INDUSTRIAL AND ENGINEERING CHEMISTRY
1144
Nomenclature So = initial free sulfur, rams/100 grams of original raw rubber S = free sulfur, grams,%00 grams of original rubber S, = combined sulfur, equivalent to rubber sulfide (RS), grams/100 grams of original rubber 9 = time of cure, usually hours R = free rubber, equivalent to (47 - S,) RX = polyprene sulfide of vulcanized rubber AO = totlal accelerator concentration A = free accelerator concentration AS = accelerator-sulfur complex k = specific reaction constant K = specific reaction constant, second order reaction Subscripts 1 and 2 refer to reactions 3 and 4,respectively, as indicated in Equation 5.
Bibliography (1) Axelrod, Cummi-Ztg., 24, 352 (1911). ENQ.CHEM.,13, 1034 (1921). (2) Bedford and Sebrell, J. IND. (3) Blake, A., Thesis, Mass. Inst. Tech., 1933. ENQ.CHEM.,22,737 (1930). (4) Blake, J. T., IND. (5) Boggs, C. R.,and Blake, J. T., Ibid., 22, 748 (1930). (6) Bray, W. C., and Livingston, R. S., S. Am. Chem. SOC.,45, 1251 (1923). (7) Cappello, V, F.,Thesis, Mass. Inst. Tech., 1931. (8) Coffin and Scarborough, Ibid., 1933. (9) Cranor, India Rubber World, 61, 137 (1919). (10) Eaton and Day, S. SOC.Chem. Ind., 13, 16 (1917). (11) Fol and Van Huern, Intern. Assoc. Rubber Cultivation Netherland Indies, Comm., 1916,330.
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(12) Glancy, Wright, and Oon, IND. ENG.CHEM.,18, 73 (1926). (13) Gottlob, Gummi-Ztg., 30, 304 (1916). (14) Hauser, E. A., Trans. Inst. Rubber Ind., 2,301 (1926). (15) Iterson, G. van, Intern. Assoc. Rubber Cultivation Netherland Indies, Comm. of Netherland Gout. Inst. for Advising Rubber Trade and Ind., Pt. 7, 239-61 (1918). ENQ.CHEM.,11, 30 (1919). (16) Kratz and Flower, J. IND. (17) Kratz, Flower, and Shapiro, Ibid., 13, 128 (1921). (18) Lewis and McAdams, Ibid., 12, 673 (1920). (19) McAdams, W. H., “Heat Transmission,” New York, McGrawHill Book Co., 1933. (20) McDonald, Thesis, Mass. Inst. Tech., 1932. (21) Nagel and Kolker, Ibid., 1931. (22) Nordlander, B. W., S. Phays. Chem., 24, 1873 (1930). (23) Nussbaum, R.,Jr., Thesis, Mass. Inst. Tech., 1933. (24) Perks, A. A.,S.SOC.Chem. Ind., 45, 142T (1926). (25) Seidl, Gummi-Ztg., 34, 798 (1919-20). (26) Skellon, S.SOC.Chem. Ind., 34, 671 (1915). (27) Smith, C.C.,Thesis, Mass. Inst. Tech., 1923. (28) Spence and Ward, Z . Chem. Ind. Kolloide, 11, 32, 278 (1912). (29) Stevens and Stevens, J. Soe. Chem. Ind., 48, 55T (1929). (30) Twiss and Brazier, Ibid., 39, 125T (1920). (31) Weber. L.. “Chemistrv of Rubber Manufaotiire.” London. - _._. - -, Charli Griffin and e o . , 1926. (32) Wilder, W. B.,Thesis, Mass. Inst. Tech., 1931. 33) Williams and Beaver, IND.ENQ.CHEM., 15, 225 (1923). (34) Wing and Moomaw, Thesis, Mass. Inst. Tech., 1934.
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RECEIVEDOctober 16, 1937. Presented before the Division of Rubber Chemistry at the 86fh Meeting of the American Chemical Society, Chicago, Ill., September 10 to 15, 1933.
