J. C. SOUTEIARD AND C. HOWARD SROMATE
1770
TABLE IV HEAT CONTENTS AND ENTROPIES ABOVE 298.1' K. CAL./G.F. w.AT 100' INTERVALS Temo., OK..
400 500 600 700 800 900 1000 1100 1200 1300 1310 1310 I400 1445 1445 1500 1600 1700 1800
--bfnrOaHT ST -. Hzss.1 Szo8.1 3,700 10.60 7,590 19.26 11,590 26.54 15,760 32.96 19,880 38.59 24,230 43.59 28,620 4 8 . 2 2 33,130 52.52 37,740 56.53 42,620 60.43
-
47,960 ~50.460 854,960 57,700 62,700 67,740 72,820
64.39 66.15 68.26 71.12 74.38 77.40 80.31
[CONTRIBUTION FROM
IN
-
ST-
HT-
H286 1
s198.1
H198.1
2,450 5,020 7,700 10,490 13,350 16,300 19,300 22,400 25,650 29,200 a29,550 832,690 36,040
7.07 12.79 17.67 21.96 25.78 29.25 32.41 35.36 38.19 41.03 41.30 43.70 46.17
2,320 4,800 7,430 10,200 13,080 15,980 18,890 21,830 24,900 27,950
12.19 16.98 21.24 25.09 28.50 31.56 34.37 37.04 39.45
31,090
41.77
39,840
48.79
34,300
43.99
HT
THE
ST
-
S198.l
Vol. 64
This table, in combination with similar tables for oxygen, carbon, and silicon, permits ready calculation of free energies a t these temperatures from whatever values of the heat of formation an investigator may select.
6.66
Summary The heat contents of Mns04, MnSiOa and Mn8C from room temperature to temperatures between 1140 and 1500" have been determined. These determinations have disclosed transitions of Mn304a t 1172O and MnsC at 1037'. A table summarizing the increments in the heat contents and entropies of these substances above room temperature a t 100" intervals has been prepared from these data and others in the literature. KIAGARA FALLS, N. Y.
RECEIVED APRIL6, 1942
METALLURGICAL FUNDAMENTALS SECTION, METALLURGICAL DIVISION,BUREAUOF MINES, UNITED STATES DEPARTMENT OF THE INTERlOR]
Heat of Formation and High-temperature Heat Content of Manganous Oxide and Manganous Sulfate. High-temperature Heat Content of Manganese' BY J. C . SOUTHARD~ AND C. HOWARD SHOMATE~ The free energy of formation of manganous oxide at high temperatures has been uncertain because of the lack of satisfactory high-temperature heat content data. Further, the heat of formation of manganous oxide has been based almost entirely on heats of combustion. The combustion of manganese metal with oxygen in the bomb calorimeter does not proceed according to any definite reaction but yields a mixture of oxides assumed to be manganous oxide and manganomanganic oxidc4#5 The mixture consists of 10 to 50 per cent. manganous oxide. The heat of formation of manganous oxide therefore has depended on the combustion of manganous oxide to manganomanganic oxide. This requires the use of paraffin oil and also yields a product of varying composition. Under these conditions the heat of reaction is only 5 per cent. of the total heat measured.6 The heat of reaction also seemed to de(1) Published by permission of the Director, Bureau of Mines, U. S. Department of the Interior. Not subject to copyright. (2) Formerly Chemist, Metallurgical Division, Bureau of Mines; present address, Titanium Alloy Mfg. Co., Nlagara Falls, N. Y. (3) Assistant Chemist, Metallurgical Division, Bureau of Mines (4) W. A. Roth, L.angcw. Chcm., 42, 981 (192Y). (5) H. Siemonsen, 2. Elckfrochcm., 45, 637 (1939).
pend on whether the fraction converted to manganomanganic oxide was determined by increase in weight or by actual a n a l y ~ i s . ~Determination of the heat of formation of manganous oxide by a completely independent, more direct, method appears advantageous. The thermodynamic properties of manganese sulfate have been studied and entropies of the substances involved already have been determined, as well as the high-temperature heat-content data, with the exception of manganous sulfate. The heat of formation of manganous sulfate has not been determined since the days of Thomsen and Berthelot, at which time pure manganese was not available. Methods and Materials The high-temperature heat contents were determined in an apparatus previously described.$ The apparatus was calibrated electrically, using the relation 1 calorie = 4.1833 Int. joules. During the measurements manganous oxide and manganous sulfate were contained in a sealed platinum-alloy capsule and manganese metal in an evacuated and sealed silica-glass capsule. The heats of formation of manganous oxide and manganous sulfate (6) J C. Southard, THISJOURNAL, 63, 3142 (1941).
