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To test the consistency of the entire method, two mixtures were prepared from analyzed cracked gasolines, and the compositions of the mixtures were determined by experiment and found by calculation. A comparison of the results is given in Table V.
Paraffins
Per Cent Saphthenes .Iromatics
can be used with other procedures, do much to recommend it as a routine method, especially for comparative purposes. As such, it should prove valuable until more exact methods are available.
Literature Cited
TABLE v. COhfPARATIVE RESULTS aaiiiiilc
VOL. 10, NO. 3
Olefins
In no case do the differences exceed 5 per cent; in most cases they are much lower. It is believed that this value represents also the limit of precision of the method.
Conclusion
It is clear that the analytical method herein outlined is not rigorously accurate. Nevertheless, in the absence of a simple exact method, the rapidity and simplicity of the operations involved in the procedure, the fact that the errors for different samples tend in the same direction, and the adaptability of the method to the analysis of smaller amounts than
(1) Anon., Petroleum Z . , 32 (23,1 and (9), 1 (1936). (2) Carriere and Lautie, Chiniie & industrie, Spec. KO. 3. 337-9 (1931). (3) Furasher, Morrell, and Levine, ISD. ESG. CHEZI.,Anal. Ed., 2, 18 (1930). (4) Francis, ISD. ESG. CHERI., 18, 821 (1926). (5) Kester and Pohle, Ibid., Anal. Ed., 3, 294 (1931). ( 6 ) Kurtz and Headington, I b i d , 9, 21 ,1937).
( 7 ) LIanning and Shepherd, Dept. of Sei. Ind. Research (Brit.), Fuel Research Tech. Paper 28 (1930). (81 hlarder et al.. Oel. Koide. Erdoel. Teer 11. 1. 41. 182 222 119351. (9) Marshall, IBD. EBG.C H E M , 20, 1379 (1928). (10) Minter, Nutl. Petroleum /Yews, 25, KO.8, 25, 27 (1933). (11) hlulliken and Wakeman, ISD. ENG.CHEW,Anal. Ed., 7, 59 (1935). (12) (13) (14) (15)
Ormondy and Craven, J . Inst. Petroleum Tech., 13, 311 (1927). Podbielniak, IND. EKG.Cmnf., Anal. Ed., 3, 177 (1931). Schildwachter and Martin, BTennstofl-Chem., 16, 301 (1935). Wugter, J. Inst. Petroleum Tech., 21, 36 (1935).
RECEIVEDJanuary 6, 1938. Presented before t h e Division of Petroleum Chemistry a t the 94th Meeting of the American Chemical Society, Rochester, N. Y.,September 6 t o 10, 1937.
Chemical and X-Ray Diffraction Studies of Calcium Phosphates HAROLD C. HODGE, MARIAN L. LEFEVRE, AND WILLIAM F. BALE University of Rochester School of Medicine and Dentistry, Rochester, N. Y.
The constancy and punty of composition
of various commercial primary, secondary, and tertiary calcium phosphates are estimated. Secondary calcium phosphates are of least variability; primary and tertiary of marked variability. Evidence of three crystalline forms each of unignited primary and secondary cal-
D
ESPITE the profusion of papers on the chemistry of the
calcium phosphates, there are many fundamental points still obscure. As Drakunov (11) points out, t h e study of these important substances involves great experimental difficulties. Larson (20)reported the preparation and properties of primary, secondary, and tertiary calcium phosphates "in pure crystalline form." However, a number of recent investigations offer contradictory evidence especially on the nature of the tertiary calcium phosphates. The work reported herewith proposes to examine the commercially prepared primary, secondary, and tertiary calcium phosphates chemically and by x-ray diffraction studies in order (a) to estimate the constancy and purity of composition of the commercial products, and (b) to interpret the analyses in the light of recent findings on the nature of these compounds. I n the interpretations, no attempt will be made to review exhaustively even the recent literature, but only such experiments or hypotheses as seem pertinent will be included. The commercially prepared calcium phosphates used in this investigation have been obtained from eight different
cium phosphates is found from x-ray studies, The commercial tertiary calcium phosphates are probably hydroxylapatite with more or less adsorbed phosphate ions resulting in empirical formulas approaching the theoretical value for Ca3Pz08. Secondary calcium phosphate may be admixed. companies-five in this country, two in Germany, and one in England. Two samples each (of different lot numbers) of the tertiary phosphates and one each of the secondary and primary phosphates were used.
