Direct Determination of Available P,05Content of Fertilizers W. H. MACINTIRE, W. k1. SHAW, AND L. J. HARDIN The University of Tennessee Agricultural Experiment Station, Knoxville, Tenn.
T
HE “official” method (1) for “available” PBOscontent of
ing and water replacements were found to be much less expeditious than a current of steam in effecting removals of engendered ammonia. The importance of rapid elimination of ammonia engendered in the boiling digestions of M ammonium nitrate is shown by the preliminary trials of Table I. The mean of the P20jextractions from the six systems purged of ammonia by current of steam was 2.2 times the corresponding mean of the Pz05extractions from the refluxed digestions. Higher final p H value and lower solvent capacity for refluxed digestions are shown for each of the six digestions of basic phosphates. Since the initial volume of the M nitrate solution was maintained in both of the boiling technics, p H constancy and greater solvent action are attributable to expeditious removal of engendered ammonia and effective dispersion of the solids by the vigorous current of steam. The reactions that take place between the basic phosphates and ammonium nitrate during the steam digestion may be assumed to produce a solution of monoammonium phosphate, as indicated by the equations
commercial fertilizers was based upon the procedure of Fresenius, Xeubauer, and Luck (6) for determining the phosphatic components other than undecomposed rock residues. Adopted by the Association of Official Agricultural Chemists in 1884 (Z), the method has been a most dependable procedure for the evaluation of phosphatic fertilizers of acidic character. It was proposed and intended, however, solely for products characterized by free acid, monocalcium, iron, and aluminum phosphates. I n recent years, ammoniation and incorporation of either dolomite or rock phosphate supplements have become common practices in the fertilizer industry. These practices have developed types of fertilizers (4, 24) that contain considerable quantities of dibasic phosphates (9, 10, 21, 2 2 ) and variable amounts of tricalcium compounds that develop during processing and curing (11, 13,15,23). Moreover, engendered tricalcium phosphate and component fluorides react to form fluorapatite during both curing and analysis by the official method (17, 20). Seven years ago, the associate referee listed the objective, “to find a laboratory method that will be applicable to the evaluation of ammoniated, as well as straight superphosphates,” and recommended “that a further study be made of the method for citrate-insoluble phosphoric acid with a view to modification that will secure more concordant results” (35’). The subsequent decrease of analytical charge to 1 gram was admittedly an advance, but the inherent difficulties were not overcome by that change. The official procedure for available PaOj calls for two eliminative manipulations and two PlO6 determinations for each analysis. Obviously, i t would be advantageous to have a rapid and dependable technic for direct determination of available PzOscontent by means of a solvent capable of effecting the same removals now made by aqueous leaching and citrate digestion.
CaHP04
+ 2KH4No3
+ +
-+ Ca(NO& (NH4)2HP04 (KHJZHPOI -t NH4H2P04 ”a/’ Caa(PO& 6KH4K03+ 3Ca(N03)2+ ~ ( N H I ) ~ H P O I2 N H d 2(NH4)2HPOd+2NH4H2PO4 2NH3 /‘
+
+
+
Scope of Present Studies Some of the extensive pilot studies that preceded adoption of the ultimate solvent and technic will be given subsequent to the presentation of the proposed procedure and analytical comparisons. For brevity, the term ‘‘solvent” will be used to connote an III ammonium nitrate-0.05 ikf ammonium citrate solution of 4.2 pH. The capacities of official citrate solution and proposed solvent were compared for samples of widely variant type, origin, and concentration, in a study of the several factors-composition, size of charge, particle size, common ion effect, concentration and constancy of p H of solvent, period of digestion, raw rock supplements, PzO6 transitions induced during analysis, and variable proportions of the basic forms of phosphates engenderd during commercial processing and aging.
Objectives and Principle of Proposed Procedure The objective of the present study was the development of a simple, rapid, and economical direct analytical procedure for all types of phosphatic fertilizers. Choice of solvent was restricted to one exerting practically the same capacity as the official citrate solution for undecomposed rock and conducive content. The studies led to complete precipitation of its Pz06 to a procedure that prescribes a single solvent for prior leaching and subsequent steam digestion of leached residue, combination of leachate and digestate to volume, and one P205determination. Direct solvent action alone enters into the dissolving of acidic phosphates, but the analysis of basic products involves exchange between the N H 4 of a boiling citrated iV solution of ammonium nitrate and the bases of the phosphatic compounds not removed by prior leaching. The engendered ammonia is removed almost instantaneously by a balanced passage of steam n-hich maintains near-constancy of p H and of volume during digestion. Use of a steam current also expedites the dissolving of the phosphates, affords vigorous agitation, assures uniform suspension of the solids, eliminates bumping, and requires a minimmi of attention. Direct boil-
SOLVENTACTION EXERTED BY ill TABLEI. COMPARATIVE AMNOXIUMNITRATE’ (Sustained volume, 100 ml., during boiling with a n d a i t h o u t p a s s a w of s t e a m , in evaluation of P ~ Ocontent S of basic phosphatic materials’ Boiling with Injection of Boiling a n d Csing Current of Reflux Condenser Steam P?Os Finn1 PiOa Final p H of disp H of dis--Phosphatic llaterialType Charge extract solved extract solved XO. .Ilg Gram
c. P. dicalcium phosphate c. P. tricalcium phosphate Calcined rock phosphate Fused rock phosphate hmmoniated superphosphate Limed superphosphate a Contained no citrate.
