I-VDUSTRIAL AND ENGINEERISG CHEMISTRY
1378
sorption, leather may be considered as a solid presenting a definite surface to a liquid, and that collagen in equilibrium with acid solutions may be considered as a gel which is completely permeable by the solution. The expressionswhich have been developed giving the adsorption as a function of the equilibrium concentration may then be used to determine constants giving provisional values for the equivalent weight of the leather or the collagen. These provisional values may have to be changed to be consistent with new data, but they may be used as working values a t present. Conclusions
1-The results obtained substantiate the theory that sulfuric acid reacts with the proteins of leather. %The equivalent weight, as a base, of the commercial vegetable-tanned steer-hide leather used in this study was
Vol. 22, KO.12
4.3 x lo3. This refers to the reaction of this particular leather with sulfuric acid. %The Gibbs adsorption equation has been applied with reasonable accuracy to the adsorption on this leather of sulfuric acid from water solutions. &The specific surface of the leather was of the order of magnitude of lo7 sq. cm. per gram. Literature Cited (1) Gibbs, T r a m . Conn. Acad., 3, 439 (1876). (2) Hitchcock, J . Am. Ckem. Sac., 48, 2870 (1926). (3) Kubelka and Wagner. Kolloid-Z., 46, 107 (1928). (4) Lewis and Randall, “Thermodynamics,” 1st ed., p . 357 (1923). ( 5 ) Morgan and Davis, J . Am. Chem. Soc., 38, 659 (1916). (6) Wilson. “Chemistry of Leather Manufacture,” Vol. I, p. 142, Chemical Catalog. (7) Wilson and Bear, IKD. ENG.CHEM.,18, 84 (1926). (8) Wilson, J. A. and W. H., J . A m . Chem. Soc., 40, 886 (1918).
Reactions Occurring during the Ammoniation of Superphosphate’ Frank G. Keenen D U POXT
AMMOXl.4 CORPORATION, ~ ‘ I L X I X G T O N , DEL.
A brief review of the patents and literature concernHE absorption of amPatents and Literature ing absorption of ammonia by superphosphate is given. monia by superphosThe mechanism of the absorption and the influence phate is not a recent The process of ammonia of temperature, nature of superphosphate, form of idea, but it is a recent ecotreatment of superphosphate ammonia used and moisture, upon the reactions ocnomic possibility, owing to was first patented in 1873 curring have been investigated. the availability of cheap synby McDougall ( I S ) , who It was found that up to 1 mol NH, per mol watert h e t i c a m m o n i a . Since claimed that “the acid phossoluble P205 (approximately 2 per cent NHJ no loss January, 1928, the Chemical phate is changed into preof available P205 occurred. More ammonia introDepartment of the Du Pont cipitated phosphate of lime duced under plant conditions-i. e., no control of Ammonia Corporation has and sulfate of ammonia: temperature or moisture-resulted in loss of available which m i x t u r e i s well investigated the process with P20jdirectly proportional to the amount of ammonia the following objects in view: adapted for use as a maintroduced. Above 2 mols ammonia per mol water(1) to determine the fact,ors nure.” B o l t o n a n d cosoluble P& the equilibrium mixture consisted of influencing the rate and exworkers (5) in 1881 sugmono-ammonium phosphate, ammonium sulfate, gested the use of acid phostent of ammonia absorption gypsum, and a precipitated calcium phosphate approxiphate as an ammonia abin the average commercial mating tricalcium phosphate. The tricalcium phossorbent in gas works. Two superphosphate; (2) to study phate so formed is of entirely different chemical and German inventors, Grahn the chemical reactions during physical behavior than mineral rock phosphate. Un(10) in 1889 and Besemammonia absorption, as to der laboratory conditions-i. e., control of temperafelder (4) in 1901, both dehow they might be conture and moisture-the reactions follow different scribed apparatus and methtrolled and the nature of courses, but in all cases result in the same final efluiods for absorption of ammothe products; and (3) to delibrium mixture. nia from waste gases by velop technic and apparatus superphosphate. for the commercial amlicaA series of patents by Willson and Haff (15) concerning tion of this process. Experimental work has been carried out in laboratory, semi-commercial, and commercial scale the ammoniation process appeared