INDUSTRIAL AND ENG INEERING CHEMISTRY
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4. Any curve (or series of curves) which satisfies a tenable hypothesis and which does not miss an experimental value by more than its error is ordinarily a satisfactory representation of the experimental facts.
Apparently the tentative proposition stated in the text covers the state of affairs. The author is of opinion that the use of calculated rates of corrosion is likely to be misleading except when the corrosion-time relationship is linear or when one has a knowledge of the nature of the corrosion-time relationship existing under the particular conditions, whatever they may be. This opinion is contrary to the practice of certain outstanding investigators. The fact that calculated rates of corrosion will change regularly or continually when the corrosion-time relationship is other than linear makes it difficult to visualize the significance of a single rate figure. This discussion has a close bearing on the meaning of the phrase “protective rust layer.”’ If the visible products of corrosion completely stop attack on the metal, there is no doubt that the rust layer is protective. If the corrosion-time relationship is linear, the rust layer is certainly not protective. However, there are many occasions when the attack lies between a linear relationship and complete cessation. In one sense of the word, the rust layers which are capable of 1 Note the distinction between a “protective rust layer” and a “protective film.” A protective film is a n oxide, etc., which is thin enough t o be invisible when in contact with the metal: it influences the initial distribution of attack and can immunize the metal from attack, as the film on BOcalled stainless materials does under many conditions.
Vol. 25, No. 11
making ferrous metals corrode a t in-between rates, as it were, are also protective. Thus, the author believes that constructive discussion on the significance of the phrase “protective rust layer” will be a valuable contribution for further discussion. LITERATURE CITED Bengough, Lee, and Wormwell, Proc. Roy. SOC. (London), 134A, 308 (1931). Bengough and Lee, J . Iron Steel Inst., 135, 285 (1932). Buck, D. M., Proc. Am. SOC.Testinn Materials, 1 9 , I I . 224 (1919). Buck, D. M., Trans. Am. Electrochem. SOC.,39, 109 (1921). Chappell, J.Iron Steel Inst., 85, 270 (1912). Dodge et al., Proc. Am. SOC.Testing Materials, 33, I (1933). Evans, “Corrosion of Metals,” pp. 12-14, Arnold, 1924. Evans and Hoar, Proc. Roy. SOC.(London), 137A, 343 (1932). Forrest, Proc. Am. SOC.Testing Materials, 29, 11, 128 (1929). Forrest, Roetheli, and Brown, I X D . EKQ.CHEX, 22, 1197 (1930). Ibid., 23, 650 (1931). Groesbeck and Waldron, Proc. Am. SOC.Testing Materials 3 1 , 11, 279 (1931). Hippensteel, Borgman, and Farnsworth, Ibid., 3 0 , I I , 456 (1930). Logan, Ewing, and Yeomans, Bur. Standards, Tech. Papers, 1928, KO.368, 447. Logan and Grodsky, Bur. Standards J . Research, 7, 1 (1931). Logan and Taylor, Ibid., to be published, 1933. Passano, Proc. Am. SOC.Testing Materials, 32, 11, 468 (1932). Passano and Nagley, Ibid., 33, I1 (1933). Pilling and Bedworth, J. Inst. Metals, 29, 529 (1923). ’
RECEIVEDJune 9, 1933. Presented a t the Third Corrosion Conference Bureau of Standards, Washington, D. C., March 30 and 31, 1933.
Holocellulose, Tota1 Carbohy dr ate Fraction of Extractive-Free Maple Wood Its Isolation and Properties GEO. J. RITTERAND E. F. KURTH, Forest Products Laboratory, Madison, Wis.
