Chemical Changes in Mixtures of Superphosphate with Dolomite and with Limestone W. H. MACINTIRE AND G. ,4.SHUEY T h e Cniversity of Tennessee Agricultural Experiment Station, Knoxville, T e n n .
Superphosphate can be mixed with either type of eraluation of such mixfures. T h i s holds for a n y limestone for immediate use utithont a n y uppreciable feasible amount and fineness. The drying effect of dolomite is more pronounced formation of insoluble Pz06. The ez!olution of carbon dioxide f r o m superphos- than that of high-calcium limestone. The changes phate mixtures of limestone and dolomile is a useful in the weights of the dolomite mixtures are neglimeans of studying the progress of the reactions in- gible, but appreciable losses occur in the high-calvolved. I n mixtures of feasible proportions, the cium limestone mixtures. It is evident that the inclusion of limestone means evolved carbon dioxide is a measure of the transition that tricalcium phosphate is formed during the of water-soluble to citrate-soluble PzOs. “hen superphosphate is mixed with dolomite, the analytical procedure‘ and that limestone is dechange in the f o r m of the phosphates is induced by cidedly more active than dolomite in this regard. both the calcium and the magnesium content of the The oficial method therefore records the presence of a dolomite. A n y magnesium phosphates formed are phosphate compound that was not present in the so readily soluble in ammonium citrate that even i f mixture prior lo analysis. W h e n high-calcium limestone is used, the amount all the Pz06were in combination with magnesium, as the di- or even the tri-salt, the PzO5 would be com- of limestone in the mixiure cannot be unrestricted. pletely dissolved by the neutral citrate in 2-gram, I n using the present oflcial method, which calls for a 200-cc. (1-gram, 100-cc.) ratio. Furthermore, the one-gram charge, the penalty against the highf u l l amount of the tricalcium phosphate formed by calcium limestone mixes will not be so great, howfhe calcium carbonate fraction of the dolomite used in ever, as would have been the case with the 2-gram a n y of the mixtures studied would be completely dis- charge, since in the new ratio of charge to citrate solted by the citrate solution. Hence, since only a solution, the solubility of tricalcium phosphate is part of either the di- or tri-forms present in a dolo- materially enhanced, even when a n excess of limemite mixture is present as the dicalcium or tri- stone remains in the mixture. Although not intended calcium ,form, and since both the solubility of the to be applicable primarily for fertilizers that condolomite in, and its vitiating effect upon, the citrate tain limestone supplements or jillers, the change to solution are less than the corresponding values for the one-gram charge now specified in the A. 0.A . C. limestone, the dolomite f o r m of limestone can be method materially affects the analysis and enhances used without detrimental effect upon the commercial the evaluation of such products.
A
GRONOMIC investigations in Tennessee (16) and
other southern states have demonstrated that the joint use of superphosphate and limestone is a rational and profitable practice. A diversity of opinion has existed among agronomists, however, as to the desirability of premixing the two materials (5, 21). A prejudice against the inclusion of limestone as a commercial filler, or as a supplement, has also existed (2, 7 ) . Agronomists have been concerned with the ultimate effect of limestone upon the solubility of the added PzOs, as measured by the growing plant, whereas the commercial interests have been concerned as to the penalty that would ensue if the included limestone decreased the amount of available P205 found by the control chemists. The cost of limestone also is greater than that of inert fillers. Furthermore, in one state a t least limestone fillers have not been sanctioned, and in general no credit could be claimed for the supplements supplied through the use of limestone. Parker (18) has recently offered convincing arguments to justify the granting of credit for such supplements. Contributions by Brogdon (S), Brackett (Z), Magruder ( l j ) , Fraps ( 7 ) , Hall (S), Harris (9), and Larison (11) have
dealt with the changes which occur in superphosphate-limestone mixtures. I n no case, however, have the activities of high-calcium and dolomitic limestone been compared, and in no case has the evolution of carbon dioxide been used to measure the speed of the reactions involved. This paper presents such a comparison and shows the utilization of the evolution of carbon dioxide as a measure of the progress of the reactions. The study was preliminary to a lysimeter investigation of phosphate-limestone and phosphate-dolomite mixtures within the soil. The objectives were to determine (1) the rapidity and the nature of the P205 changes that the farmer may anticipate when he mixes the separate materials for immediate use; (2) the speed of the PzOstransitions and the forms present a t intervals in commercial mixtures of superphosphate with limestone and with dolomite when the mixes are “cured” or stored; (3) the influence of added limestone and dolomite upon the accuracy of P205determinations by the official analytical procedure. The analyses of the high-grade commercial phosphate and the two limestones used in all of the mixtures are given in Table I.
933
I SD US TR IA L A N D E N GI NEER IN G CHE M ISTR Y
934
TABLEI. ANALYSESO F
SUPERPHOSPHATE -4XD
Moisture
%
a
SUPERPHOSPHATE-PzOa in WaterCitrateTotal so1.a sol.
%
9.75 21.81 3.289 as free acid.
TABLE11. EFFECTO F
DOLOMITIC AND
HIGH-CALCIUM
LIMESTOXES USED
IN
Vol. 24, No. 8
LIMESTOSE-PHOSPHAT~
MIXTURES
--
-
DOLOMIT~C LIMESTOKE-CaCOa equivalent-
Citrate. insol.
-HIGH-CALCICM LIMESTONE-CaCOa equivalent-
Total
Calcium
Magnesium
Total
Calcium
%
%
%
%
%
%
%
%
%
19.52
2.22
0.07
96.81
52.17
44.64
99.40
98.27
1 13
MIXING SUPERPHOSPHSTE‘ W-ITH
Magnesium
~OO-MESHHIGH-CALCIESI LI>~ESTOXE* AND DOLOMITIC LIMESTOSEC !Pros content)
PROPORTION SUPERPHOSPHATE TO
~OO-MESH
TOTnL
%
--WATER-SOLUBLEOris. .ifter mixt. 1.5 hr.
%
%
After 72 hr.
%
--CITR.ATE-SOLUBLE-Orip. After After mixt. 1.5 hr. 72 hr.
%
%
Limestone 1 : l IO.9s 9.76 7.70 4.58 1.11 3.15 Dolomite 1 : l 10.91 9.76 9.46 9.09 1.11 1.41 Limestone 3 : l 16.40 14.64 13.29 10.71 1.67 2.97 Dolomite 3 : l 16.36 14.64 14.45 14.00 1.66 1.86 PnOa content: total, 21.81; water-soluble, 19.52; citrate-soluble, 2.22; citrate-insoluble, 0.07; moisture, b Contained 0.15 per cent PlOa. c Contained 0.01 per cent PzOa. d Two-gram charge per 100 cc. of ammonium citrate solution.
--CITRhTE-INaOLijBLEd-Orig. After After mixt. 1.5 hr. 72 hr.
%
%
6.24 1.77 5.54 2.30 9.75.