HIGH-TEMPERATURE HEAT CONTENT OF MANGANESE
ilug., 1942
1771
TABLE I HEATOF SOLUTION
OF
MANGANESE, MANGANOUS OXIDE AND MANGANOUS SULFATE I N 1.006 N SULFURIC ACID 1 G. F. W. I N 100.27 KG. ACIDAT 298.1' K. Manganese sample A, cal./g. f. w.
-54,023
Mean C o r m for evap. of water Corm. for diln. by water Corrected mean
MnO, cal./g. f. w.
-54,041 -54,008
-30,607 -30,643 -30,653
- 54,024 111
-30,634
Manganese "quenched," sample B, cal./g. f . w.
MnSO4, cal./g. f . w.
- 11,621
-54,081 54,111 -54,089 -54,075
-
-11,644 -11,623
* 18
- 11,629110
-54,089111 -332
- 11,629
-54,421
-332 -54,356
2 -30,632
were determined by the solution of manganese, manganous oxide and manganous sulfate in 1.006 N sulfuric acid solution in a calorimeter also described previously.' The time of solution was about twelve minutes for manganese and manganous sulfate and about twenty to thirty minutes for manganous oxide. The manganese metal was an electrolytic product a t least 99.9 per cent. pure. It was degassed by heating to 850" in a vacuum corresponding t o mm, and allowed to cool slowly (sample A). A portion of this sample was quenched from 800' in the high-temperature calorimeter (sample B) for use in certain heat-of-solution measurements. The metal was sized by passing through a 20onto a 28-mesh screen. The manganous oxide was prepared by Millar8 by reduction of higher oxides with hydrogen at 1100'. It was further purified for this work by removing visible particles of silica by flotation with tetrabromomethane, followed by drying in a high vacuum up t o 250'. Analysis showed that it contained less than 0.04y0 silica and 77.42, 77.45% M n (calcd. 77.44%). Manganese sulfate was prepared from a hydrated "c. P." preparation. It was found t o contain 36.33% Mn by analysis (calcd. 36.38%). It was dried to constant weight in the capsule and bulbs a t 400' before being weighed and sealed.
Results
Heat of Formation.-The heats of solution of manganese, manganous oxide, and manganous sulfate are summarized in Table I. Determinations were made a t the dilution of 1 gram-atom of manganese to 100.27 kg. of acid solution. Correction for the vaporization of water by evolved hydrogen was made on the assumption that none of the hydrogen remained in solution by the time equilibrium was attained, and that i t was saturated with water vapor when i t left the solution. The partial pressure of water vapor over the acid solution was taken to be 23.34 mm. a t 25" with a temperature coefficient of 0.14 mm. per degree. The heat of vaporization of water from 1 N sulfuric acid was taken to be 10,501 cal./g. f. w. a t (7) J. C.Southard, I n d . Enp. Chem., S4, 442 (1940). (8) R. W. Millar. THIS JOURNAL, 60, 1876 (1928).