in the United States equipment. More than one thousand samples containing during the period 1912-16. These patents deal with treatammoniated superphosphate have been made and analyzed ment of ordinary or double superphosphate with gaseous and their physical condition and behavior on storage deter- ammonia up to 6 per cent NH3 in the former and 10 to 15 per cent in the latter. They specify that to keep the PZOS mined. The present paper deals primarily with the chemical in the citrate-soluble form it is essential to use “dry” phosreactions occurring during ammonia absorption by super- phatic material (6 per cent water). I n 1924 a French comphosphate and the composition of the resultant material. pany (St. Gobain) patented (14) and placed on the market The manner in which temperature, moisture, and the pres- Superam. This was made by using an excess of acid in the ence of other fertilizer ingredients influence these reactions superphosphate and introducing ammonia from a 5 per cent is explained. A review of the patent and journal literature ammonia in air mixture so that no free water was ever present. pertinent to the chemistry of the process also is included; Matignon (12) has described this process in detail. Simultaneous with the Superam patents a Danish patent ( 1 ) was this review is not complete, however. granted to Andreasen and Raaschou. This had three major Presented as a part of the symposium 1 Received September 22, 1930. claims: (1) Superphosphate mas treated with ammonia on “Action of Ammonium Citrate on Superphosphates” before the Division from a dilute ammonia-air mixture so that no free water of Fertilizer Chemistry a t the 80th Meeting of the American Chemical Sowas present in the superphosphate; (2) the temperature TV.H ciety, Cincinnati, Ohio, September 8 to 12, 1930.
T
A -
INDUSTRIAL A-VD ENGINEERING CHEMISTRY
December, 1930
always kept below 75" C.; (3) the product so obtained was analyzed for available P20Swith an ammonium citrate solution slightly acid (pH 6). The journal literature on the chemistry of the ammoniation process is meager. Bassett ( 3 )found that pure dicalcium and monocalcium phosphates reacted with ammonia in the presence of moisture to form precipitated tricalcium phosphate and ammonium phosphates. He found that the re-
1379
process before attempting to make definite recommendations for commercial application of the process. Specifically some of the points studied mere: (I) the reactions actually occurring in the commercial ammoniation process and the influence of free acid, moisture, and temperature of the superphosphate upon the course of these reactions; ( 2 ) the influence of the yarious ingredients of a complete fertilizer mixture upon these reactions; and ( 3 ) the nature of the precipitated calcium phosphates formed in superphosphate which has absorbed more than 1 mol ammonia per mol of water-soluble P20Sunder commercial conditions. Experimental
The first laboratory experiments, using gaseous ammonia and relatively dry superphosphate and keeping the temperature below 75" C., resulted in absorption of nearly 2 mols of ammonia per mol of water-soluble P20Swithout loss of available P205 after 1 week. However, after 4 months' storage ! I all samples containing more than 1 mol NH3 per mol water1 2 3 4 5 soluble P20j showed loss of available Pp05. Meanwhile %AMMONIA Figure 1-Insoluble P ~ O in S Superphosphate after Ammoniation other studies had indicated that gaseous ammonia was uneconomic because of the large capital investment necessary action followed a different course above 75-80" C. than below to adapt its use to the typical existing fertilizer process. This these temperatures. Brioux ( 6 ) and Gerlach (8) both used left anhydrous liquid ammonia as the only source of dry commercial superphosphates and concluded that such mate- ammonia. The use of this form of ammonia appeared atrial, when saturated with ammonia, had reacted as follows: tractive for the following reasons: (1) The vaporization of the ammonia occurred in the reacting mass and thereby CaHa(PO4)z 2CaSOa.2H20 4NH3+ prevented excessive rise in temperature; ( 2 ) no free water was Cas(PO4)z 2(NH4)~S04 2H20 added; and (3) the technic of adding anhydrous ammonia to Both of these investigators carried out field tests with such the superphosphate was