THE JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
I 16
4-The interference of vanadium u p t o at least per cent V in t h e determination of phosphorus is prevented in a simple way and t h e t r u e phosphorus is obtained from ferrovanadium containing t h e very high vanadium content of 56.7 per cent. ACKNOWLEDGMENT
Credit is due Mr. F. D. Hawkins for his careful analytical work when making t h e trial analyses required b y t h e author t o prove t h e foregoing. RESEARCH DEPARTMENT AMMERICA PITTSBURGH, PA.
CRUCIBLE STEEL COXPANY O F
SOME MIX-CRYSTALS OF CALCIUM FERRITE AND ALUMINATE By EDWARD D. CAMPBELL Received June 25, 1918
1 2
8
4
THISJOURNAL,
5 (1913), 627. I b i d . , 6 (1914), 706. I b i d . , 7 (1915), 835 A m . J . Sci., 28 (1909), 293.
II?
So.
2
showed t h e existence of a definite calcium aluminate of t h e empirical formula 5Ca0.3A1203 and gave the melting point in a pure state as 1386’ C., which was lowered b y the addition of a small amount of CaO t o 1382’. I n a later publication by Rankin and Wright1 t h e melting point of pure 5Ca0.3Al2O3 is given as 1455’ C., which is first lowered b y t h e addition of lime t o 13g5’, and then gradually raised as t h e concentration of t h e solution increases until, when the concentration reaches t h a t of t h e empirical formula 3CaO.AlzO3, i t has reached 1535’. I n formulating a hypothesis of t h e formation of clinker b y recrystallization of t h e basic silicate, assumption was made t h a t t h e aluminate which acted as a solvent was t h e one having t h e empirical formula gCa0.3A1203 and also, although there was no experimental evidence t o support i t , t h a t since i t had been shown t h a t tricalcic silicate could be crystallized from calcium ferrite as easily as it could from calcium aluminate, probably a calcium ferrite of the empirical formula j C a 0 . 3Fe203 might exist and function exactly like t h a t of t h e jCa0.3A1203. I n a “Preliminary Report on the System LimeFerric Oxide,”2 Sosman and Merwin seem t o have demonstrated pretty clearly t h e probable existence of only two calcium ferrites having t h e formulas, t h e dicalcic ferrite, zCaO.Fe203, and t h e monocalcic ferrite, CaO.FezO3. I n t h e present investigation, t h e experimental work of which was carried out by W. C. Kwong, B.S.E., there were two points on which i t was hoped t o secure some additional information: t h e first was t o redetermine t h e existence or non-existence of a calcium ferrite of t h e empirical formula gCa0.3Fe203; and t h e second, to obtain some experimental evidence as t o what is formed when a mixture of calcium oxide, ferric oxide, and alumina is melted and then cooled at a rate slow enough t o permit t h e material t o be nearly in equilibrium during t h e entire cooling period.
2.6
About five years ago in an article on “The Constitution of Portland Cement Clinker,”l some experimental evidence was given t o show t h a t t h e formation of Portland cement clinker comprises essentially a series of solutions of certain silicates and lime in a magma which is fluid a t the clinkering temperature and serves as a solution in which t h e recrystallization of t h e basic silicates characteristic of Portland cement takes place. As early as 1897 Tornebohm had applied t h e t e r m celite t o the magma in which t h e crystalline portions of t h e clinker were imbedded, and states t h a t this fusible magma promoted t h e crystallization of t h e alite, as t h e basic silicates were termed. Prior t o 1913 no satisfactory method for separating celite from alite had been described, b u t in t h e article above referred t o a method was given for separating t h e celite present in clinker a t different temperatures, and i t was further shown t h a t t h e celite of ordinary Portland cement clinker consists essentially of a mixture of calcium aluminate and ferrite in which both ortho-calcium silicate and lime are soluble, t h e solubility of these being a function of t h e temperature of the fluid solution. I n an article on “Synthetic Celite and Large Crystals of Tricalcic Silicate,”2 i t was shown t h a t if pure silica, alumina, and calcium oxide were mixed in t h e same molecular proportions as those in which they had been shown t o exist in t h e celite previously obtained from Portland cement clinker and t h e liquid mixture was very slowly cooled, t h e tricalcic silicate crystallized out in large thin plates, thus demonstrating t h a t it was t h e aluminate which constitutes t h e solvent in which t h e crystals had formed. I n a third paper on “The Function of Ferric Oxide in t h e Formation of Portland Cement Clinker,”3 i t was shown t h a t if a mixture of pure silica, ferric oxide, and calcium oxide of t h e same molecular proportions as those found in t h e celite drawn off from t h e Portland cement clinker is melted and slowly cooled, large crystals of tricalcic silicate will separate, thus demonstrating t h a t calcium ferrite may act as a solvent for both calcium silicate and lime in a manner almost exactly similar t o t h a t of t h e calcium aluminate. As early as 1909, Shepherd, Rankin, a n d Wright4
Vol.