Analytical Procedure In each case, samples were taken from the top and bottom of the bottle; inssmuch as no difference was found, these two values served as duplicate determinations on each product. The samples were dried at 105' C., cooled in a desiccator, and analyzed for calcium and phosphorus according to the gravimetric methods (accuracy: Ca, 0.3 per cent; P, 1.0 per cent) of Washburn and Shear (28). For ignition, a third sample was similarly dried, cooled, weighed into a platinum crucible, heated for 1 hour at 900" C . , cooled, and weighed, and samples were taken for analy-
sis as before.
X-Ray Diffraction Procedure For x-ray powder diffraction photographs, an apparatus was used similar in design to the General Electric diffractive apparatus Type YWC, Form D, described by Davey (8). In order to
obtain intensity measurements of diffraction maxima, a series of standard densities was obtained by a graduated, accurately
MARCH 15, 1938 5. 4, 3. 2.5 I
ANALYTICAL EDITIOS 2 I
INTEPPLANAE DISTANCE 17 . 1.5 13 12 1.1 1.a950.9o.m I
1
I
l
l
1
/
1
1
157
primary calcium phosphates. The theoretical values for primary calcium phosphate monohydrate and calcium metaphosphate are included for comparison. The calcium values range from 13.5 to 16.6 and phosphorus from 24.2 t,o 29.9 per cent, the theoretical values for Ca(HzI’Oa)z.H20being calcium 15.9 and phosphorus 24.6. Sample 12, having a high calcium content and a high calcium-phosphorus per cent ratio, together with a l o x loss on ignition, may be a mixture containing about 6 per cent of secondary phosphate. All the other samples have calcium percentages less than and phosphorus percentages greater than the theoretical value. The calcium-phosphorus per cent, ratios of two samples vary less than 5 per cent from the theoretical; of two clthers the variation exceeds 15 per cent. TABLE I.
COXSTAKCS O F CO.\IPOSITI(JK .4ND
EFFECT O F IGNITION
!I hour a t Y O O O C , o n \,arious samples (,f co~nnierci:il Dririiary calcium pliospliates’s Sample Before Ignition After Ignition Yo, Ca P Ca:P Loss Ca P Ca:P Source
7 A
B I)
E F
11 12
14 6 13 5 15 3
15
1R 6 15 4
14
I6 G 17 Theoretical ior CaH+OtH20 Theoretical for CaPzOa
BPAGG ANGLE 8
FIGUFCE 1. X-RAYDIFFRACTION PATTERNS The “ignited primary” pattern is probably t h a t oi calcium metaphosphate. Only this pattern was found after ignition. Before ignition three types of patterns were found a h i c h indicate the existence of three crystalline modifications of primary calcium phosphate.
timed series of exposures from a constant x-ray source. The film used for the standard was cut from the same sheet on which the diffraction maxima were separately recorded. The standard and the diffraction films were developed together by hand agitation in fresh x-ray developer. Density measurements were made of the diffraction lines, the background adjacent to each line, and the exposure scale. The densitometer utilized an optical slit, a vacuum-type photoelectric cell, and an FP54 electrometer tube with an appropriate electrical circuit. From these data, the intensities of x-ray diffraction lines and of the adjacent background were calculated in terms of the t,ime required for a standard x-ray beam to produce an equal density. Each chart of an x-ray diffraction diagram has as ordinate the relative intensities of the diffraction maxima over the adjoining background with the intensity of the strongest line set at 100. The abscissas are given both in units of the Bragg angles, 8, and the interplanar distance, d. With hydroxylapatite, powder diffraction measurements were made utilizing both the photographic means and a Bragg-type ionization spectrometer. The resulting relative intensity measurements are similar, indicating that the photographic method gives approximately correct results. Since no correction is made of different amounts of absorption undergone by rays refracted at different angles, only the relative intensities of lines in the same portion of the spectrum may be legitimately compared.
Primary Calcium Phosphates I n Table I are given the calcium and phosphorus percentages, the percentage weight loss on ignition, and the calciumphosphorus per cent ratio before and after ignition of the
0
7 24 24
4
9
%
%
0.587
0.545
% 18 9
%
%
28.3 30 6 30 ‘3 30.3 31 3 30.6
0.668 0.575
Y4:8
17.6
2b.4 22.3 24.7
21.0
13.8
24.9 24.8
0 61.5 0 688 0 616 0.553
15 9
24 6
0.646
21.4
.,
..
...
..
. .
..