143
0.25 0.25 0.25 0.26 0.50 0.50
(i.0 6.0 6.6 6.2 5 .O 5.6
68 27 36 48 26 6
4.0
4.2
4.4
4.0 4 .O 4.0
129 101 88
73 42 37
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144
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3
Direct Determination of P20j-Availability in Fertilizers by Citrated Amiiionium Nitrate CITRATTED AhI%fOSIUM NITR.4TE SOLVENT.Prepare a stock solution, each liter to contain 80 grams of P205-freeammonium nitrate, 50 ml. of M citric acid, and 7 5 ml. of M ammonium hydroxide. This dual salt solution (Xnitrate-0.05 AI citrate) should have a pH of 4.2. PKOCEDURE FOR MIXED FERTILIZERS. Weigh a 1.0-gram charge into a small porcelain dish; wet, carefully wit11 5 nil. of solvent, triturate, transfer onto a 9-cm. gravity filter, and leach into a 150-ml. beaker vith several 10-ml. portions of the cold solvent. Add 0.5 ml. of 0.04 per cent solution of bromocresol green to the leachate. If a blue or bluish green color develops, add dropwise suficient 1 9 nitric acid t o produce a change to light green. Continue leaching to a final volume of 100 ml., and maintain color as before. Transfer the filter to the 250-ml. "fertilizer" flask, A of Figure 3, and add 100 ml. of the solvent. Stopper the flask tightly and disintegrate the filter by vigorous agitation. Rinse the stopper and the neck of the flask with a small amount, of distilled water. Adjust outlet B t o trap E and bring the suspension to boiling by means of a small Bunsen burner, C, provided with a flame guard. Connect tube D with a steam generator and pass steam through the suspension in flask A for 30 minutes, regulating flame to maintain volume of approximately 100 ml. Remove flame and disconnect flask from steam generator; wash both outside and inside of inlet tube and the liquid from the safety tube, back into the digestion flask, A . Place an inverted beaker over the neck of the flask and cool under tap and then add the prior 100-ml. leachate; make to volume and mix. Filter a sufficient quantity through an 18.5-cm. fluted filter, and discard the first 25 to 40 ml. Use a 25-m1. (0.1-gram equivalent) aliquot and precipitate ammonium phosphomolybdate as in the official method. PROCEDURE FOR STAXDARD SUPERPHOSPHATES. Proceed as for mixed fertilizers, but reduce the steam digestion period to 15 minutes. PROCEDURE FOR TRIPLE SUPERPHOBPHATES. Proceed as for standard superphosphates, but use a 0.5-gram charge. 2. fhEAlhl GENERATOR O F FIGURE 1, .4FTER INSCLAPROCEDURE FOR CALCIXED M D FUSED ROCKPHOSPHATES. FIGXW: TIOX .4KD COSNECTIOX \VITH DIGESTION FLASKS -4ND GUARDS Use a 0.5-gram charge and roceed as for mixed feItilizers. Proceed as for mixed ferPROCEDURE FOR BONE tilizers. digestion with 5 nil. of concentrated nitric acid at the boiling PROCEDURE FOR BAsx SLAG. Proceed as for mixed fertilizers. point for l5 minutes, cool, nearly neutralize, and proceed in PROCEDURE FOR h'hTAPHOSPHATES. Proceed as for calcined tile ofhcialmetliod. and fused rock phosphates. Hvdroh-ze a IO-ml. aliquot' by Introduce directly illto p n o C E D cFOR ~ E ROCK PHOSPHATES. flask A , 1-gram charge and 100 ml. of solvent, and proceed to digest as in mixed fertilizers. Cool and make to volume. Filter, .~ and rrfilter if necessary, until filtrate is perfectly clear. Irse a 25-ni1. aliquot and proceed as in the official method.
+
KEA,.
Experiment a1 IX'CLUSION OF CITRATE IS SOLVEST.Following prelimi-
COPPER 4 - t - m ~S m o i GESERITOR FIGURE1. HOME-MADE
nary trials, M concentration of ammonium nitrate was used in all comparisons. Boiling steamed digestions b-ith this solution gave values comparable with those obtained by the official methods for some materials, but not for all. Pilot studies were then conducted as to the effect induced by the 1 concentrations of aminclusion of 0.025 J1 and 0.05 A monium citrate in the il.1 ammonium nitrate solution. Both concentrations enhanced the capacity of ammonium nitrate solution to dissolve superphosphates of high iron content, ammoniated superphosphates, basic slags, and bone meals. The 0.05 M citrate concentration imparted maximal capacity to the 'If ammonium nitrate solution in comparison with the official procedure and was therefore adopted for the prescribed solvent. Resnlts by the official method and by steam digestions of ammonium nitrate, alone and with inclusion of 0.05 M ammonium citrate, are given in Table 11. I n the absence of the citrate, values by ammonium nitrate digestions were invariably less than by the official method. comparable values were obtained, however, for the acidic materials by citrate and solvent digestions. A somewhat higher value was found for the ammoniated triple superphosphate by solvent. The value for the precipitated tricalcium phosphate by the conventional citrate digestion was only 42.6 per cent as against 97 per cent by digestion with solvent.
MARCH 15, 1938
ANALYTICAL EDITION
Quantitative precipitation of ammonium phosphomolybdate cannot be made from the official citrate solution, even after dilution of one-tenth aliquots. Direct PzOj precipitations from solvent can be macle quantitatively, however, since its citrate concentration is only one-ninth of that of the official solution. With aliquots of solvent containing 2.25, 4 9.0, and 18 mg. of P20s,no retardation of molybdate precipitation was indicated until citrate content was fire times that stipulated for solvent. B
CLAMP
a
0
2 4 0 cc.VOL. FLASK
SCALE :=I"
145
obtain maximal solyent action of neutral ammonium citrate in the analysis of acidulated materials by th: official procedure. Prior leaching with cold solvent m s tlierefore used to diminish tlie amounts of P20jand salts so that the subsequent boiling digestion with solvent would be subject t o less ilepression by p H change and conimon ion effect. The P20jremova1.j effected by leaching acidic ant1 basic phosplintes iritli d r e n t are $lion-n in Talde 111. Removals n-ere in the range of 95 per cent for superphosphates, 83 per cent f o i , iriisetl fertilizers, GO to 90 per cent for ammoniated materials, 10 to 50 per cent for basic types, and about SO per cent for >lags and bone meals. LIoreorer) calcium sulfate was almost completely reniored by t h e prioi. ~ ~ - a s h i nwith g solvent, whereas Jacob and Treme:irne ( 1 4 ) have shoxvn that only about 35 per cent is removed by aqueous leaching. The comparisons of Table I T - sliow the PZO5 values obtained for expe~inientalbasic materials by tlie two steps of prior leaching arid digestion with solrent, in comparison with direct digestion. The mean of t,he 12 values obtained by prior leaching with $olvent was 92 per cent against 81 per cent for the tlirect digestions. Aqueous varhing of basic phosphatic nintwials that contain fluorides is conducive to the dwelopnienf- of insolubility through liyciroiy,sis and through foimation c)f fluorapatite. This tendency is lespened, if not obviated, by the use of the acidic solvent for tlie prewrihetl lwching. Higher results for the leached aiiinivriiated products can also be attribiited
BUNSEN BURNER WITH FLAME GUARD
FIGURE 3.