even simpler than adding an aqueous material and reported that the availability of P205 to plants solution. Fas not decreased (9). Brioux stated, "The tricalcium phosA semi-commercial installation for the treatment of superphate which is so re-formed is very different from the original phosphate with either anhydrous or aqueous ammonia was natural phosphate and is soluble in weak reagents." Gerlach designed and has been operating a t the Du Pont Experimental used 2 per cent citric acid and found practically all the P z O ~ Station in Wilmington, Del., for more than a year and a half. to be soluble. A patent ( 7 ) was granted to Gerlach for his The greater part of the results has been obtained from this ammoniation process. and from actual works-scale experiments. The analytical In an obscure Danish technical journal Andreasen and Raaschou ( 2 ) published results of a study of ammoniation of superphosphate. They confirmed the conclusions of earlier workers-namely, that free water and elevated temperatures promoted reversion to insoluble P205, and also established conclusively that gypsum did enter into reaction above 1 mol NHI per mol water-soluble PZO6. Furthermore, they found that the "reverted" or precipitated calcium phosphate exhibited peculiar solubility behavior in citrate solutions. Two per cent citric acid dissolved it entirely, ammonium citrate solution slightly acidic (pH 5) dissolved two-thirds 1 I / of it, and a more nearly neutral solution (pH 6) dissolved 1 2 3 4 5 % AMMONIA only half the P205in this form. The natural mineral form Figure 2-Influence of Other Materials on Insoluble PZOSi n of calcium phosphate did not show these variations. Ammoniated Superphosphate Following this a recent United States patent was granted to Hagens and eo-workers (11 ) which indirectly touches upon methods followed in this first phase of the work were those ammoniation of superphosphate. The Hagens patent specifies of the Association of Official Agricultural Chemists, making that under certain conditions a mixture of monocalcium the ammonium citrate solution to exact neutrality (pH 7), phosphate and gypsum may react with ammonia ( 2 mols using phenol red indicator in a colorimeter. All experiNHI per mol water-soluble P2OJ to form dicalcium phos- ments mere run in duplicate, one sample being treated with phate and ammonium sulfate. aqueous ammonia solution (25 per cent KH3) and the other The treatment of superphosphate with ammonia on a half with anhydrous liquid ammonia. The ammonia was incommercial scale was first adopted in this country during troduced within 2 or 3 minutes in all cases and no attempt 1928. A 25 per cent aqueous ammonia solution was used, but made to control temperature or moisture content. When recent trends are toward the direct use of anhydrous liquid more than 2 per cent ammonia was added, the temperature ammonia. From the review of the literature, including with liquid anhydrous ammonia would rise above 75-80" C. patents, it appeared that there were still many unknown The ammoniation n-as done in a small mixer of the same type factors in such a process which should be studied. For this as is used in the fertilizer industry for dry mixing; conreason the Du Pont Ammonia Corporation has carried out sequently there was little chance for moisture to escape during considerable research over the past two and a half ycars in ammonia introduction. These were the conditions the order to gain insight of the fundamental chemistry of the ammoniation process would meet in large-scale application.
+
+
+
+
I S D C S T R I A L AAI*DEAt7GINEERISGCHEMISTRY
1380
T a b l e I-Composition
of A m m o n i a t e d SuDerDhosDhate Z-GRAM
TOTALS
NHJ
H20
so4
P,Oj
CaO
~
Free acid
100 CC. CITRATE
%
70
%
70
70
%
0.0 2.3 3.3 4.2 5.0 6.0 0.0 3.0 2.5 3.7
29.6 28.4
20.0 20.5 19.7 20.0 20.5 18.9 18.2 18.0 18.4 18.6 45.2 42.5 18.2 44.1 16.7
35.3 34.6 34.5
4.0
1.3
4:5
... ... ...
2816 28.0 26:2 25.9 25.7 25.5 17.6 16.4 26.6 46.5 36.0
10:5 5.8 1.0 1.2
... ...
..
33:5 32.2 35.2 34.6 34.8 34.6
3:5 13.5
..
..
33:5
...
... ...
9:0 6.3
3.0
.. .. ..
...
..
35: 1
6.0
1
I I
I
PZOS
I
1
I
CaO
SO4
C I T R A T E RESIDUE
CaO
NH3
~ 2 0 6
%
%
%
1.2 1.6 2.4 4.7 7.1 7.2 1.1 3.8 1.2 3.4 0.3 1.3 5.0 27.0 6.3
2.0 2.1 2.8 5.1 9.8 8.0 1.4 4.8 1.4 4.0 0.5 1.5 6.9 33.1 8.4
Fe and Alp04
~
... ... ...