20 2
31.3
0.646
i
24 8 24 2
19 4
19.6 17.3
0.628 0.693 0.631
0.566
On ignition, the primary phosphates show percentage losses of 20.4 to 24.8 with an average of 23.1. The theoretical percentage loss for the conversion of the primary monohydrate to calcium metaphosphate is 21.4. The ignited samples were dissolved only after hours of acid hydrolysis, being t h e r e fore probably principally calcium metaphosphate. The calcium-phosphorus per cent ratios all show evidence of slight loss of PIOaon ignition, a loss possibly explained through the equation of Bassett (2): 2CaH4P20e.H20 CanP20r -f
+ P206 t + 6H20t
In Figure 1 are shown the charts of the x-ray diffraction patterns of primary phosphates before and after ignition. Only one pattern was obtained after ignition from any primary phosphate, regardless of its pattern type before ignition; this “ignited primary” pattern is probably that of calcium metaphosphate. If the ignition product is a mixture of polymers, approximately the same mixture must have occurred in each sample. Hinds (14) stated that calcium metaphosphate is the product of heating primary calcium phosphate, but Larson (20)offers stoichiometric evidence that the product after 170 hours a t the temperature of the Meker burner is calcium pyrophosphate. Since the analytical values for the ignited product correspond closely to the theoretical values for CaPzOe and since the “ignited primary” diffraction pattern for samples ignited for 1 hour a t 900’ C. is different from the “ignited secondary” pattern, there seems to be reason under these conditions for agreement with Hind’s conclusion. The three types of primary phosphate patterns before ignition were obtained from samples taken directly from the bottles without drying. I n an effort to connect the types of patterns with the water content, samples were heated for periods up to 1224 hours a t 105” C. with loss determinations and x-ray diffraction patterns made at 14, 38, 110, 158, 422, and 1224 hours. K i t h the exception of sample E, there was 7.69 to 12.2 per cent loss during the first 14 hours, and less than 2.88 per cent during the next 24 hours, with additional losses ranging from 1.55 to 5.10 per cent up to 1224 hours. Sample E, which probably contained secondary phosphate, showed only 0.69 per cent loss after the first 14 hours and
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5.90 per cent after 38 hours with an additional loss of 2.63 per cent up to 1224 hours. Although all the samples gave Type I patterns at the start of the drying and most of them gave Type I1 and Type I11 after increasing lengths of time, there was no apparent regularity nor dependence of pattern type on the water content. Sample E, for example, gave only Type I1 pattern u p t o 1224 hours; sample B gave Type 111 after 422 hours and Type I1 after 1224 hours. The three types of patterns indicate three crystallographic entities. Only one such pattern has been previously reported (2O),a pattern corresponding to Type 11. It has been accepted for many years (4) that there are two forms of primary calcium phosphate, the monohydrate and the anhydrous. It would seem that either one may exist in more than one crystalline modification or that there is another hydrate. This third form is unidentified. S e c o n d a r y Calcium Phosphates I n Table 11 are given the calcium and phosphorus percentages, the calcium-phosphorus per cent ratios before and after ignition, and the percentage weight loss on ignition of the dried secondary calcium phosphates. The theoretical values for anhydrous secondary ptosphate and for calcium pyrophosphate are included for comparison. The calcium values range from 28.5 to 31.4; phosphorus from 21.3 to 22.7 per cent. The theoretical values for 9 4, 3. 25
2.
INTEFPLANAR DISTANCE 1.7 15. 13 12 1.1 I. 0.95 0.9 a85 I
I G N I T E D SECONOALY
loo>
T Y P E IU,SECONDAFY
I
I
I IIiI I I T Y P E II,SECONDAPY
CaHPO, are calcium, 29.4, and phosphorus, 22.7 per cent; most of the samples correspond closely to the theoretical values. Sample C has a high calcium, low phosphorus content, and a low loss on ignition; a mixture of approximately 30 per cent Ca3P20Yand 70 per cent CaHP04 would give the values found. TABLE 11. CONSTANCY OF COYPOBITIOK AXD EFFECT OF IGXITION (1 hour a t 900’ C. o n various samples of commercial dicalcium phosphates) Sample Before Ignition After Ignition KO, Ca P Ca:P LOSS Ca P Ca:P Source
B
22 23 D 24 E 25 F 26 G 27 Theoretical for CaHP01 Theoretical for CanPzOi C
%
%
%
%
%
%
%
29.6 31.4 28.9 28.5 29.3 29.3
22.4 21.3 22.7 22.7 22.7 22.5
1.32 1.48 1.28 1.26 1.29 1.30
7.25 6.30 8.13 8.03 7.62 8.42
32.1 33.7 31.9 31.5 31.8 32.1
23.0 22.0 22.1 24.0 23.7 23.1
1.39 1.53 1.44 1.31 1.34 1.39
29 4
22.8
1.29
6 62
..
