INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1944
obtained from mixtures tsiniulating blast-furnace gas and electricfurnace gas were 30 and 34% by volume, respectively. The initial concentration of carbon monoxide in electric-furnace gas i s much greater than that in blast-furnace gas, but the oxidation of the higher phosphorus content of the electric-furnace gas necessitates use of much more'air. The final concentration of carbon monoxide obtained from electric-furnace gas by preferential oxidation of the phosphorus is therefore not greatly different from that obtained from blast-furnace gas. I n producing phosphoric acid from electric-furnace gas by a one-step process, preferential oxidation offers an advantage over complete oxidation, in that there is considerably less heat to be dissipated and the phosphorus pentoxide is diluted with less nitrogen. I n the preferential oxidation of blast-furnace gas in the presence of phosphate rock to form calciuni metaphosphate, the percentage of CO in the exit gas was in the range 23 to 26%. In actual practice, somewhat higher concentrations of carbon monoxide probably could be obtained, because the normal blast-furnace gas contains a somewhat smaller proportion of phosphorus than was used in the experiments. T o attain the carbon monoxide concentration of about 30% that would be required for preheating the blast, exact control of the operation of both the preferential oxidation furnace and the blast furnace would be required.
933
ACKNOWLEDGMENT
The authors acknowledge the advice given by R. L. Copsoii and J. W. H. Aldred in supervising this work, and the assistance of G. V. Elmore in preparing the paper. Helpful advice was also given by P. H. Emmett and J. F. Shultz, formerly of the United States Department of Agriculture. LITERATURE CITED
Britzke, E. V., Brit. Pat,ent 229,768 (March 2, 1925); 242,650 (June 3. 1926). (2) Brkzke, E. V., and Pestov, 1,. E., Trans. Sci. Inst. Fertilizers (1)
(U.S.S.R.), NO. 59, 5-160 (1929). (3) Brown, E. H., Morgan, H. H., and Rushton, E. R., IND.ENO. CHEM.,ANAL.ED., 9, 524-6 (1937). (4) Brunauer, S., and Shultz, J. F., IND.ENO.CHEM.,33, 828-32 (1941). (5) Buehrer, T. F., and Schupp, 0. E., Jr., J . Am. Chem. Soc., 49, 9-15 (1927). (6) Curtis, H. A., Copson, R. L., Abrams, A. J., and Junkins, J. N.. Chem. & Met. Eng., 45, 318-22 (1938). (7) Dunaev, A. P., Udobrenie i Urozhai, 2, 397-409 (1930). (8) Emmett, P. H., and Shultz, J. F., IND.ENG.CHEM.,31, 105-11 (1939). (9) Frear, G. L., and Hull, L. H., Ibid., 33, 1560-6 (1941). (10) Klugh, B. G., U. S. Patent 1,463,959 (Aug. 7, 1923). (11) Pistor, G., and Suohy, R. (to Chemische Fabrik Griesheim Efektron), German Patent 408,925 (Jan. 28, 1925). (12) Sigrist, J., French Patent 640,287 (Aug. 30, 1927).
.
HIGH-TEMPERATURE HEAT CONTFNTS OF
Ferrous and Magnesium Chromites B. F. NAYLOR Pacific Experiment Station,
U. S. Bureau of
The heat contents above 25' C. of high-grade synthetic samples of ferrous chromite and magnesium chromite were determined i n the temperature range 25-1500' C. A table summarizes the heat contents and entropies above 25' C. of these substances a t 100" intervals; the data are also adequately represented by equations.
I
NVESTIGATIONS at this Station on the metallurgy of chromium have revealed the need of accurate thermodynamic data for both ferrous and magnesium chromites. High-grade samples were prepared in the laboratory, and this paper presents high-temperature heat content data for both substances in the range 25" to 1500' C. The measurements were made by a modification of the "method of mixtures"; in this case the samples, enclosed in platinumrhodium capsules, were heated to a determined temperature and then dropped into a copper calorimeter, previously calibrated by electrical means (1 calorie = 4.1833 international joules). The method and apparatus have already been described (2). A platinum-rhodium capsule sealed with platinum was used for the ferrous chromite; an open-neck platinum-rhodium capsule having a tightly fitting cap was employed for the magnesium chromite. The ferrous chromite was prepared by heating a stoichiometric mixture of high-grade sponge iron, reagent-grade ferric oxide, and chromic oxide of high purity according to the reaction, Fe
+ FerOa + 3 C r Z 0 1 4 3 F e C r ~ 0 ,
Mines, Berkeley, Calif.
a t a temperature of 1300-1350' C. for several days in a slow stream of helium. Analysis of the product showed that it contained 24.77% Fe (theoretical 24.95%) and 46.09% Cr (theoretical 46.46%). A small amount of silica was also found. Treatment of the pulverized sample with hot concentrated hydrochloric acid for several hours revealed only traces of soluble iron. The magnesium chromite was prepared in a similar manner by reacting reagent-grade magnesium oxide with reagent-gradc chromic oxide at 1400' C. Analysis gave 12.58% Mg (theoretical 12.64%), 54.07% Cr (theoretical 54.08%), and 0.14% Fe. Treatment of this sample with hot concentrated hydrochloric acid showed that only traces of free MgO and CrzOa were present. The crystal structures of the samples were examined at the Salt Lake City Station of the Bureau of Mines. The pattern of the ferrous chromite sample checked those previously reported for synthetic and natural chromite quite well, showing a cubic lattice with a parameter of 8.358 A. No other material was present in sufficient quantity t o show additional lines. Likewise, the magnesium chromite checked the known spacings. Its parameter was found to be 8.31 A,, and no lines corresponding to other Abstances were found. The experimentally determined heat contents above 298.16' h'. of ferrous and magnesium chromites are given in Table I. Thc columnslabeled T oK. give the absolute temperature of the Sample before being dropped into the calorimeter; the columns for HT H B ~list . ~the ~ heat liberated per gram molecular weight of material in dropping frcm T o to 298.16' K. Small correc-
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
934
TZBLE I. HIGH-TEMPER tTt7RE H E Z T C0NTE:Pi.P r--
T o K.
