June, 1925
I S D r S T R I A L A N D ENGINEERING CHEMISTRY dH 15,600 _ -dn (n 1.737)?
for the nitric acid partial pressures. With nitric acid the plotted results actually show this to be the case. With water the lines are nearly parallel, as they should be because the value of B varies little with concentration.
+
dh= dN
8974
+ 1.737 N ) 2
(1
-4few calculations of B with the aid of Equations 4 and 5 follow, taking the latent heat of " 0 3 to be 7500 calories and of H20, 10,OOO calories. Per cent d z & B B HXOa by weight 20 40 70
n 14.0 5.25 1.50
N 0.071 0.19 0.67
dn 63 320 1490
dN 7410 5070 1920
635
Ha0
10,063 10,320 11,490
HNOa 14,610 12,570 9,420
According to the above the slopes of the log p vs. 1/T lines should increase with increasing concentration for the water part'ial pressures and decrease with increasing concentration
Bibliography I-Roscoe, J . Chem. SOC.(London), 13, 146 (1861). 2-Creighton and Githens, J . Franklin Insl., 119, 161 (1915). 3-Carpenter and Babor, Am. Insl. Chem. Eng., preprint Denver meeting, July, 1924. 4-Berl and Samtleben, 2. angew. Chem., 36, 201 (1922). Mem. poudres, 20, 4 0 (1923). 5-Pascal, 6-Burdick and Freed, J . A m . Chem. SOC.,43, 526 (1921). 7 S p r o e s s e r and Taylor, Ibid., 43, 1784 (1921). 8--Rlemenc, Vienna, private communication, August 1, 1924. 9-Saposhnikoff, 2. p h y s . Chem., 13, 225 (1905).
Hygroscopicity and Cakiness of Fertilizer Materials' By A. B. Beaumont and R. A. Mooney ?vf ASSACHUSETTS AGRICULTURAL COLLBGE, AMHERST,MASS.
HE behavior of fertilizer materials stored under different conditions of humidity is important to the manufacturer, dealer, and consumer of fertilizer materials or mixed goods. There is little in the literature bearing on the subject. Van Harreveld-Lako2 investigated the hygroscopicity of several nitrogenous materials under the conditions of humidity prevailing on the island of Java, and Edgar and Swan3 determined the vapor pressures of the saturated solutions of several types of fertilizer materials. The results of a study of the hygroscopicity and cakiness of eighteen fertilizer materials and three mixtures under conditions of temperature and humidity prevailing in Massachusetts during the summer season, the season of greatest humidity, are here reported. The average mean monthly temperature for June, July, and August for the period 191923 was 20.1' C., and the average mean monthly relative humidity for this period was 78.0 per cent. The maximum relative humidity for the same period was 97.5 per cent. These two points of humidity, as well as the point midway between them-namely, 87.75 per cent-were chosen for study. The relative humidities of 73.0 and 68.0 per cent were selected as having the greatest promise of establishing conditions under which no moisture would be absorbed, based upon calculations involving Edgar and Swan's data.
T
When samples were very moist it was necessary to give them a preliminary drying in a desiccator before subjecting them to the higher temperature, in order to prevent "crawling." For the study in cakiness the materials were exposed in a similar manner, except that the amount of acid was increased to correspond with larger amounts of material used and the time was extended to 14 days. After exposure the material was immediately transferred to molds of LL1/pinch"(1.6 cm. inside diameter) brass pipe 3.2 cm. long, greased, and lined with paper to prevent sticking, and with the exception of muriate of potash and ammonium nitrate, which were dried in an oven a t 40" C., were allowed to dry a t room temperature. After drying, the cylinders of caked fertilizer were cut to 1.28-cm. lengths and placed in a testing machine for determination of the crushing strength. Sufficient replicate determinations were made in each case to reduce the experimental error, which was found to be especially high in the crushing tests, to a point where differences might be significant. I n the humidity determinations five to ten replicates were run and in the crushing tests it was necessary to run five to twenty-nine tests. The probable error of the mean of each series of tests u-as worked out by Peter's formula. Results
Methods
The static method was employed. Desiccators (15.2 cm. diameter) were converted into humidors and dilutions of sulfuric acid based upon tables of Landolt-Bornstein and Roth were used to maintain the necessary conditions of humidity. All determinations were conducted in a constant-temperature room maintained a t 20.1" C. The material studied, all passing a 0.5-mm. sieve, was placed in aluminium boxes (5.1 cm. diameter) to the depth of 5 to 7 mm., and the boxes were placed on a coarse wire screen support immediately over the sulfuric acid solution and exposed for 7 days, 200 cc. of acid being used in each humidor. The inorganic materials were dried to a constant weight a t 130" C. according to the official method,4 and organic substances were dried a t 100" C. 1
2
3 4
p. 1 .