MATERIALS U S E D
-
Kahlbaum’s purest analyzed calcium carbonate and ferric oxide were used as t h e source of CaO and Fe203, t h e &Os being t h e purest available ignited oxide, giving b y analysis 99.60 per cent AI&. These materials were thoroughly dried at about 105 ’ before being accurately weighed in molecular proportions prior t o mixing and melting. The mixture t o be melted was placed in a flatbottom cylindrical platinum crucible 48 mm. in diameter and 5 5 mm. deep, having a capacity of about IOO cc. Enough material was used for each experiment t o give from 7 j t o 92 g. of t h e final melt. It was usually necessary t o heat t h e mixture in two lots over night t o a temperature of about 1100’ in order t o shrink it sufficiently t o enable the entire charge t o be p u t in the crucible before melting. During t h e melting and cooling t h e crucible was covered, first with the platinum cover on which was placed enough ignited magnesium oxide t o fill t h e concavity of the cover, and then with a pure magnesium oxide crucible cover. This arrange1 2
Am. J . Sci., 39 (1915), 1. J . Wash. A c a d . Scz., 6 (1916), N o . 15.
Feb., 1919
TETE J O U R N A L OF I N D U S T R I A L A N D ENGIi\7EERIXG
ment was made in order t o prevent a too rapid loss of heat during cooling b y upper radiation from t h e surface of t h e liquid melt. T h e meltings, slow cooling for crystallization, and subsequent treatment for absorption of liquid cons tituents were all carried out in a modified Meker furnace which has given very satisfactory results in this laboratory for similar work carried on for t h e past four years. During t h e time a sample was being melted a n d slowly cooled for crystallization, the temperature was measured b y means of a platinum-rhodium thermocouple protected b y means of a fine closed Marquart tube, the bead of t h e thermo-couple being placed within 2 mm. of t h a t portion of t h e crucible containing t h e fused material. The thermocouple was standardized, before using, a t t h e melting point of pure silver taken as 961" C. I n making slow coolings for crystalIization, t h e sample was first allowed t o heat over night, this usually bringing t h e temperature t o 1100'. I n t h e morning, blast was p u t on and t h e temperature raised until it h a d reached t h e point from which i t was desired t o begin slow cooling. When t h e thermocouple indicated t h e maximum temperature, this was held for 1l/4 t o 1 1 / ~ hrs., after which t h e gas supplying t h e burner was very gradually reduced so t h a t t h e temperature would fall a t t h e rate of 25' per hr. Although t h e temperature recorded could not of course be claimed t o represent t h e absolute temperature t o within less t h a n s o , a variation of about I ' could be observed, and when readings were recorded every 1 5 min. it was possible t o hold t o a time-temperature schedule so t h a t a t any time during t h e 6 t o 8 hrs. of slow cooling t h e temperatute indicated was within '2 t o 3' of t h a t desired. After crystallization h a d been completed, t h e gas was turned off and the furnace allowed t o cool over night before removing t h e crucible. When t h e melt in t h e crucible was cold, i t was removed b y means of a hardened steel drill in t h e form of pieces which could be used for subsequent work. The absorption of pure magnesia discs of those components which were liquid at a given temperature was carried out in a manner somewhat similar t o t h a t used heretofore for t h e same purpose. Two discs, each about 4 cm. in diameter and 1 5 mm. thick, made of pure magnesium oxide burned a t IS~O', were first accurately weighed and then stacked in a pure magnesium crucible, 5 cm. inside diameter a n d 5 5 nim. deep. The bare wires of a standardized platinum-rhodium thermocouple were then led through fine slits sawed in t h e upper edge of t h e crucible and t h e wire bent in such a way t h a t t h e bead of t h e thermocouple rested on t h e surface of t h e upper disc. Accurately weighed pieces of t h e material t o be treated, in most cases from g t o 14 g., were placed on t h e upper magnesia disc, and a third somewhat smaller disc was placed on top of t h e pieces t o weight them down in order t o insure good contact and absorption b y capillary action. The cover was then placed on t h e magnesia crucible and t h e whole allowed t o heat over night, t h e temperature in t h e morning usually being 1100'. Experience showed t h a t when t h e fur-
