INDUSTRIAL AND ENGINEERING CHEMISTRY
JANUARY, 1936
lar mixtures. The use of partial quantities as described by Lewis and Randall ( 1 ) furnishes a suitable means for such evaluation. The partial specific heats a t constant pressure in the liquid mixture at bubble point were calculated both for n-butane and for crystal oil as functions of composition of the solution for a series of temperatures. The method used for these calculations was the graphical one described by Lewis and Randall ( 1 ) . The results are shown in Figure 12. The partial specific volume a t bubble point was also calculated by the same method. Such results are given as a function of the composition for a series of temperatures in Figure 13. These partial quantities are probably accurate to approximately 5 per cent.
Melting Points
of Eutectics SIDNEY J. FRENCH Colgate University, Hamilton, N. Y.
TEIKMETZ (3) stated in 1918: “When looking up the literature for eutectic alloys of low melting point, records of a large number were found, but most of them proved not to be eutectics, and the given melting points were frequently erroneous, due to disregarding of the undercooling of the alloy.” A Bureau of Standards circular ( 2 ) reviewed the literature on quaternary alloys of bismuth, lead, tin, and cadmium in 1930 and stated: “Considerable confusion still exists in the literature. . . The fallacy of a 60” melting point still persists in recent articles. . I n one case, the statement that Parravano and Sirovitch’s eutectic (49.5 per cent Bi, 27.27 per cent Pb, 13.13 per cent Sn, 10.10 per cent Cd) melts a t 70” C. is followed by the statement that Wood’s metal (50 per cent Bi, 25 per cent Pb, 12.5 per cent Sn, 12.5 per cent Cd) melts a t 60” C. . , . When the composition approximates that of a quaternary eutectic, the alloy usually is called Wood’s metal or, less commonly, Lipowitz metal. Both names are applied loosely to any metallic alloy which is completely molten a t temperatures below 100” C., or more specifically to alloys which melt not far above 70“ C.” Table I gives the reported melting points of Lipowitz alloy and Wood’s metal from a number of sources. Some sources report a higher melting point for one than for the other, and vice versa. Few references indicate that both alloys should have the same melting point. The International Critical Tables assign to the eutectic alloy the composition: 50 per cent bismuth, 27 lead, 13 tin, 10 cadmium. h-o name is given to the alloy. Most references agree in calling the alloy of this (approximate) composition Lipowitz alloy, and the alloy of the composition, 50 per cent bismuth, 25 lead, 12.5 tin, 12.5 cadmium, Wood’s metal.
OS .
. .
111
I n acknowledgment, thanks are due the American Petroleum Institute for financial support and active interest in this work. J. E. Sherborne and H. S. Backus assisted in the experimental measurements.
Literature Cited (1) Lewis, G. N., and Randall, M., “Thermodynamics,” pp. 33 and
36,New York, McGraw-Hill Book Co., 1923. (2) Sage, B. H., Backus, H. S., and Lacey, W. N., IND.ENG.CHEM., 27, 686 (1935). (3) Sage. B. H..and Lacev. W. N., Ibid.. 27. 1484 (1935). (4j Sage; B. H., Schaafsma, J. G., and Laoey, ‘W. N., Ibid., 26, 1218 (1934). RECEIVED M a y 21, 1935.
Lipowitz Alloy and
Wood’s Metal Much confusion exists concerning both composition and melting points of the socalled Lipowitz alloy and Wood’s metal. Although they differ slightly in composition, these alloys have the same meltingfreezing range (69.7’ to 71.1’ C.). The alloy of composition 50 per cent bismuth, 27 lead, 13 tin, 10 cadmium, approaches the eutectic composition more closely than does the alloy composed of 50 per cent bismuth, 25 lead, 12.5 tin, 12.5 cadmium. Many of the abnormally low points reported in the literature may be those of undercooled alloys or amalgams. Confusion can best be eliminated by dropping both names, calling the eutectic alloy simply a quaternary eutectic, and stating its composition and meltingfreezing range. A number of factors have probably been responsible for the confusion existing regarding both names and melting points of these alloys, including (1) lack of understanding of the nature of alloys approximating a eutectic composition, ( 2 ) melting and freezing ranges found in eutectics, (3) methods of determining melting and freezing points, (4)impurities in the metals used, (5) lowering of melting points by the addition of mercury, and (6) loose application of names to sundry lowmelting alloys.
Nature of Eutectic Compositions A true eutectic should have characteristic cooling and melting curves and sharply defined melting and solidifying
INDUSTRIAL AND E N‘GINEERING CHEMISTRY
112
TABLE I. MELTINGPOINTS REPORTED FOR LIPOWITZ ALLOY AND WOOD’S METAL Reference
--Melting Lipowitz alloy
Point-Wood’s metal
c. International Critical Tables Mellor “Inorganic and Theoretical Chemistry” Hodgdan, Handbook of Chemistry and Physics, 18th ed. Partington, “Textbook of Inorganic Chemistry,’’ 4th ed. Latimer and Hildebrand “Reference Book of Inorganic Chemistry,’’ ?,kt ed. Roscoe and Schorlemmer. Treatise on Chemistry.” 1913 Molinari, “Treatise oy, General and Industrial Inorganic Chemistry 1912 Watts, Dictionary of Chemistry, 1890 Threfall ( 8 ) Gilbert ( 8 ) Parravano and Sirovitch (3) Honnell ( 8 )
e
c.
70-74 76-76
74+5
70-74
65.5
60-65
71
60
71
60
71
60-70
60-72 68
...
8&i(5 70 66 60 63 70 75-76 60-68 68-74.5
74 60.6
... ...
...