0.11 0.04 0.09 0.06
%
0.13 0.04 0.14 0.05
%
0.16 0.05 0.15 0.06
SHORT-PERIOD MIXTURES FOR IMMEDIATE USE LIMESTOKEus. DOLOMITE.Two proportions of super-
sampling in the open agitates the mass, activates the reactions, and necessitates determinations of the variations in phosphate and 100-mesh limestone, and also dolomite, were moisture content. Furthermore, the decrease of original used-1 to 1 and 3 to 1. The mixtures were made in closed acidity and the accumulation of dibasic forms of phosphate, containers, aspirated, and analyzed for the several P20, in particular, necessitate comparison of results obtained under occurrences after periods of 1.5 hours and 72 hours, as repre- different analytical conditions and by a method that was sentative of minimum and maximum periods that would never intended for use with mixtures carrying insoluble probably ensue between home mixing and drilling. The carbonates. X large amount of analytical work is also reanalyses given in Table I1 were made by the official A. 0.A. C. quired for the frequent successive determinations. I n the present studies the progress of the reactions was methods, as of 1928, when the work was done. From the data of Table I1 it is evident that, although a determined by measuring the evolution of the carbon dioxide considerable quantity of diphosphate was formed, there was from closed containers, constantly aspirated. This method no appreciable increase in the citrate-insoluble. The di- permitted the accurate daily determination of the evolved phosphates of calcium and magnesium are given the same and constantly aspirated carbon dioxide, its limestone equivarating as the monophosphates in control analyses, and there lent, and its PZOsequivalent, in any proportions and with a is considerable evidence that the dicalcium phosphate is minimum of analytical work. The variations in weights equal, if not preferable, to the monophosphate, especially of the containers, corrected for the weight of carbon dioxide in soils where readily soluble forms of calcium are deficient. evolved, also give the changes in the moisture content for Under such a condition the fixation of the PO, ion by iron any period. The limestone and dolomite were added to the and aluminum is not so rapid when the dicalcium material previously introduced materials, the containers were sealed, is used. The dilution of the PZOSin the limestone or dolo- and the contents thoroughly mixed and compacted. The mite mixtures also facilitates a more uniform incorporation. containers were fixed on the workbench by paraffin molds, I t will be shown later that results similar to those of Table and aspiration of air, purified by sodium hydroxide soluI1 are obtained when the mixtures are made in one-ton lots. tions, was begun immediately. The continuously aspirated For home mixing and use within the 72hour period, any carbon dioxide was determined daily during the first two problem involved in phosphate-limestone combinations there- weeks and a t frequent intervals thereafter for periods of six months or longer, with subsequent intermittent aspirations fore applies only after incorporation within the soil. The premixing of limestone and superphosphate was recom- up to 283 days. The analyses of the components of the mended in circulars of the Tennessee and Kentucky stations mixtures are given in Table I. M A K E - U P OF MIXTURES.Two proportions (8 and 30.5 per in 1922 and 1923, respectively (17, 19). I n another state two official recommendations were given for the joint use cent) of 100-mesh limestone and dolomite were used. Doloof superphosphate and limestone. One (5) stipulated that mite of 20-mesh fineness containing 63 per cent of 100-mesh the phosphate and limestone should be mixed prior to incor- material was also used. It was assumed that the someporation with the soil, whereas the other (21) stipulated what coarse material would give a better mechanical condithat the limestone should be drilled in the soil 10 days be- tion with less chemical activity. Potassium chloride was fore the incorporation of the phosphate, presumably on the also included in each of the 30.5 per cent mixtures, but amassumption that the limestone would be disintegrated by the monium sulfate was not, since it had been shown (12) that soil within the 10-day period. The latter practice would the admixture of this material with limestone and with dolobe essentially a mixture between phosphate and a soil-lime- mite could be made without penalizable loss of ammonia. The percentage compositions of the six superphosphate stone medium, since studies of the speed of disintegration of ground limestone have shown that the amount of limestone mixtures studied were as follows: “fixed” by the soil within a 30-day period would be small, A B c D E F especially in a dry mulch (16). %
EXTENDED LIMESTONE-PHOSPHATE REACTIONS PROCEDURE. I n each of the cited studies, the PZOschanges induced by limestone have been measured by comparison of initial and subsequent analyses to determine “available.” This technic is open t o a number of objections. Frequent
%
%
%
%
%
Superphosphate 60.0 90.5 60.0 90.5 60.0 90.5 Dolomite, 20 mesh 30.5 8.0 .. Dolomite, 100 mesh .. ,. 30:5 s:o Limestone, 100 mesh 30:5 i:o KC1 s:o .. s:o .. 8.0 Organic conditioner 1.5 1.5 1.5 1.5 1.5 1:5 NOTE: Mixtures A-1 t o F-1 and A-2 t o F-2 are of corresponding respective make-up, the PzOa being supplied, however, by c. P. mono- and di-salts.
..
..
..
August, 1932
INDUSTRIAL AND ENGINEERING
PzOs EQUIVALENTS OF EVOLVED CARBONDIOXIDE. The periodic carbon dioxide determinations from the six phosphate mixtures for the 6.5-month periods are given in Table 111. The cumulative computations for carbon dioxide and for the equivalents of Pzo5 and calcium carbonate are also graphed in Figures 1 to 6, with the near horizontal throw-back lines representing the supplemental 8&, 87-, and 103-day periods of intermittent aspiration. The two limestone mixtures started off more vigorously and also gave greater ultimate carbon dioxide evolutions than their corresponding dolomite mixtures. The lesser reactivity of the dolomite is due not only to the lesser solubility of the dolomite, but possibly also to another factor. For each mole of Pzo5 as CaHP04.2H20 accounted for by the reaction between CaH4(P04)2.H20 and limestone, two moles of water are fixed; in the dolomite mixtures 12 moles of water of crystallization would be fixed by the analogous magnesium reaction, provided the dimagnesium salt contains the 7 moles of water generally accredited to it. This factor will be dealt with in a separate contribution. The chemical drying effect of each mole of PzOa accounted for by magnesium phosphate formed is therefore six times that of the analogous calcium salt. This difference in change from hygroscopic