After ammoniating and analyzing approximately five hundred batches during the first 8 months of this work, the following conclusions were reached: There was no difference in the chemical behavior of liquid anhydrous and aqua ammonia in the superphosphate mixture. Figure 1 illustrates this point. Certain materials, when mixed with superphosphate before or after ammoniation, apparently obtained at any given decreased the amount of insoluble PZO5 ammonia content above 2 per cent "$4.e. 1mol ammonia
40
S A X P L E PER
WATER EXTRACT
SAMPLE
KO KO-4 KO-5 KO-6 KO-7 KO-2 KR-1 KR-2 KR-4 KR-8 KD-1 KD-2 KD-3 Pure M o n o Pure Super
Vol. 22, No. 12
I\
70
%
%
16.3 11.3 9.5 7.8 6.1 3.1 14.9 8.2 10.0 8.9 39.0 25.0 4.1 2.7 0.2
13.5 4.8 3.3 3.8 5.7 2.5 12.6 9.0 3.7 8.0 14.9 0.3 6.5 0.0 6.4
13.0 7.6 8.9 13.4 20.1 18.9 13.0 17.9 7.8 18.8
..
24:9 14:4
.. .. ..
3.4 4.2
... ...
... ...
2.9
3.6
...
... ...
1.0
...
% 0.3 0.4
... ... ... ...
0.8 0.9
... ...
... ... ...
0.0 0.0
that whenever more than 1mol of ammonia per mol of watersoluble P205 was introduced into ordinary superphosphate in such a manner that the temperature was kept between the limits 40" and 70" C. only a few hours, slow reversion of the PzO5 to the insoluble form occurred during the first month of storage. When, however, the temperature during or following ammonia introduction to this extent exceeded 70-80" C., practically no reversion took place on storage. To be sure, the samples ammoniated a t relatively high temperatures showed higher insoluble P~05a t the time of making, but at the end of 4 months the insoluble P205 was practically equal in both the low- and high-temperature series. These facts in connection with laboratory experiments led to the following conclusions as regards mechanism of the ammonia absorption: At low temperatures (below 70" C.) it was possible to absorb more than 1 mol of ammonia per mol of water-soluble P2O5 (over 2 per cent NH3 in the average material) apparently in accordance with the equation,
+ 2s"
CaH4(P04)2
--f
CaHP04
+ (NHd)zHP04
(1)
But diammonium phosphate in the presence of moisture and in intimate contact with gypsum was broken down to monoammonium phosphate and the mol of ammonia so released reacted to form precipitated tricalcium phosphate,
%AMMONIA
F i g u r e 3-Change in C o m p o s i t i o n of S u p e r p h o s p h a t e Caused by A m m o n i a t i o n . KO Series, Florida S u p e r p h o s p h a t e 5-Precipitated tricalcium 1-Gypsum 2-Monocalcium phosphate phosphate 3-Monoammonium phosphate 6-Ammonium sulfate 4-Dicalcium phosphate 7-Rock phosphate
per mol water-soluble P2O5. Figure 2 shows this effect in the case of sulfate of ammonia and muriate of potash. Other materials, sulfates and other potash salts, showed variable effects, indicating that the reactions of the added materials were entirely specific, and no general conclusions could be drawn. It was true that any material added, even sand, lowered the insoluble PzO5found; however, it was later learned that this was an analytical effect due to the physical dilution of the sample, which decreased the amount of ammoniated superphosphate being extracted with 100 cc. of citrate. I n connection with the temperature factor, it was learned
At high temperatures (80" C.) the decomposition of diammonium phosphate was so rapid as to bring about Reaction 2 in a few minutes or hours, whereas it required months at low temperatures. This also indicated why so many investigators recommended that free water be kept out of the ammoniation process. Diammonium phosphate is much more unstable in the presence of moisture. Consequently, it was possible to introduce nearly 2 mols of ammonia per mol water-soluble P205 without loss of citrate-soluble P2OS,but the conditions necessary to accomplish this were not those existent, or even readily attainable, in present fertilizer practice. Composition of Ammoniated Superphosphate