DIAGRAM OF
APPARAT~S
PRIOR WASHIXG WTH COLDSOLVEST.K h e n 1- and 0.5gram charges of superphosphates and triple superphosphates are digested directly with solvent, pH is not mate~ially altered. Decided increase in pH is induced, however, by full charges of tricalcium phosphate and heavily ammoniated and limed materials. Austin (3) and Jacob and Tremearne ( I C ) have pointed out that prior aqueous mashing is requisite to TABLE 11. EFFECT OF IXCLUDED CITRATE UPOS SOLVEKT CAPACITY OF A!f AMIMONITJM NITRATE DCRIKG BOILISGDIGESTION
Code" lOG0 1066 1087 1378 1337
Phosphatic AIateriai
Total P20: 20 80
--;\rxilabie PgOe-Neutral S o r n i a l Citrated ammo- ammo- ammonium niuni nium citrate6 nitrateetd nitrateC>e 20.07 18.4 19.7 19.9.5 20.13 20.90 18.2 20.9 1G.90 16.75 46 32 4318 46.50 44 9,j 44.80 44.iG 42.4 44.65 46 24 .. 46.80
Superphosphate Suuerohnsnhate 20.00 Superphosphate 21.00 20.50 S'iperphosphate Triple superphosphate 46.70 1338 4 3 00 Triple superphosphate Triple superphosphate 47.80 1368 1415 48.80 Triple superphosphate Ammoniated super1518 phosphate 4i.60 4,: 80 42.0 47.0 Mixed fertilizer 1522 20.86 20 i4 18 4 20.60 16.00 Nixed fertilizer I526 16 78 16.2 16 40 39.60 .. Tricalcium phoiphate 16 90 .. 38.4 Numbers are those of Bureau of Chemistry a n d Soils. b Official procedure. e I-gram charges of standard superphosphates, O.5-gram for concentrated materials. d .I4 ammonium nitrate without citrate, otheruise as in 6 . M arninonium nitrate-0.05 .TI ammonium citrate, p H 4.2; prior ieaching and boiling digestion f o r 15 minutes.
FIGURE 4. SISGLEALL-GLASSEXPE:RIMESTAL CKIT,WITH SEP.IRATE O F STE.II\f I S L E T AKD OUTLET O F nIGESTION F L ~ S I C
INDUSTRIAL AND ENGINEERING CHEMISTRY
146
TABLE111. ATAILABLE P,Or FRACTIOS REMOVED FROM PHOSPHATIC hf.kTERIALs BY 100-hfL. COLD CITRATED AhfXONICN NITRATELEACHIXGS -.‘.vailahle Code
I I1 sample
,\lateriala
1’906-
111 100 1\11. of 1.earliate .Actus1 F r a c t i o n
70
70
770
1060 1378 1365 Ma Mb %Ic
Superphosphate 19.7 18 i 95 Superphosphate 16.8 14.0 83 Triple superphosphate 44.8 43.i 96 16.8 10 i 64 Ammoniated superphosphate 16.5 10.5 61 Ammoniated superphosphate Ammoniated triple superphosphate 40.0 35.0 88 1508 Mixed fertilizer 8.8 6 3 i 2 1522 ,\fixed fertilizer 1523 LIixed fertilizer 20.6 10.3 187..83 85 84 1526 Mixed fertilizer 16.4 14 4 88 12.1 3.9 32 T-3 Basic s l a p 18.6 5 0 27 S-1 Raiv bone 8-2 Steamed bone 18.2 6.E 37 J-1 Steamed hone 23 6 7.8 33 J-t Dicalcium phosphate 50.2 22.1 14 Tricalcium phosphate 28.5 21.5 56 34.2 16.1 4i Ca hydroxyphosphateb ;-t 615 C a fluorophosphatec 16.6 7.0 42 a 35-mesh fineness; 1-pram charges for all materials except triple superphosphate a n d di- a n d triphosphates, for which 0.5-gram chargee were used. b Supplied b y K . D. Jacob, Bureau of Cheniiptry a n d Soils. A labcratory product.
TABLE IV. EFFECTIVEKEGS OF PRIOR LEACHISG (Excespirely-limed and ammoniated laboratory-prefiared surerpllcsyliates n-ith cold citrated ammonium nitrate so1utioi.a in promoting P!@a reniovak b y subsequent boiling extractions) --hvnilahle PzOrContent Found
Direct nitrate Superphosphate 3Iixtures T y p e of super- Additions t o Mixtures Code phosphate hlaterial Proportion Ma Mh
Standard Standard
Me Mf 1168 1165 Me Md
Standard Standard Standard Standard Triple Triple
571 573
Triple Triple Triple Triple
576
XH8 KH3 Dolomite Dolomite Dolomite XHa Ca(0H)zd NH3 ”3
Dulomite Limestone Dolomite XHr
Total
ploS
leacllirigc Prior and suhsequent boiling
rrith digestion digestion uithout citrated prior ammonium leachingb nitrateb
%
%
70
%
4 . 49 01 10 00 10.00 30 00 8 70 16.67 8.65 7.94 10 00 30 00 30.00 12.40 7.96 50.00
18.4: 19.30
8821 . 89
9942 . 31
19:iO 16.05 19.40 17.30 39.75 37.50
9k.4 97 2 69 5 73 4 90 3 91.3
98 4 99.7 84.5 83.1 100.0 07.6
7b.4 90.2 79 79.3
50.5 93.i 86.6
..
,
44.70 41.40 43 70 2 4 .. 6. 0
.
-
...
. .
KHr 88.6 Gypsum ,.. a M ammonium nitrate-0.05 M . ammonium citrate, p H 4.2. 1-gram charges for “standard” mixb Boiling digestion for 30 minutes; tureq’ 0.5-gram charges for triple mixtures. 0 ?sshing with 100-ml. of solution noted in a by gravity. Leachate a n d boiled extract comtined to 250 ml. for PzOs determinations. d From slurry, 1 p a r t C a ( O H ) z a n d 5 parts of superphosphate: aged 1 week; dried a t 45’ C. (see 2 4 , p. 280). 580
partly to substantial diminution of the common-ion effect during the subsequent digestion with solvent, an effect that will be considered further. SIZE OF CHARGE.The data of Table V show values obtained by official procedure, and by direct digestions of 1and 0.5-gram charges with a N ammonium nitrate solution that contained only a 0.025 M concentration of citrate, or one-half of that ultimately prescribed. The digestions were made without the preliminary leaching subsequently prescribed for the proposed procedure. For the Seven acidic materials, the official method gave values in accord with those obtained by the use of both 1and 0.5-gram charges in the direct digestions with the nitrate solution. Values by the direct nitrate digestion of the 0.5gram charges of the ammoniated materials exceeded those found for the 1-gram charges. It el-ident that a Prior leaclling and a citrate concentration greater than 0.025 M would be required to asslire adequate d u e s when 1-gram charges of some ammoniated and basic niatc,rials arr used.
VOL. 10, KO. 3
I n a supplemental series of eleven highly ammoniated and dolomite-treated products, five of superphosphate and six of triple superphosphate, 0.5- and l.O-gram charges were analyzed by the official technic. The mean total Pz06content of the eleven materials was 29.4 per cent. The mean coefficient of availability by the official method was 84.7 per cent. When 0.5-gram charges were used, the corresponding mean by the official technic was 89.8 per cent, as against 92.5 per cent for the ultimate procedure with solvent.