moisture to water of crystallization apparently exerts a distinct drying effect and minimizes changes in weights of the dolomite mixtures. The ultimate total for each of the three 30.5 per cent admixtures was greater than that for its corresponding 8 per cent mixtures, the greatest spread being found for the highcalcium mixtures. The decrease in effective moisture, caused by the introduction of the larger amounts of dry limestone or dolomite, and the decrease in initial amounts of H,P04 and CaH4(P04)zwere apparently offset by the greater surface of the two limestones in immediate contact with the acid materials. On the average, the evolutions of carbon dioxide from the several mixtures for the first 10 days were about one-third of the totals for periods of 195 days and 180 days of aspirated contact for the dolomite and limestone mixtures, respectively. The amounts of carbon dioxide during the earlier periods can be attributed in the main to the free H3P04 content (20) of the superphosphate, 3.289 per cent P205, or 16.95 TABLE111. REACTION OF SUPERPHOSPHATE
WITH
CHEMISTRY
935
per cent of the initial water-soluble. This point will be considered later. Initially, when free &Po4 was present, the 100-mesh dolomite mixtures were more reactive than the two corresponding 20-mesh dolomite mixtures, but the latter gave greater aggregate evolutions of carbon dioxide. Later it will be pointed out that this has been found true also for bulk mixtures. It is probable that the greater surface of the finer bone-dry dolomite produced a greater drying effect and a retardation of the second step in the reactions. The total values of 8.03 and 6.63 per cent were found for the PZO5transitions registered by the evolved carbon dioxide in the dolomite mixtures A and B during the 195-day period of aspiration. Of the total of 8.03 per cent for mixture A , 41 per cent had occurred a t the end of 34 days and 53 per cent a t the end of 60 days, whereas fractions of 53.5 and 67.7 per cent of the 6.63 per cent total were found for mixture B. For the 194-day period the corresponding values for mixture C a t the end of 32 days and 60 days were 51.4 and 67.6 per cent of the total of 7.31 per cent of reacting P&. For mixture D the reactions during the first 32-day and 60day periods were 50.7 and 64.9 per cent of the total of 6.44 per cent found after the 194-day period. For the maximum of 10.40 per cent of PzOs transformed in the 30.5 per cent limestone mixture during 180 days of aspiration, 52.3 per cent occurred during the first 36-day period and 69.9 per cent during the first 68 days. Of the total P z O ~ change of 6.72 per cent for the 8 per cent limestone mixture, 50.2 per cent occurred during the first 36 days and 66.1 per cent during the f i s t 68 days. Some accelerations in the carbon dioxide evolutions are evidenced for the 75-85 day period for the dolomite mixtures and for the 146-161 day period of sampling for the highcalcium limestone mixtures. At these periods 20 per cent fractions of the totals then extant were removed for analysis, and the remainders were replaced in the containers with minimum disturbance of the remaining bulks. The acceleration in each 20-mesh dolomite mixture was more pronounced than that found in the corresponding 100-mesh mixture. INFLUENCE OF &Pod. The free acidity of a well-made superphosphate should be attributable to H3P04. The superphosphate used had this characteristic, being devoid
DOLOMITE AND LIMESTONE DURINQ 6-MONTH PERIODS
(Measured periodically b y determination of evolved COI with continuous aspiration; CO1 per 250 grams of mixture) CUMULATIVE CUMULATIYE
DAY 1 2 3 4 5 6
7 8 9 10 12
13 14 21 34 41 50 60 75" S5 97 113 131 161 195b Total
BY PERIODS B
A Gram 0.5346 0.3069 0.1815 0.1573 0.0902 0.0825 0.0792 0.0653 0.0770 0.0645 0.1082 0.0598 0.0645 0.4125 0.3014 0,2090 0.2442 0.2508 0.3564 0.3860 0.4169 0.3823 0.3438 0.5640 0.5968
6.3356
Gram 0.4202 0.3025 0.1936 0.1815 0.1089 0,1067
(i:%1) 0.0836
B
% '
%
0.21 0.34 0.41 0.47 0.51 0.54 0.57 0.60 0.63 0.66 0.70 0.72 0.75 0.91 1.03 1.12 1.22 1.32 1.46
0.17 0.29 0.37 0.44 0.48 0.53
(i:0.62 d58SY)
0.0649 0.1060 0.0862 0.0589 0.3751 0.5244 0.2420 0.2442 0.2420 0.2706 0.1430 0.2255 0.1513 0.1815 0.2205 0.4661
1.74 1.89 2.03 2.25 2.49
0.64 0.68 0.72 0.74 0.89 1.10 1.20 1.30 1.39 1.50 1.56 1.65 1.71 1.78 1.87 2.06
5.1433
2.49
2.06
1.57
DAY 1 2 3 4 5 6 7 8 10 11 12 19 21 32 40 50 60 70 75* 85 95 111 129
160 194b
BK PERIODB C D Gram Gram 0.6523 0.5819 0.3058 0.2662 0.1404 0.1716 0.1353 0.1232 0.1254 0.1190 0.0781 0.07.52 0.1170 0.1005 0.0898 0.0655 0,1445 0.1126 0.0741 0.0642 0.0733 0.0589 0.4015 0.3036 0.1166 0.0770 0.4488 0.4081 0.3740 0,2805 0.3047 0.2530 0.2420 0,1782 0.3124 0.1364 0.0770 0,0802 0.4587 0.2941 0.1360 0.1580 0.1511 0.1511 0.1786 0.1786 0.2862 0.2697 0.2459 0.3557
- -
Total 5.6695
4.8639
FACTION D
%
%
0.26 0.38 0.44 0.49 0.54 0.57 0.62 0.66 0.72 0.74 0.77 0.94 0.98 1.16 1.31 1.43 1.53 1.65 1.69 1.87 1.92 1.9s 2.05 2.17 2.27
0.23 0.34 0.41 0.46 0.51 0.54 0.58 0.60 0.65 0.67 0.70 0.82 0.85 1.01 1.12 1.22 1.30 1.35 1.38 1.50 1.56 1.62 1.70 1.80 1.95
2.27
1.95
DAY
1 3 4 5 6
-6
10 11 12 13 14 16 17 18 20 22 24 36 41 56 6s 81 97 115 146" 161
180b
BY PERIODS E F Gram Gram
0.6025 0.4961 0.2211 0.1617 0.2519 0.2090 0.2138 0.3152 0.1716 0.1562 0.1232 0.1199 0.1386 0.1012 0.0792 0.1518 0.0968 0.0946 0.5159 0.2266 0.5343 0.4444 0.3520 0.3146 0.3322 0.7125 0.6538 0.2761
0.6067 0.5060 0.1683 0.1287 0.1144 0.0792 0.0847 0.1166 0.0660 0.0523 0.0374 0.0231 0.0506 0.0385 0.0319 0.0605 0.0506 0.0418 0,3576 0. 1056 0.4510 0.2728 0.2816 0.2706 0.2706 0.4316 0,2700 0.2480
CUMULATIV~
FRACTION E F % %
0.24 0.44 0.53 0.59 0.69 0.78 0.86 0.99 1.06 1.12 1.17 1.22 1.27 1.31 1.34 1.41 1.44 1.48 1.69 1.78 1.99 2.17 2.31 2.44 2.57 2.85 3.12 3.22
0.24 0.45 0.51 0.56 0.61 0.64 0.68 0.72 0.75 0.77 0.78 0.79 0.81 0.83 0.84 0.87 0.89 0.90 1.05 1.09 1.27 1.38 1.49 1.60 1.71 1.88 1.99 2.09
- - - -
Total 8.0668 5.2166 3.22 2.09 Definite fraction of total weight withdrawn for determination of forms of PzOb. Subsequent carbon dioxide evolutions computed t o full-charge baais. b Continuous aspiration discontinued.
(I
I N D U ST R I A L A X D E N G I N E E R I N G C H E M I S T R Y
936
I I
IO
I
to
yo
10
I
80
I
I
I
I
lbo pts/&J
Vol. 24, No. 8 I
I
/yo
i
I
160
I
I
I&
I I
.Is
-*-----I Superphosphate, 90.5 Per Cent; 20-Mesh Dolomite, 8 ; Organic Conditioner, 1.5 7---
Figure 2 . Figure 1
Superphosphate, 60 Per C e n t , 20-Mesh Dolomite, 30 5 , Potassium Chloride, 8, Organlc Conditioner, 1 5
Io
to
yo
LO
&Q
impsaito
Io
p----&t#c&&-
Figure 4. Figure 3.
Superphos hate, 60 Per Cent: 100-Mesh Dolomite, 30.5; Potassium Ehloride, 8 ; Organic Conditioner, 1.5
I(O
mffl
----
Superphosphate, 90.5 Per,Cent; 100-Mesh Dolom:te, 8; Organic Conditioner, 1.5
44
?A
a1 Lo 72
LC 5(
4.8 9.0
I2 LY
Figure 6.
