CHEMISTRY OF WESTERN PINES Ponderosa Pine Stumps as Potential Source of Rosin and Other By-products' ARTHUR B. ASDERSOS IT esterii P i n e Associatinri Resmirch Laboratory. Portlctntl 2: O r e g . T h e determination and analysis of extractibes from p o n derosa pine stumps indicate that this forest waste material m a y be a potential commercial source of resin acids, fatt? acid-, and other extractive by-products. Ponderoan pine stumps which hale seasoned up to fi\e years >ielcl approximately 17.0% acetone-so!uble extracti\es. This extract contains the following components, named i n approximate order of quantity present: (1) resin acids, (2) unfree fatty acids, and (5) bolatile saponifiables, (3) esters, (i) terpenes. Stump remota1 for extractibe recovery and other uses would not only make the cutober and selcctiiel? logged areas more adaptable to adianced forest nianagement and improied reforestation practices, but would libewise be another step in further utilization of w esterii pine forest areas.
I
'
K THE commercial production of extractives from southern pine trees, four different methods are employed m this country. These processes include solvent extraction of pine stump wood, collection of oleoresin from the living tree, recovery of tall oil from the sulfate pulping process, and the destructive distillation industry. All these industries, in the main, are confined to the southeastern states, predicated upon the fact that southern pines, largely longleaf and slash, are the richest source materials for these products and are particularly adaptable t o these processes. The average annual value of these combined pine extractive products gives them a foremost place among southern industries. Some thirty-two years ago Betts (4) and Schorger (9) found that it is possible t o obtain considerable yields of naval stores from living ponderosa pine. I n any case, no consequential conimercial installation for turpentining ponderosa pine has been put in operation, perhaps because it could not compete with the n-ell established southern pine naval stores industry. Perhaps another contributing factor \vas the beginning some thirty years of rosin, turpentine, and pine oil from southern pine stumps which augmented the naval stores supplied by ilie living tree. I t is of interest that the genesis of the stump lvood extraction industry was based largely on the premise, since proved erroneous, t h a t the living tree would soon cease to be a commercial source of rosin and turpentine. The practice of the n.ood rosin processing industries is to allow the stump to remain in the ground t,en years or so, Tyhich permits the bark and relatively anemic sapIvood to slough off and leave the rosins and other extractives in the more concentrated heartwood. The harvested stumps are shipped to the plant, hogged. and extracted with a suit,able volat,ile solvent, usually a petroleum naphtha cut. Solvent, turpentine, intermediate ,terpene cuts. and finally pine oil are fractionally separated, and a residue of crude ~ o o rosin d remains. The crude rosin is composed of approximately 85V0 resin acids, 5% esters, and l0W resenes (6). These seasoned pine stumps are reported to analyze approximately 18% water, 5% terpene oils, 227, rosin, and about 4% of a gasoline-insoluble resin ( 7 ) . I t appears t h a t these percentages have been niaterially reduced in some instances, particularly w11ere younger stumps are being used xhich contain more moisture and 1
T h e first three articles i n this series appeared i n 1944 ( I ) a n d 1946 ( 2 . 3 ) .