CHEMISTRY
117
nace had come t o equilibrium t h e inner couple, which was in direct contact with the absorbing disc, usually indicated a temperature about 25' lower t h a n t h a t of t h e couple in t h e annular space just outside t h e magnesia crucible. The temperatures of absorption recorded in this work are those shown b y t h e inner couple which was in direct contact with t h e absorbing disc and material under treatment. I n making absorptions of t h e pure ferrite, E5 and Ee, t h e temperature was raised gradually over a period of 3 hrs. from 1100' t o 1300' and was then held constant for 5 hrs. longer. I n all t h e other absorptions t h e temperature was raised within less t h a n an hour from about 1100' t o t h a t a t which i t was desired t o carry on t h e absorption, and then held constant for 8 hrs., after which t h e furnace was allowed t o cool over night. During t h e period t h e temperature Was supposed t o be held constant, i t did not vary more t h a n '5 in any case. When t h e material was cold, t h e pieces were removed from the disc and t h e amount which had been absorbed was determined from t h e loss of weight. Analyses of t h e absorbed material were made b y dissolving nearly t h e entire upper absorption disc and taking aliquot portions such t h a t each would contain about 0 . 4 g. of t h e absorbed material. T h e results reported were all obtained b y means of at least two closely agreeing determinations. Blank analyses were made on t h e absorption disc t o correct for t h e small amount of ferric oxide and alumina contained in t h e magnesium oxide which was free from calcium oxide. The correction required did not exceed o.ooj g. for 6 g. of the magnesia. The temperature ranges through which t h e different samples were cooled a t the rate of 25' per hr. in order t o facilitate crystallization are shown in Table I: MATERIAL
TABLEI
E6 ..............................
Ea.. ............................ Ea.. ............................ Gs..............................
EGs ..............................
-
Range of Slow' Coolinrc 1525' down to 1375O 1525' down to 1375O 1575" down t o 1375' 1575' down t o 1400O 1475' down t o 1275O
By heating accurately weighed portions of t h e original crystallized materials on t h e magnesia discs, they could be quantitatively separated into crystals remaining unabsorbed on t h e discs and the portion absorbed b y t h e discs a t t h e given temperature. Analyses could then be made of the two portions and the effect of absorption studied. The first three samples prepared consisted of calcium ferrite alone. T h e first, Es, had t h e empirical formula gCa0.3Fe203, or equally well, z(zCa0.Fe203) CaO.FezO8. A section of this material showed i t t o be made up of large, very dark brown, tabular crystals embedded in a nearly opaque magma from which they had evidently crystallized. Eo had t h e empirical formula 6CaO.gFezOa or 3(zCaO.Fe203). A section of this material showed i t t o consist apparently entirely of t h e large, dark brown crystals which constituted a portion only of Es. E8 had t h e empirical zCaO. formula 8Ca0.3Fe203 or 3(2CaO.Fe203) Samples of Ej,Ee,and E8 were finely ground and pats made, as in testing Portland cement, t o determine
+
+
whether the ferrites werc hydraulic and for indications of the presence of free lime. All three set on mixing with enough water for normal consistency, E6 and E8 taking initial set in from 14 t o 2 2 min. and final set in about three-fourtiis of an hour. On subjecting the pats, after standing in moist air for 24 hrs., t o the action of boiling water, Ea and E8 remained sound and free from cracks, E, being somewhat harder than E,; b u t ES soon compleiely disintegratcd in boiling water, indicating the prescnce of a considerable amount of free lime. On heating a sample of E, for j hrs. a t 1300' there was a loss of weight of 20.5 per cent, the unabsorbed crystals remaining on the magnesia discs constituting 7 9 . 