Superphosphate, 90.5 Per Cent; 100-Mesh Limestone, 8; Organic.Conditioner, 1.5
1.1
ne IO
Figure 5 .
to
yo
LO
#so m s
Ka
1,_ - - - _ _
IW
M
shckmsd
_--_ 4 0
k 6Q
Superphosphate, 60 Per Cent;, 100-Mesh Limestone, 30 5 ; Potassium Chloride, 8; Organic Conditioner, 1.5
of sulfuric acid (20). Initially, the H3P04 present in the 30.5 per cent mixtures A , C, and E \\as equivalent to 1.97. per cent PzO5 and 2.98 per cent PnOjin the 8 per cent mixtures B, D , and F . After 75 days, 0.08 per cent free acid remained both in mixture B and mixture C, and 0.36 and 0.22 per cent in mixtures B and D , respectively; a t the end of 146 days there was none left in the 30.5 per cent limestone mixture E , and only 0.15 per cent in the 8 per cent limestone mixture F . Assuming that the P2Oj equiralent of the decreases in free H3P04had passed through the nionoform into the di-combinations, the following computations were made. In dolomite mixture A , 1.90 per cent, or 40.4 per cent of the total P205 transition of 4.70 per cent during 75 days, was due to the free H3P04. I n dolomite mixture C, 1.90 per cent, or 35 per cent of the total P205that reacted during 75 days, was due to the free H3PO4. I n the 30.5 per cent limestone mixture E , no free H3P04 was preqent a t the
SPEED OF REACTIONS INDUCED BY DOLOMITE AND BY LIMESTONE L4DDITIONSTO SUPER ( A C I D ) PHOSPHATE, A S 3 T E A S U R E D BY CARBONDIOXIDE EVOLVED DURING OF ASPIR4TION
6 . 5 - 3 f o x ~PERIODS ~
end of 146 days. Since the limestone was more active than the dolomite, and since there was a free-acid residue of only 0.08 per cent Pz05in the corresponding dolomite mixtures a t the end of 7 5 days, it may be safely assumed that none was present in the 30.5 per cent limestone mixture a t the end of 68 days and that 27.3 per cent of the P 2 0 j transformed a t that period was attributable to the free H3P04. In the 8 per cent dolomite mixture B , 0.96 per cent, or 19.8 per cent of the total P 2 0 stransition of 4.84 per cent during 75 days, was due to the free HsP04. I n dolomite niixture D , 1.10 per cent, or 24.6 per cent of the PsOs transformed during the same period, was due to free H3P04. Giving the same reactive value to the dolomite and limestone, 24.8 per cent of the transformed P 2 0 j in mixture F was due to free H3P04. ~ I E A S U OF R EFIXALFORMS OF P20s. The conventional method of leaching to determine water-soluble P2O6 is not permissible in the limestone mixtures. The carbon dioxide
August, 1932
INDUSTRIAL
AND ENGINEERING CHEMISTRY
TABLE Iv. EFFECTO F STASDISG IN MOBILEMOISTATMOSPHERE
-
PnOa INITIALLY
CONTENTS P E R T O NOF MIXT. 7 Superphosphate Dolomite Total yo r0 Mesh %
Water-
20a 13.09 30.5 100 13.09 30.5 20a 19.74 8 8 100 19.74 a Retained on 50 mesh. 12.9700; retained 60 60 90.5 90.5
OS
--Pros
MIXTURES O F SUPERPHOSPHATE WITH DOLOMITIC LIMESTONE AFTER
75 DAYS-Citrate- Availinsol. able
sol.
Citrateinsol.
Available
Total
Watersol.
%
%
%
%
%
%
%
13.27 13.01 19.75 19.62
6.72 5.99 13.58 14.29
0.24 0.15
13.03 12.86 19.59 19.43
11.71 13.04 0.05 11.71 0.05 13.04 17.67 0.06 19.68 17.67 0.06 19.68 o n 100 mesh, 3fi.9r0
data may be more useful for this purpose. If it be assumed that the residual fraction of the original water-soluble P206 content of 11.71 per cent for mixtures A , C, and E , and a similar content of 17.67 per cent for mixtures B, D , and F had prevented the occurrence of tricalcium salts in the mixtures, and hence that the respective carbon dioxide evolutions represent the actual changes from water-soluble to citrate-soluble, the following conclusions may be drawn from the carbon dioxide determinations: At the end of 195 days the 20-mesh and 100-mesh mixtures of 30.5 per cent dolomite had remaining 3.68 and 4.41 per cent water-soluble, or 31.4 and 37.7 per cent, respectively, of the common amount originally present. For the 20-mesh and 100-mesh 8 per cent dolomite mixtures, there remained 11.04 and 11.32 per cent, respectively, or 62.5 and 64.1 per cent of that originally present. For the 100-mesh limestone mixtures of 30.5 and 8 per cent, the water-soluble P205 occurrences a t the end of 180 days TTere 1.31 and 10.94 per cent, or residual fractions of 11.2 and 61.9 per cent, respectively. I t will be bhown later that no appreciable formation of insoluble P205occurred in the dolomite mixtures after long periods. I t will also be shown that "insoluble" in the limestone mixtures results from the leaching process, and that this result occurs only when the diphosphate is formed in considerable quantities. Furthermore, no evidence of tricalcium phosphate was found by magnification of 800 under the microscope for the 30.5 per cent mixtures of dolomite and of limestone after 4 years. The P205equivalent of the respective carbon dioxide evolutions may thewfore be taken as actual measurements of the formation of diphosphate. The carbon dioxide values also record directly the calcium carbonate equivalent of the dolomite and limestone disintegrations.
937
0.16 0.19
,--P~n0s
AFTER
Water-
195 Davs--
sol.
Citrateinsol.
%
%
%
%
13.47 13.16 19.86 19.78
4.20 5.40 13.09 13.76
0.36 0.18 0.18 0.22
13.11 12.98 19.68 19.56
Total
hvailable
if any, will probably be less than that of similar limestone mixtures. USE
OF
c.
P. PHOSPHATES IS LIEU OF QUPERPHOSPHATE IS MIXTURES
EVOLVED CARBONDIOXIDE. I n some studies on the formation of insoluble in phosphate-limestone mixtures, c. P. salts have been used as a source of P206in lieu of superphosphate. Limestone and dolomite mixtures with c. P. salts were used by the authors in the determination of evolved carbon dioxide. The superphosphate mixtures were paralleled as to amounts of P205,dolomite, limestone, and moisture by the use of both monocalcium and dicalcium c. P. phosphates. The estimated amounts of CaS042H20 carried by superphosphate were included, but no free H3P04was added. Any further differences were made up by the use of quartz sand. These mixtures were aspirated continuously, and frequent determinations of evolved carbon dioxide were made over a 50-day period. The cumulative carbon dioxide results and the computed P205and calcium carlionate values are charted in Figures 7 to 12. The values found for the four dolomite-monocalcium phosphate mixtures are about 75 per cent greater than those found for the corresponding superphosphate mixtures. The losses in moisture also greatly exceeded those found in the superphosphate mixtures. dlthough of the same moisture content as the corresponding superphosphate mixtures, the moisture in the c. P . salt mixtures was much more mobile and effective. Because of this and even with no free H3P04present, the 100-mesh dolomite was decidedly more active than the 20-mesh material in the monophosphate reactions, a relationship the reverse of that found for the superphosphate mixtures. Although every
TABLE v. EFFECTO F ST.4SDING I N MOBILEMOIST-4TMOSPHERE O S MIXTURES OF SUPERPHOSPHATE WITH 100-MESH HIGH-CALCIUM LIMESTOSE CONTENTS PER TONO F MIXT. SuperHighphoscalcium Dhate limestone
P r o ~INTIALLY Total
Watersol.
Citrateinsol.