Hygroscopicity of Fertilizer Mixtures Effect of Calcined Phosphates HEN Phosphate rock containing 5 Per cent Or more of silica is heated at 1400” c. in the presence of water vapor, its phosphorus content is rendered citrate soluble to a degree dependent upon the extent to which the duorine contained in the rock is volatilized (11, 14, 16). Thus, under optimum conditions, it is possible t o volatilize upwards of 99 per cent of the fluorine and convert the same proportion of the phosPhorus into the citrate-soluble condition, The available PhosPhorus in the Product (calcined phosphate) is only slightly water soluble but has a fertilizing value at least equal to that of the available phosphorus in superphosphate and other well-known phosphatic fertilizer materials (10, 17). Inasmuch as the greater portion of the phosphatic fertilizer material used in this country is marketed in mixture with other fertilizer materials, i t is important to know the effect of new p h o s p ~ t i c materials on the physical condition of fertilizer. since the physical condition is largely determined by the amount of atmospheric water absorbed, a study was made of the relative hygroscopicity of calcined phosphate and of its mixtures with certain nitrogen and potassium salts. Comparative experiments were carried out with sup@rPhosPhate and double superphosphate.
COLIN W. WHITTAKER, J. RICHARD ADAMS, AND K. D. JACOB Fertilizer Research Division, Bureau of Chemistryand Soils, Washington, D. C.
Materials and Method The calcined phosphates were prepared experimentally in a direct oil-fired rotary kiln by he:tin Tennessee brown-rock phosphate at approximately 1400 Cf The superphosphates and double Superphosphates were thoroughly cured commercial materials. Partial analyses of the phosphatic materials are given in Table I. More complete analyses of samples 1315, 1316, 1337, and 1362 were publishkd previously (7). The nonPhosphatic compounds were C. P. grade and, except where stated otherwise, were ground to pass a 100-mesh sieve. All analyses were made by the official methods (6). All hygroscopicity determinations were made b measuring the gain in weight on exposing small samples of unizrm amount in a thin layer in shallow Parr weighing dishes about 25 mm. in diameter, to a series of relative humidities in steps of roughly 2 per cent. These relative humidities were obtained by means of a series of saturated salt solutions in desiccators kept in a constant-temperature room at 30” C. Only those salts were used the vapor pressure of whose saturated aqueous solutions had been accurately determined a t 30” C. Except where otherwise stated, the samples were kept one week at a low relative humidity, and the gain in weight was noted. The sample was then kept for a week a t the next higher relative humidity and so on until the sample became very wet or until the highest relative humidity used (97.6 per cent) was reached. Work a t humidities higher than 97.6 per cent is difficult owing to condensation of moisture on the side walls of the dishes containing the samples. The amount of water taken up in experiments of this t y e varies somewhat in check runs, but the curves always show tge same trend. One week at each relative humidity is in some cases not long enough to permit complete attainment of equilibrium
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INDUSTRIAL AND ENGINEERING CHEMISTRY
but it is closely approached. Uniform conditions as to surface exposed, particle size, depth of layer, and other factors were maintained within each set of experiments so that the results are strictly comparable. In addition to determining the gain in wei ht, the mechanical condition of the samples was noted. In the fiscussion the terms used have the following significance: “Caked” means that the sample offered resistance to the insertion of the blade of a small spatula and usually broke up into chunks. “Sticky” means that a large proportion of the particles adhered to the bright and originally dry spatula blade. Samples in this condition “ball up” on squeezing in the hand. The word “wet” is used to describe a condition such that droplets of solution could be seen on the s atula blade after inserting it in the sam le and knocking off tge adhering particles. When sufficient soktion was present to flow visibly on tipping the dish, the mixtures were said to contain “free solution.” These terms are approximate and the personal factor in making the observations is large.