The above reactions were largely hypothetical and there were still many unexplained results a t this point. The investigation was then taken back to the laboratory and studied largely from the analytical aspect. A scheme of analysis was set up whereby the lime, P&, sulfate, ammonia, iron, and alumina compounds, etc., were determined in the total sample and the water-soluble, citrate-soluble, and residual portions. From such a complete analysis it was possible to calculate the principal compounds apparently existing
December, 1930
INDUSTRIAL A,VD ENGINEERlNG CHEMISTRY
in any sample, and by following the changes in the composition with varying factors to set up the reaction mechanism more definitely. Table I presents such analytical data. I n this table KO represents a series of ammoniated superphosphates from a relatively dry, Florida pebble rock material ammoniated with liquid anhydrous ammonia. KR represents a similar series from a relatively fresh, moist, high free acid, Tennessee rock superphosphate. KD-1 is an ammoniated triple superphosphate, and KD-2 is the same material mixed with gypsum to simulate ordinary superphosphate composition. The last two samples were the precipitates obtained from saturating a solution of monocalcium phosphate a t 80" C. with ammonia (Pure Mono), and from a mixture of monocalcium phosphate and gypsum treated similarly (Pure Super). These were studied to determine what influence the imwrities in commercial super might have upon the analytical methods and calculations. A s a typical example of the calculations employed, KO-4 has been selected: Water-soluble C a O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 Assume all water-soluble SOa t o be gypsum, requires.. . . . . 4 4 CaO CaO present as monocalcium phosphate.. . . . . . . . . . . . . . . . 0 . 4 CaO Water-soluble PzOs.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 0.4 CaO as monocalcium phosphate requires.. . . . . . . . . . . . 1 0 PzOa P20: present as ammonium phosphate.. . . . . . . . . . . . . . . . . . 1 0 . 3 PsOs 2.3 NHs water-soluble as monoammonium phosphate requires.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 . 8 PzOj Citrate-soluble PzOj. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5
-
Table 11-Calculated SA\IPLE
KO ~ 0 . 4 KO-7 KO-2 KR.1 KR-8 KD-1 KD.~
2;;:;N; PHATE
(POa)?
caso4.-H,O
Po4
2Hz0
%
%
%
%
%
25.0 1.7 0.0 0.0 0.0 0.0 17.5 0.0 1.3 0.0 70.0 0.0 0.0
4.7 14.0 9.8 3.8 0.0 0.0 1.0 6.0 10.0 4.8 10.0 23.5 17.4 18.0 10 5
2.8 2.5 2.5 2.5 2.5 2.5 2.4 2.2 2.4 2.2 0.65 0.65 0.30
0.0 1.0 8.5 18.5 26.0 30.5 0.0 5.8 0.0 10.5
0.0 16.0 13.0 12.0 10.0 5 ~ 3
fze3150n0 Pure Super
Composition of Superphosphates
caHa-y2(Poi)?
1381
li:O
11.0 75.0 25.0
% 0.0 0.0 4.5 9.5 13.8 20.0
3:s
13:O 15.0 14.0
0.0 6.9
%
%
62.0 62.0 56.5 50.0 42.5 22.0 63.0 57.0 63.0 53.0
4.0 4:5
..
3:5 13.5
..
9:0
6.3 9:7 Al~d35,O(~H~)2HPO4 6.5 18.8 40.0 53.0
. Finally the precipitates from ammoniation of pure monocalcium phosphate Mono and Super in Table I1 give results similar to those from commercial materials. These precipitates were obtained by passing ammonia gas into a suspension of the phosphate material in water a t 80" C. Since the precipitate was not washed, the small amount of sulfate of ammonia and ammonium phosphate was adherent to the precipitate in the mother liquor. Thus it appears that the impurities in the commercial materials do not influence the main reactions in ammonia absorption.
The citrate-soluble CaO is calculated as: Total CaO found., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Total SO4 as gypsum, requires., . . . . . . . . . . . . . . . . . . . . . . . . . . . CaO as phosphate.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CaO as insoluble plus CaO as monocalcium phosphate., . . , , Ratio CaO.PzOs
5
28.40
.