TRICALCIUX PHOSPHATES; SOLUBILITY BY ~ M M O h ~ I U . \ I CITRATEAND BY PROPOSED PROCEDURE. Since ammoniation and incorporation of calcic materials in superphosphates engender precipitated tricalcium phosphates and fluorapatite (16, 17, 18, 20, d3), the solubility of these phosphates is an important factor in the analysis of ammoniated materials. Values obtained by the conventional citrate digestions of three precipitated tricalcium phosphates, one hydroxyphosphate, and a synthetic fluorapatite were therefore compared with those obtained by the proposed procedure. As shown in Table VI, citrate digestion gave only about 40 to 50 per cent of the P206 content of c. P. tricalcium phosphates, as against a range of 82 to 96 per cent for solvent. If a tricalcium phosphate is of uniform composition, the fraction undissolved by citrate should have the same composition and evaluation as the substantially equivalent fraction that is not dissolved by the citrate digestion, unless a more basic and less soluble form is developed during the citrate digestion. The practically complete dissolving action of solvent therefore seems a more equitable measurement of the value of tricalcium phosphate and accords with the values found by collaborative plant-growth studies (8, SO, 31). By both citrate and solvent digestions, the values for precipitated phosphates exceeded those for the hydroxyphosphate and fluorapatite. Granting that hydroxyapatite develops in commercially processed superphosphates, its solubility by the proposed procedure approaches that found for ordinary tricalcium phosphate. The synthetic fluorapatite mas the least soluble of the three phosphates in both citrate solution and solvent. The marked disparity in the values obtained for synthetic fluorapatite by the two methods was considerably diminished, however, when a 0.5-gram charge of fluorapatite was used in the citrate digestion. The solubility of synthet’ic fluorapatite will be considered further in a study of its mixtures with various proportions of di- and tricalcium phosphates.
OF SIZEOF AKALYTICAL CHARGE UPOK TABLE V. IKFLLTXCE Pz05 AVAILABILITY DETERMINATIONS
( M Ammonium nitrate-0.025 M ammonium citrate solvent)
Code
Phosphatic hiaterial
-Available By Neutral Ammonium Citrate Procedure Total I-gram pZo5 charge
% 1508
8.88 20.74
11.30 17.90
1.92 14.02
izi; iii;;; f;;;$:;; 1526 1104 1105 1378
1168 580
J J J (1
%
9.40 20.66 10.60 Mixed fertilizer 16.90 13.83 >Yet mixed base goads 9.70 Wet mixed base goods 20.50 Standard superphosphate Smmoniatedsuperphosphate 19.40 Ammoniated superphosphate 2 4 . 6 0
,\Tixed fertilizer
10.53 16.78 12.83 6.70 16.90 13.80 19.50
-
PzO-
By Citrated Ammonlum Kitrate Procedure I-gram 0.5-pram charge charge
%
%
20.55 10.60
8 70 20.60 10 60
16.60
16.60
12.58
12.60
6.96 17.30 13.30 18.65
17.40 16.60 21.80
1.65 11.05
15.40
8.60
7.00
~Steamed ~ ~ bone ~ ~ meal i ~ : ~ ~ ~34.00 :”,:: ~ ~ ~ ti1:;:9F . 5 0~ h 20.25 ig:;; h ~ ~ 2:::% 5~ . 8~6 B a t t ; ~ Basic slag, l o w C Basic slag, high0
2.20
Straight ammoniated product aged 6 weeks a t 54’ C .
b0 Ammoniated Samples highly product basic containing a n d gave strong dolomite ammoniacal a n d aged 6odor weekswhen a t 54‘wetted C.
with solvent.
MARCH 15, 1938
ANALYTICAL EDITION
147
ion effect induced by the ditOF PRECIPITATED FORMS OF TRICALCICM PHOSPHATE solving of those compounds TABLE VI. AVAILABLEP,Os CONTEXT (As determined b y ammonium citrate digestion a n d b y citrated ammonium n i t r a t e digestion of proposed procedure) that are not removed by the --PzOr Values b y Digestions withprior cold leaching. Citrated Increase in .4vailaS e u t r a l Ammonium Ammonium bility b y Citrated DI- AKD TRIC-&cIU&f PHOSCitrate“ Xtrateb .in;monium S i PHATE MIXTURESWITH SYX.&railable Available t r a t e Digestion .Is .Is AS THETIC FLUORAPATITE; IXFLUTricalcium Phosphate Total Insoluiraction fraction fraction ENCE OF PROPORTIONS AND SIZE Type Source PZOS ble Actual of t o t a l Actual of total Actual of t o t a l 5% % % % % % % % OF CHARGEUPON SOLUBILITY Precipitated J. T. Baker Co. 40.50 23.60 16.9OC 4 1 . 7 38.40 94.8 21.5 53.1 IN SOLVENT. Values obtained 40.00 19.50 20.50 51.3 38.40 96.0 17.9 84.7 Baker &. .&damson f o r h i g h l y ammoniated and 40.40 22.90 17.50 43.3 33.30 82.4 15.8 39.1 Eimer & Amend Hydroxyapatited Bureau of Chemistry limed superphosphates, as well a n d Soils 41.83 29.91 11.928 2 8 . 5 33.40 79.8 21.5 51.3 3Ca3(PO&as concentrated single mateCaFz Laboratoryproducti 3i.60 29.50 8.108 21 5 13 80 3G.7 5.7 15.2 rials, such as tricalcium phosa S t a n d a r d charge 1 gram per 100 ml. of solution, 1.09 sp. gr. phates, are materially affected b Charge of 0.5 gram digested i n 100 ml. of citrated ammonium n i t r a t e solution after 100-ml. a a s h i n g with cold solvent. by variation in a n a l y t i c a l c Use of 0.5-gram charge gave 31.00 per cent. charge, when the official techI h!ade b y reaction between CaJ(POd)z.HzO a n d CaFz. d Supplled b y K. D. Jacob. 