25". The final temperature lay between 25.0 and 25.2 O in every case. The heat of formation of manganous oxide, according to Eq. 5 , is calculated from the heats of the following reactions, all a t 298.1 O K. Mn,
+
49.05 H601.5299 HzO(soln.) ---f MnS0~48.05H2SO~5299HzO(soln.) Hz(g) (1) MnO(s) 49.05 HzSO~5299HzO(so1n.) + MnSOp.48.05 H 9 0 ~ 5 3 0 0HzO(so1n.) (2) MnS0~48.05H z S 0 ~ 5 2 9 H20(soln.) 9 4- HzO(1) + MnS0~48.05HzSOp.5300 H20(soln.) (3) Hz(d I/zOz(g) +HzO(1) (4) Mr4r l/zOdg) +MnO(s) (5) AH5 = A H 1 AH4 A H 2 f AH%
+
+
+ +
+
-
The heats of reactions (l),(2) and (3) are given in Table I. The heat of reaction (4) was determined by Rossinig as -68,318 * 9 cal./g. f. w. The heat of formation of manganous oxide from the elements a t 298.1' K. is thus computed to be -92,040 * 110 cal./g. f. w. The limits of error are estimated as the sum of the average deviations from the mean of the heats of solution of manganese and manganous oxide, plus 0.05% of the total energy measured, plus 10% of the correction for vaporization of water plus 9 calories uncertainty in the heat of formation of water. The value computed here allows the maximum correction for vaporization of water by the evolved hydrogen. Any other assumption would decrease the magnitude of the heat of formation. A comparison of the present value of the heat of formation of manganous oxide with those previously determined is given in Table 11. Virtually all previous data were obtained by combustion methods from Le Chatelier's day on. The value determined here by solution methods is believed to be more trustworthy than that obtained by combustion methods, for two reasons. (1) The combustion process does not proceed ac(9) F. D. Rossini. Bur. Sfondords 1.Res., 42,407 (1939).
J. C. SOUTHARD AND C. HOWARD SHOMATE
1779
1701. 64
290" K. as -17,350 calories. No correction was made to 298.1 " K., and the error is estimated a t AHm.1 *50 cal. The heat of reaction (11) must necesYear Method cai./g. f. w 1.r Chatelierl" 1896 Combustion w i t h o. sarily be assumed the same as that of reaction (6) and charcoal but little error can arise from this source because Guntz" 1896 Not stated -98,200 Kotha 1920 Combustion with oxygen -96.200 the ionic strengths of the solutions are the same. and oil The heat of formation of manganous sulfate from Sirmonsen' 1939 Combustion with oxygen -93,100 aud oil the elements is thus calculated to be -254,180 * This work 1942 Solution in 1 .Y sulfuric -22,040 * 110 250 cal./g. f. w.a t 298.1 K. The limits of error dcirl are estimated as the sum of the average deviations cording to any definite reaction, while the initial from the mean of the heats of solution of mangaand final states in the solution method are wellnese and manganous sulfate, plus 0.05% of the defined. ( 2 ) The total amount of heat per g. f . w. total energy measured, plus 10% of the correction of manganous oxide measured in the combustion for vaporization of water by the hydrogen in Eq. 1, method is 5 to 7 times that measured by the soluplus 100 calories in the heat of formation of sultion method. The agreement between the presfuric acid plus 50 calories for the heat of reacent work and that of Siemonsen is evidence of tion (10). extremely careful calorimetry on his part. The Previous determinations of the heat of formaresult of Roth and Muller is higher because they tion of manganous sulfate a t room temperature by used a sample contaminated by silicon and alumiThomsen (AH= -249,730) and Berthelot (AH num and probably because it contained hydrogen. = -249,400) are discussed by K e l l e ~ . ' ~MaierIG The heat of formation of manganous sulfate has calculated a value of A H 2 9 8 . 