..
..
..
31 5
24.4
.. 1.29
The percentage weight losses on ignition range from 6.30 to 8.42 with an airerage of 7.63. The theoretical loss for the conversion 2CaHP04 to Ca2P207and HzO is 6.62. Although the calcium-phosphorus per cent ratios after ignition are uniformly slightly higher than those before ignition, there is no obvious explanation for the loss of P20a. Since the analytical values for the ignition product correspond closely to the theoretical values for CazP207,it is probably principally calcium pyrophosphate. Hinds (14) stated that calcium metaphosphate is the final product of heating secondary calcium phosphates, a conclusion probably incorrect for products obtained by igniting for 1 hour a t 900” C. The difference between the “ignited primary” and “ignited secondary’’ diffraction patterns confirms the differences postulated on the basis of analytical results. I n Figure 2 are given the charts of the x-ray diffraction patterns of the secondary calcium phosphates. The “ignited secondary” pattern is probably that of calcium pyrophosphate. Only one pattern was obtained after ignition, regardless of the pattern type before ignition. Several p r e vious reports have included patterns of secondary calcium phosphate. Of the three types of patterns found before ignition (Figure 2), Type 111 apparently corresponds to the pattern of Larson (20) and of Schleede et al. (24). Type I1 shows some similarity to the pattern obtained by Schleede on a sample hydrolyzed for 80 hours in warm water. Type I is somewhat like the pattern given by Roseberry e t a1 (23). Of these, only Larson’s sample was identified crystallographically; he gave the formula as the “tetrahydrate,” Ca,Ha (P0&.4H20, a formula which, lacking further evidence as t o the molecular configuration, seems unnecessarily complicated. Only two secondary calcium phosphates have been accepted as unquestioned (4), the dihydrate and the anhydrous. Two others have been described, 3CaHPO4.2H20 (17, 22) and 4CaHPOd.HpO (IO). The three types of patterns found indicate the existence of three crystallographic entities. The findings of Drakunov (11) and Davies (9),that there is no definite temperature a t which the dihydrate loses its water, may be some evidence that a lower hydrate is present whose formation is a step in the conversion of the dihydrate to the anhydrous. T e r t i a r y Calcium Phosphates
I
5
IO
I5 BPAGGANGLE 9
20
23
FIGURE 2. X-RAYDIFFRACTION PATTERNS The “ignited secondary” pattern is robably t h a t of calcium pyrophosphate. Only one pattern is founzafter ignition. T h e three types of patterns before ignition indicate t h e existence of three crystallographic entities.
I n Table I11 are given the calcium and phosphorus percentages, the calcium-phosphorus per cent ratios before and after ignition, and the percentage weight loss on ignition of the tertiary calcium phosphates. The theoretical values for CasPzOs~HrO,hydroxylapatite, and Ca3P20Bare given for comparison. The calcium percentages found before ignition
-4XALYTICAL EDITION
MARCH 15. 1938
range from 33.1 to 38.0, the phosphorus from 17.9 to 20.2; the theoretical values for Ca3(P04)2.H20are calcium, 36.6, phosphorus, 18.9 per cent. Comparing the calcium-phosphorus per cent ratios to the theoretical. four samples vary by 0 to 2.5 per cent, five by about 5 per cent, four by about 8 per cent, and two by about 13 per cent (compare 2, 7, 12). The composition of Sample B, a and b, may be approximated by a mixture of 60 per cent Ca3(P04)2and 40 per cent CaHPO,; actually, the x-ray diffraction patterns of these two samples showed lines of both tertiary and secondary calcium phosphates. Such an x-ray finding has been previously reported (28). This mixture has almost exactly the calciumphosphorus per cent ratio given by Bassett (3) for the intersection of the equilibrium curves of secondary and tertiary phosphates in the system CaO-PzOs-HcO. TABLE111. COSSTANCY OF COMPOSITION AKD EFFECT OF IGNITION (1 hour a t 900‘
C. on various commercial samples of tertiary calciuni phosphate) -Before Ignition--After IgnitionCa P Ca:P Loss Ca P Ca:P
Sample Source Lot KO. a b a b a b a b a
b n
b
a b a
b
31 311 32 322 33 333 34 344 33 355 36 366 37 377 38 388
Theoret ical for CaaP*l0vHz@ Theoret ical for hydro xylapatite Theoretical for CaaPIOs
%
%
%
%
36 0 37.9 33 4 33 1 36 6 37 1 36 8 37 4 37 0 37 4 36 9 38 0
18.8 18.0
1.92 2 10 1.6i 1.69 1 99 2.03 2.02 2.04 2 05 2 00 1.94 1.97
5.27 4.72 7.30 7.29 4.98 6.67 4.88 6.10 4.78 4.71 4.73 1 05 24.3 6.94 5 58
20.1
20 2 18.3 18.3 18.2
18.3
37 2 35 4 3.5 5
18.0 17 9 19 0 19.3 0 0 18 2 19.7 19.6
36.6
18.9
1.94
5.49
39.8
18.5
2.15
..