Received March 2, 1925. d r c h . Suikerind., 20, 1254 (1921). J . A m . Chem. SOL.,44, 570 (1922). .4ssoc. Ofiicial Agr. Chem., Methods, Revised to November 1, 1919,
Table I-Materials Phosphoric Ammonia acid Potash MATERIAL Per cent Per cent Per cent ilmmonium nitrate (crystalline),, , . , , 40.07 Ammonium nitrate (granular) . , ., , , , . 41.20 Ammonium sulfate.. . . . . . . . . . . . . . . . 24.96 ... 32.50 Ammonium sulfate nitrate . . . . . . . . . . ... Calcium cyanamide. . . . . . . . . . . . . . . . .. . . . 2 4 . 2 8 ... ... Calcium nitrate, . . . . . . . . . . . . . . . . . . .. . . . 1 5 . 7 8 ... ... Sodium nitrate.. . . . . . . . . . . . . . . . . . . . . . . 1 8 . 2 1 ... ... Urea. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5 . 5 0 ... .,. Cottonseed meal. . . . . . . . . . . . . . . . . . .. . . . 7.28 3.00 1.00 Dry ground f i s h . . . . . . . . . . . . . . . . . . . . . . 9.00 LO0 ... . . . . 9.99 4.58 ... Bone m e a l . , . . . . . . . . . . . . . . . . . . . . . . .. . . . 4.83 24.00 ... Acid phosphate.. . . . . . . . . . . . . . . . . . . . 16.00 ... ... Calcined phosphate . . . . . . . . . . . . . . .. . . . ... 27,00 ... Rock phosphate.. . . . . . . . . . . . . . . . ... 32,OO Kainite. . . . . . . . . . . . . . . . . . . . . . . . . . . . ... ... 12:oo Muriate of potash . . . . . . . . . . . . . . . . . . ... ... 50.00 Potassium sulfate. . . . . . . . . . . . . . . . . . . . . ... ... 48.00 "4-8-4 4 8 4 4 4 8 (3j 4 4 8 (1) Made of nitrate of soda, acid phosphate, and muriate of potash; no filler added. (2) Same as (1) except half of ammonia was supplied by tankage; no filler added. (3) Same as (1) except peat was added as filler.
... ... ...
