.99 6.84 93.7 0.0 0.7 30-35 19.11 6.69 93.7 0.69 35-40 0.3 0.6 19.17 5.11 93.8 0.5 0.46 40-45 0.5 a Analyses made a t U. S. Nitrate Plant No. 2 using the methods previously outlined. b Analyses made a t Fixed Nitrogen Research Laboratory. Sample Nitrogen Cm. Per cent
The total water and carbon dioxide were also present in the largest amounts in the first 15 em. of material, after which they gradually decreased as the interior of the silo was approached. Rhodes, Jones, and Dougaqh in recent investigations on the air slaking of calcium limes, found that the moisture content increased rapidly at first until practically all the calcium oxide was converted into the hydroxide, and then decreased slowly as the hydroxide was changed to the carbonate. Moreover, the rate of absorption of carbon dioxide was relatjvely much slower than the rate of absorption of moisture. This was due, as the authors point out, to the fact that the concentration of carbon dioxide in the air is relatively much lower than the concentration of water vapor. It is interesting to note that the absorption of water and carbon dioxide by calcium cyanamide proceeds in much the same manner as in the case of calcium oxide. The top layer of the material in the silo consisted of a hard crust, probably 2.5 or 5 cm. thick, covered with a thin layer of dust, probably 5 mm. thick. Below the crust the material was unoaked. Loss of nitrogen from calcium cyanamide stored in the silo was calculated from the decrease in the nitrogen-calcium ratio during storage. The results were not entirely consistent, but taken as a whole they indicated the following points: (1) The greatest losses of nitrogen occurred in the first 10 cm. of material where the maximum quantities of water and carbon dioxide were absorbed. ( 2 ) The loss of nitrogen progressively decreased with increasing depth in the material. (3) Loss of nitrogen apparently occurred in two stages-a slight loss occurring when the freshly prepared Calcium cyanamide was first placed in storage, which was probably due to the action of moisture on traces of easily decomposable metallic nitrides, and further losses occurring as the calcium cyanamide decomposed probably due to the hydrolysis of urea. (4) After 30.5 months’ storage 8.6 and 5 per cent, respectively, of the total nitrogen originally present were lost from the 0 to 5 and 15 to 20 cm. layers of material.
ACKNOWLEDGMENT The authors wish to acknowledge assistance rendered by E. J. Fox, L. A. Pinck, M. A. Kelly, K. S. Love, M. S. Sherman, Chem. Met. Eng., 28, 1066 (1923).
Vol. 16, No. 7
J. A. McCormick, W. Rosett, and L. Smith in obtaining the analytical data presented in this paper.
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