..
..
51 5
2 :04 1.80 1.81
5.21
%
%
38.1 39 3 36.0 35.8 38.8 39 0 38.8 38.9 38.9 38.9 38.8 38.4
19.9 18.7 20.7 21.5 19.3 19.0 19.2 18.9 18.9 18.8 20.0 19.7
2 0.5 2 01
38.9 37.7 37.6
18.9 20.4 20 6
2 00 1 83 I 82
.. .. 38.7
% 1 92 2 IC 1
io
1 66 2 00 2 06 2 0: 2 07 I Y4 1 95
, .
.. 20.0
+ 2CaHP04
4Ca,P20s
TABLE Iv. COMMERCIAL TRICALCIUM PHOSPHATES (Correlation of C a : P per cent ratios and x-ray diffraction pattern- after ignition) Sample Ca:P Remarks % 311 355 344 377
2.10 2.07 2 06 2.06
Predominantly hydroxylapatite pattern after ignition
35 333 34 ..
2.05 2.05
Predominantly @-CaaP2@spattern after ignition
2
ni
33
2.00
366
1.95
36 31 388 32 322
1.94 1.92 1.82 1.70 1 66
Only B-CasPlOs pattern after ignition
although the particle size is extremely minute the precipitated tertiary phosphate is crystalline. From phase-rule and other studies (2, 6, 6, 10, 13, 16, 19, 20, 63-27, 29) two principles may be laid down: If the precipitated phosphate has a composition approximating Ca3P208, the ignited product gives the pattern called pCa3P208; and if the composition approximates .hydroxylapatite, the lattice is heat-stable a t 900” C. This interpretation is shown to be valid by the comparison of the diffraction patterns of the ignited commercial tertiary phosphates and their respective calcium-phosphorus per cent ratios (Table IV). Four samples whose calcium-phosphorus per cent ratios average 2.07 give predominantly hydroxylapatite patterns after ignition; five samples whose calcium-phosphorus per cent ratios average 2.01 show small amounts of hydroxylapatite but predominant amounts of P-CaaPzOs; five samples whose calcium-phosphorus per cent ratios average 1.81 show only the P-CasPzOx pattern after ignition.
1 44
The tertiary phosphates show weight losses on ignition ranging from 1.15 to 7.30 per cent with an average of 5.34 per cent, (This does not include the value of 24.3 per cent on Sample G, a, which was found to be calcium hydroxide.) The theoretical value for the loss of one molecule of mater from Ca3(P04)2.H20 is 5.49 per cent. Calculating calcium and phosphorus percentages for the ignited product shows that no loss of either occurs, a fact borne out by the experimentally found identity of calcium-phosphorus per cent ratios before and after ignition. The charts of the x-ray diffraction patterns of the tertiary calcium phosphates before and after ignition are shown in Figure 3. The patterns of the various samples before ignition were either that of an apatitelike substance or of a superimposing of this pattern on that of CaHPO4. Only one new pattern is found after ignition; this pattern corresponds to that called the P-Ca3P203pattern (16). The various samples after ignition gave either the P-Ca3P2O3,the original hydroxylapatite pattern, or the two superimposed. After ignition of the samples containing CaHP04 there were no lines evident of the “ignited secondary” pattern, a fact which may be tentatively attributed to a reaction between hydroxylapatite and secondary calcium phosphate a t high temperatures as follows : Calo(P04),(OH)2
159
+ 2H20 f
Thus, only the pattern of /3-Ca3P20a was obtained from Sample B, a and b, after ignition (compare Tables 111 and IV). On the basis ,of the diffraction patterns and the cheniical data. it is possible to give a fairly coherent description of the tertiary phosphates. It should be emphasized that
5 4
’
3 25
INTEPPLANAP DISTANCE 2 17 15 13 1, I1
II
IGNITED TERTIARY
I
5
109503085
HY DEOXYL- APATITE
IO
15
20
25
8 FIGURE 3. X-RAYDIFFRACTION PATTERNS B P A G G ANGLE
The “ignited tertiary’’ pattern is t h a t of B-CaaPpOs (f.7). After ignition the commercial tertiary calcium phosphates gave either this pattern only or this pattern superimposed o n the hydroxylapatite pattern. The hydroxylapatite pattern was obtained from all the tertiary phosphates before ignition. I n certain samples the pattern of secondary calrium phosphate was also present.