R
E S E A R C H workers The total carbohydrate portion of extractivedetermination a n d i s t h e r e free here termed (~hOIOCellUloSe,~~ fore objectionable for routine h a v e long had t h e work. Accordingly, the Forest desire to develop rapid is in “lid form by a rapid method Products L a b o r a t o r y undermethods for isolating, in a solid f r a c t i o n , the e n t i r e c a r b o deaebed at the Forest Products Laboratory for took t h e d e v e l o p m e n t of a hydrates in wood which has been routine work. rapid m e t h o d . It was found extracted with alcohol-benzene The total acetyl groups, the total carbon di- that repeated alternate treats o l u t i o n and with hot water. oxide-forming and a part of the mentsof theextractive-free wood with chlorine and alcohol-pyriSuch a wood fraction methoxyl groups Of the wood are in the hobdine solution removed in about afford a c o n v e n i e n t means -_ celluLose* 10 hours all except a small perf o r s t u d y i n g the nature and centage of the lignin; the rethe relationship of the c a r b o hydrate components and their substituent groups, acetyl, maining small percentage was removed in 30 minutes with a carboxyl, and methoxyl. Some of these components and solution of calcium hypochlorite. The residue remaining substituent groups are partially or wholly lost in the isolation from the foregoing procedures is the carbohydrate fraction. I n one phase of this study the chemical characteristics of Cross and Bevan cellulose which constitutes only about of the material are compared with those of Skelettsubstanzen. 80 per cent of the carbohydrates. Chlorine dioxide in a solution of pyridine in water has In stating those comparisons a short appropriate name for been used by Schmidt (12) in isolating a carbohydrate frac- the material is desirable. Since the material is composed of tion designated Skelettsubstanzen which constitutes practically hemicelluloses and cellulose, it has been termed “holocellulose, the total carbohydrates of extractive-free wood. Schmidt’s meaning whole or entire cellulosic material. procedure requires approximately one month for making the MATERIAL 1 The author8 Dropose the word “holocellulose” as preferable t o Skeletb ~
.
.
subatanrcn, maintaining that the latter term does not describe the material correctly either from the physical or chemical point of view. The word “holocellulose” ae yet has not been formaUy or generally accepted by workere in this field.
i \ / ~ ~ ~ l ~ (60-80 mesh) that was extracted with and with hot Water was used’ alcohol-benzene The alcohol-pyridine solution was prepared by diluting
November,
1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
1231
15 cc. of c. P. pyridine with enough 95 per cent ethyl alcohol t o form 100 cc. of solution. The calcium hypochlorite solution was prepared by extracting commercial chlorinated lime with distilled water and decanting off the supernatant clear solution. The resulting solution was cooled t o below 10" C. and made just acid to litmus before use.
12 per cent hydrochloric acid method ( 2 ) , methoxyl by the Zeisel method ( I ) , acetyl by the toluene-sulfonic acid method ( d ) , and pentosans by Tollen's method ( I ) . Extractions with 1.0 per cent sulfuric acid and 2.0 per cent sodium sulfite were made by treating 1 gram of the material with 50 cc. of the solution at boiling temperature of the solutions for 45 minutes. For comparative purposes the same analytical treatments were made on each of the following nine materials: QUANTITATIVE PROCEDURE FOR ISOLATINQ HOLOCELLULOSE FROM EXTRACTIVE-FREE MAPLESAWD LTST (1) Maple sawdust extracted with alcohol-benzene and hot Since repeated alternate chlorine and alcohol-pyridine water. (2) Material 1 treated with -gaseous chlorine and alcoholtreatments leave 1 to 2 per cent of lignin in the holocellulose, pyridine solution. it is necessary to determine the stage in the procedure at (3) Material 2 treated with calcium hwochlorite solution ". which the calcium hypochlorite treatment should be applied (holocellulose). (4) Material 1 treated with chlorine dioxide in water-pyridine for the final delignification treatment. That stage can be approximated by following the loss in weight of wood samples solution (Skelettsubstanzen). ( 5 ) Material 3 treated 45 minutes with 1 per cent boiling whose lignin content has been previously determined. De- sulfuric acid. termining the loss in weight, however, requires drying the ( 6 ) Material 4 treated 45 