!ess resinous material. =Inother contributing factor for layer yields is that some areas are being restumped and these less resinous stumps, which were formerly passed by, are now being processed. This reduction in the quality of southern pine stumps has caused extractive recovery t o be reduced to as little as 240260 pounds of rosin and 70 pounds of volatile per ton of stumps in some regions. Ponderosa pine, in addition to being able to produce gum oleoresin, is relatively rich in extractives as shown in previous investigations ( I , 2 , Sj. The distribution of extractives in ponderosa pine is not urliforni in the trunk of the tree, and the greatest quantity of this eoniponent r-ras found a t the b u t t log nearest the stump ( 2 1 . This suggested that ponderosa pine stumps might contairi sufficient quantities of extractives to warrant their removal and subsequent processing for extraneous components. This would be conducive to better forest practices and management since stump removal n-ould, among other things, make the area mnre adaptable for reforestation by natural propagation or tree farming methods. This investigation is concerned with the quantity and nature of acetone-soluble extractives from ponderosa pine stumps. -icetone mas chosen as the solvent, since i t has good extractive pon-er for the various extraneous components in this conifer. METHOD OF SAMPLING
Since the distribution of extractives is not uniform, a iiietliod of stump sampling had to be devised which would be representative After several attempts the following sampling procedure m-as found satisfactory. Three holes were bored, at ground level, to the pith of the stump with an auger and bit, each hole being about 120" apart. This was repeated a t the middle and top levels of the stump (Figure 1). T h e borings from the nine holes lvere thoroughly mixed and sent in moisture-tight containers to the laboratory for analysis. From five to ten stunips n-ere sampled a t each site. Trained and experienced foresters collected these samples, and after thc site was decided upon, the stumps for sampling were chosen a t random to give as nearly as possible the total percentage of extractives t h a t would be obtained if all the st,umps a t that site were removed and processed. T h e best forest practice would necessitate the removal of all the stumps and not just a portion of them. I n the event that such a procedure mould be prohibitive because of the too l o ~ vover-all extractive yield, it would be relatively simple to select only the richer stumps, whether it amounted to 5070, more or less, of the stumps in any one part,icular area. Whichever procedure would eventually be employed, whether it be total or partial removal, its adoption 11-ould be beneficial to forestry practice in addition to supplying additional revenue from the cutover and selectively logged areas. The western pine stumps are now viasted, and any profitable use to which they could be put would be advantageous from Inany points. It is important to note here that these samples represent the entire stump, including sapwood as well as heartwood, since most stumps Pvhich have seasoned u p to five years are sound throughout. I n the case of southern pine stump extraction, as previously noted, only the richer heartwood is included in the main. This initial report on ponderosa stump extractives deals with st,umpe 1664
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1947
1665
t.hat have seasoned in the ground a maximum of four years, repreaenting 108 stumps taken from thirteen sites and four st>ates-namely, Orcgon, Washingt,on, California, and Arizona. T h e samples viere collected between the latter mont'hs of 1944 and early 1948. EXTRACTION AND ANALYSIS
Upon arrival at the laboratory, the stump borings were ground in a TTiley mill to pass a 2-mm. screen. Four t o six grams of the composite ground sample x e r e weighed in duplicate into alundum extraction thimbles and extracted in all-glass Soxhlet extractors w i t h C.P. acrtone for 8 hours. After extraction, the extracted resitlucs and thimbles were p u t in tared weighing bottles, airdried for several hours, transferred to a 105' C. oven for 16 hours, cooled, arid weighed. T h e loss in v,-eiglit here represented the amount of moisture and extractives present in the sample, uncorrected fur solvent retention. T h e moisture content of the samples was deterniixied by the toluene method ( I O ) since oven procedure would cause t,he value to be high because of the presence of volatile oils in the stump. T h e acet,one solvent retention in ovendried extracted stump wood was also determined, as report,ed previously ( 2 ) and vias found to average 0.57', based on the oven-dry weight of the estracted wood residue. The quantitative analyses reported here have been corrected for solvent retention. T h e cstract from all the samples from each site v a s combined arid an:tlyzed for water and ether insolubles, water solubles, resin acids, i i et: fatty acids, volatiles, esters, and unsaponifiables, according t o tlie procedure adopted for the analysis of acetonesoluble est 1,:tctires from various parts of the ponderosa pine tree (b). T h e amount of each of these components is reported in per cent)based on w i g h t of extract and in per cent based on the green weight of the stump (Table 111). QUANTITY OF EXTRACTIVES
Table I suiiiniarizes the amount of acetone-soluble extractives found in ponderosa pine stamp sapwood and in heartwood. Eleven stumps which had seasoned for 2 months t o 5 years in the ground were sampled separately for sapn-ood and for heartwood to rktermine the amount of extractives which each of these parts of the stuiiip would yigld. The average of the heartwood sections yielded 26.9co extract, based on the moisture-free stumps, Khile the sapn'ootl gave 9.1% extract, or approximately one third as much as t h o former. Thus i t is apparent t h a t if only the richer heartwood nere used in extraction, a material increase in extractive yicltl would be realized over that obtained from the whole stump. Table I1 li'sts the yields of extract,ires from 108 whole stumps (sapwood and heartnood). There is a wide variation of extractive coni en1 in the various stumps, the poorest containing E1.87~ e x t r u t , n-hile the richest analyzed 34.37, extract based on the g r e w weight of the stump. Hoxever, from the standpoint, of coniincwitil stump extraction, the over-all average yields xhicli m y 1i:irticular stump site might give is of greater significance for
>eil>l'lll , I L(
I'lllle
.