Relative Hygroscopicities of Phosphates The relative hygroscopicities of each of the phosphates listed in Table I (except 12 and 79) were determined, using onegram samples of each. The results for calcined phosphate 1375, superphosphate 1315, and double superphosphate 1337, which are typical of those obtained for all samples of the three classes of materials, are shown in Figure 1. All hygroscopicity tests in this group were made simultaneously. The samples were not dried previous to the hygroscopicity tests, because drying, in the case of the superphosphates, might have caused loss of water of crystallization which would have been reabsorbed during the tests (8). Since superphosphate 1315 and double superphosphate 1337 contained 6.37 and 3.65 per cent of water, respectively, as determined by drying over P20s,the position of the curves for these samples in Figure 1 represents the water absorbed rather than the total water content. Calcined phosphate 1375, however, as well as all other calcined phosphates that were studied, lost practically no weight on drying over PzOS. The curve for this material therefore shows the actual total water content a t the various relative humidities, which in this case is probably closer to an equilibrium value than in the cases of superphosphate and double superphosphate. The calcined phosphate samples did not absorb any important amount of water even a t the highest humidity used (97.6 per cent), and the mechanical condition of the material remained satisfactory a t all humidi-
TABLE I. ANALYSESOB PHOSPHATES 7
Sample Mesh No. Source of Phosphate Fineness Total Calcined Phosphate 1374 Tennessee brown rock -100 36.17 1376 Tennessee brown rock -80 36.09 Superphosphate 19.60 -80 79 Florida land pebble 19.20 -100 1315 Florida land pebble 1316 Tennessee brown rock -100 18.86 Double Superphosphate 48.37 -100 1362 Tennessee brown rock 46.21 -100 1337 Floridaland pebble 12 Florida land pebble -40 46.66
PIOS,%
Watersol.
...
Citrateinsol.
Free acid
...
3.91 2.67
.. .. ..
17.00
16.70 12.20
0.06 0.12 0.27
1.00 2.73 3.61
42.20 38.30 40.64
0.48 0.49 0.08
0.62 1.44 7.40
ties. The superphosphates and double superphosphates, however, absorbed important amounts of water a t about 88 per cent relative humidity and became slightly to definitely sticky. A small further increase in the humidity resulted in the absorption of larger amounts of water and a wet condition. The results show that calcined phosphate stored under any ordinary conditions short of actual contact with liquid water remains in good mechanical condition and contains practically no moisture. This phosphate would not, therefore, contribute to the initial moisture content of any mixture in which it might
1145
In a study of the hygroscopicity of calcined phosphate it was found that this material did not absorb any significant amount of water at any relative humidity, and that mixing it with fertilizer salts did not lower the relative humidity at which these salts began to take up water. Superphosphate and double superphosphate, however, absorbed water at the higher humidities, and mixtures of these phosphates with fertilizer salts in most cases began to take up water at relative humidities below those at which the admixed salts would absorb it. Reactions which involve the formation of considerable water-soluble phosphorus began to occur in mixtures of calcined phosphate with either sodium or potassium carbonate at the relative humidity at which the mixtures began to absorb large quantities of water. No reaction that affected the solubility of the PzOb occurred between calcined phosphate and potassium chloride or sulfate. Attempts to use calcined phosphate to reduce the rate at which urea absorbs moisture were unsuccessful. Calcined phosphate did not cause significant loss of available potash in the mixtures studied.
be incorporated. Superphosphate and double superphosphate, however, contain varying amounts of “free” water initially in addition to water of constitution and crystallization (8) and, if exposed to very high humidities during storage, will take on more water and become sticky or wet.
Hygroscopicity of Phosphate Mixtures with Other Fertilizers The results of hygroscopicity tests on mixtures containing one gram of either calcined phosphate 1374, superphosphate 1316, or double superphosphate 1362, and one gram of one of the pure salts, sodium nitrate, potassium nitrate, potassium chloride, or urea, are shown in Figure 2. Ammonium salts were not included because of their known tendency to lose ammonia when in contact with calcined phosphate (6). The relative humidity corresponding to the vapor pressure of a saturated aqueous solution of the pure salt, which is also the relative humidity above which the pure salt begins to absorb moisture, is indicated on the humidity axis. All mixtures containing calcined phosphate began to absorb significant quantities of moisture very close to this humidity, indicating that the calcined phosphate was entirely inert, the hygroscopicity of the mixture ,being determined solely by that of the admixed salt. The mixtures containing ordinary or double superphosphates, on the other hand, all began to take up large amounts of water a t relative humidities considerably below those a t which the pure salt would absorb it. The or-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1146 IO(
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OF MOISTURE BY PHOSPHATES FIQURE 1. ABSORPTION