9 L s e of 0.5-gram charge gave 12.20 per cent. 8 Use of 0.5-gram charge gave 17.17 per cent. nic is used (7, 8,I7’, 20,23,28). Recognition of this fact led to decrease of charge to 1 gram CALCIUM SULFATE AND CALCIUM FLUORIDE AS FACTORS IN (SO) and further decrease to 0.5 gram has beensuggested. CITRATE AND SOLVEXT DIGESTIOSS.Both calcium sulfate Separate 0.5-gram charges of pure dicalcium phosphate are quickly and completely dissolved by solvent digestions, and calcium fluoride decrease the solvent capacity of ammonium citrate for tricalcium phosphate (IS). Component whereas a corresponding charge of precipitated tricalcium calcium fluoride will also combine with tricalcium phosphate phosphate is almost completely dissolved. A. I-gram charge of an ammoniated superphosphate will not contain 0.5 gram to form the less soluble fluorapatite during the official ammonium citrate digestion (17, 20). The influence of the sulof these phosphates, however, either singly or jointly. Failfate and of the fluoride upon the capacity of the solvent was ure to extract all of the engendered basic phosphates is therefore attributable to interference by other components and to therefore studied in the four systems of Table VII. Each mixture contained 0.5 gram of tricalcium phosphate formation of new compounds during the analytical procedure. and 0.1 gram of diammonium phosphate, with a total P20a The amount of fluorapatite engendered in processed supercontent of 21.6 per cent on the basis of a 1-gram charge of phosphate is governed by proportions of tricalcium phosphate hypothetical material intended to simulate the phosphate and fluorides, moisture, temperature, and period of aging. makeup of a I-gram charge of a highly ammoniated and Extensive transition of tricalcium phosphate to the synthetic reverted superphosphate devoid of fluorapatite. Immedifluorapatite during processing can be considered primarily ately before analysis, sufficient CaS042,H20was added to responsible for any incomplete recovery of P,Oo from “resupply 30 per cent of SO3 to a 1-gram charge. It has been verted” materials that are subjected to the prescribed washing pointed out that aqueous leaching leaves a major fraction of and digestion with solvent. The capacity of solvent to discomponent sulfate to influence the solvent capacity of the solve fluorapatite in association with variable proportions of citrate solution ( I d ) , whereas washing with solvent removes di- and tricalcium phosphate was therefore studied. practically the entire sulfate content. T h a t fraction of the TABLEVII. DEPRESSION IN P20s AVAILABILITY sulfate addition that was unremoved by leaching exerted a (Induced b y additions of calcium sulfate and calcium fluoride immediately meager depression upon the solvent action of official citrate before analysis of a mixture of tricalcium phosphate and diammonium reagent, whereas no common-ion effect was induced in the phosphate, as registered b y official a n d citrated ammonium nitrate procedures) digestion with solvent. PzOa Values b y Two Procedurea-Available The additions of calcium fluoride supplied 1.6 per cent of De ression, Induced Additions M a d e Increased \ y Additions fluorine and were also made immediately before the analyses Immediately value b y I n citrated before Analysis Citrated citrated In ammonium of the phosphate mixtures. The added fluoride caused a of Phosphatic Official ammonium ammonium citrate nitrate decrease of 3.7 per cent in citrate-solubility, whereas the Mixturesa citrate nitrate nitrate system system same addition plus calcium sulfate caused a further decrease % % % % % h’one 19.9 21.2 1.3 ,.. ... to 5.8 per cent. These two decreases in citrate-solubility 19.6 21.1 1.5 0.3 0.1 CaSOib were twice those induced by the fluoride in the corresponding 16.2 19.3 3.1 3.7 1.9 CaFz CaSO, + CaFzbSe 1 4 . 1 1 8 . 2 4 . 1 5 . 8 3 .0 digestions with solvent. For the phosphate mixtures to which a Simulating a n excessively ammoniated superphosphate. constant of additions of calcium sulfate, calcium fluoride, and calcium 0.4 gram tricalcium phosphate a n d 0.1 gram d i a m m o n i i m phosphate, computed,as 21.67’ PzOa content of a 1-glam charge. sulfate plus calcium fluoride had been made, higher respective b Additions of 0.645 e r a m of Cas04 2H20. t o S U.D _ D~ - , comuuted . - V30 Der cent SOa in a I-gram charge. values of 1.5, 3.1, and 4.1 per cent were obtained by solvent. Constant of 0.035 gram, computed t o supply 1.6 per cent fluorine in a Considered in connection with the data of Tables I11 and 1-gram charge. I V that show the extent and effect of removals of phosphatic The mixtures of Tables VI11 and IX were intended to components from basic fertilizers, the results of Table VI1 simulate ammoniated materials containing variable proporindicate that the analytical error attributable to formation of tions of synthetic fluorapatite and one of the two basic phosfluorapatite during ammonium citrate digestions is appreciable phates. The mixtures of Table VI11 contained decreasing when the citrate is rendered alkaline by the dissolved mixproportions of dicalcium phosphates and increasing proportures of tri- and dibasic phosphates in the presence of fluorides, tions of synthetic fluorapatite, with a constant of 50 per cent (17, 2O). Removal of basic phosphates by prior leaching of calcium sulfate. The mixtures of Table IX were identical with solvent tends to minimize the change in initial p H during with those of Table VIII, except t h a t tricalcium phosphate the boiling digestion. Formation of fluorapatite cannot take was substituted for dicalcium phosphate. The proportions place, however, a t the initial p H of solvent. Any depressive of the two phopphates present during the digestion were effect upon the capacity of the boiling digestions to dissolve different from the initial proportions because of the variable phosphates is therefore attributable primarily to the commonC
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VOL. 10, NO. 3
TABLEVIII. EFFECTO F
PROPORTIOSS O F D r c a L c r u n r P I i O s P H h T E AKD SYKTHETIC APATITE, A S D O F CHARGE, C P O S PLO~-AT..XIL.IBILITY
FL~OR-
Citrnted ammonium nitrate proceduie)
---
i r a l l a b l e PjOs F o u n d
7
Phosphatic Components of 1-Gram Ch:irges By XT-eight P:Os as FluorFluorCaHPO; apatiteb CaHPOi apatiteb Gram Gram 52 %
06 0 4 0.3 0.2 0.1 0
Total
P?Oj %
O f Charge-
Increase due t o derreased 0.5gram charge
1 gram 07
(0
2G 70 0 70 70 20.50 3 IF 24.32 16 42 7..a? 2 9 94 10 28 I 1 ?Y 21.56 3.14 15 04 20.18 0 18.80 18.80 a C o n s t a n t 0.5-Kram content of calcium sulfate b . I laboratory product.