minutes with 1 per cent boiling sample which renders some of the holocellulose soluble. sulfuric acid. (7) Material 3 treated 45 minutes with 2 per cent boiling I n the quantitative isolation of holocellulose it is, therefore, sodium sulfite. advantageous to weigh triplicate samples of sawdust whose (8) Cross and Bevan cellulose from material 1. lignin content has bclen previously determined by the 72 per (9) Lignin from material 1. cent sulfuric acid method (IO), using one sample as a control The holocellulose and Skelettsubstanzen were treated with in following the lignin removal and the other two for check the dilute acid and dilute sulfite in order t o determine what determinations. The detailed procedure used at the Forest Products Labo- proportion of the polyuronides, the remaining methoxyls, and the acetyls was removed by such treatments. The ratory for isolating holocellulose is as follows: compositions of the residues (materials 5, 6, and 7) were Weigh ap roximately 1.7 grams of air-dry extracted sawdust compared with that of Cross and Bevan cellulose. I n order in an alungum crucible, moisten the material with distilled water, and remove the excess moisture by suction. Transfer the to determine the distribution of the methoxyl in the wood, sauTdust to a 250-cc. beaker and treat the material with chlorine it was necessary to determine the methoxyl content of the gas in a chlorinating chamber for 3 to 4 minutes; remove from lignin. the chamber and add a few cubic centimeters of alcohol-pyridine Table I gives the actual composition of each of the nine solution to the contents in the crucible to neutralize the acid materials; Table I1 gives the composition of each material formed durin chlorination; transfer to the alundum crucible and remove t8e excew solution by suction. Transfer the cru- calculated on the basis of the extractive-free sawdust in order cible with its contents to a Soxhlet apparatus and extract with to indicate what proportion of extractive-free wood compoalcohol-pyridine solution for 2.5 hours; remove from the extractor and wash with cold distilled water. Repeat the chlorina- nents and substituent groups remain in the different residual tion and extractive treatments three times or until the loss in materials. weight of the control is within 1 to 2 per cent of the lignin conTABLEI. YIELDSAND RESULTSOF ANALYSES OF EXTRACTIVEtent previously determined. FREESAWDUST AND ITS VARIOUS FRACTIONS To remove the remaining lignin, transfer the residue to a 400-cc. beaker and add 300 cc. of the cold dilute solution of (Yields of materials based on oven-dry weight of extracted wood; results of analyses of materials based on oven-dry weight of the materials) calcium hypochlorite, which has been made just neutral to litmus LIQNIN with acetic acid. The bleach then has a pH of approximately MATERIAL YIELDS(72% HzSO1) OCHa COz CHaCO PENTOSAN ASH 7.0 as determined by the glass electrode. Maintain a tempera% % % % % % % ture of 10" C . and stir the mixture occasionally during a period 100.0 22.8 19.6 0.30 of approximately 30 minutes. When the residue is bleached to a 78.0 1.9 24.5 uniform white, filter it, wash well first with cold distilled water 76.2 0 24.9 o:i9 75.8 and then with alcohol. Dry in a vacuum oven and weigh. 0 24.8 0.16 58.2 61.4
PHYSICAL P~ZOPERTIES O F HOLOCELLULOSE I n color, holocellulose resembles well-bleached Cross and Bevan cellulose; in physical structure it more nearly resembles wood sawdust in that it tends t o retain the general structure of the original wood, although the cleavage between the structural elements is weakened considerably, as is shown by a rather high percentage of single detached fibers. It is possible that retention of the wood structure in the carbohydrate material is due largely to a mechanical binding between the fibers and ray cells which is reenforced by occasional tiny flakes of residual cementing material, perhaps hemicelluloses. Before a more conclusive explanation of the structure is offered, further chemical and microscopic research will be required.
0
68.7 63.1 22.8
0 0 0
..
21.0
..
..
12.6 16.2 13.1 18.3
..
TABLE 11. COMPOSITION O F EXTRACTIVE-FREE SAWDUST ITSVARIOUS FRACTIONS
0.12 0.08 0.08
0.10 0.39 AND
(Results based on oven-dry weight of extractive-free sawdust) LIQNIN MATERIAL YIELDS(72% 4sa .. HzSOd OCHa COX CHaCO PENTOSAN % % % % 100.0 78.0 76.2 75.8 58.2 61.4 58.7
63.1
22.8
22.8 1.6 0
19.6 19.1
19.0 18.8 7.3
0 0 0
9.9 7.7
0 0
..
4.8
..
..
11.5
..
0.30
..