2 -2
,~~c~,l:!,t Illirllrlls
1 ye:ir
1yrnr 1 year
1 year
2 years 2 year, 3 years 3 years 4 years
Estrac;ives, Heart
Diaiii , Inci.es
19 1 23.3 29 20.I
22 16 36
22 30 29 32 28
26 8 22 0 26.5 36.8 26.2
40 40
26 Average
a
Hxaed
UII
iiiuiature-free wood.
28.9 36.8 26,9
c;
Yap 10 3 13.7 12.1 10.4 5.2 10.4 10.5 10.9 1.1
6'3 9.1
.
Figure 1.
JIethod of Sampling Sturrlps
interpreting end value. T h e poorest site, Wahler Creek, Calif., averaged ll.6yOextract; the richest sit,e, Bates, Oreg., averaged 21.8y0 extract (gre'en st.ump weight). The average for all the sites was 17.0% or 340 pounds of extract per ton of stumpwood. If this l a t h figure is compared with the yield of 31% extractives from the ten-year-old heart stumpwood of southern pine, the average of these western pine stumps will give a little over half the amount of extractives reported for southern pine stumps ( 7 ) . However, this comparison in extract yield from each of these pines is hardly justified, because of the many contributing factors which affect extract yield; among t h e m m s y be mentioned percentage of heartirood processed, age of stump, amount of moisture present, nature of stump site, and degree of stump selection. XATURE OF STUMP EXTRACTIVES
Table 111 gives the approximate composition of ponderosa pine stump extract. The first figure represents percentage composition based on w i g h t of the extractives; the second figure represents percentage yield based on green weight of the stump. On the whole, the nature of the extractive isolrted from enell site does not vary a great deal in composition. I n general, the composition of stump extractives is not expected to be effected materially from freshly cut to five-year-old stumps. Thus the average ponderosa pine stump extractive composition mny be summarized brie5y as follows (Table 111) : This fraction may consist of phloH 2 0 - E INSOLUBLE. ~ ~ ~ ~ baphenes, natural pigments (8), and perhaps some resenes. This component is a minor entity, amounting t o only 1.67'~ of total extractives, and may be in the same category as the gasolineinsoluble resenes found in southern pine stump extract. H.0 SOLUBLE. Perhaps this component would include sugars, cycloses, simple carbohydrates, and salts, if present (8). This constituent is likewise a minor one and, again, may be comparable to the xvater solubles in southern pine stump wood. T h e quantity present is only 1.6% of total extract. RESIXACIDS. This is the major entity in ponderosa stumpwood extract, amount,ing to 58.7% of the extract. This fraction
INDUSTRIAL AND ENGINEERING CHEMISTRY
1666
11.
T.4BLE
Rite
KO.
Location
1
Crow Creek, R'allowa,
2
U. S. Forest Service,
Oreg.
n'allowa. Oreg. Wallowa, Oreg. R e n d , Oreg. Seneca, Oreg. Bates. Oreg. Snoqualine S a d . Fore-t Wash. Glen;rood, Wash. Glenwood, Wash. N a t l . Forest Skull Creek Calif. \T-'aiiler,'Creek, Calif. Defiance Creek, Ariz. Defiance Creek, Ariz.
3 4 5 6
7
8 9 10
11 12 13 a
ACETOSE-SOLUBJX
EXTRACTIVES FROM
S o . of Stum s Extcf
Appron. Elevation, Feet
Tear Trees Felled
11
4000
9 10 9 9 10
5800 3800 3800 4800 4200
5 7
7
7
6 10 8
NO.
1 3 4 5 6 7 8 9 10 11 12 13 verage
+
Extractives, % a D r y basis Green basis Range Av. Range Av.