Available
--
Total
PtOa A F T E R 146 DhYS WaterCitratesol. insol.
rlvailable
%
%
%
%
%
%
%
%
%
%
60.0 90.5
30.5 8.0
13.13 19.75
11.71 17.67
0.09 0.08
13.04 19.67
13.59 20.33
1.94 12.73
2.81 0.86
10.78 19,47
CARBOSDIOXIDE LOSSESvs. LOSS IN WEIGHTOF MIX- effort was made to simulate the superphosphate mixtures, The weight changes of the mixtures during aspira- except for the presence of H3POa, it is evident that in such tion are also significant. The dolomite mixtures B, C, and experiments the speed and extent of the reactions of C.P. D had suffered no loss in weight during the first 75-day monophosphate mixtures are in excess of those to be anticiperiod of aspiration, and mixture A had lost only 1.36 per pated when commercial superphosphate is used. cent, although the weights of evolved carbon dioxide were I n each of the four dolomite-diphosphate mixtures, with 1.50, 1.69, 1.38, and 1.46 per cent, respectively. At the an absence of monophosphate, the evolved carbon dioxide end of 195 days of aspiration, the dolomite mixtures A , B , showed that the amount of P z O ~ converted t o the tri-form C, and D had lost in weight 2.20, 0.6, 0.55, and 0.2 per cent, was close to 1.2 per cent; in the 30.5 and 8 per cent mixrespectively, although the carbon dioxide evolutions were tures of the more soluble high-calcium limestone, the carbon 2.49, 2.06, 2.27, and 1.95 per cent. The influx of moisture dioxide data show that P206transitions of 3.5 and 2.4 per in the aspirated air was therefore sufficient to maintain the cent, respectively, took place. The carbon dioxide evoluinitial total weights of the dolomite mixtures. But, after tions, as a measure of the actual CaHPOl CaC03 reac146 days the two high-calcium limestone mixtures, E and F , tion, will later be compared with P?05analyses by digestions had lost in weight 3.35 and 2.85 per cent, respectively, of the di-salt mix, with and without the conventional prewhereas the corresponding weights of evolved carbon dioxide liminary leaching, to show the analytical error inherent in were only 2.8j and 1.88 per cent. It appears that a loss in the leaching of the mixes containing limestone in comparithe weight of the mass of phosphate-dolomite mixtures, son with those containing dolomite. TURES.
+
938
INDUSTRIAL AND ENGINEERING CHEMISTRY
Pz06 CHANGES IN ASPIRATED SUPERPHOSPHATE
MIXTURES
Vol. 24, No. 8
per cent; water-soluble, 12.37 per cent; citrate-insoluble, 0.84 per cent; and available, 18.91 per cent. The foregoing results show that no commercially penalizable change in P206combinations is to be expected when as much as 600 pounds of dolomite is carried by a ton of mixture. Furthermore, increased proportions of dolomite do not give increases in citrate-insoluble PzOS. On the other hand, a considerable decrease in sale value occurred when as little as 8 per cent of high-calcium limestone was included, whereas the correlated increase in ci t r a t e - i n s o l u b l e induced by the 30.5 per cent inclusion Ab was t h r e e and a half times ~ t s 9.. great. It, will be shown l a t e r 16 that the e n h a n c e m e n t of in5 u soluble shown for high-calcium 8z 2Y l i m e s t o n e m i x t u r e s by the official m e t h o d is d u e , in the 11 main, to the formation of tri0.8 calcium phosphate during the d M w mso yo Jo analytical procedure.
At the end of the 75-day and 195-day periods of aspiration, the mixes A to F were analyzed for water-soluble, citrate-soluble, and citrate-insoluble P20b by the A. 0.9.C. method, using 2-gram charges, 100 cc. of citrate solution, and digestion for 30 minutes. It should be noted that the citrate-digestion solutions were filtered rapidly, as it is essential to minimize hydrolysis of the a c c u m u l a t e s of d i p h o s p h a t e . T h i s w a s d o n e by means of macerated pulp a t e r s on perf o r a t e d h a r d - r u b b e r disks in Pyrex tubes and with suction. The results in Table IV show that the dolomite a d d i t i o n s materially reduced the waters o l u b l e and increased the citrate-soluble o c c u r r e n c e s of PzOswithout appreciable deFigure 8. Same as crease in “available.” I n all four Figure 2 m i x t u r e s t h e increase in insoluble was less than 0.2 per cent after 75 days, and also in three of t h e f o u r m i x t u r e s after the 195-day period. The values found after c o m p u t a tion of the slight differences in original and subsequent weights w e r e n o t s u f f i c i e n t l y different to be substituted for the a c t u a l determinations. T h e magnesium p h o s p h a t e c o m pounds were c o m p l e t e l y dissolved, as would h a v e b e e n true even if the full PZOScontent had been in such forms. Moreover, the fraction of the Figure 9. Same as Pzo6 content that was combined Figure 3 with the calcium of the dolomite Figure 10. Same a6 was reduced to the point where Figure 4 i t also w a s c o m p l e t e l y dissolved by the c i t r a t e solution. Haskins (10) has s h o w n t h a t a one-gram c h a r g e of dicalcium phosphate is completely soluble in 100 cc. of this solution. The high-calcium limestone results a t the end of the 146 day period are given in Table V. The w e i g h t - c h a n g e computation reduced the final total from 13.59 to 13.15 per cent for the 30.5 per cent mixture. S i m i l a r computations for the other v a l u e s a r e c a r r i e d in parentheses. The water-soluble P205in the 30.5 per cent mixture had decreased from 11.71 to 1.94 p e r c e n t (1.87); t h e insoluble had increased from 0.09 Figure 11. Same as Figure 12. Same as to 2.81 per cent (2.72); whereas Figure 6 Figure 5 the a v a i l a b l e had d e c r e a s e d SPEED OF REACTIONS INDUCED BY DOLOMITE AND BY from 13.04 to 10.78 p e r c e n t LIMESTONE ADDITIONS TO c. P. MONO-AND DI(10.42). Corresponding compuCALCIUM PHOSPHATES, AS MEASURED BY CARBON tations for the 8 per cent limeDIOXIDE EVOLVED DURING 50-DAYPERIODS OF ASPIRATION s t o n e m i x gave: total, 19.75
I
CHANGESIN PzOjCOMBINATIONS IN BULKSUPERPHOSPHATELIMESTOSEMIXTURES It may be t h a t t h e f o r e going results do not register the full extent of changes that take p l a c e i n l a r g e p i l e s of phosphate-limestone mixtures, where the generated heat and the evolved carbon dioxide are not d i s s i p a t e d so s p e e d i l y . Some data on this point are a t hand. I n 1920 the senior author suggested to a representative of A r m o u r & Company that a series of b u l k m i x t u r e s be tried, on the assumption that the d o l o m i t e would be so insoluble that there w o u l d b e a minimum reaction b e t w e e n it and the acid phosphate. The results obtained with six proportions of acid phosphate of 11 per cent moisture content and 5 different calcium-magnesium materials in one-ton mixtures, after 30 d a y s , w e r e k i n d l y f u r n i s h e d , a n d are given in Table VI. T h e r e s u l t s were not corrected for moisture variations. The limestone and the precipitated c a l c i u m carbonate proved to be m o s t r e a c t i v e . The increase in citrate-insoluble i n d u c e d by the T e x a s limestone was greater than the minimum c h a n g e - t h a t i n d u c e d by the dolomite. The dolomite, however, shows a calciummagnesium r a t i o e q u i v a l e n t of 1.50 to 1.00, and cannot be d e s i g n a t e d as a t r u e dolomite. The calcium carbonate c o n t e n t above t h e a m o u n t in the 1 to 1 proportion may be considered a s e s s e n t i a l l y
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1932
TABLEVI.