(3
it),
INDUSTRIAL AND ENGINEERI-VG CHEMISTRY
636
Table 11-Hygrbscopicity a t Higher H u m i d i t i e s PERCENT WATERBASEDo s OVEN-DRY WEIGHT 97.5% 87.7570 78 0% Humidity. ,” 36.5 +O. 1 27.5 t 0 . 2 Ammonium nitrate (crystalline) . . . . . . . . . 17.010.1 23.6 t o . 1 Ammonium nitrate (granular), 29.8t0.3 1 1 . 5 10.1 22.4 t 0 . 7 16.010.3 2.410.0 Ammonium sulfate.. . . . . . . . . . . . . . . . . . . . 36.2h0.2 25.9 a 0 . 1 Ammonium sulfate nitrate. 11.6 1 0 . 1 6 4 . 1 10.1 5 3 . 5 10.1 4 2 . 1 10.1 Calcium nitrate.. ...................... 3 7 . 5 10.1 2 4 . 0 *O 1 17.4t0.1 Sodium nitrate.. ...................... 26.8 1 0 . 2 40.9 1 0 . 2 8.7tO.l 21.1 1 0 . 3 1 3 . 0 10.0 6.1tO.0 2 7 . 7 10.1 20.710.0 12.8tO.O 10.9AO.O 20.110.0 17.5 t O . 0 d fish.. ...................... 1 6 . 1 10.0 9,210.0 10.410.0 2 9 . 6 h 0 .O 22.9*O.O 1 5 . 7 10.0 15.710.1 29.6k0.2 4.lt0.0 0.510.0 1 . 5 10.1 0.4tO.O 4.2tO.O 6.710.0 2.810.1 23.5t0.1 3 0 . 9 10.1 12.7*O.O 1 4 . 5 10.1 32.81 0 . 2 4 0 . 0 10.3 9.9*0.l Sulfate sf potash.. ..................... 15.510.0 2.6*0.0 4 3 . 4 10.1 60.2 1 0 . 1 2 7 . 1 10.1 “4-8-4” (1) (See Table I) 55.810.3 36.7t0.1 2 0 . 0 10.2 65.8*O. 1 57.410.2 ( 3 ) . ......................... 31.81 0 . 1 MATERIAL
..........
....
.
~~
.............
....
111-Hygroscopicity
at Lower H u m i d i t i e s
-HUMIDITY73.0% 8.9t0.1 0.610.0 7.210.1 4.710.0 30.610.2 5.8*0.1 ............................ 3.210.0 .............. 9.310.0 6.110.1
MATERIAL Ammonium nitrate (granular) Ammonium sulfate. ............. Ammonium sulfate ............ Calcium cyanamide ...........
Table IV-Cakiness,
68.0% 3.910.1 0.510.0 2.610.2 3.810.0 19.6*0.1 4.110.0 2.010.0 5.4t0.1 4.9t0.1
-
Kilograms of Crushing Force per Square Centimeter HUMIDITY-MATERIAL 97.5% 87.75% 78.0% Ammonium nitrate (crystalline). .. 1 8 . 7 2 t o . 67 4 . 9 9 1 0 . 4 1 3 . 8 2 10.26 Ammonium nitrate (granular).. 1 . 5 0 *O. 12 4 . 3 4 10.25 2 . 0 2 1 0 . 20 4 . 2 6 1 0 . 11 2 . 7 6 10.13 0 . 0 0 10.00 Ammonium sulfate., 5 . 1 5 1 0 . 2 4 1 1 . 9 8 1 0 . 5 6 12.91 1 0 . 3 4 1.71*0.06 0 . 6 6 t 0 . 0 5 0 . 5 7 t 0 . 0 5 Calcium nitrate.. Out of 30 trials 29 failed to break with a force of 52.81, one broke a t 4 4 . 4 0 Sodium nitrate (ground). . . . . . . . . 4 . 2 5 10.17 3 . 2 8 1 0 . 1 9 2 . 4 3 10.07 Sodium nitrate (not ground). . . . . . 2 . 9 8 10.12 1 . 0 4 1 0 . 0 7 0 . 8 3 1 0 . 0 7 Urea.. .. 1.9210.06 3.02*0.11 1.9810.08 Cottonseed meal. None None None None None None None None None 19 4 . 7 9 1 0 . 1 7 1 . 2 4 * 0 , 1 1 None None 55 1 2 . 4 8 t 0 . 4 6 5 . 9 7 1 0 . 1 5 39 36.19.tO.38 1 9 . 7 7 t 0 . 6 5 38 3 . 0 9 * 0 . 1 0 None 1 6 . 3 8 t 0 . 2 5 11.34*1.46 None 42 4 . 6 4 t 0 . 2 4 None 57 1 . 0 7 t 0 . 1 1 None
... ............
..
............... .....
..