FeCr20r-HT -
-.
Hzss.1b.
oal./g. mol. w t . 2.940 7,090 11,820 16,300 22,000 26,200 29,860 33.920 38;880 43,7011 46,870 51,670 ~ , 3 2 n 57.250 63,040 63,990
386.2 498.7 616.6 725.4 861. o 959. z 1041. 1133.6 1242. D 1350,s 1418.8 1622.8 1622.1 1845. D 1769. o 1786.2 1786.9
--
sIgCr20i----
H T - Hzsn.16, eal./g. mol. w t .
T o Ii.
2,930 8,900 i3,mn 19,740 35,970 80,810 37,570 43.600 24,980 19,270 53,0511
387.1 546. o 658.9 816.1 961,s 1077,6 1232. n 1370.1 1400. i 1473.8 1581.6 1644.9 1782. s
55,900
tx.140
64,090
Vol. 36, No. 10
the smooth curves, and calculated entropy increments at even 100' intervals from 298.16' K. to temperature T are summarized in Table 11. No previous high-temperature heat content data of comparable accuracy appear in the literature. From the specific heats a t 298.16' K., Cp = 31.98 and 30.30 calories per degree per mole for ferrous and magnesium chromites, resprctively ( I ) , and the heat content data, the following algebraic rqnations were derived. Below 600' K. the heat content equation for ferrous chromite may be in error by as much as 150 calories; at higher temperatures it has an average deviation of 0.2% with a maximum deviation of 0.4% around 1200" K The heat content equation for magnesium chromite fits the data within 30 calories below 600" K.; above that temperature it has an average deviation of 0.15%, the maximum error being about 0.3%. The specific heat equations wcre obtained by differentia tion : FcTr,O,:
7'62
T 400 500 600 700 8ao 900 1000 1100 1200 1300 1400 1500 1600 1700 1800
3,450 7,100 11,150 15,280 19,450 23,660 27,960 32,390 36,920 41,460 46,000 50,550 55,200 59,860 64,600
9.88 18 03 25 41 31 77 37 25 42 31 46 84 51 OR
55 0 0
58 64 6 2 . 00 H5.14 68.14 70.97 73.67
3,350 7,040 10,930 14,920 19,050 23,280 27,500 31,800 36,120 40,460 44,920 49,390 53,880 58,360 62,860
9.63 17.86 34.95 -31. 10
C,
= 38.96
MgCrs04: H T -
40.02T
'"*
--____
T
10-32'2
+
-
14,410 (298-1800' K.)
T
X 106 - 7.62 T --
+ 1.78 X 10-3T2 -f - 15,310 (298-1800° K.) 9.58
CP = 40.02 + 3.56 x 10-3 T - --Fi
60,68 63.76 66,66 69,38 71 95
tiong were made to the values ill Table I for the silica ( 2 ) arid iron impurities. The silica of the ferrous chromite wah taken as 0.75% and the iron in the magnesium chromite was considered to be present as 0.5% ferrous chromite. All molecular weights accord with the 1941 Interriational Atomic Weights. No discontinuity is discernible in the heat rontent curve of eithrr substance. The heat contents, read from
'"6
+ 5.34 X
Hz98.16=
36.62
41.60 46,04 50.14 53,90 57.38
+ 2.67 X
H T - H298.18 = 38.961'
x
106 --
ACKNOWLEDGMENT
Both samples were prepared and chemically analyzed at this station by F. S. Boericke, assisted by W. M. Bangert. The x-ray examination of the chromites was kindly carried out under the direction of E. v. Potter at the Salt Lake City Station. LITERATURE CITED
C . H., IND.ENG.CHEM.,36,910 (1944). (2) Southard, J. C., J. Am. Chem. Soc., 63, 3142 (1941). (1) Shomate, PURLISRED
by permission of the Director, U. S. Bureau of Mines.
Nomogram to Convert Weight and Mole Percentages in Binary Systems ROBERT F. BENENATI AND JOHN G . HARRISON, JR. Polytechnic Institute, Brooklyn, N. Y.
A
NALYTICAL results are almost always expressed as weight percentage, but the physical chemist, the engineer, or the operator in synthesis usually works with mole fraction or mole percentage. The physical chemist best understands ideal solutions and deviations from them when dealing in mole fractions. The chemist in synthetic work considers his reactions in terms of moles of reactants and moles of products. The chemical engineer designs much of his equipment in unit operations by working with mole fractions. Since both additive and multiplicative operations are involved in this conversion, a mathematical solution is imposed to which no ready short cut is available even when a whole series of similar calculations is to be made. Several graphical calculators to effect
this conversion of weight per cent to mole per cent arid vice vtma have appeared in the literature'. Each of these, however, requires an arithmetic calculation, and in some cases the chart is complicated. The nomogram presented here involves no calculation and furnishes a direct solution for mole per cent when composition by weight and molecular weight of the two components are known. A solution is also possible for weight per cent when mole per cent is known.
* Baker, J. S.,Chem. & Met. Eno., 45,166 (1938); Bridger, G. L., Ibid., 44, 451 (1937); Nevitt. E. C., I b i d . , 39, 673 (1932); Patton, T. C., Ibid., 41, 148 (1934); Winnioki, H. 9.. and Chellis, L. N.. Ibid., 47, 694 (1940); Underwood, A. J. V.,Trans. A n . I n s t , Chern. Enyrs., 10,145 (1932).