5 per cent of the original weight. On submitting a sample of E, t o the same conditions, the loss of weight b y absorption was only 0.80 per cent. Analysis of t h e material absorbed in the case of E, showed it t o contain 2 6 . 9 4 per cent CaO and j 3 . 0 6 per cent Fe20s. If this is assumed t o be a mixture of monocalcic ferrite, CaO.Pe&, and dicalcic ferrite, zCa0.Fe203, the absorbed material would be made up of y 3 . 78 per cent monocalcic ferrite and 6 . 2 2 per cent dicalcic ferriie. The crystals remaining on the absorption disc gave, by analysis, 38.87 per cent CaO and 61.07 per cent Fez08. Assuming these crystals also t o he made up of monocalcic and dicalcic ferrites, they would be composed of i j . 26 per cent monocalcic with 8 4 . 7 4 per cent dicalcic ferrite. Since one would expect a certain proportion of the liquid solvent t o adhere t o the surface of the crystals, it is only reasonable t o assume that the crystals themselves are probably pure dicalcic ferrite. The very small amount, 0 . 8 0 per cent, absorbed in the case of Er would go t o indicate that this latter consisted wholly of dicalcic ferrite. The results obtained on E,, Ee, and Es may thus be taken t o confirm the work of Sosman and Merwin, and their statement t h a t the monocalcic ferrite and dicalcic ferrite are the only two definite compounds of lime and ferric oxide. In a previous paper on "The Formation of Tricalcic Aluminate,"' it was shown t h a t if a mixture having the empirical formula 4CaO.Al2O3is very slowly cooled from 1 6 0 0 ~C., a t which temperature probably n'early all the lime would be in solution, calcium oxide crystailizes out as the temperature is lowered, the concentration of the solution thus becoming decreased with falling temperature, but no large crystals of tricalcic aluminate could be observed in a section of the final material. The hypothesis was advanced that tricalcic aluminate was not, strictly speaking, a stable phasc, but was probably either a saturated solid solution of CaO in 5Ca0.3Alr03, or this latter aluminate with lour molecules of lime of crystallization. I n order t o see whether tricalcic aluminate could be obtained in large crystals, provided there was no excess of lime t o iorni crystals of calcium oxide, thus impoverishing the liquid solution and preventing the formation of large crystals, a mixture, GB. having the empirical formula 8CaO.3AI2O1 was made. 'This mixture w a s melted and cooled a i the rate of 2 j y an hour from 157 j" 1
nrli J ~ U W ~ , .9. (191;).
943.
t o 1400'. That the absence of any crystals of calcium oxide will permit the solution t o be supersaturatcd, thns inducing the crystallization of tricalcic aluminate, is strikingly shown in Fig. I . 'rvliicli is a photograph, j u s t slifilitly less than the natural size. of t.be crucible containing the melt as it was taken irom the iurnacc.
mi;. I
A sample oi Gs, consisting of three pieces weighing 10.3026 g., was hcld for 8 hrs. a t 1450".
The crystals from which the fluid magma had been drawn off by the capillary action of the magnesia disc, weighed j . 1 1 3 2 g., thus constituting 6 9 . 0 per cent of the original material. The fluid magmn absorhkd b y the magnesia disc thus constituted 3 1 . 0 per cent of the whole. Fig. 2 shows, in natural size, the crystals from which the fluid magma had been drawn out b y the action of the magnesia disc on which they rested during the absorption.
PlG. ?
Analysis of the crystals showed them t o contain CaO, 61.86 per cent, and AI2O3, 3 7 . 9 3 per cent. This would give a n empirical formula 2.98 Ca0.AI?03, or corresponding almost cxactly with that of the tricalcic aluminate. The material absorbed b y the magnesia disc gave, by analysis, CaO. j 3 . 6 4 per cent, and AIzOi, 46.36 per cenl. This would give a molecular ratio of 2 . 1 1 CaO t o one Al-.Ol. The percentage composition of the material absorbed a t 1450' is in very close agreement with that shovvn in the iimealumina diagram of Rankin and Wright' for the composition of matcrial having t,he melting point of 7
Ann. .I. .Y'i.,
38 (1915), I .
14jo'. Fig. 3 is a section of G Rmagnified 100 diameters and shows very clearly tlie general structure of thc large crystals of tricalcic aluminate and the cmbedding magma in wliich t h e y formed.
Fic. ~ - - S L ; C T I U Nor, Ca M A C N I Y I I ~ DI O l I I J m M E ' T I H S
.