1 = -250,700 from the elements (Eq. 8) is calculated from Eq. (1) from the dissociation pressure measurements of above, in combination with the following reactions, M a r ~ h a 1 . l ~This value is not changed much by all a t 298.1O K. using the present high-temperature heat-content H r + S(rM + 202 -I- MnS04.48.05 HzSOa.5299 H20(soln.) dattl, but may be changed by the proposed in+ MnSO4.49.O5H2SOi.5299H20(soln.) ( 6 , vestigation of the heat of formation of mangano'LInS04(sl + 49.05 H2SO4.5299 HzO(so1n.) + manganic oxide. However, Marchal's data lead MZnSO449.05 HzS005399 HzO(so1n.) ( 7 ) hln, + S ( r h j + 2O%(g)-+ MnSOa(s) to an abnormally high entropy of manganous sul(8) A H 8 = A H , +- AH6 - AH, fate so that not much weight can be given to The heat of reaction ( 7 ) is given in Table I. A H 0 values of the heat of format'on calculated from is calculated from the heats of the reactions them. Hdg) S(rh) 2Odg) --+ HrS04(1) The difference in the heats of solution of an(9) I-i2SOril)+ 4!1.09 HSOl.5299 KzO(soln.) + nealed and "quenched" manganese is computed 50.08 H2S0~.5299H?O(soln.) (IO) from Table I to be 65 calories per g. f. w. This H d g ) + S'rh: -I- 202(gi + 49.05 HzS04.5299H20(soln.) heat is required for the calculation of heat contents +50.05 H2SO4.9299 HpO(SOlI1.) (11) of manganese above the transition a t 1012" K. A H i i == AEZg + AHLo High-temperature Heat Contents.-The measThe heat of reaction 9 was calculated to be urements of the heat content a t T o K., minus the - 194.100 * 100 cal./g. f. w. from the heat of forheat content a t 298.1" K. for manganese, mangamation of sulfur dioxide of Eckmann and Rossini12 nous oxide, and manganese sulfate, are given in and the heat of oxidation of sulfur dioxide and Tables 111, I V and V. Manganous oxide and heats of solution of sulfur dioxide, sulfur trioxide manganous sulfate show no transitions. Manand sulfuric acid obtained by Roth, Grau and ganese metal shows a transition at 1012" K. Meichsner.13 It was necessary to correct some of Known transitions a t higher temperatures could the data to 25". The limits of error are those set not be investigated in this work because of devitby Koth. The heat of reaction (10) has been calculated from the data of Grau and RothI4a t about rification of the silica-glass capsule and reaction o f the manganese with it. The correction of 6.5 110) H. Le Chatelier, Gompt. rend., 122, 80 (1896). (11) Guntz, ibid., 122, 4G5 (189G). cal./g. f . w. must be applied to the data of Table (12) J. D. Eckmann and F. D. Kossini, Bur. Standards J . Res., 3, 111 above 1012' K. because the manganese did 597 (1929). TABLE
I1
HEATOF FORMATION OF MANGANOUS OXIDE
+
+
(13) W. A. Roth, R. Grau and A. Meichsner, 2. anorg. Chsm., 198, 169 (1930). (14) R . Grau and W. A. Roth, ibid., 188, 195 (19301,
(15) K. K.Kelley, Bur. Mines Bull., 406, 101 (1937). (16) C. G. Maier. Bur. Mines knf Circ. 6769,623 (1934) (171 G. Marchal. J. chrm. fihrr., 94, 559 (1925).
Aug., 1942
HIGH-TEMPERAURE HEATCONTENTOF MANGANESE
1773
not come t o the same final state in the calorimeter when dropped from temperatures above this as when dropped from temperatures below it. It is not supposed that this quantity represents the difference in heat content between a and /3 manganese at 298.1' K. but merely that it is a correction that must be applied to the calorimetric heat obtained when the capsule was dropped from the temperature range in which /3 manganese is stable.