0.0 0.1 0.2 0.3 0 4 0.5
2C 20 1F 12
70
%
%
5%
70 2 4 00
0 3 4 5 4 5 0 6 0 3.9
100 85 74 63 51 37
100
76
00
?? 30
90 60 i n 20 6 00
Of T o t a l P!Os 1 gram 0.5 grain
CI ,o
19 20 16 30 10 60
09
97 90
p;
TABLE IX. EFFECTOF
PROPORTIOKS OF TRICALCIThl PHOSPHATE AND SYSTHETIC FLUORAPATITE, A S D O F CHARGE, CPON P 2 0 5 - A ~ . ~ ~ ~ . ~ ~ ~ ~ (Citrated ammonium nitrate procedure) c \\ailable PlOs F o u n d Of ChargePhosphatic Components of I - G r a m Charge0 Increase By It eight P?Os as due t o FluorFluorTotal decreased Of T o t a l P10s Ca3(POd)z apatiteb C a 3 ( P O h apatiteh PgOs 1 gram 0.5 gram charge 1 gram 0.5 gram Gram Gram % R % 70 % % % 9%
~ ~ ~
--
0.5 0.4 0.3 0.2 0.1
0
0.0 0.1 0.2 0.3 0.4 0.5
20.25 16,20 12.15 8.10 4.05 0
0 3.76 7.52 11.25 13.04 18.80
20.23
19.96 19.67 19.38 19.09
19.25 14.00 11.70 9.85 5.50
18.80 0 C o n s t a n t 0.5-gram content of calcium sulfate. b A laboratory product.
amounts removed by the prior leaching to which the several mixtures were subjected. The data of Table VI11 show that, in absence of fluorapatite, 0.5- and 1-gram charges of dicalcium phosphates were dissolved completely by solvent. Of the total P,Os content supplied by the two phosphates, deficiencies of only 1 per cent and 3 per cent in recovery were induced by the fluorapatite in its 1 to 4 and 2 to 3 mixtures with dicalcium phosphate, when analytical charges of 0.5 gram were used. When 1-gram charges of the same two mixtures were used, the corresponding deficiencies were 15 and 26 per cent. Deficiencies in PaOa recovery were decreased to the minimal values of 37 and 57 per cent, respectively, for the 1- and 0.5gram charges of the fluorapatite alone. But, in the mixture that contained 4 parts of CaHPOa of 100 per cent solubility, and one part of 57 per cent soluble fluorapatite, furnishing 84.5 and 15.5 per cent of the total P,OS content of 24.32 per cent, a recovery of 99 per cent was obtained by the use of the 0.05-gram charge. Beginning with respective recoveries of 98 and 95 per cent from the 1- and 0.5-gram charges of c. P. tricalcium phosphate, the data of Table IX show the same order of values that were brought out for the dicalcium phosphate mixtures of Table VIII. Tables VI11 and IX show that the use of the smaller analytical charge gave a higher P205 solubility for each mixture that contained synthetic fluorapatite and either di- or tricalcium phosphate. Recoveries decreased as fluorapatite proportions increased in both di- and tricalcium phosphate mixtures and the recorery from each tricalcium phosphatefluorapatite mixture was less than the recovery from the corresponding dicalcium phosphate mixture. Since the full charges of both di- and tricalcium phosphatesamounts beyond those to be encountered in the analysis of 1-gram charges of fertilizers-were completely dissolved by the digestions with solvent, any indications afforded by the proposed procedure as to undue retrogradation in ammoniated superphosphates should therefore be charged primarily to the formation of fluorapatite in the “reyerted” material
19 90 18 30 16.10 13.80 12.50 10.80
6.90
0.65 4.30
5.00 3.95 4.00 3.90
95 70 59
51 45
37
98 93 82 71 65
.5 7
Comparisons between Official and Proposed Procedures SUPERPHOSPHATES AND MIXED FERTILIZERS. The comparisons of Table X show results for 20-mesh standard and “triple” superphosphates, mixed fertilizers, and ammoniated triple superphosphate and a c. P. tricalcium phosphate. The proposed procedure gave a somewhat higher value for the ammoniated triple superphosphate and 97 per cent solubility
TABLE X. AVAILABLE P20iCONTENT OF SL-PERPHOSPHATES AND MIXEDFERTILIZERS ArailableP?Oa b
70 1060 1066 1087 1378 1622 1526 1337 1338 1368 1415
..
Standard superphosphatee Standard superphosphate S t a n d a r d superphosphate Standard superphosphate >fixed fertilizer N i x e d fertilizer Triple superphosphated Triple superphosphate Triple superphosphate Triple superphosphate Triple superphosphate
(15’. D.31.847)
%
%
20.80 20.00 21.60 20.50 20.86 16.90 46.iO 45,OO 47.80 48.80
20.07 19.70 19.95 20.13 20.90 20.65 16.90 16.75 20.74 20.80 16.78 16.40 46.52 4 6 , 5 0 44.95 44.80 44.76 44.65 46.24 46.80
48.65
47.05
47.40
9% -0.37 +0.18
-0.25 -0.15 -0.14 -0.38 -0.02 -0,15 -0.11 +0.56
+0.36
-4mmoniated triple super+1 20 47,60 45,BO 47.00 phosphate -0 31 12.83 12.5Z4 13.83 Base goods +0.28 6.70 6.98 9.70 1105 Base goods -0.13 8 . 8 8 8.i.5e 9.40 1508 X i x e d fertilizer -0.11 20.74 20 63 20.86 1522 Mixed fertilizer -0.27 10.53 10.30 10,60 I523 l l i x e d fertilizer -0 30 10.65 10.35 10.80 1524 X x e d fertilizer -0.07 8.92 8.85 9.10 1525 Slixed fertilizer -0 43 16.78 16.35 16.90 1526 ZIixed fertilizer +0.01 8.44 8.45 8.50 1527 hlixed fertilizer +0.78 l5,60 16 38 17.80 R LIixed fertilizer ~. ,, Tricalciumphosphate 39.60 16.90 38.40 +21.50 S u m b e r s are those of Bureau of Cheinistry a n d Soils. b .If ammonium nitrate-0.05 M ammonium citrate soiution, pH 4.2; preliminary leaching a n d 15-minute boiling digestion. c 1-gram chargee of standard products. d 0.5-gram charges of t h e concentrated material?. Base goods a n d mixed fertilizers same as b, except boiling digestion period was 30 minutes.
1518 1104
~~~
(.
@
~
AXALYTICAL EDITION
MARCH 15, 1938
for the precipitated tricakium phosphate against 43 per cent by the ammonium citrate digestion. I n the 10 comparisons of Table X, fairly concordant results were obtained by official and proposed methods for the group of two "base goods" and eight mixed fertilizers, using 1-gram charges for both methods and a 30-minute period of boiling digestion with solvent. The maximal variation was a plus value of 0.78 per cent by the proposed procedure. E X P E R I M E S T A L BASICLfATERIALS. Each of the 14 materials used in the comparisons of Table XI was an experimental mixture. Ten were ammoniat'ed products, with or without dolomite, and four vere unammoniated materials that contained either limestone or dolomite. I n ten of the fourteen comparisons, the deviation v a s a plus value for solvent. A11 of the higher values in the 2.2 to 2.9 per cent range were for the highly ammoniated products. The three minus deviations of 0.45 to 0.50 per cent were for products that had been ammoniated beyond the limit found feasible in practice. TABLE XI.