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30" C. ( I @ , which is the point indicated on the humidity axis for these mixtures (Figure 3). As in the preceding series, the calcined phosphate curves always broke a t the relative humidity above which the admixed salt or salts begin to absorb water. Comparison of Figures 2 and 3 shows that the inclined portions of the curves for calcined phosphate and double superphosphate are much lower relative to the position of the superphosphate curves in the first series of mixtures than in the second series. This can be explained, a t least in part, by the fact that, with the uniform weight of sample (2 grams) used in both series of experiments, the calcined phosphate and double superphosphate mixtures of the second series contained larger total quantities of admixed soluble salts than did the corresponding superphosphate mixtures, whereas in the first series all mixtures contained the same quantities of admixed soluble salts. The various materials used undoubtedly absorb moisture a t somewhat different rates, and the different proportions used in the two series may thus have intro-
96, , , , , , , , , , 801 , , , , , , 1 1 dinary and double superphosphate mixtures also became sticky, in most cases slightly below the relative humidity a t which the admixed salt becomes wet. The calcined phosphate mixtures, on the other hand, except for slight caking in a few cases, retained their good mechanical condition up to the humidity at which they suddenly began to take on water. Above this humidity they rapidly assumed a decidedly wet condition or showed free solution. The superphosphate mixtures did not usually assume the wet condition until the relative humidity had been increased several per cent beyond the point where the first stickiness was noted. I n no case did the condition of a superphosphate mixture remain good longer than that of the corresponding calcined phosphate mixture. I n the experiments just'described, equal weights of a nonphosphatic salt and of a phosphate were used. In order to obtain data more directly applicable to actual practice, mixtures were prepared in which the Total Gain in Weight. Per Con1 materials were used in such proportions that the ratio FIGURE 2. RELATIVE HYGROSCOPICITIES OF MIXTURES CONTAINING of total nitrogen to available PZOSto available KzO EQUALAMOUNTS OF A PHOSPHATE AND OF A PURESALT had one of the followine: values-1:Z:O. 1:3:0. l:Z:l, or 1 :3: 1. No filler was used in any case, each mixture duced a velocity factor. It is believed, however, that the difconsisting solely of one of the phosphates and the desired salt ferent relative positions of the curves in the two series is due or salts. Calcined phosphate 1374, superphosphate 79, and mainly to the change in the amount of soluble salt present. double superphosphate 12 were used in these experiments. Figure 3 also shows that, in mixtures containing two adThe materials were taken in such amount that each mixture mixed salts, the inclined portion of the calcined phosphate weighed 2 grams. Although not all of these tests were run curves are near or actually below the inclined portion of the simultaneously, the same equipment and procedure were used double superphosphate curves, whereas in all mixtures of both and the results (Figure 3) should be entirely comparable. As series containing only a single admixed salt, the calcined phosin Figure 2 the relative humidity corresponding to the vapor phate curves are always above those for both the other phospressure of a solution saturated with the admixed salt or salt phates. The information available at present is not suffipair is shown on the humidity axis. ciently complete to permit an adequate explanahion of this The results obtained with this series of mixtures were, in phenomenon except in the most general way. As will be general, similar to those obtained with the preceding series. shown later, the presence of calcined phosphate in a mixture With the exception of those containing the reciprocal salt pair, not only did not change the hygroscopicity of the admixed salt, sodium nitrate and potassium chloride, all mixtures containbut also had little or no effect on the velocity of moisture abing superphosphate or double superphosphate began to absorption by that salt. It would appear therefore that the obsorb significant quantities of water a t lower humidities than served shift in the relative position of the curves for the mixdid the corresponding mixtures containing calcined phosphate. tures containing salt pairs was due not to any action of the I n these two cases the calcined phosphate mixtures remained calcined phosphate in increasing the hygroscopicity but to dry longer than the double superphosphate mixtures, but the some effect of the superphosphate or double superphosphate absorption curves "broke" simultaneously with those for the in decreasing the hygroscopicity. It is evident that a greater superphosphate mixtures. I n the mixtures initially containing variety of chemical reactions can occur in the mixtures consodium nitrate and potassium chloride, the former was in such taining superphosphate or double superphosphate than in excess that the vapor pressure of the system a t equilibrium those containing calcined phosphate, because of the greater shouId correspond to a relative humidity of 61.3 per cent a t I
-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
solubility, variety, and amounts of reactive substances present in the first two cases. Some of these reactions may have changed the hygroscopicity of the mixtures by changing the relative amounts of the compounds present or by the formation of new compounds not present initially. The effect of chemical reactions may be different in mixtures containing different proportions of the reactants. For example, the reaction between urea and monocalcium phosphate is known to change the hygroscopicity of the mixture in a manner dependent on the relative amounts present (18). It is possible that there is a different explanation for each case, and it would be unsafe to draw general conclusions concerning this type of mixture from the limited number of examples shown here.