CITRATE:-ISSOLUBLE
939
PzOb FOUSDIN VARIOUS MIXTURES
(2000-pound mixtures of acid phosphate" with 6 proportions oi limestone, dolomite, precipitated calcium carbonate, and precipitated magnesium carbonate:b 2-gram charge per 100 cc. of ammonium citrate solution) LIMINQ COMPUTED MATERIALS CITRATEPPT. MgCOab TEXASLIMESTONE/ PPT.CaC03 DOLOMITE. LIMESTONEd IN INSOL. When After When After When After When After When After ORIQIXAL PZOSIN made 4weeks made 4neeks made 4 weeks made 4 weeks 4 weeks MIXT. MIXTURESC made % % % % % % % % % % Lb. % 0.37 0.40 0.35 0.38 0.45 0.48 0.47 0.59 0.40 0.48 50 0.39 0 . 4 8 0 .50 0.42 0.55 0.40 0.65 0.45 0.45 0.46 0.60 100 0.38 0.54 0.57 0.44 0.68 0.48 0.63 0.40 0.55 0.52 0.65 200 0.36 0 . 6 0 0 . 66 0.46 0.62 0.40 0.65 0.63 0.78 0.52 0.80 300 0.34 0.64 0.70 0.45 0.55 0.46 0.70 0.66 0.88 400 0.32 0.63 0.93 0 . 7 1 0 . 7 5 0.58 1.00 0.41 0.59 0.54 0.75 0.67 0.93 500 0.30 a Cured acid phosphate, 17.65% total and 0.40% citrate-insoluble PzOs; 2.5% free acid, calculated as HzsO4; 11% moisture. b 3MgCO~.Mg(OH)~.3HzO. c Insoluble Pros in natural stones not included. d CaCOa, 91.41 MgC03 2.21%. # CaCOa 61 6 1 p : MgC03: 33.60%. / CaCOs: 98:40%:
.
the equivalent of a calcite addition to a true dolomite (13)*
As another example, a 30-day mixture of 1500 pounds of superphosphate with 500 pounds of dolomite in 10-ton lots may be cited. I n a verbal presentation of some of these findings before a group a t a meeting of the Southern Agricultural Workers, in Atlanta, February, 1931, it was stated that the 20-mesh dolomite had proved somewhat more reactive than the 100-mesh material in superphosphate mixtures. One manufacturer was skeptical, but he was interested enough to try mixtures of two finenesses in 10-ton lots, and kindly furnished the data given in Table VII. The 30-mesh dolomite was the more effective in diminishing the amount of free acid, and neither of the two dolomite mixtures gave a penalizable change in citrate-insoluble. When the results were calculated to the moisture-free basis, there was found no decrease in available. TABLEVII. CHANGES IN Pzo6 COMBINATIOSS DURIXQ 3 0 - D A Y PERIOD"
(10-ton mixtures of 1500 pounds of superphosphate with 500 pounds of 30-mesh and of 100-mesh dolomite) 3O-MEsE ~OO-MESH ANALYSISOF DOLOMITE MIXT. DOLOMITE MIXT. SUPERWhen After 30 W.hen After 30 PHOEPHATE~ mixed days mxed days
%
%
%
Moisture 12.66 9.10 9.10 Total PzOs 18.42 14.05 14.30 Insol. PZOS 0.40 0.48 0.40 Available P P O ~ 18.02 13.65 13.82 Free acid 3.20 0.48 0.16 Available PsOs. moieture-free basis: Theor b 14.93 14.93 Found 15.01 16.20 a A. 0 .A. C. method as of April 1931. b Assumption bone-drg limestode, PzOr-free.
... ...
%
%
9.30 14.22 0.50 13.72 0.72
8.80 14.42 0.48 13.94 0.00
14.93 15.13
14.93 15.29
The f i s t advocacy of commercial large-bulk phosphatelimestone mixtures, with supporting data, was probably the contribution of Brogdon (3). He gave analyses from 10bag lots that contained 80 per cent phosphate and 20 per cent limestone. The relative merits of limestone and dolomite were not considered and the analysis of the limestone used was not given. Either a dolomite or a high-magnesium material was probably used, however, since the calciummagnesium equivalent ratios of 1.27, 1.33, and 3.91 to 1 were given as representative of commercial Georgia limestones. No decrease in available was found after periods of 3 and 7 months, and only small moisture changes were observed. Similar results were obtained when 1000-ton lots containing 5.5 per cent of limestone (probably dolomitic) were stored 4 months and were obtained with complete mixtures after 42 days when 435 pounds of limestone per ton were used. Larison ( 2 1 ) mixed 20-mesh high-calcium limestone with treble superphosphate in proportions 3 to 1, 2 to 1,l to 1,and 1 to 3; exposed the mixtures for 90 days; and found that H3P04 had disappeared. With the 45 per cent PsOs material, the transitions apparently progressed only to the di-form, since the losses of available were 0. 0.27, 0.33, and 0.18 per cent, respectively.
INFLU~NCE OF LIMESTONE ADDITIONS UPON ACCURACY OF OFFICIALMETHODFOR P ~ O S The A. 0.A. C. method ( 1 ) was developed primarily to show the residual quantity of undisintegrated natural rock p h 0 5 phate in superphosphates and mixtures, where the monosalt predominates, with smaller quantities of the di-salt. It was not anticipated that the method would be used for the analysis of phosphates to which alkalies or alkali earths are added. The inclusion of limestone materially increases the amount of the dicalcium phosphate, and these studies indicated that the greater the quantity of the diphosphate, the greater the hydrolysis (4, 6) and formation of tricalcium phosphates during the analytical leaching. There is the further factor that the amount, type, and solubility of the limestone excess affects the reaction of the prescribed ammonium citrate solvent. These points were considered by determining the effect of variations in the analytical charges of aged superphosphate mixtures, and by the use of aged and immediate mixtures of limestone and of dolomite with c. P. calcium phosphates. TABLEVIII. INFLUENCEOF SIZEOF CHARGEUPON DETERMINATION OF WATER-SOLUBLE AND CITRATE-INSOLUBLE P206 (In aspirated and aged superphosphate mixtures with dolomite and limestone) -CITRATE-~NSOLUBLE-2-gram charge with COMPONENTS, PER 200 cc. TONI N MIXT. -WATER-~OLUBLammoSuper0.5120.512- nium phos- Dolo- Lime- gram gram gram gram gram citphate mite stone charge charge charge charge charge c y t z e rate
%
%
%
60 30.5 60 36:5 8.0 90.5
... ...
%
%
%
%
z:45
4 95 2:ie 13.38
4.08 1.86 12.94
o:46
..
..