Approx. King Count
1943
18-38
150-200
16.1-28.2
21.5
14.5-25.8
19.4
1943 1944 1944 1944 1944
22-36 18-40 20-36 18-32 32-49
150-300 130-250
21.8 20.6 20.6 17.2 26.5
10.0-27.9 10.6-34.3
250-300 250-300
10.9-29 9 12 2-39 9 10 7-37 9 14.1-22 9 19.8-32.9
20.2 18.0 18.3 14.9
3000 2000 3200
1944 1942 1941
24-30 20-36 14-42
'225-305 125-175 100-300
10.1-26 8 7.2-:35.6 8.8-35 1
4600-5100 4000-5350 7600-7700 7600
1941-43 1942-44 1944 11143
28-48 31-42 18-39 13-39
130-30(1 200-3bC 173-488 213-428 Averaee
n
10.i-26 7
TABLE 111. H20 ether insol. 1.6-0.31 1.6-0.32 0.7-0.13 0.8-0.15 0.6-0.09 0.7-0.15 2,4-0.35 1.1-0.17 0.8-0,14 2.7-0.42 2.5-0.29 2.7-0.47 2.4-0.39 1.6-0.26
P O N D E R O S A PISE STUMPS
D i a m . of Stump, Inches
H u e d u n weight of srunipaood
Site
Vol. 39, No. 12
'200-250
A%PPROXIXIATECOllPOSITION O F STUYI'
8 0-28
9.1-18.8
13.4-25.0 11 6-29.9
10.2'33.8
12.2-19.9 17.1-29.5
21.8
17 5 17.0 19.5
7.9-23 4 6.4-32.4 8.0-32.7
14.7 15.3 17.9
16 8 16.5 19.0 17.6 19.4
5.8-19 4 6.7-15.7 9.8-24.2 12.1-23.0 10.1-26.3
15.6
EXTRACTIVES
Per Cent&
HzO sol. 1.2-0.23 1.2-0.24 1. 0-0 . 1 8 1.2-0.22 2.2-0.33 1.4-0 31 1.1-0.16 1.3-0.20
1.5-0.27 1.3-0.20 1,0-0.12 2.6-0.45 4.1-0.66
Resin acids 62.0-12.03 60.1-12.32 60.4-10 87 57.7-10.56 57.0-8.49 59.2-12.90 65.8-8 20 60.2-9.21 60.9-10.90 54.9-8.56 60 8-7.06 55.8-9.65 68.0-9 40
Free f a t t y acids 8.8-1.71 8.4-1.70 8.9-1.60 10.9-1.99 9.7-1.45 9 0-1,96 9.1-1.34 8.3-1.27 6 . 9 - 1 23 10.1-1.58 10.0-1.16 9.5-1.64 8.1-1.31
1,6-0,27
58.7-10.01
9.1-1,53
Volatile 4.2-0.81 5.4-1.09 4.3-0.77 5.7-1.04 4.6-0.69 6 . 3 - 1 37 5.9-0.87 3.9-0.60 8.9-1.59 8.0-1.27 4.7-0.54 4.1-0.71 5.2-0.84 5.4-0.94
Esters 9.3-1.80 11.0-2.22 11.3-2.03 8.1-1.48 11.4-1.70 8.9-1.94 13.1-1.78 11 . 7 - 1 . 7 9 7.9-1.41 9.6-1,50 9.5-1.11 14 0-2.42 9.8-1.59 10.3-1.76
Knsaponifiable 12.8-2.48 12.1-2.44 13.4-2.41 15.5-2.83 14.5-2.18 14.5-3.16 13.5-1.98 13.5-2.07 13.2-2.36 13.4-2.09 11.5-1.33 11.3-1.95 12.3-2.01 13.2-2.25
-
Lb / i o n of stumps 5.2 5 4 200.2 30.6 18.8 35.0 45.0 a F i r s t figure in each column, p e r cent based o n weight of extractives; second figure, p e r c e n t yield based on green weight of stumps.