2020 8.9 2 0 6 2
0 83, which is approximately dicalcium phosphate
Therefore the composition of the sxnple is apparently: Per Cent 0 . 4 CaO as monocalcium phosphate 7 . 5 PzO, as dicalcium phosphate 1 . 6 PzOn as insoluble phosphate 10 0 PzO, a s monoammonium phosphate 34.8 SO4 as gypsum
Per cent
1 . 7 CaH4(P04)z 14 0 CaHPOa rock 3 5 Caz(PO4)z 16 0 N H ~ H I P O P 62 0 CaSO4.2HzO
+
From such calculations Table I1 was compiled. The graphical presentation of the compositions of the KO series is found in Figure 3, of the KR series in Figure 4. The principal differences in the two series were the higher free acid and the higher iron and alumina in the K R series. It was found that approximately 1.75 per cent of the citrate-soluble P205in the KR series was iron and aluminum phosphates, rather than dicalcium phosphate. This gave a fairly comprehensive indication of the reactions occurring and two experiments were made to check the above data and calculations. Triple superphosphate (KD-1) containing no gypsum absorbed 10.5 per cent NH3 and it is seen in Table I1 that this is held largely as diammonium phosphate (KD-2). Another sample (KD-3) of triple super mas mixed with gypsum to approximate the ratios in ordinary superphosphate (60 per cent gypsum, 20 per cent monocalcium phosphate) and ammoniated to saturation. This mixture contained no diammonium phosphate and was quite comparable in composition to members of the KR and KO series. Thus it was shown that the instability of diammonium phosphate in ordinary ammoniated super is due to its intimate contact with gypsum in the presence of moisture. It has been possible to introduce far more ammonia than 1 mol NH3 per mol water-soluble Pz06into dry superphosphate (3 per cent moisture) a t low temperatures without loss of available P205 and to obtain a product stable for several months. But any such mixture in the presence of free moisture and a t temperatures slightly elevated (30-40" C.) shows slow loss of available PzOr.
%AMMONIA
Figure 4-Change in Composition of SuperphosKR Series, phate Caused by Ammoniation. Tennessee Superphosphate 1-Gypsum 5-Precipitated tricalcium 2--Monocalcium phosphate phosphate 3-Alonoammonium phosphate 6-Ammonrum sulfate 4-Dicalcium phosphate 7-Rock phosphate 8-Free acid (HaPOa) ~~
Kow the reactions for absorption of ammonia can be written from the above data with a fair degree of certainty. (1) Up t o 1 mol NH, per mol water-soluble P z O ~ (about 2 per cent NH3 in the average material) after the free acid is neutralized, the monocalcium phosphate reacts as: CaH4(P04)2 NHs.----t NHdHzP04 CaHPO4 (1) The manner of ammonia introduction and subsequent treatment does not influence this reaction and no loss of available PtOr occurs. (2) More than 1 mol NH3 per mol water-soluble P z O ~(2 to 6 per cent NH3) with rapid introduction of the ammonia and no control of temperature or moisture results in several reactions occurring to some extent simultaneously. From Figures 3 and
+
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INDUSTRIAL A S D E-VGISEERI-VG CHEMISTRY
1382
T'ol. 22, KO.12
4 it can be seen that the dicalcium phosphate disappears more to leach away this precipitated material from the rock phosrapidly than the monoammonium phosphate. Up to 4 or 4.5 phate by properly adjusting the relationship between sample per cent NH3 the temperature during ammoniation is between size and volume of citrate. Field and pot tests are now being 70" and 90" C., and the first major reaction is apparently 2CaHP04 CaS04.2HzO 2NH3 + conducted by the U. S. Department of Agriculture and several CadP04)~ (NH4)2SO4 2H20 ( 2 ) state experiment stations on the fertilizer value of these resiAs this progresses and more ammonia is absorbed the temperature gradually rises and a t the higher temperatures (90" to 100" C.) dues from ammoniated superphosphate. Thus, in conclusion, it can be said that ammonia absorption the monoammonium phosphate reaction is accelerated. By the time the dicalcium phosphate has all reacted, the reaction pro- by superphosphate follows three or four separate major ceeds as: reactions. Temperature and moisture are apparently the NH4HZP04 CaS04.2HzO NHI + controlling factors in determining the extent and rate a t (hTH4)zSO4 CaHPO4 2H20 (3) The dicalcium phosphate so formed may subsequently react as which each of these three occurs. However, the direct ab(2), but from an analytical study of the precipitated phosphate sorption of anhydrous ammonia under present works condimaterial it apparently remains largely as dicalcium phosphate tions up to 1 mol NH3 per mol water-soluble Pz06(approxiintimately mixed with more basic phosphate compounds. The fact that monoammonium phosphate gradually decreases as mately 2 per cent NH3) does not decrease the availability the ammonia absorbed is increased above 1 mol NH3 per mol of the PZO5 as determined by present analytical methods. water-soluble P205 indicates that (3) occurs simultaneously with More than 1 mol h'H3 per mol water-soluble does decrease (2). the available P2O6. This decrease may be slow if the am(3) Under controlled conditions, low temperature and mois- monia is introduced under controlled conditions, or it may be ture content, it is possible to direct the reactions as follows: within a few hours if the ammonia is introduced in the direct CaH4(PO& 2NH3 +CaHP04 (NH&HPO4 Consequently, Reaction 2 above does not occur until after 2 and most economical way. The physical condition of mols of NH3 per mol water-soluble P205 have been introduced, or ammoniated superphosphate is markedly superior to superthe temperature rises. Superphosphate ammoniated under such conditions is not an equilibrium mixture and slow reversion may phosphate, and since the ammoniated material is of different composition than unammoniated superphosphate, the reoccur.