T i s . .I
An E G s sample was prepared from a mixture of Gs and E8 taken in such proportion t h a t one-fourth of the. R20i was Fe,OJ and three-fourths was A1,03. White the general formula of EGs mould be RCaO: 3R108,it might be expressed as 9(3Ca0.A1203) 2(zCa0.Fe203) CaO.FezOa. This mixture was melted and finally cooled a t the rate of 2 5 ' an hour from 1 4 7 j ' down t o 1~7j'. A prcvious melting and slow cooling, which was stopped a t 13;j0, showed t h a t a t this latter temperature too large a portion of the material was still liquid so that a second crystallization was made a t lower temperature. A pat made from EGs showed that it, like the other samples, was hydraulic, but thc pat on being submitted t o the usual boiling test completely disintegrated, thus showing the presence of free lime. A section of EGs showed it t o consist apparently of large, light brown crystals embedded in a very dark brown, almost black, magma from which they had apparently crystallized. The appearance of this section of EGs magnified zoo diameters is shown in Fig. 4. A comparison of the sections illustrated in Figs. 3 and 4 shows that while the size and general form of the large crystals are much alike, the appearance of the EG, crystals is very suggcstive of that of certain pearlitic or sorbitic steel in which certain solid solutions on slow cooling have scparated into two components. Four absorption tests were made on samples of EGs. I n the first test the sample WZLS held for 8 hrs.
+
a t r300°, but on examining tlie material aftcr t I , t * furnace was cold, no sign of any melting or :ihsorplion could be observcd. I n the second test, t h e same s:ini-
+
--SI:CI,ON
"I
Ix:r h l * < i N I P l l i D
100 nr*VITTli*h
pie was used and the temperature was increased t o 1 4 0 0 ~and held again for 8 hrs. The crystals remaining on the absorption disc a t i 4 0 0 ° were a uniform light brown in color and constituted 4 0 . 9 per cent of the original weight. The portion which was liquid a t i400Q and ahsorbed by the disc was therefore j q . I per cent of the original. I n the third absorption test the temperature was held for 8 hrs. a t 13 joo, but the amount of material absorbed was so small that it pruduced only a slight stain on the upper surface of the absorption disc. The fourth absorption wus made by raising the temper:tture t o 1370", a t which i t was again held for 8 hrs., the same sample as that previously heated t o r 3 j o D being used in this test. The crystals remaining on the absorption disc after heating for 8 hrs. a t 1370' constituted 52.3 per cent of the original material, while the magma, liquid at 1370' and absorbed by the disc, made up 27.7 per cent of the whole. An examination of the crystals showed t h a t they were made up of twu distinct kinds, one portion light brown in color like those remaining on the disc after the absorption a t r4oo0, the other portion made up of crystals which were very dark brown in color, almost indistinguishable from the magma in which they had formed. I n order t o get a scparation of the light brown from the dark brown crystals, the mixture was carefully crushed and, after removing the very fine powder, was poured into methylene iodide and stirred. The pure, dark brown crystals, having a specific gravity greater than that of
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
I20
Per cent Original Material 100.0 20.5 79.5 100.0 100.0 100.0 31 . O 69.0 100.0 27.7 24.0 48.3 59.1 40.9
. . . . . . . . . . . ... . . ...... .. .. .... ... . . .. .. .. .. ... .....
... ...
centAh03
...
... ... ...
4.0: k0
46.36 37.93 28.81 20.54 21.95 27.55 25.25 29.05
methylene iodide, settled t o the bottom, while the pure, light brown crystals a n d those having a small amount of the dark crystals adhering t o them would float. The mixture of crystals was thus separated into two portions which mere washed with benzol and dried before making the analyses. T h e light brown crystals recovered by flotation with methylene iodide constituted 48.3 per cent of t h e original, while t h e dark brown crystals made up 24.0 per cent of the same. The small proportion of dark brown adhering to the light brown crystals recovered a t 13 7 0 O would account for the increased proportion of these, 48.3 per cent as compared with 40.9 per cent of pure light brown crystals, recovered a t I ~ O O ' , a n d also for the smaller ratio of Fez03 t o A1203 in the latter crystals. The results of all analyses are summarized in Table 11, in which are also given the molecular per cents, the molecular ratio of CaO t o one Rz03, t h e proportion of FeaO3 and Alz03 in one RzO3, and, finally, t h e proportion of Fez08 a n d A1203 in eight molecules of Rz03. Compos/S/on-?kmpemfure Diagmm o f +he Sysfems GOFe& md CoPakO?
Mokculur finenfuqe FIG.5
I n t h e article by Sosman and Merwin,' previously referred to, they give a composition-temperature diagram for t h e system CaO-Fez03in which the ordinates represent the melting points and the abscissas t h e molecular per cents of CaO and Fez03. I n t h e paper on "The Ternary System Ca0-A1z0rSi02,"2 Rankin and Wright give a concentration-temperature diagram for the system Ca0-A1203, in which the ordi1 2
J . Wash. A c a d . Sci., 6 (1916), No. 15. A m . J . Sci., 39 (1915), 1.