would include both tlie oxidized and unoxidized resin acids, together viith some resin acid transformation products. Resin acids are likewise the major component of southern pine stump heartwood extract, amounting u p t o as much as 18.7y0 of the stump weight; ponderosa pine averages about 10.056 of resin acids, based on the green stump weight. FREEFATTY ACIDS. T h e quantity of free fatty acids in ponderosa pine stumps amounts t o 1.53y0or 30.6 pounds per ton of raw material. This constituent appears t o be foreign to southern pine stump extract. T h e source of free fatty acids from southern pines occurs in tall oil processing, yielding about 25 pounds of this product per ton of air-dry pulp manufactured which requires about 2 tons of r o o d ( 6 ) . VOLATILES..Approximately 5.470 of the extract is in tlie form of tcrpcnc fraction, auiounting t o about 0.9yo of the stump weight or approximately 18 pounds per ton of raw material. Southern pine stumps, on the other hand, are reported to yield up to 100 pounds of terpenes per ton of stumps ( 7 ) . ESTERS.This is the third greatest entity in ponderosa pine stumpwood, amounting t o 10.3% based on extract, 1.75% on stump weight, or 35 pounds per ton of stumps. Since southern pine rosin averages about 570 esters, a ton of t.his stumprvood would yield about 22 pounds of this fraction (6). UNSAPOXIFIABLE. T h e second greatest component of ponclerosa pine stump extract is unsaponifiable material, amounting t o 13.2% of total extract, 2.25% on stump weight, or 45 pounds per ton of stumps. On the other hand, southern pine rosin contains 1Oyo of resenes or 44 pounds per ton of stumps. T o summarize briefly, whole ponderosa pine stumps ivhich have seasoned u p t o five years will yield about 175; or 340 pounds of extract. per ton of stumpwood. Hence from cxtract yield standpoint the younger ponderosa stumps do not yield so much as the older southern pine stumps; however, it appears t h a t the more seasoned, sound ponderosa pine stumps (heartwood) will approach the extractive yield of the southern pine stump. I n addition t o quantity of extract, the nature of each entity must be taken into consideration, irrespective of stump species which play an important role in evaluating stump extraction processes. Thus characterization of each component isolated will help t o evaluate
11.6
17.3 16.2 17.0
E x t r a c t i r e a , yo Dry Green basis basis 21.5 19.4 21.8 20.2 18.0 20 6 18.3 20.6 14.9 11.2 21.8 26.5 14.7 17.5 15.3 17.0 17.9 19.5 l5,6 16.8 11.6 16.5 17.3 19.0 16.2 17.6 19.4 17.0
-._.-
_---
340
i n part ponderosn pine stump extractives, and this irivwtigation is underway at this laboratory. In addition to amount and nature of extractives, many other contributing factors enter into the commercial feasibility of stump extraction processes. AI'PLICATION O F R E S U L T S
The determination and analysis of acetone-soluble extractive8 from ponderosa pine stumps indicated t h a t this forest, waste material is a potential commercial source for rosin and other extractive by-products, including free fatty acids, esters, volatile terpenes, and unsaponifiable material. If this n e y industry is established in the western pine region, which includes tivclve western states, not only u-ill .the cutover and selectively logged areas become more adaptable to advanced forest management and improved reforestation practices but the value of western pine forest areas will liken-ise be enhanced. As the result of the cardinal research activities by the leading naval stores iritlustries and some of the Federal Government research laboratories during the last decade, rosin and the other extractives from the pine tree have found a myriad of new uses; it seems probable that the d o mand for these pine extractive products will continue. I t has been estimated t h a t the wood naval stores industry is responsible for annually clearing approximately 200,000 acres of cutover southern pine lands and releasing them for agricultural uses ( 7 ) . This source is not renewable, since the present southern lumber production is Ini,gely from young second-growth stands, and the stumps left from second-groxth material, which consists largely of sapwood, are not being used b y the wood naval stores industries because of their low extractive content. hIillions of acres of po.nderosa pine stumps are a n untapped potential source for the commercial production of extractives, and other millioris uf acre8 of virgin ponderosa pine forests will be available t o ensure an adequate supply of raR- material for many years t o come.
December 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
A pilot plant with an extractor capacity of 680 cubic feet per charge has been erected for the purpose of extracting ponderosa, sugar, and Idaho white pine lumber, stumps, and other western pine forest and mill wood waste with solvents to determine whether such extraction processes are practical on a commercial basis. ACKNOWLEDGMENT
The author is indebted t o Carl Rasmussen, George Schroeder, C. V. Zaager, George I. Garin, and Ernest Kolbe for collecting the samples and to Albert Hermann for comments and suggestions.
1667
LITERATURE CITED (1) Anderson, IND. ENG.CHEX.,36, 662 (1944) ( 2 ) Ibid., 38, 450 (1946). (3) Ibid., 38, 759 (1946). (4) Betts, U. S.Forest Service, Bull. 116 (1912;. (5) Bray, Paper T r a d e J . , 115, N o . 10, 2 (1942). (6) Georgi, Ibid., 100,No. 12, TAPPI See. 156-8 (1935). (7) Humphrey, IND. ENG.CHEM.,35, 1063 (1943). (8) Kurth, ISD.ENG.CHEM.,- 4 s ~ED., ~ . 11, 203 (1939). (9) Schorger, E. S. Forest Service, Bull. 119 (1913). (10) Wise, "Wood Chemistry," B.C.S. Monograph 97, pp 563-4, New York, Reinhold Publishing Corp., 1!244.