the present work of a transition reported by Gaylor a t 943' K. Previous measurements on the high-temperature heat content of manganese have been surveyed by Kelley.20 The present work lies between that of Umino and that of Wiist, Meuthen and DurrerZ1and not far from that of LaemmeLZ2 The present work is believed to be more reliable because it was done with a higher-purity sample of manganese, completely protected from oxidaTABLE I11 TABLE IV tion, and with a higher-precision calorimeter than HIGH-TEMPERATUTE HEAT HIGH-TEMPERATURE HEAT was previous work. CONTENT O F MANGANESECONTENT O F MANGANOUS No previous determinations have been reported (g. f . w. = 54.93) OXIDE on the heat content of manganous oxide and (g. f. W. = 70.93) HT - Hrsr.1 T, K. cal./g. f. w. manganous sulfate a t high temperatures. HT - Hsos.1 963.8 5030 T, ' IC. cal./g. f. w. Table VI is a summary a t 100' intervals of the 4987 962.8 1268.6 12,050 heat content and entropy above 298.1' K. of 4686 925.6 1270.1 12,080 manganese, manganous oxide and manganous sul2622 669.0 1041.6 8,980 2626 669.3 1043.5 8,980 fate. The 65-cal. correction to the heat content of 1264 486.4 774.6 5,600 manganese in the /3 range has been applied. Table 1206 774.6 5,572 481.7 VI also includes values of the free energy of forma4307 880.7 519.8 2,517 tion of manganous oxide from gaseous oxygen and 4298 879.2 2,503 518.9 the form of manganese stable a t the stated tem5016 15,490 962.5 1519.0 5361 1003.9 1511.0 15,310 petature. The present value of -92,040 cal./ 5134 977.6 10,440 1153.8 g. f. w. for the heat of formation of manganous ox6103 1027.1 1258.5 11,850 ide is used in conjunction with the values 7.61, 6395 1071.8 1773.4 18,980 24.52 and 14.4 for the entropies of manganese, 1075.4 6431 TABLE V '/2 oxygen and manganous oxide, r e s p e c t i ~ e l yto ,~~ 1013.0 5988 HIGH-TEMPERATURE HEAT calculate a free energy of formation of manganous 2d serif S CONTENT O F MANGANESE oxide of -86,760 cal./g. f. w. at 298.1' K. Values 4116 855.5 SULFATE a t higher temperatures were calculated with the 7221 1153.0 (g. f. w. = 150.99) 1161.6 7331 aid of the present high-temperature heat-content HT - H29I.l T, K. cal./g. f. w. 8246 1260.1 data on manganese and manganous oxide and the 8276 1264.5 870.3 18,180 tables of free energy of oxygen given by Johnston 1307.3 8666 873.5 18,250 and Walker.24 Comparison may be made with 8640 681.5 11,620 1307.3 the experimental data of Aoyama and Oka26 for 1105.8 679.9 11,480 6737 1379.1 9505 497.0 5,520 HzO(g) Ft MnO Hs(g). the reaction Mn 483.3 5,070 They made five determinations in the tempera1083.6 26,140 ture range 1,048 to 1,460" K. Their data were 1082.3 26,060 recalculated to the reaction Mn ' / 2 0 2 + MnO The heat of transition CY --+ /3 manganese is cal- by adding the free energy of formation of water culated from the heat-content data to be 615 cal- vapor, which was calculated from the tables of ~ ' the free ories per g. f. w. a t 1012' K. This includes the A. R. Gordonz6and W. F. G i a u q ~ e , and energy of formation of water vapor a t 298.1' K. above-mentioned 65 calories. Gaylor'* reported the transition as occurring a t 1013 f 2' K., with (20) K. K. Kelley, U.S.Bur. Mines Bull., No. 871, p. 34 (1934). (21) F. Wiist, A. Meuthen and R. Durrer, Forsch. Arb. Vcr. deul. distilled manganese. Uminolg observed that this Ing., No. 204 (1918). transition occurred at 1108' K., accompanied by a (22) R. Laemmel, Ann. Physik, 16, 551 (1905). (23) K. K. Kelley, Bur. Mines Bull. 484, 115 (1941). heat effect of but 68 calories per g. f. w. Other in(24) H. L. Johnston and M. K . Walker, THISJOUR"., 66, 183 vestigators of the high-temperature heat content (1933). (25) S. Aoyama and Y.Oka, Sci. &pis. TGhoku I m p . Uniu., B2, observed none at all. There was no evidence in
+
+
+
(IS) M. L. V. Gaylor, J . Iron Steel Znst., 116, No. 1, 393 (1927). (19) S.UminO, Sci. &#is. Tcfhoku Im). Uniu., 16, 7711 (1927).
824 (1933). (26) A. R Gordon, J . Chem. Phys., 2,65 (1934). (27) W, P.Giauqua, TEIS Jooaudsi, Iu, 8818 (1880).
GILBERTX. LEWIS,THEODORE T. MAGELAND DAVID LIPKIN
1774
1701. 64
TABLEVI HEATCONTENTS AXII ENTROPIES OF MANGANESE AND MANGANOUS OXIDEABOVE 898.1' K. AND THE FREEENERGY OF FORMATION OF MANGANOUS OXIDEAT 100' INTERVALS >In -
. .
NT
?',
K.
298.1 400 500 600 700 800
- H?SS
cal,!g.