0.22 0.12
0.07
0.05 0.05 0.06 0.09
RESULTS AND DISCUSSION CHEMICALCOMPOSITIONOF HOLOCELLULOSE I n order t o characterize the holocellulose, the following determinations were made: Lignin was determined by the 7 2 per cent sulfuric acid method (IO), carbon dioxide by the
Yields and actual chemical composition of the materials prepared in this study are listed in Table I. Material 2 which was prepared from material 1 represents the cellulosic product which was obtained by repeated
1252
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 25, No. 11
TABLE 111. COMPOSITION OF MATERIAL REMOVED BY CHEWICAL TRE.4TMENTS MATERIAL A Holocelldose
TREATMENT
B
Ertrsctirbfree maple wood
%
%
SUMMARY OP INDIVIDUAL LOSUES Pentosan Acetyl E F
OCHa 1 Ash G H
Lignin
Summary of individual losses
%
%
%
%
%
J %
I
Extn. with boiling 2% NalSO, HISO( Extn: with boiling 1% HzSOI
17.6 17.9 14.4
3.04 3.12 2.88
10.8 10.9 8.2
2.78 2.16 2.21
0.71 0.66 0.69
0.17 0.16 0.07
0 0 0
17.30 18.99 14.06
Cross and Bevan
36.9
2.66
7.6
2.66
0.87
0.16
22.8
36,. 40
H o ~ o o ~ ~ ~Extn u ~with o Bboiling ~ 1 8krld:wbrtonzsn
Uronic acid TOTALLoss anhydride IN WEIQHT (CObX 4) C
alternate treatments with chlorine and alcohol-pyridine. Except for lignin content its yield and chemical composition correspond closely with that of holocellulose which was prepared from material 2 by means of the calcium hypochlorite treatment. This indicates that very little substance other than lignin was removed by the hypochlorite treatment. It may be noted that in both yield and chemical composition holocellulose corresponds closely with the Skekttsubstanzen which was isolated by the chIorine dioxide procedure. Because of the removal of the lignin and the retention of practically all of the other components in isolating the holocellulose, it is richer than material 1 and Cross and Bevan cellulose in carbon dioxide-forming components, pentosans, methoxyl, and acetyl groups. Further, some of each of these components and groups are still retained in the residue remaining after holocellulose is hydrolyzed with boiling dilute acid and alkaline solutions as shown by the composition of materials 5 and 7. Moreover, the chemical composition of material 5 is similar to that of material 7 which was prepared from Skelettsubstanzsn by means of 1.0 per cent acid hydrolysis. From the carbon dioxide yields of material 8 it is shown that polyuronides are still present in Cross and Bevan cellulose. This finding is contrary to the limited distribution of polyuronides as suggested by Hawley and Norman (6). The slight difference between the theoretical and the experimental yields of holocellulose can best be shown by calculating the analytical results on the basis of the extractive-free wood as was done in Table 11. If the lignin value is subtracted from the extractive-free wood value, there appears to be a theoretical carbohydrate fraction of 77.2 per cent (100 - 22.8 = 77.2) as compared to 76.2 actually isolated, indicating a loss of 1.0 per cent. The data indicate that 0.6 per cent of pentosans in the wood are missing in the holocellulose, which would increase the yield of holocellulose to 76.8 per cent. If the 0.6 per cent of pentosans is added to the holocellulose and the lignin (0.6 76.2 22.8 = 99.6), there is still a discrepancy of 0.40 per cent for the analysis of the extractive-free wood. Most of this discrepancy is due to loss of methoxyl. I n the isolated lignin and the holocellulose is found 5.75 per cent of methoxyl (4.8 0.95 = 5.7.9, leaving 0.35 per cent unaccounted for (6.1 - 5.75 = 0.35). From the data it is impossible to say whether the loss in methoxyl occurred in the lignin or the holocellulose, but in either case it should be added to the lignin and the corrected holocellulose values, making a total of 99.95 per cent (99.6 0.35 = 99.95). Aside from a small percentage of pentosans, the holocellulose, therefore, represents practically the total carbohydrates of the extractivefree wood. I n addition to yields, Table I1 also shows the proportion of the total components and substituent groups that remain after the chemical treatments employed for preparing the various materials. METHOXYLS.Methoxyl to the extent of 0.95 per cent, which is 15.6 per cent of the total (0.95 f 6.1 X 100 = 15.6) is present in the holocellulose. This finding disproves the conception that all of the methoxyl in wood is associated with the lignin and confirms published results ( 7 , l l ) .