Effect of Calcined Phosphate on Rate of Moisture Absorption by Urea Although calcined phosphate has no effect on the relative humidity a t which salts mixed with it become wet when exposed for a week, it was thought that its presence might tend to reduce the rate a t which moisture was absorbed. Accordl o o / ,
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1147
ingly, six mixtures were prepared; each contained 0.5 gram of 100-meshurea, 1.5 grams of 80-mesh calcined phosphate 1374, and 0.5 gram of the same phosphate ground to pass a 200-mesh screen. The finely ground phosphate was introduced with the idea that it might form a protective coating over the urea particles. Two of these mixtures, together with two 0.5-gram samples of the pure urea, were stored a t each of three relative humidities higher than that a t which urea begins to take up water (72.5 per cent a t 30" C.) and were weighed daily a t the same hour for 10 days. The results are shown in Figure 4 in which the average total gains in weight are plotted against the time in days. The gain in weight is computed in both cases as per cent of the urea present. I n every case the urea mixed with calcined phosphate absorbed water a t a slightly greater rate than urea alone. In view of the preceding results, this can hardly be due to absorption by the calcined phosphate; it was probably due merely to increased surface, the calcined phosphate having served to separate the urea crystals and prevent agglomeration. In another experiment uncoated grained urea was found to absorb moisture a t about the same rate as grained urea covered with a rather thick coating of 200mesh calcined phosphate. The method of graining and coating used was described by Ross and Hardesty (16). l l l l
Reactions and Hygroscopicity of Mixtures Containing Alkali Carbonates The effect of relative humidity on reactions between calcined phosphate and potasI i I I sium chloride, potassium sulfate, potassium carbonate, and sodium carbonate was studied by determining water-soluble and citrateinsoluble PZOSin mixtures containing equal amounts of calcined phosphate 1374 and one of the foregoing salts, before and after storage for 2 weeks a t various relative humidities. Mixtures Containing Sodium Nitrate No change in either water-soluble or citrateN P205 KpO 1.3 0 insoluble PZOSwas noted in the mixtures conI I I I taining potassium chloride or sulfate a t any Super hosphaten and relative humidity. It was concluded, thereI Doubye Superphosphate0 Sal d. NaNO,+KNO, fore, that no reaction occurred that affected I ,Soh. the solubility of the Pz06. I n the mixtures containing potassium carbonate (Figure 5), the water-soluble P20s in: l / l I / / 1 i Mlxtures containing I creased from 0.2 to 1.4 per cent in passing Sodium Nitrate and Potassium Nitratefrom 29 to 47 per cent relative humidity, indicating that somewhere in that range sufficient moisture was absorbed to initiate a reaction between the potassium carbonate and the calcined phosphate. I n the sodium carbonate mixture the water-soluble PzOa increased from 0.2 to 0.4 per cent in passing from 64.5 to 72.4 per cent relative humidity, but increased suddenly to over 7 per cent N: P205: Kg0: : I : 2 : I water-soluble PZOSat 83.2 per cent relative I N :I 4 0 5I : K20: I :I :I3 : I 1 I I I I I humidity coincidental with an increase in weight from 10 to 60 per cent. I n both cases the large gain in water-soluble PZOS occurred coincidentally with a large increase in weight, but much higher relative humidities were required to obtain this increase in the case of sodium carbonate. These reactions appear Sodium Nitrate and Potassiui Chloride I N 1PZO, 1KzO 1 I 31 I I to be similar to those observed by Meyers (IS),who converted the citrate-soluble phos0 10 20 $0 40 50 60 70 BO 90 100 0 IO 20 30 40 50 60 70 80 90 IO0 Total Gain in Weight, Per Cent phorus in calcined phosphate to the watersoluble condition by digestion with an aqueFIGURE3. F~ELATIVE HYGROSCOPICITIES OF MIXTURESCONTAINING A PHOSPHATE AND A PURESALTOR SALTS, IN THE RATIOS USEDIN FERTILIZERS ous solution of ammonia and carbon dioxide. N P205 K20 I 2 0
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1148
j
75.2 % Relative Humidity’
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sulfate, or nitrate for 4 weeks a t a fairly high
for reaction; the in-soluble potash was determined in the residue remaining: after washing: the mixture by the former official method (Sj or the present revised procedure (4). Neither method showed a significant decrease in the availability of the added potassium.