11,
No.
2
TABLEI1
-Weight Per CaO FenOs Original. . . . . . . . . . . . . . . . 36.91 63.09 26.94 73.06 Absorbed a t 1300' C.. .... 38.87 61.07 Crystal a t 1300' C ...... 41.26 58.74 Original. .... 48.36 51.64 Original, .... 59.40 Original. 53.64 Absorbed a t 1450' C . . 61.86 Crystal a t 1450' C . . . . . . . . . . . 56.19 15:oo Original. . . . . . . . . . . . . . . . . . . . 46.95 32.51 Absorbed a t 1370' C . . ... 56.25 21.88 Dark cryst. at 1370' C 62.15 10.20 Light cryst. a t 1370" C 50. 79 23.96 Absorbed a t 1400' C . . 64.46 6.70 Crystal a t 1400' C . . ( a ) Points on composition-temperature diagram, Fig 5.
.... ... ................ * . . ...............
Vol.
-Mole ,cular Per centCaO Fez03 Altos 62.50 37.50 51.26 48.74 ... 64.48 35.52 ... 66.67 33.33 72.73 27.27 . . . 2;:27 72.73 67.84 ... 32.16 74.83 25.17 72.73 6 : 8 l 20.46 67.39 16.43 16.18 74.02 10.11 15;87 76.85 4.44 18.71 69.53 11.51 18.96 77.91 2.85 19.24
... ...
CaO
-8
RzOs 1.67 1.05 1.82 2.00 2.67 2.67 2.11 2.98 2.67 2.07 2.85 3.31 2.28 3.53
1.00 1.00 1.00 1.00 1.00
..
.. 0:is 0.50 0.39 0.19 0.38 0.13
, ,
.. ..
..
1:oo 1.00 1.00 0.75 0.50 0.61 0.81 0.62 0.87
R2 O s--
Fe2Os Altos 8.0 8.0 . . .
...
8.0
8.0 8.0
... ...
... ,..
...
8.0 8.0 8.0 210 6 . 0 4.0 4 . 0 3.0 5.0 1.5 6 . 5 3.0 5 . 0 1.0 7.0
nates show the melting points, but in which the abscissas represent t h e composition in weight per cent rather t h a n in molecular per cent, as shown in Sosman and Merwin's diagram. Fig. 5 is a compositiontemperature diagram in which the ordinates represent the melting points and t h e abscissas the molecular per cents of CaO and Rz03, in which diagram t h e curve for the pure ferrites is taken from Sosman and Merwin's diagram, while t h a t of the pure aluminates is computed from t h e d a t a given by Rankin and Wright. A study of the d a t a given in Table I1 and oE the diagram shown in Fig. 5 would seem t o lead t o t h e following conclusions : I-That the statement t h a t t h e dicalcic ferrite and the monocalcic ferrite are the only definite compounds of CaO and Fe208is correct. 11-That pure tricalcic aluminate may be recovered by crystallization from a solution of CaO in gCa0.3AlZO3as a solvent, provided t h e concentration of CaO a t the beginning of the crystallization is less t h a n t h a t which would be required t o form tricalcic aluminate with all the A1203 present. 111-That if a solution with t h e empirical formula S C a 0 . 3 R ~ 0 3 ,containing both Fez03 and A1203 in t h e molecular proportion of 2 t o 6, be slowly cooled, mixcrystals with Fez03 a n d A1203 in the ratio I t o 7 crystallize out until the Fez03-Al203 ratio in t h e solution has been increased t o 3 t o 5 . IV-That when the Fez03.Al208 ratio has been increased until it has become 3 t o s, mix-crystals of this latter ratio crystallize out, producing a further increase in the Fez03.A1203 ratio until a t about 1 3 7 0 ~ i t has become 4 t o 4. V-That t h e aluminatesin which part of the A1203 is replaced by Fez03 are capable of holding in solid solution less calcium oxide t h a n t h e pure aluminates, as indicated from the boiling test on EGg a n d t h e abnormally high ratio of 3 . 5 3 CaO t o I RzOa in t h e crystals recovered a t 1400°, since the crystals of free lime . present would remain mixed with the crystals of aluminate recovered a t 1400'. The experiments described herein suggest a possible explanation of the general formation of m a n y minerals which apparently consist of mix-crystals which are formed in a slowly cooling magma. CHEMICAL LABORATORY UNIVERSITY O F MICHIGAN ANN ARBOR,MICHIGAN