+
+
+
+
Difference (E - J) I(
% -0.20
-0.91 -0.35 -0.47
Even after the holocellulose is hydrolyzed with boiling 1.0 per cent sulfuric acid for 45 minutes, the remaining material 5 still retains 4.8 per cent of the total methoxyl (0.29 + 6.1 X 100 = 4.8). I n a like manner, as shown by material 7, the holocellulose hydrolyzed with boiling 2.0 per cent sodium sulfite solution for 45 minutes also retains 4.0 per cent of the methoxyl in the wood. And material 8, Cross and Bevan cellulose, likewise retains 7.0 per cent 6.1 X 100 = 7.0). of the methoxyl (0.43 i CARBONDIOXIDE-FORMINQ MATERIAL.The total materials that liberate carbon dioxide in the extractive-free wood are present in the holocellulose. While they are attacked by acid and alkaline hydrolysis, nevertheless more than 25 per cent of them withstand those treatments, as is shown by the carbon dioxide in materials 5 and 7. Further, approximately 43.0 per cent of those materials are retained in the maple Cross and Bevan cellulose. This percentage of carbon dioxide liberated from the maple Cross and Bevan cellulose is higher than that found in catalpa Cross and Bevan cellulose (Q),indicating that the polyuronide content of Cross and Bevan cellulose from different woods may vary. ACETYL^. Acetyl groups present in the wood withstand the treatments for isolating holocellulose and Skelettsubstanzm and they can be recovered quantitatively in those two residual products. Those acetyl groups are partially removed by mild acid and alkaline hydrolysis and also by the treatments employed for isolating Cross and Bevan cellulose as indicated by materials 5, 7, and 8, respectively. The presence of acetyls in Cross and Bevan cellulose confirms results by another investigator (8). The finding of those groups in holocellulose, in materials 5 and 7, and in Cross and Bevan cellulose therefore disproves another conception-namely, that the acetyls are present in the lignin. PENTOSANS.Holocellulose contains 96.9 per cent of the pentosans of the extractive-free wood. When holocellulose was hydrolyzed with boiling 1.0 per cent sulfuric acid and 2.0 per cent sodium sulfite solution, respectively, it sustained a decided loss in pentosans as shown by the composition of materials 5 and 7 in which the pentosans content is lower than that in the Cross and Bevan cellulose.
SUMMATION OF IKDIVIDUAL LGESEBCUE TREATMENTS
TO
CHEMICAL
After subjecting wood fractions to chemical treatments, difficulties are generally experienced when attempts are made to account for the total losses by summarizing the individual losses. As already shown, such was not the case in preparing materials 3 (holocellulose) and 4 (Skelettsubstanzen) from material 1. This scheme of analysis was tested still further concerning its quantitative aspects. The test was made by determining and summarizing the individual losses sustained by material 1in the preparation of Cross and Bevan cellulose, by the holocellulose in the preparation of materials 5 and 7, and by Skelettsubstanzen in the preparation of material 6. The treatments employed and the total losses suffered by the three materials are recorded in columns B and C of Table 111. To make a summary of the individual losses required the calculation of the carbon dioxide (column D, Table 111)
November. 1933
I N D US TR I A L A N D E N G I N EE R I N G C H E M I S T R Y
in terms of uronic acid anhydride, its mother substance. That is done according t o the following formula: Uronic acid anhydride = carbon dioxide X 4. During the pentosan determination, uronic acid anhydrides liberate 16.6 per cent of their weight as furfural (6) which, in terms of pentosans, is equivalent to 22.8 per cent of the uronic acid anhydride. Consequently, a correction factor equal to 22.8 per cent of the uronic acid anhydride value must be subtracted from the pentosan value as determined by the method used. This has been done in column E, Table 111. Losses in methoxyl and ash sustained in the isolation of Cross and Bevan cellulose require further explanation because some of each of those losses is recovered in the lignin. Thus, when Cross and Bevan cellulose was isolated from the wood, 5.67 per cent of methoxyl was lost (6.1 - 0.43 = 5.67). Of this amount 4.8 per cent was recovered in the isolated lignin, leaving a net loss of 0.87 per cent (5.67 - 4.8 = 0.87), line 4, column G. During the same procedure 0 2 4 per cent (0.30 - 0.06 = 0.24) of ash was lost and of that amount 0.09 per cent was recovered in the lignin, leaving a net loss of 0.15 per cent, as shown in line 4, colurrin H. The individual losses are summarized in column J. Column K points out the close agreement between the sum of the individual losses and the total loss in weight, column C. In Table 111, then, it appears that the carbohydrates removed by the treatments in column B consist of uronic acids and pentosans, perhaps in the form of polyuronides. With these materials methoxyl and acetyl groups are also removed. The nature of the chemical combination between