RECEIVEDJune 10, 1946
Acid Pyro- and Metaphosphates Produced bv Thermal Decomposition of Monocalcium Phosphite J
W. L. HILL, S. B. HENDRICKS, E. J . FOX, AND J . G. CADY Dizrision of Soils, Fertilizers, and Irrigation, U . S . Department of Agriculture, Beltsville, M d .
Information o n the products formed by heating monocalcium phosphate a t temperatures below- 600' C. has a practical significance in connection with t h e thermal treatmeut of superphosphate to produce mineral feed of low fluorine content. 3lonocalcium phosphate monohydrate is known to undergo partial fusion when it is heated rapid? i n t h e open a t 150' to 200' C., and t h e resultant mixture is converted to stable 8-calcium metaphosphate a t 600" to 700" C. Fusion can be avoided bq first heating the charge a t 125' to expel water of crystallization, b u t further heating in the range 200' to 600" yields a n unpredictable mixture of phases, consisting of glasslike amorphous material and one or more of a t least three crjstalline phases. O n t h e other hand, t h e anhydrous salt, obtained either by drying t h e hydrate or by crjstallization from solution, readily loses water in an
atmosphere of steam a t 275" to 300' C. arid changes smoothly into calcium acid pyrophosphate with the formation of little or no amorphous material. A n es*entiall) pure amorphous material can be prepared by heating extremely thin flakes of monocalcium phosphate monohydrate., A t 325' to 350" in steam crystalliue acid pyrophosphate is converted into a mixture of two crystalline compounds with more or less amorphous material. The latter, soluble in water, can be leached from insoluble crystalline compounds. One of these compouuds is tetracalcium dihydrogen hexaphosphate; t h e other, y-calcium metaphosphate. Formation of another cr)stalline nietaphosphate from calcium acid pyrophosphate is enhanced b y t h e presence of sulfate. This modification is structurally similar to, and apparently forms a solid solution w ith, anhydrous calcium sulfate (anhydrite).
P
to which free acid was removed and represent, respectively, ( a ) material separated from mother liquor with the aid of a porcelainbasket centrifuge, suspended in acetone and centrifuged again, ( b ) the same after two suspensions in acetone with intervening centrifugation, and ( c ) the same after four similar Kashings with acetone. Sometimes monocalcium phosphate monohydrate c r i stallizes in extremely thin flakes which, being undesirable for most puiposes in commercial practice, are customarily discarded or redissolved. One crop of crystals (No. 2 ) obtained in the laboratory showed unusual uniformity in this respect and was included in the study. When this fluffy material R & S found t o change completely into the amorphous state at 300' C., conditions for its ready preparation were successfully worked out. Several lots of fluffy monocalcium phosphate that yielded good amorphous material were prepared by heating 500 ml. of 45% phosphoric acid and 200 grams of monocalcium phosphate monohydrate in a covered beaker in an oven a t 110" C. until the solution was saturated, decanting the clear hot solution into a 600ml. beaker, and allowing it to cool in air. The crust t h a t formed a t the surface as the solution cooled was broken up by occasional gentle stirring until presently the solution turned rapidly to a
R O D C C T I O S of feed-grade phosphate by thermal defluorination of superphosphate has raised questions about compounds formed from monocalcium phosphate when it is heated alone or in the presence of calcium sulfate (4). The reactions involve loss of water Kith formation of such compounds as calcium acid pyrophosphate, CaH,P?O,, and calcium metaphosphates. As the temperature is increased pgro- and orthophosphates can be formed with accompanying loss of sulfur trioxide when calcium sulfate is present. Preliminary attempts to identify the compounds in laboratory and commerical preparations indicated a complexity to the reactions that is generally characteristic of metaphosphate salts. Further work reported here was undertaken t o obtain reliable information on the compounds that may be formed from monocalcium phosphate. Several monocalcium phosphates from various sources, thought to be typical of both laboratory and commercial food-grade preparations, were used as starting materials. These materials (Table I ) differ with respect to the nature and amounts of impurities, crystal habit, and compounds produced upon heating. The laboratory preparations v w e crystallized from aqueous phosphoric acid solutions essentially as described in a previous article (8). Materials Xo. l a , Ib, and I Cdiffer only in the extent