.kVAILdBLE P206 C O S T E S T S O F Ak31MO?iIATED A X D
BASICSUPERPHOSPHATES
-Treatment.immoniated with CodeD KHa Additional 1169 117.5 1168 hla 5SO Me \If Mb hlc 576 1518 571 573 Md
P?Osby-
----.ivailable Total
PlOs
%
%
%
2.5 5.4 8.7 4.9 8.0 0 0 4.4 8.7 12.4 6.0 0 0 7.9
Sone Kone Xone None Sone Dolomite, 10 Dolomite,30 Dolomite, 10 None Sone Sone Limestone,30 Dolomite, 30 Dolomite, 10
20.60 19.40 19.40 19 30 24.60 19 10 16.05 18 45 40.00 43 70 47.60 44 70 41.40 37.50
Citrated ammoOfficial nium procedure nitrateb.
% 18.90 18.00 13.80 14.30 19.50 18.10 15.10 13.90 37.15 39.70 45.80 34.40 37 80 34.05
C
Difference by citrated ammonium nitrate
%
%
18 80
-0 10 -0.50 -0.50 +2.50 -0.45 4-0 4 0 +0.50 + 2 60 1-2.85 +O 95 f1.20
17.50 13.30 16.80 19.05 18.50 15 60 16.50 40 00 40 65 47.00 36.15 38 60 36 30
+1 i 5
+O.&O + 2 21
Surnerals those of Bureau of Chemistry a n d Soils; letters those of samples supplied by F. G. Keenen of d u Pont b m m o n i a Experimental Station. 6 1-gram charges of s t a n d a r d products: O.5-gram charges of triple superphosphate products. .M ammonium nitrate-0.05 JI citrate solution; p H 4 . 2 ; preliminary leaching a n d 30-minute period of boiling digestion.
UREA-AMMOKIA IMPREGNATED MATERIALS, CUREDAT 2 TEMPERATURES. Keenen and Morgan (16) have emphasized that development of citrate-insolubility during curing is materially increased by rise of temperature and the same effect has been found for mixtures of tricalcium phosphate and precipitated calcium fluoride (20). This factor was studied in the comparisons of Table XIT. Three superphosphates and three mixed fertilizers were ammoniated by different quantities of urea-ammonia liquor. One-half of each of the ammoniated superphosphates was aged a t 43" C. and the other a t 54" C. for 38 weeks. The ammoniated mixed fertilizers were likewise divided and aged for 42 weeks. In 11 of the 12 comparisons, the proposed procedure gave PzOJavailabilities either higher or in accord with those obtained by the official method. Each of the six mixtures cured a t the higher temperature showed a lower PIOa availability by both the official and proposed procedures. The mean of decreases induced by the 12" elevation was 1.93 per cent by the official procedure and only 1.25 per cent by the proposed procedure. h-o citrate-insolubility developed in a control series, however, when a fluoride-free triple superphosphate was ammoniated to a 12 per cent ammonia content and aged a t 65" C. for 6 days. The results of Table XI1 also register the effect of more extensive rem01 a1 of sulfates and basic phosphates by prior washing with solvent. The basic phosphates, unremoved by aqueous leaching, vitiate the pII and solvent capacity of the citrate solution. Both hydrolysis of phosphatic components
149
and formation of fluorapatite occur during official analysis. In contrast, the smaller residues from solvent leaching influence the dissolving capacity of the boiling solvent primarily, if not solely, through diminished common-ion effect. TABLE XII. COMPARISON OF AVAILABLE P20, IN HEATED AMMOKIATED STSPERPHOSPHATES~ -Phosphate
Code
Type
Fertilizer-Urea ammonia liquor Total additions P10s
Lb./ton
%
dvailable P3OsCitrated Difference ammo- b y citrated Official nium ammonium procedure nitrate nitrate
7 . -
70
70
70
I-A I-B 2-A 2-B 3-.i 3-B 4-A 4-13 5-A 5-n 6-1
Superphosphateb 200 19.0 16.35 l(i.93 $0.58 Superphosphate 200 15.0 12.40 14.00 +1.60 Superphosphate I70 19.5 17.30 17.55 +0.25 Superphosphate 170 19,s 14.20 1L45 +1.25 Superphosphate 140 20.0 19,50 111.10 -0.40 Superphosphate 140 20.0 18.05 18.78 +0.73 Mixed fertilizer< 90 9.5 8.86 8.83 -0.03 Mixed fertilizer 90 9.5 7.60 8.40 +0.&0 XIixedfertilizer 120 9.5 7.26 8.48 +1.22 Mixed fertiiizer 120 5.5 7.00 7.85 +0.85 Mixed fertilizer 90 13 75 13.45 13.35 -0.10 6-B Mixed fertilizer 90 13.75 11.75 12.23 +0.48 All values obtained by use of I-gram charges. b All of the superphosphates were aged 38 weeks; suffix . I connotes aging a t 43' C . ; suffix B connotes aging a t 54' C:. All of mixed fertilizers were aged for 42 weeks: suffis A connotes aging a t 43' C . ; suffix B connotes aging a t 54' C .
ROCK PHOSPHATE SUPPLEMENTS; EFFECTUPON P,O AVAILABILITY. Rock phosphate is used as a fertilizer filler and it is claimed that a higher available P20scontent is thereby obtained by the official method. Analytical charges of the 10 fertilizers of Table XI11 were supplemented by 10 per cent additions of substantially 300-mesh brown Tennessee rock phosphate and analyzed by the proposed procedure and by citrate digestions, with inclusion of filter (12). If the PzOs solubility were a constant, when separate raw rock charges of 0.1 and 1.0 gram are subjected to boiling digestions with solvent, the available PzOscontent of each of the 10 fertilizers should be increased 0.23 per cent by the rock supplements. But the smaller charges of raw rock, corresponding to the amounts encountered in analysis of rock-supplemented fertilizers, give slightly higher values when digested
TABLEXIII. EFFECTO F 10 P E R C E N T SCPPLEMEKTS O F ROCK PHOSPHATE TPON AVAILABLE P20sVALUEB
Code
(Citrated ammonium nitrate procedure) --Available I'jOo ValuesbIncrease Without With due to Citraterock rock rock Insoluble supplesupplesuppleP*Oha nientse mentsd mente Phosphatic Material
St.