1253
those substituent groups and the polyuronide components is unknown. Before that combination is discovered, it will be necessary to isolate and identify polyuronide components to which methoxyls and acetyls are attached. As a f i s t step in that direction the products removed by mild hydrolytic treatments of the maple holocellulose are being identified. Whether results similar to those reported in this paper will be obtained when other woods are treated according to the procedure employed for maple will be ascertained later. LITERSTURE CITED
(1) Bray, M. W., Paper TradeJ., 87,59-68 (1928). (2) Dickson, A., Otterson, H., and Link, K., J . Am. Chem. Soc., 52, 775 (1930). (3) Dore, W. H., J. IND.ENQ.CHEM.,12, 475 (1920). (4) Freudenberg, K., Ann., 433, 230-7 (1923). (5) Hawley, L. F., and Norman, A. F., IND.EXG.CHEM.,24, 1190 (1932) (6) Norman, A. F., Biochem. J., 23, 524 (1929). (7) O’Dwyer, M. H., I b i d . , 22, 381 (1928). (8) Ritter, G. J.. IXD.ENG.CHEM.,16,947 (1924). (9) Ritter, G. J., and Fleck, L. C., I b i d . , 20, 371 (1923). (10) Ritter, G. J., Seborg, R . hf., and Mitchell, R. L., I h i d . , ilnal. Ed., 4, 202 (1932). (11) Schmidt, E., Meinel, K., and Jandebeur, W.,Celiulosechem., 13, 129-39 (1932). (12) Schmidt, E., Tang, Y . C., and Jandebeur, W.,I b i d . , 12, 201 (1931). I
RECEIVED April 29, 1933. Presented before the Division of Celluloae Chemistry at the 85th Meeting of the American Chemical Society, Washington, D. C., March 26 to 31, 1933.
Factors Affecting the Phosphoric AcidPhosphate Rock Reaction H. L. MARSHALL, L. F. RADER,JR., AND K. D. JACOB,Bureau of Chemistry and Soils, Washington, D. C. using the batch or intermittent Process to about 40 Per Cent in those using the c o n t i n u o u s Obtained treating by the quantity, concentration, and purity of the strong-acid p r o c e s s ( l r ) , In phosphate rock with phosphoric the acid, the IYPe and Particle size Of the the ordinary method of double acid, has considerable promise time and temperature of mixing, and the time of superphosphate m a n u f a c t u r e as a concentrated p h o s p h a t e fertilizer in this country. Alstorage of ihe mixtures. The Concentration of this acid is usually concentrated the acid and the time of storage of the mixtures are to 50 to 65 Per cent Hap01 and though the d o m e s t i c output is then mixed with ground phosamounts to less than loo,ooo the most important of these factors. The best phate rock. The damp product tons annually, its production cont!ersions to a d a b l e phosphoric oxide Were is allowed to remain in the curand importance to agriculture obtained in mixtures prepared with phosphoric ing pile for about 2 w e e k s or will increase, no doubt, with the l o n g e r , in order to obtain the development of cheaper methacid containing 55 to 65 per cent &PO4 and maximum c o n v e r s i o n of the ods for the m a n u f a c t u r e of stored 4 day,?or longer. phosphate into available forms, phosphoric acid. principally monocalcium Double superphosphate is a desirable fertilizer partly because of its content of calcium, phosphate. The material is then dried and, after crushing an element of major importance to plant growth ( I S , 16). and screening, is shipped to the trade. The combination of the manufacture of double superFurthermore, double superphosphate can be treated with anhydrous ammonia to give a product having satisfactory phosphate with its ammoniation and mixing with potash mechanical properties and containing approximately 8 to 10 and other fertilizer substances offers interesting possibilities per cent of ammonia and more than 40 per cent of available for the production in one continuous operation of complete high-analysis mixtures in a granular, nonsegregating form phosphoric oxide (6, ?). With one exception, all domestic, double superphosphate (14). Such a procedure would permit the utilization of the plants use phosphoric acid manufactured by the sulfuric heat of reaction between ammonia and double superphosphate acid process. The concentration of the acid produced di- and would reduce handling costs in the plant. Also, it might rectly by this process is different in different types of plants, be possible to use weak phosphoric acid in a process of this and usually ranges from about 20 per cent HaPOrin plants kind, thereby eliminating a t least a part of the cost of concen-
D
OUBLE or triple superphosphate, the product
A study has been made of the reaction between phosphoric acid and phosphate rock as affected