FIGURE 4. RATESOF MOISTURE ABSORPTION BY PURE UREAAND BY UREA MIXEDWITH CALCINED PHOSPHATE
Contrary to the results obtained with the other salts, probably none of which reacted with the calcined phosphate, mixtures of this phosphate with the alkali carbonates took up water a t a relative humidity below that corresponding to a saturated solution of the admixed carbonate. This is shown in5Figure 5 where the relative humidities corresponding to KzCOa ( I ) and Na2COs.10H20(9) are indicated on the humidity axes. Mixtures containing superphosphate or double superphosphate and an alkali carbonate are, however, less hygroscopic than the admixed carbonate. This is due to the reaction in which carbon dioxide is liberated and the less hygroscopic monopotassium phosphate is formed; the vapor pressure of the saturated solution of monopotassium phosphate corresponds to 92.9 per cent relative humidity a t 30” C. (2). When mixtures, containing one gram of either superphosphate 1316 or double superphosphate 1362 and one gram of potassium carbonate, were exposed successively to ascending relative humidities starting a t 46.7 per cent, they lost weight a t first because of the evolution of carbon dioxide. The
Literature Cited (1) Adams, J. R.,unpublished data. (2) Adams, J. R., and Merz, A. R., IND. ENQ. CHEM.,21, 305-7 (1929). Official Agr. Chem., Methods of Analysis, 3rd ed., p. 25 (3) ASSOC. (1930). (4) Ibid., 4th ed., p. 30 (1935). (5) Ibid., 4th ed., pp. 19-23 (1935). (6) Beeson, K. C., and Jacob, K. D., paper presented before Divi-
sion of Fertilizer Chemistry a t 92nd Meeting of A. C. S., Pittsburgh, Pa., Sept. 7 to l i (1936). (7) Hill, W. L., and Hendricks, S. B., IND.ENQ.CHEM.,28, 440-7 (1936).
(8) Hill, W. L., and Jacob, K. D., J. Assoc. Oficial Agr. Chem., 17, 487-505 (1934). (9) International Critical Tables, Vol. 111, p. 372, New York, McGraw-Hill Book Co., 1928. (10) Jacob, K. D., Bartholomew, R. P., Brown, B. E., Pierre, W. H., Reid, F. R., and Tidmore, J. W., J. Agr. Research, 50, 837-48 (1935). (11) Marshall, H. L., Reynolds, D. S., Jacob, K. D., and Rader, ENQ.CBEM..27,205-9 (1935). L. F.. Jr.. IND. Mer; A. R., Fry, W. H., Hardesty, J. O., and Adams, J. R., Ibid., 25, 136-8 (1933). Meyers, H. H., U. S. Patent 1,846,347 (Feb. 23,1932).
Reynolds, D. S., Jacob, K. D., Marshall, H. L., andRader, L. F., Jr., IND.ENQ.CHEM.,27,87-91 (1935). Revnolds. D. S.. Jacob, K. D., and Rader, L. F., Jr., Ibid., 26, -. i06-12’(1934).
Ross, W. H., and Hardesty, J. O., Commercial Fertilizer Year Book, pp. 28-33 (1937). Ross. W. H., and Jacob, K. D., J . Assoc. OflciaZ AUT.Chem., 20, 231-49 (1937).
Whittaker, C. W., Lundstrom, F. O., and Shimp, J. H., IND. ENG.CHEM.,26,1307-11 (1934). R~CEIYE July D 27, 1937. Presented in part under the title “Chemical and Physical Properties of Fertilizer Mixtures Containing Calcined Phosphate” before the Division of Fertiliser Chemistry a t the 92nd Meeting of the American Chemical Society, Pittsburgh, Pa., September 7 to 11, 1936.
EFFECTOF RELATIVEHUMIDITYON HYQROBCOPICITY AND WATER-SOLUBLE Pz06 IN MIXTURES OF ALKALI CARBONATES AND CALCINED PHOSPHATE
FIGURE 5.