The data show that there are significant differences (if the difference is 3.8 times its probable error the chances are 30 to 1 and the difference is considered significant) between the hygroscopic values for the same substance at different humidities, and that there is a changing relationship among the materials as to their hygroscopicity, depending upon conditions of humidity. Differences tend to lessen with increasing humidity. Calcium nitrate was the only material to absorb sufficient moisture at 78.0 per cent humidity to show free water. At 87.75 per cent humidity ammonium nitrate (both samples), ammonium sulfate nitrate, calcium nitrate, sodium nitrate, and muriate of potash showed free water; and at 97.5 per cent urea and kainite showed free water. None of the remaining inorganic materials nor any of the organic materials or mixtures showed free water under the conditions of the experiments, although the moisture content was w r y high in some cases and the substances appeared moist. Urea, although chemically organic, behaved like an inorganic substance. The fertilizer materials studied were such as are ordinarily used in the trade and therefore of varying degrees of purity. The presence of impurities probably explains the high moisture content of certain materials and mixtures, for, as Edgar and Swan2 point out, the vapor pressure of a solution of a mixture of salts is lower than that of any constituent.
5’01. 17, S o . 6 AS~ 100 COMPARED WITH C A ~ N O 97.5% 87.75% 78.0% 57.0 51.5 40.3 29.0 46.5 44.0 5.7 35.0 30.0 27.5 56.5 48.4 100.0 100.0 100.0 41.2 58.5 44.8 20.6 63.8 50.0 14.5 33.0 24.3 30.4 43.1 38.8 25.8 31.3 32.8 21.8 25.1 19.5 37.2 46.1 42.8 46.1 29.4 9.8 3.4 0.9 0.8 15.3 7.8 6.7 48.3 44.0 30.1 34.5 62.4 61.4 24.3 18.5 6.3 64.4 93.9 81.1 87.1 68.6 47.4 75.5 102.7 107.2
Curves plotted from the hygroscopicity data with relative humidity as abscissas and water content as ordinates would show a sharp drop from 97.5 to 78.0 per cent humidity, with a tendency to converge a t a critical point about 70.0 per cent in the case of hygroscopic inorganic materials. Curves for the organic materials would be flatter. Therefore, water intake seems to be due to absorption and adsorption. With the inorganic materials adsorption is slight, but may be dominant at the lower humidities, whereas absorption, which depends upon the vapor pressure of the saturated solution, becomes dominant a t higher humidities. With the organic materials adsorption is always dominant and the total amount of water held may be very great a t high humidities owing to the large amounts of internal surface of such colloidal materials. The appearance of the material may not be a reliable criterion for judging its moisture content. The crystalline inorganic materials, including urea, usually appear moist with moisture contents of 5 to 10 per cent and show free water a t 20 to 30 per cent. The organic materials will adsorb 10 to 20 per cent moisture without showing it, and will not show free water at the highest humidity studied. This property of organic materials explains their value as conditioners and fillers in mixed goods. Calcium cyanamide and acid phosphate act similarly, but to a lesser degree as conditioners. Under the conditions of the experiment-namely, the spreading of the material in a comparatively thin layerthe moisture intake may be considerable; e. g.., sodium nitrate takes up 44.81 per cent water a t a relative humidity of 87.75 per cent in 7 days. Under ordinary storage, fertilizer is not spread out in a thin layer, but the data indicate that the moisture intake through its effect on weight may be great enough in some instances to warrant its consideration in the buying and selling of materials. It would seem also that with a knowledge of hygroscopicity of materials it would often be feasible to select or modify conditions of humidity prevailing in storage so as to prevent undesirable effects. The data show that the experimental error of the method employed was high. I n many cases the differences between crushing forces for the same material a t different humidities, as well as the difference for different materials a t the same humidity, are not significant. Calcium nitrate sets the hardest when allowed to dry from a wet condition. Muriate of potash and salts or mixtures containing potassium chloride rank second. I n general, the most hygroscopic inorganic materials are those which set hardest, and in general the hardness of a single material varies with the humidity to which subjected. The unusual behavior of ammonium sulfate nitrate is difficult to explain, but appears related to manner of recrystallization. The effect of organic materials in reducing cakiness is brought out by the mixtures with tankage and peat.