I n an attempt to obtain some light on the mechanism of the precipitation and the nature of the precipitated “tertiary” calcium phosphates, the mode of precipitation was studied in relation to the composition of the precipitate. I n a paper which must be considered as preliminary, this approach was offered by Tromel and ILIoller (27). From the method for
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TABLE V. EFFECTOF MODEOF PRECIPITATION AND ANOUNTS OF Ca Sample
Before Ignition Ca P Ca:P
%
%
%
Loss
900OC.
%
After Ignition Ca P Ca:P
%
%
LYD
Sample
%
POa ON CHEMICAL ComosITIow Before Ignition Ca P Ca:P
%
%
%
OF
Loas 900° C.
Ca
%
%
PRECIPITATES After Ignition P Ca:P
Theoretical Amounts of C a and Po4 Used t o Prepare POI Added to C a H1 38.4 18.3 2.10 39.7 H2 38.4 18.2 2.11 2141 39.8 H3 38.4 18.2 2.11 2.75 39.8 H4 38.0 18.4 2.07 3.10 39.5 H5 38.2 18.2 2.10 2.96 39.6 H6 38.0 18.3 2.08 3.10 39.6 D. Theoretical Amounts of C a and PO4 Used t o Prepare C a Added t o PO4 HR1 36.8 18.7 1.97 3.78 HR2 36.9 18.7 1.97 3.35 HR3 37.0 18.7 1.98 3.50 HR4 37.1 18.7 1.98 3.68 HR5 37.1 18.6 1.99 3.46 HR6 37.4 18.7 2.00 ..
%
%
Theoretical Amounts of C a and PO; Used to Prepare CmPzOs, C a Added t o PO4 18.7 1.92 3.46 37.8 19.7 1.92 35.9 T1 18.6 1.94 3.26 38.0 19.6 1.94 36.1 T2 18.7 1.93 3.36 37 7 19.5 1.93 36.1 T3 18.6 1.92 3.39 37.5 19.4 1.93 35.8 T4 18.6 1.97 3.09 37.6 19.4 1.94 36.7 T5 B. Thecxetical A,mounts of C a and POI Used, to Prepare CaaPdh, PO4 o C .a Added t.~ 3.52 39.9 18.8 2 . 1 2 18.1 2.11 TR1 38.2 4.48 39.3 19.2 2.05 18.4 2.03 37.4 TR2 2.95 39.4 17.6 2.24 17.9 2.14 38.3 TR3 18.0 2.11 3.50 39.8 18.7 2.13 38.0 TR4 3.62 39.3 18.9 2.08 18 0 2.12 38.1 TR5 2.87 39.6 18 7 2.12 18.1 2.12 38.4 TR6
C.
preparing "pure, crystalline" tertiary calcium phosphate described by Larson (20), conditions were established for precipitation. Four sets of preparations were obtained by (a) following Larson's procedure in which calcium chloride solution was added dropwise to Ka2HP04solution in calculated amounts to give Caa(PO&, (b) adding the phosphate to the calcium solution, and (c) and ( d ) repeating (a) and (b) using amounts of calcium and phosphate to give hydroxylapatite instead of tricalcium phosphate. The analytical data are given in Table V for the precipitates before and after ignition. It is evident from part A that precipitates may be prepared having the theoretical calcium-phosphorus per cent ratio of tricalcium phosphate with far less variation than is found in the commercial samples. Furthermore, the composition of the precipitated phosphates is seen to depend upon the mode of precipitation rather than on the amount of reactants (in the ranges used). When the diffraction data are correlated with the analytical data (Table VI), it seems evident that the stable precipitated phase, under the conditions described, has the hydroxylapatite lattice. I n those precipitates having a calciumphosphorus per cent ratio less than the theoretical value for hydroxylapatite, apparently the excess phosphate may, on ignition, react with the hydroxylapatite to produce CaaPiOa in amounts limited by the amount of excess phosphate (18).