Superphosphate
% 0.20
%
%
%
19.60 19.70 19.60 19 75 0.13 6-585 Superphosphate 0.35 20.20 20.25 20.30 20.30 0.03 1378 Superphosphate 3.60 16.65 16.95 16.85 17.05 0.25 4-A 0.64 S. 75 9.20 Ammoniated superphosphate 8.90 9.i5 0.35 1.90 8.45 8.35 4-I3 Ammoniated superphosphate 8.35 8.55 0.05 1.24 8.45 8.50 5-A Ammoniated superx.50 8.60 0.08 phosphate 8.00 2.50 7.85 5-B Ammoniated super7.235 s 00 0.15 phosphate 0. IS 46.50 46,80 1337 Triple superphosphate 4 0 50 46 90 0 35 1338 Triple superphosphate 0 . 0 5 4 4 , SO 45.10 44.60 4 5 20 0.45 S-44 Triple superphosphate 5 . 0 4 41.50 41 50 41 50 0 03 41.50 41.40 41 60 a B y official method without supplements. b B y citrated ammonium nitrate, prior washing. c Constant charge of 1 gram for superphosphate a n d O..j-gram for triple superphosphates. d Constant charge of 1 gram for superphosphate a n d 0.5-gram for triple iupeiphocpharea plus a constant 10 per cent supplement of rock phosphate.
IUDUST t’lI.\L AUD ENGIKEERISG CHEMISTRY
150
But when present as a supplement in ammoniated superphosphates, the solubility of raw rock in solvent is decreased by the protective effect of concomitant occurrences of the engendered basic phosphates. Substantial residues of undecomposed rock phosphate, such as the 5 per cent citrateinsoluble PiOs content of the triple superphosphate, 5-44, 1ikewi.e decrease the action of solvent upon added raw rock.
TABLEXIV. AVAILABLEP20sCOSTESTO F ROKE MEALS \Determined by digestions n-ith neutral ammonium citrate and with citrated ammonium nitrate) Citrate3 Diiiererice .i.ytn,~h y Citrnted Neutral niuni Ammonium Total Ammonium (‘riden Type of Boneb P~OS CitrateC Sitiated N:trate
70
%
%
VOL. 10,NO. 3
%
Raw 21 00 13 08 18 5 5 t i 47 sa Steamed 23 40 14 68 18.15 t3.47 JI Steamed 34.00 19.50 23.65 74.65 a Xumerak are those of Droducers. 5 Constant charges of 1 Oram. C Official 1.09 sp. g r . solution: 1-hour digestion period a t 6’; C., 9-om. filter included. d .if ammonium nitrate-0.05 .’$ cltrate solution: p H 4 . 2 ; preliminary leiching a n d 30-minute boiling digestion period.
SI
TABLEX I T .
Ivailable P205by Citrate and Solvent Digestions BOSE MEAL. Determination of citrate-soluble PPOs in bone meal is not prescribed specifically in the methods of A. 0. A. C. This material can be considered, however, as
“nonacidulated samples other than basic slag” (1, p. 11). Table XIV shows a mean solubility of 60 per cent by citrate Pi05 I N CBLCIKED (DEFLUORINATED) ROCKPHOSPHATES digestions against 77 per cent by the proposed procedure. .ivailable P~05CALCINED (DEFLUORINATED) ROCKPHOSPHATE. Analysis Insoluble PtOa Difference of this relatively new product is not prescribed specifically By citrated by citrated By am- By citrated By ammonium ammonium ammonium monium ammonium by the A. 0. A. C. methods. From collaborative studies, citrate nitrate nitrate citrate nitrate digestionb digestionc digestion digestion digestion Ross and Jacob (31) concluded, however, that the ammonium % 70 % % % citrate digestion, with included filter, is applicable for the 27.16 29 2 +2.24 6.26 4.02 evaluation of calcined phosphates. 29.2 29.6 Table X V shows that the proposed procedure gave PzOs 22.21 25.8 +3.69 11.76 8.07 values of from 1.68 to 3.69 per cent beyond those found by 26.0 citrate digestions. The mean total PZOScontent of the six 29.46 32 0 +2.34 4.75 2.41 31.6 calcined phosphates was 35.02, of which 83.8 per cent was 31.26 33 0 $1.84 3.91 2.07 available by the citrate digestion and 90.2 per cent by boiling 33 2 32.52 34.4 t1.65 2.57 0.89 digestion with solvent.
.4VAILdBLE 7 -
Codea
Total P9Osb
1322
34.42
1325
33.97
132i
34.21
1374
35,17
%
1375
35.09
34.0 35.2 +1.68 3.73 2.05 35.2 h‘umbers a r e those of Bureau of Chemistry a n d Soils. b Values f o r total a n d citrate-soluble PgOs n e r e furnished b y H.D. Jacob, Bureau of Chemistry a n d Soils. C Using prescribed 0.5-gram charge. d Charges of 0.25 a n d 0.5 gram gave respective values of 34.4 and 34.4 per cent. 1478
37.25
33.52d
with solvent. The supplements, therefore, impart a greater Pa05 value than the one indicated by a separate analysis of a I-gram charge of raw rock. To a more marked extent the same is true for citrate digestions. I n six of the ten comparisons, however, the resultant increases were less than the analytical tolerance of 0.2 per cent. The mean increase in P?os availability induced by the raw rock additions, representative of approximately 200 pounds per ton, was 0.19 per cent for the ten fertilizers. TABLE XVI.
AVAILABLE
Pzob COXTENT
FUSEDPHOSPHATE ROCKS;INFLUENCE OF PARTICLE SIZE. Particle size exerted a marked effect upon the solubility of the calcined materials of Table XVI. Decrease in particle size gave greater solubility by both citrate and solvent. There was a much greater spread, however, betm-een the values found by citrate digestions for coarsest and finest separates. The solvent gave the higher PiOs value in each of the 15 comparisons. Reasonable concordance was shown, however, by citrate and solvent digestions of the finer separates. The mean difference between citrate values for 50-mesh and 325mesh separates was 10.92 per cent, as against 5.5 per cent for digestion with solvent. The mean of values obtained by solvent for the rocks in the 22 to 30 per cent range was 2.9 per cent more than the mean value by citrate digestions. Most of the respective differences in PZOSvalues by the two solvents are less than the variations induced by a mere
OF
FIXEDTENNESSEE ROCKPHOSPHATES PIOSDissolved b y
c
Type Fused brown No. 256, quenched
Analytical Charge Mesh Gram 0.5
Citrate digestion0
%
Citrat,ed ammonium nitrate digestionb
%
%
50-100 100-200 < 200
19.72(20.60) 23.41(28.10) 27.79(28.85) 29.62
23.2 26.5 29.3 30.0
+3.48 1 3 09 1-1.51 +0.38
50-100 100-200 < 200