+
+
+
+
+
+
+
+
+
+
actions when mixed with other ingredients to complete fertilizers result in much less tendency to setting or caking.
Conclusion
It is beyond the scope of the present paper to give detailed results from the analytical study of this precipitated calcium phosphate material. It can be said, however, that the Pz06precipitated by ammonia from such material as superphosphate exists as a mixture of several calcium phosphates, largely tricalcium phosphate, but also dicalcium and some even more basic compounds than the tricalcium salt are present. This mixture is approximately half as soluble in neutral citrate solutions as is dicalcium phosphate, and many times more soluble than natural rock phosphate. The CaO:Pz06ratio in the residue from neutral citrate extraction of ammoniated super (2 grams per 100 cc. citrate) is between 1.0 and 1.4. If the volume of citrate is iacreabed or sample she decreased, this ratio increases and approaches that found in rock phosphate, 1.5 to 2.0. Hence it is possible
L i t e r a t u r e Cited (1) Andreasen and Raaschou, Danish Patent 33,605 (1924) (2) Andreasen and Raaschou, Nordisk. Jordbriig, 5-6, 285-(1923). (3) Bassett. Z . anori. Chem . 63. . 49 (1907). . Besemfelder, German Patent 117,795 (1901). Bolton, U. S. Patent 248,632 (1881). Brioux, Compt. rend. acad. agr. France, 4, 632 (1914). Gerlach, German Patent 282,915 11916). Gerlach, 2. angew. Chem., 29 (11, 13 (1916). Gerlach, I b i d . , 29 ( l ) , 18 (1916). Grahn, German Patent 47,601 (1889). Hagens, U. S. Patent 1,699,393 (1929). Matignon, Chimie et industrie, 10, 217 (1923). McDougall, U. S. Patent 135,995 (1873). St. Gobain, French Patent 570,266 (1924). Willson and Haff, U. S. Patents 1,040,081, 1,062,869, 1,112,183, 1,122,183, 1,127,840, 1,145,107, 1,146,222, 1,161,473, 1,166,104.
.
Viscosity Data in Graphical Form' R a y m o n d P. Genereaux EXPERIMENTAL STATION, E. I .
DU
PONTDE NEMOURS & COMPAXY, WILMIKGTON, DEL
HE viscosity factor enters into many calculations used in chemical engineering research, design, and operation. The wide variety of fluids encountered in practice often necessitates a search for viscosity data which are scattered in tables, handbooks, and journal articles. The data are often in units not readily applicable to the formulas, requiring conversion to some consistent set of units. For example, the data on aqueous solutions of strong electrolytes in International Critical Tables, Vol. V, p. 12, are given in terms of relative viscosity, the viscosity of the solution being referred to the viscosity of water, both a t the same temperature. I n other sources values are found as seconds on the Redwood, Engler, or Saybolt viscometer. Other units used are kinematic viscosity relative to specific gravity or to density. C. g. s. units are often found, but involve a factor of 10". Confusion and error are certain
T
'
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1 Received September 8, 1930. Contribution No. 44 from the Experimental Station, E. I. Du Pont de Nemours & Company.
with such diverse units. With a view to correlating the available data and simplifying the presentation, the accompanying charts were constructed. The method of plotting used is that suggested by Ravenscroft (8). The centipoise was chosen as the unit for expressing viscosity values. The poise is the c. g. s. unit of viscosity; the centipoise is 0.01 poise. The viscosity of any fluid in centipoises is numerically equal to the viscosity relative to water a t 20" C. Use of the centipoise requires no more than two or three ciphers after the decimal point and avoids the confusion encountered in using powers of ten. An exhaustive search was made for data on each fluid represented on the charts. The appended bibliography includes some of the sources of data. Values were plotted on log-log paper with viscosity in centipoises us. the absolute temperature. This is the method as used by Herschel (3) and, as with his data on oils, the points for most of the fluids on these charts fell along a straight line. For those few