moved by heating for long periods a t 300', then 500' and then even a t 7.50' C. (20). (3) On ignition of heat-stable hydroxylapatite precipitates, there is always a marked sharpening of the diffraction lines, indicating the increase of crystal size due to the addition of the less perfectly orientated atoms to the apatite lattice (21). During precipitation, if the solution is rich in phosphate (Table VI, 1 and 4), many multipolar phosphate ions are drawn around the tiny crystals, attach themselves weakly with only a partial loss of their attractive forces for the water shell, and constitute, together with the crystal, coacervated particles. This precipitate will consequently contain an excess of phosphate, the calcium-phosphorus per cent ratio will be less than the theoretical for hydroxylapatite, and, upon ignition, there may be a reaction between the excess phosphate and the crystal of hydroxylapatite producing the @-CarP20slattice in amounts limited only by the amount of excess phosphate. Thus, depending on the calcium-phosphorus per cent ratio of the ignited precipitate, the pattern may be hydroxylapatite, intermixtures of hydroxylapatite and /3-Ca3P208,or &CaaP20s. This hypothetical mechanism is similar in many respects to that offered by Tromel and Moller (27) on the basis of their preliminary work.
A.
AND AMOUNTS TABLE VI. EFFECTOF MODEOF PRECIPITATIOK OF Ca AKD PO,
(On the chemical composition and crystal lattice of precipltates before and after ignition) Average Theoretical C a P% Mode of Amounts of Ratio X-Ray Diffraction Pattern After Precipi- C a and PO4 Before After Before tation t o Give lgnition igmtion igmtion ignition C a + POI CaaPiOs 1 93 1 93 Hydroxylapatite 8-Ca3PzOa PO,-+Ca CaaPtOs 2 120 2 12 Hydroxylapatite Hydroxylanatite PO4 -+ C a Hydroxyl- 2 . 1 0 2.10 Hydroxylapatite H;droxylapatite apatite 1 . 9 8 Hydroxylapatite Predominantly 8-CasPzOs C a 4 POI Hydroxyl- 1.98 apatite a One precipitate having a C a : P % ratio of 2.03 is not included.
A tentative mechanism for these precipitations may be derived if the precipitates are considered as coacervates (16). The phosphate ions being multipolar do not rapidly lose their water shell and assume, with the calcium and hydroxyl ions, the complicated space orientation of the apatite unit celI. Evidence to this effect may be found (1) in the extremely minute crystals always obtained cm. in length, approximately, 1) and ( 2 ) from the high water content of the precipitates-e. g., one precipitate which weighed 2 grams contained 0.2 gram of dry (100' C.) phosphate or approximately 1000 per cent of water. This water is partly lost a t 100" C. but some is so tightly bound that successive amounts are re-
Hydroxylapatite, 18.9 18.8 18.7
19.0
2.10 2.12 2.13 2.08 2.11
18.8 18.9 2.10 Hydroxylapatite,
Summary Commercial primary and tertiary calcium phosphates vary considerably from the theoretical composition. Secondary calcium phosphates are of greater constancy of composition and vary little from the theoretical values. Primary and secondary calcium phosphates each exist in three crystallographic modifications. I n each case, one form may be a hydrate, another the anhydrous, while the third is unidentified. Regardless of the crystallographic form of the primary calcium phosphate, there is only one crystal form after ignition, probably calcium metaphosphate. Regardless of the crystallographic form of the secondary calcium phosphate before ignition, there is only one crystal form after ignition, probably calcium pyrophosphate. Commercial tertiary calcium phosphates are probably hydroxylapatite with more or less adsorbed phosphate ions to give empirical formulas approaching the theoretical. On ignition a t 900' C. for 1hour, a reaction between the hydroxylapatite and the adsorbed phosphate ions takes place which produces /3-Ca8P208,the amount of change depending on the amount of adsorbed phosphate ions.
Literature Cited (1) Bale, Hodge, and Warren, A m . J . Roenfgenol. Radium Therapy, 32, 369 (1934). ( 2 ) Bassett, J . Chem. Soc., 111, 620 (1917).( 3 ) Bassett, 2. anorg. allgem. Chem., 59, 1 (1908). (4) Bassett, 2. Mineral., 53, 3 (1907).
MARCH 15, 1938 (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)
(15) (16) (17)
ANALYTICAL EDITION
Bredig, Franck, and Fiildner, Z. Elektrochem., 38, 158 (1932). Britton, J . Chem. Soc., 130, 614 (1927). Cameron and Hurst. J . Am. Chem. Soc., 26, 885 (1904). Davey, Gen. Elec. Rev., 29, 127 (1926). Davies, Chem. News, 64, 287 (1891). Dieckmann and Houdremont, Z . anorg. allgem. Chem., 120, 129 (1922). Drakunov, Udobrenie i Urozhai, 2, 409 (1930). Glass and Jones, Quart. J. Phurm. Pharmacol., 5, 442 (1932). Hendricks, Hill, Jacob, and Jefferson, IND. ENQ.CHEM.,23, 1413 (1931). Hinds, quoted from Larson (BO). Holt, La Mer, and Chown, J. Bid. Chem., 64, 509 (1925). de Jong and Kruyt, Kolloid-Z., 50, 39 (1930). Julian, Am. J . Sci. and Arts, series 11, 40, 367 (1865).