%
%
%
0 27 0 32 i : i 9 2:70 i : i i 0.78 0.93 0.81
SIZEOF CHARQEB.Up to this point all the analyses for water-soluble, citrate-soluble, and citrate-insoluble were made with %gram charges. The results in Table VI11 show that the size of charges is an important factor in the analysis of limestone mixtures, whereas it is less important in the analysis of dolomite mixtures. The decrease in water-soluble, coincident with increase in charge, indicates that, although the reaction between the limestone and the monocalcium salt had practically ceased in the aged dry mixture, it becomes operative again, and to an appreciable extent, during analysis. The concomitant formation of citrate-insoluble is also evidenced, the amount found with a %gram charge being practically six times as great as that found with a 0.5-gram charge. When the 1-gram, 100-cc. proportion was maintained by the use of 2-gram charges with 200 cc. of citrate solution, the results were comparable for the two charges, in this and also in a number of similar trials. Laker, after the mixtures had aged 3 years, 1- and 2-gram charges of the 30.5 per cent dolomite and limestone mixtures were analyzed by the use of 200 cc. of ammonium citrate of p H 5.96. The values of 0.176 and 0.216 per cent were obtained for the
910
INDUSTRIAL AND
ENGINEERING CHEMISTRY
dolomite mixtures, whereas the citrate-insoluble in the limestone mixture was found to be 0.509 and 1.530 per cent for the 1- and 2-gram charges, respectively. The pH value of the well-buffered citrate solution was found to be raised to only 6.0 in each case. REACTIVE VALUE OF C I T R h T E SOLCTION.I n many of the pioneer studies of the present Official method it was shown that the reaction value of the ammonium citrate solution is an important factor-the more acid the solution, the lower the citrate-insoluble results, and vice versa. The specific solubility of the limestone residues was, therefore, a vitiating factor in the determination of insoluble, especially in the case of the 30.5 per cent mixtures. Even in the three 8 per cent mixtures there was a limestone residue of more than 3 per cent in each case after 283 days. The full equivalent of a 30.5 per cent addition of dolomite and of limestone carried initially in a 2-gram charge was compared with approximately four- and eightfold additions of 100-mesh material in a constant volume of 200 cc. of an acid ammonium citrate (pH 5.96) and digestion for 30 minutes a t 65" C. The results of Table IX show that the full 0.61-gram charges of both dolomite and limestone were completely dissolved without producing a colorimetrically measured pH change in the concentrated well-buffered solution. The 2.5- and 5.0-gram charges of limestone gave increased pH values of 7.0 and 9.20, whereas the two corresponding charges of dolomite raised the respective values to only 6.10 and 6.20. These values reflect the respwtive solubilities of the dolomite and liinestone in the acid ammonium citrate solution.
Vol. 24, No. 8
gram charges of previous mixtures. The diphosphate was digested directly with 200 cc. of neutral (pH 7) ammonium citrate and also after being leached as in the Official method. Mixtures of the two phosphate charges with equal quantities of dolomite and of limestone were likewise leached, and the citrate-insoluble content of each residue determined. The results are given in Table X.
x. EFFECTO F DOLOMITE AND O F LIMESTOSE UPON CONVERSION OF CITRATE-SOLUBLE INTO CITRATE-IXBOLUBLE P,06
T.4BLE
(During washing process prescribed in A . 0.A . C. methods, as measured b y digestions of 100-mesh dolomite- and limestone-dicalcium phosphate mixtures" with 200 cc. of neutral ammonium citrate solution (PH 7 . 0 ) for 30 minutes a t 65' C . : citrate-insoluble P10sfound, per cent of diphosphate charge) 0.35 GUM EACH 0 . 7 0 G R l h f E.ACH D I c a L c i v h f PHOSPHATE ALONE O F DICALCIUM OF D I c a L c I r - h f Direct digestion .-\iter washing PHOSPHATE PHOSPHATE 0.85 0.70 0.35 0.70 DoloLimeDolo- Lime$ram gram gram gram mite stone mite stone 0 026 0 066 0 026 0 066 0 063 0 263 0 16 2 30 Corresponding to 1- and 2-gram charges of previous mivtures
The directly digested charge and its washed residue gave the same result for citrate-insoluble P205in the respective 0.35- and 0.7-gram charge comparisons, although the relationship between the proportions of P205carried by the two charges and the citrate-insoluble P2O6 found was not constant. The absolute effect of the dolomite in the 0.35gram mix during washing was not extensive, although a 2.4-fold increase in citrate-insoluble P206was found, whereas the increase caused by the limestone was tenfold. With the 0.7-gram charge the dolomite again caused the citrateinsoluble P z O ~to increase only 2.4 times, whereas the limestone induced an increase of thirty-five fold. TABLEIx. EFFECT OF 1oo-hlESH DOLOMITE A S D LIMESTOYE From the foregoing data it is evident that the results by IN CHASGISGPH VALUE the Official method are influenced by (1) the size of the (ZOO-cc. volume of acid ammonium, citr,ate solution, p H 5.96, filtered after charge and its proportion of dicalcium phosphate, (2) the 30 minutes' digestion a t 65" C.) O . ~ ~ - G R A .M ~DDITION 2 . &GRAM.-\DDITION ~ . O - G R . A.-\DDlTIOX M of tricalcium phosphate present in the wateramount LimeLimeDoloDoloLimeDoloextracted residue, (3) the proportions of PzOs transformed by stone mite stone mite stone mite P 15 PH P PH calcium and magnesium carbonates, (4) the extent to which PH 6 10 7 00 6 20 8 20 5 96O 5 96a the dolomite and limestone increase the pH value of the a Charge completely dissolved ammonium citrate, and (5) the extent of reaction between Although the pH value of an acid ammonium citrate was the acid phosphate and limestone and d o l o m i t e t h e latter not materially changed, a considerable vitiation was pro- being less soluble-during the leaching process. FORMATION OF TRICALCIUM PHOSPHATE I N DRYMIXTURE. duced by the calcium carbonate equivalent of limestone or dolomite inclusions in 1-gram charges of mixtures carrying I n an agitated aqueous system, the order of the reaction be25 per cent limestone and 75 per cent superphosphate, when tween the components of the superphosphate and limestone the ammonium citrate had a pH of 7. I n a direct test, would be free acid, mono-salt, and di-salt. But, under conduwithout phosphate, separate charges of 0.25 gram of CaC03, cive moisture conditions, any triphosphate formed would react 0.34 gram of MgC03.3H20, and a combination of 0.125 with the original mono-salt and thus cause an inversion to and 0.17 gram of the two carbonates were dissolved in 100 the di-salt. I n the relatively dry mixtures, however, it may be cc. of neutral ammonium citrate. After shaking for 30 that triphosphate, of fineness beyond microscopic obserminutes, the pH value of 7.7 was found in each case. The vation, is formed on the surface of limestone nuclei, although same value was obtained for each system after the aspira- the amounts of evolved carbon dioxide demonstrate that a tion of the carbon dioxide for a further period of 30 minutes. large fraction of the mono-salts have not been converted The three systems were then digested for 30 minutes a t to the di-form. Again, if the phosphate mix dries out rapidly 65" C., and the pH value of 7.8 was obtained in each case. and sufficiently, the end reaction between the di-salt and It follows that the solvent capacity of the citrate solution limestone may be obviated; but, with sufficient moisture, is therefore diminished by the undisintegrated residues of as in the case of the mixes of the c. P. dicalcium phosphate, limestone and that the effect is more pronounced with high- Figures 7 to 12, the di- to the tri-reaction will proceed, and in accord with the solubility of the specific limestone. calcium limestone. I n the dolomite and limestone mixtures with c. P. CaHP04.As previously stated, the initial step LEACHING FACTOR. of leaching to remove the water-soluble brought a further 2Hz0, the evolved carbon dioxide, of course, is a true index reaction between the residual mono-salt and the excess of of the formation of tricalcium phosphate. The speed of each limestone in the aged dry mixtures, where reaction had carbon dioxide evolution and its P205equivalent from these practically terminated. There was also reaction between mixtures are shown in Figures 7 to 12. The data in Table the limestone and the accumulates of dicalcium phosphate, XI show the amount of P205converted from the di- to the tri-form by dolomite and by limestone mixtures of 30.5 per cent as measured by enhancement in citrate-insoluble P z O ~but , the result was not pronounced until the amounts of dicalcium over a period of 50 days, when measured by the evolved phosphate reached several per cent. This point was studied carbon dioxide and also by digestion of 1- and 2-gram charges by citrate-insoluble determinations upon charges of c. P. of the 50-day mixtures with neutral ammonium citrate. dicalcium phosphate corresponding to those of 1- and 2- Against the computed carbon dioxide equivalent of 1.286
I N DUSTR IA L A 3D EN GI N EER IN G CHE M ISTR Y
August, 1932
per cent P20jfor the dolomite mixtures, the citrate-insoluble determination gave only 0.020 and 0.053 per cent for the 1- and 2-gram charges, respectively, and with no change produced in the reaction value of the citrate solution by either charge. OF P20jFROY DI- TO TRI-FORM TABLEXI. CONVERSIOS
( I n mixtures of c. P. dicalcium phosphate a i t h 100-mesh dolomitea and limestones during 50-day period, as measured b y evolved CO1 and b y citrate insoluble) PzOr I N DIPHOSPHATE MIXISSOLVBLE TURES
CITRATE SOLS.