E
i
lr
tM1 136.1
2100 2871 3668
900 1000 1012cr
448(1
101213 1100 1200 1300 13408 1340-y 1400 1500
fii153
-.
.,3"X',
513h Gi5U 734 8fi72 SO&
9220)
i 9770 ;lo690
I&--
.-
S T - Sr8a.,, cal./deg. i. f . \v.
1 . 8H 3 . ,46 .4,80
5.99 7.05 3.00
s.90 9.01 9,H2 10.26 11.11 3 1.86 12.14 (12.28) (12.69) (13.33)
- H I MI.
FIT
cal./g. f .
K
1130
ST - s298.1 cal.ideg. g.
f.
R.
3.26 5.82 7.99 9.85
mation, cal./g. f. w.
ST - sZ98.1.
-86,760 -84,970 -83,240 -81,520 - 79,820 -78,120 - 76,430 -74,730
2680 5630 8850 12210 15710 19280 22970
i . 70 14.28 20.14 25.32 29.99 34.18 38.07
- 73,000
26730
11.65
!U50 I 1100 12470
13.56 16.73 17.82
-71,260 -69,500
13840 15210
18.84 19.79
-67,740 -65,980
[CONTRIBUTION FROM THE CHEMICAL
- H~e8.l.
cal./deg. g. f. w.
12.95 14.30
given by R o s ~ i n i . ~The three lowest of Aoyama and Oka's points lie within a few hundred calories of values interpolated from Table VI, which may be said to be in good agreement. In general, however, their data give a larger aE-I and A S for the reaction than may be calculated from the third law. Summary The heat of formation of manganous oxide has been determined to he -92,040 * 110 calories per g. f . w and or' manganous sulfate to bp
HT
cal./g. f. w.
2380 3470 4680 3900 7 150 8430
11.18
MnSOd-
7 -
A F of for-
-254,180 * 250 calories per g. f . w. a t 25'. The heat contents of manganese, manganous oxide, and manganous sulfate from room temperature to temperatures between 811 and 1500° have been determined. These observations have disclosed a transition in manganese a t 739". A table summarizing increments of heat contents, entropies and free energies a t 100' intervals has been prepared from these data and others in the literature. NIACARA FALLS, N. Y.
LABORATORY O F THE
RECEIVEDAPRIL6, 1942
UNIVERSITY O F CALIFORNIA]
Isomers of Crystal Violet Ion. Their Absorption and Re-emission of Light BY GILBERT N. LEWIS,THEODORE 7'. MAGEL. AND DAVID LIPKIN
The possibility of a new type of isomerism ill such substances as triphenylmethyl and its ions was pointed out recently.' An extensive investigation of the light absorption of the free radicals llas not given US Dositi1-e evidence of such isointhe i t h e r hand, in the derivati\,es erism.2 (1) Lewis a n d Calvin, Chem. Rcu., 25, 2 i 3 (1939). (2) The two absorption bands of triphenylmethyl in the visiblc which were obtained by Meyer and Wieland [Bel,., 44, 2.537 (191 1) 1 and which were resolved into three bands by Anderson [THISJ O U R XAL, ST, 1673 (1936)l were shown by Dr. o. Goldschmid [ m . D . Thesis, University of California (1939)] t o be vibrational bands belonging t o a single electronic band. This was shown by comparison uf the absorption a n d fluorescence spectra of triphenylmethyl. W e have further confirmed his results, but with a very high resolution we have found much niwe intricate structure. This will be dist,ussr.d i n another place
of triphenylmethyl ion we have sought, and believe to have found, these isomers. It is often observed that the absorption curve of what is apparently a single substance, such as the ion of crystal violet (tris-(dimethyl-P-aminophenyl)-methyl ion, Fig. 6) as it exists in neutral or alkaline solution, has a shoulder as seen in Fig. 1. This shoulder SUggWtS the SUperpOSitiOn of two neighboring bands, which might fronl (1) a partial resolution of the vibrational struclevel, which, ture belonging to a single according to the work of Dr. Goldschmid,zseems to shoulder in the adbe the explanation of a sorption cwrw of methylene blue, or ( 2 ) two neigh-