(18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29)
161
Klement and Trdmel, 2. physiol. Chem., 213, 263 (1932). Korber and Tramel, 2. Elektrochem., 38, 578 (1932). Laraon, 1x0. ENQ.CHEM., Anal. Ed., 7, 401 (1935). Naray-Szabo, Z. Krist. Jfineral., 75, 387 (1930). Rindell, Compt. rend., 134, 112 (1902). Romberry, Hastings, and Morse, J. Biol. Chem., 90, 395 (1931). Schleede, Schmidt, and Kindt, 2 Elektrochem., 38, 633 (1932). Taylor and Sheard, Proc. Soc. Ezptl. Bid. Med., 26, 257 (1928). Tromel, Phosphorsaure, 2, 116 (1932). Trbmel and Moller, 2. anorg. allgem. Chem., 206, 227 (1932). Washburn and Shear, J . B i d . Chcm., 99, 21 (1932). Wendt and Clark, J. Am. Chem. Soc., 45, 881 (1923).
RECEIVED M a y 13, 1937. Rockefeller Foundation.
The work was supported by a g r a n t from the
Analysis of Caustic Liquors for Traces of Impurities 0. S. DUFFENDACK
AND
R. A. WOLFE, University of Michigan, A n n Arbor, Mich.
T
HE technic for the spectrochemical analysis of caustic liquors for small traces of aluminum, calcium, chromium,
copper, iron, lead, magnesium, mankanese, silicon, and strontium has been worked out a t the Physics Laboratory of the University of Michigan for The Mathieson Alkali Works, Inc., under the auspices of the Department of Engineering Research. It became important in the alkali industry to be able to determine correctly the amounts of certain elements present in caustic liquors, especially the caustic materials supplied to the rayon industry. Some of the elements cannot be determined very precisely by chemical methods in the range of abundance in which they occur in caustic liquors. The problem was undertaken because the development of spectroscopic methods had reached the point where it seemed possible to attain the necessary precision in this manner. I n addition, saving of time is an important item and is enhanced because the spectroscopic analyses for all the elements can be carried out in one operation. The problem was not a simple one. The material to be analyzed was caustic liquor, a solution of sodium hydroxide, .01 009 008 ,007 ,006 ,005 .004
,003
d z N
.\.'
,0002
.0001
/
I
LOG AI
3090 M o 31 58
FIGURE1. TYPICAL WORKIWQ CURVE
which could be controlled as to strength; but, no matter what the concentration of the solution, the ratio of the impurities to the sodium hydroxide was extremely small. Since sodium is ionized and excited very easily, it was a problem to find a type of source in which the impurities would be sufficiently excited in the presence of the overwhelming abundance of sodium to permit accurate measurements on their lines. The source had to possess all the characteristics of constancy and sensitivity required for precise analytical work. The method employed has been previously described (8). It is a method of internal control (8) in which the analysis is made from measurements on the relative intensities of spectral lines of the test elements and of a control element which is present in or is introduced into the specimen in a definite and constant amount. The relative intensity of such s pair of lines is therefore a function of the abundance of the test element, and this function must be determined for each element. By measuring the relative intensities of a selected pair of lines excited in a suitable spectroscopic source for a series of prepared solutions in which the amount of the test element is varied over the range desired, the required function can be discovered. The function is usually expressed as a relationship between the logarithm of the relative intensities of a selected line of the test element and of the control element and the logarithm of the percentage abundance of the test element. The graph of this function is used as the working basis for the determination of that element. Those lines are used ordinarily which give a linear function when plotted as described; a typical working curve is shown in Figure 1. The relative intensities of the spectral lines are measured by well-proved methods of spectral photometry (4). The technic has been developed to such a degree of reliability that repeat measurements on a single plate agree within * 1 per cent and on different plates usually within *3 per cent. The principal problem, therefore, in the development of a technic for spectrochemical analysis lies in the discovery or development of a suitable spectroscopic source of sufficient constancy.
Development of Source After trying several sources suggested by previous experience, the high-voltage alternating current arc (1) w w found the most suitable. This consists of an arc between two electrodes of carbon of the highest purity, upon each of which a drop of the test solution has been dried.