A F T E R DIGESTIOX A N D FII.TRITION~
Found, citrate digestion, without preliminary washing DoloLimestone mite
Computed from CO? evolved from dry mix Dolo.. Limemite stone
Limestone PH % % 70 % 7.3 0.020 0.082 1.286 2.703 7.6 0.053 0.729 t o acid phosphate and limestone proportions of 60%
Dolomite
PH 1-gram charge 7 . 0 2-eram rharee 7 . 0 a Corresponding and 30.5%. b Volume 200 cc., pH 7.0. i~ ~ ~~~
I
The citrate digestion of the I-gram charge of the limestone mixture showed only about one-sixteenth of the amount of tricalcium phosphate that the carbon dioxide results demonstrated was present, and the neutral citrate solution increased to a p H of only 7.3. But, against the computed carbon dioxide equivalent of 2.703 per cent insoluble P2Oj for the limestone mixture, 0.729 per cent citrate-Insoluble was found by ammonium citrate digestion of the 2-gram charge, with a p H increase to 7.6. The solvent action of the ammonium citrate solution upon the tricalcium phosphate formed \vas therefore 2.621 and 1.974 per cent for the
941
1- and 2-gram charges, respectively, of the high-calcium limestone mixture. Because of the differences between the properties of calcium and magnesium phosphates, the chemistry of the reactions between superphosphate and dolomite embodies some interesting points. These will be dealt with in a separate contribution.
LITERATURECITED Assoc. Official .Igr. Chem., Methods, pp. 2-4, 1925. Brackett, R. X., and Freeman, B., J. IND. ESG. CHEM.,7, 620 11QI.i) \ - - - - ,
Brogdon, J. S., 4 m . Fertilizer. 39,9 (1913). Buch, 2. anorg. Chem., 52,323 (1907). Burgess, J. L., N. C. State Dept. d g r . , Bull. 228 (1917); 265 (1920). Cameron, F. K., and Bell, J. M., Bur. Soils, Bull. 41 (1907). Fraps, G.S., Texas Agr. Expt. Sta., Bull. 223 (1917). Hall and Vogel, J. South African (‘hem. Inst., 7, 11 (1924). Harris, H. C., J . Am. SOC.A y r o n . , 20,381 (1928). Haskins, H. D., J . dssoc. Oficial A g r . (‘hem., 5,460 (1922). Larison, E. L., Am. Fertilizer, 73,548 (1030). MacIntire, W.H., and Sanders, K. B., J . Am. SOC.r l g r o n ., 20, 764 (1928).
Maerntire, W ,H., and Shaw, W. M., Ibid., 22, 14 (1930). MacIntire, W’.H., and Shaw, W.M., Ibid., 22,272 (1930). Magruder, E. W., J. IND.EBG.CHEM.,9, 155 (1917). Mooers, C. A , , Tenn. Agr. Expt. Sta., BdI. 90 (1910). Mooers, C. A , Ihid., Circular. 1922. Parker, F. W., Ani. Fertilizer, 76, 2, 13 (1932). Roberts, G., Kentucky A g r . Expt. Sta., C‘ircu’ar, 192:3. Shuey, P. M., IND. ENG.CHEM.,17,269 (1925). Williams, C. B., N. C. Agr. Expt. Sta., C‘irc. 24,6 (1916). RECEIVED March 14, 1932.
Detection of Washed, Abrased, and Oiled Eggs PAULFRANCIS SHARP,Department of Dairy Industry, Cornel1 University, Ithaca, N. Y.
U
SDER the ordinary system of poultry management a very considerable percentage of the eggs gathered are dirty. I’ennington and Pierce (6) examined eggs entering the S e w York market, and in one series of 258,496 dozen they found 12.58 per cent dirty; in another series of 238,446 dozen. 13.40 per cent were dirty. Perhaps some of the eggs which they reported as clean had been washed ( 5 ) . S o one knoas how many of the “clean” eggs on the market are actually cleaned dirty eggs. Huttar ( 2 ) found that the percentage of dirty eggs produced by the Corndl poultry flock vaned from 9.8 per cent in July to 24.6 per cent in March. Van Wagenen ( I O ) , in extending Huttar‘s studies, found that the percentage of dirty eggs varied from 77 with straw litter and no nesting material t o 23.2 per cent 11 it11 5traw litter and shavings for nesting material. The bacterial spoilage of dirty eggs is very much greater than the bacterial spoilagr of eggs d i i c h have never been dirty (1, 4 , 5). For this reason, aq ne11 as becau.e of their unsanitary appearance, buyers pay less for dirty eggs than for clean ones. This cut in price has led poultry producers to clean their dirty eggq. If the cleaning has been careledy done or the eggs just wiped, a stain remains on the shell and the cleaning can generally be detected. If the cleaning has been carefully and thoroughly done, no stain remains and there has been no ~ a ofydetecting the fact that the eggs have been cleaned (5). If cleaned dirty eggs are used locally or pass rapidly through the channels of trade, they may go into immediate consump-
tion before the bacteria which may be present in a considerable number of the eggs cause marked spoilage. If either cleaned dirty or dirty eggs are held a t relatively high temperatures or for appreciable periods of time, bacterial deterioration may take place in about 3 to $50 per cent or more, depending on the amount of dirt on the shell and the subsequent treatment of the eggs. If the eggs have never been dirty and are properly cared for, only about 2 to 3 per cent will show bacterial growth ( 1 , 4, 7 ) . The spoilage in cold otorage of a large number of eggs each year is often attributed by egg dealers to the storage of washed eggs unknowingly. I t seems to be desirable for intelligent marketing and disposal of eggs that tests for cleaned eggq be available. Cleaning removes the dirt which when present would be evidence leading to the expectation that a considrrable nunher of the eggs would eventually show bacterial spoilagcl. Heavy bacterial infection is not always detected by candling, as Jenkins and Hendrickson (a‘) have shown. Jenkins, Hepburn, S w n , and Sherwvood (4)found that after storage a larger number of dirty eggs contained bacteria than normal clean eggs, and that a larger number of washed dirty eggs contained bacteria than dirty un\i ashed eggs. Bryant ( I ) found that the kind of solution used in wa ing eggs apparently has no marked influence in controlling bacterial spoilage. This indicates that the bacteria map have already penetrated the shell, and that the solution5 used in cleaning the qhell do not reach the bacteria which are already