65.5 60.5 74-75 65.5 88.5-73
points represented by the horizontal parts of the curves. In
a noneutectic some of the ingredients should solidify before the eutectic temperature is reached, causing a shift in the time-temperature curve and in the composition of the alloy which then approaches the true eutectic composition. The solid ingredients coming out of solution should thicken the mixture and, if present in considerable amounts, may cause complete solidification before the eutectic temperature is reached. If present in small amounts, the solid material should have little effect on the fluidity of the mixture which remains a practical liquid until the eutectic temperature is reached. In other words, if the composition of an alloy varies but slightly from that of a eutectic, it should solidify at the eutectic temperature, although the horizontal portion of the cooling curve will be shorter than that of a true eutectic. Steinmetz (3) varied the proportions of some of the metals in Lipowitz alloy as much as 20 per cent and obtained the same final freezing point, although the horizontal temperature range was somewhat shortened and the alloy somewhat thickened before solidification. The very small differences in the composition of Lipowitz alloy and Wood’s metal indicate that the two should have appreciably the same freezing and the same melting points. To determine the melting and freezing points of the two alloys and to compare their cooling and melting curves, 50-gram samples of each were prepared from the purest c. P. metals obtainable. In the preparation of each alloy, the metals used were cut from the same piece or came from the same container so that any impurities, if present, would appear in both alloys to an equal extent and affect both alike. In each case the lead was first melted and each metal was added in turn to the liquid. The alloys were kept in a molten condition for some time and were constantly stirred t o insure complete mixing. The order of 76
Li
w
L Y
7‘
3 b-
a
cc a w
P
w i-
70
66
61
T I M E IN MINUTES
FIGURE1. COOLINGCURVESOF LIPOWITZ ALLOYAND WOOD’SMETAL
VOL. 28, NO. 1
addition of the metals made no difference in the melting points. Preliminary work1 indicated that both alloys had the same freezing point. The samples were placed in large test tubes, both of which were immersed side by side in the same bath. In all, some twenty-five studies were made of cooling and of melting curves, using various cooling and heating rates and various baths, including single water baths, double water baths, air and water, air, and asbestos. The best results were obtained with a double water bath and a temperature-time interval of 0.3’ to 0.6” C. per minute. The alloys were constantly stirred during cooling and during melting as soon as the were sufficiently fluid to stir. The water bath was stirred wit{ a motor stirrer. The thermometers used were compared with one another and differed by no more than 0.2” C. at any point within the range used. Furthermore, the thermometers were frequently transposed to correct for the small error. Later, both thermometers were compared with a Bureau of Standards certified thermometer. The average deviation of the thermometers over the range of temperature used was f0.2” C . The deviation at the freezing and melting points was +0.2” C. Figure 1 shows typical cooling curve and Figure 2 a typical melting curve for the two alloys. The curves not only indicate clearly the similarity of the two alloys, but they also show that the Lipowitz alloy approaches the eutectic composition more closely than does Wood’s metal. Nevertheless, the horizontal portions of the curves coincide, as was to be expected. The actual points a t which the alloys could be regarded as completely solid or completely molten were difficult to determine and sometimes appeared to lie just beyond the horizontal portion of the curves. Considerable subjective judgment was involved in v’
7b
w
ng
7%
a r Y
P Y
z 68
+
Y
“ 0
4
8
I1
TIME IN
I6
20
14
18
MINUTES
FIGURE 2. MELTINGCURVESOF LIPOWITZ ALLOYAND WOOD’SMETAL
deciding what constituted the completely solid or molten state. However, the lag was always small and was not more than 0.2” C. in any case. The actual solidifying and melting temperatures of Wood’s metal was sometimes 0.2” to 0.3” above that of Lipowitz alloy but usually no difference could be detected. The freezing point (69.7’ C.) and melting point (71.7” C.) reported here are the temperatures represented by the horizontal portion of the curve. Steinmetz (3)reported 69.5” C. as the freezing point of the eutectic.
Melting a n d Freezing Ranges of Eutectics Ideally, a eutectic should melt and freeze a t the same temperature, but practically the ideal is never reached, as is evidenced by the wide melting and freezing ranges reported for eutectics. Such alloys usually melt several degrees above the point of solidification even under the best conditions. This phenomenon was discussed by Budgen (1) and attributed by him to surfusion. In this work the melting points were found to be 2 O C. above the freezing points. Even though the rate of heating was changed considerably and precautions were taken against superheating, the difference between melting and freezing points was constant. If only one temperature point is indicated, it seems necessary to specify either freezing or melting point. Otherwise the range between the two points should be reported. 1 The preliminary work was carried out by Edwin Phillips and Donald Saunders, students at Colgate University.
JANUARY, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
Means of Determining Melting and Freezing Points
ANALCITE
Thebe alloys readily undergo undercooling unless they are constantly stirred during cooling. Several cooling curve studies were made during which tlie alloys were not stirred. In all of these cases undercooling occurred, the eutectic alloy Ireezing a t 65" to 66" C. and Wood's metal slightly above. During freezing, the temperature rose several degrees but did not reach the true freezing point. It seems quite likely, therefore, as Steinmetz suggested, that some of the lower freezing points recorded in the literature may be erroneous because undercooling was permitted.
Preparation and Solubility between 1 8 2 O and 2 8 2 O C.
Effect of Impurities 'rlie effect of the presence of impurities other than those of metals making up the eutectic is discussed by Steinnietz ( 3 ) . Unless the impurities are present in considerable amount and form a eutectic with other ingredients present, the effect on tlie melting point should be negligible.
Effect of Mercury on Melting Point The low melting points reported might also be due to another cause. These alloys take on considerable amounts of inercury and still maintain their metallic luster and nature, although malleability and luster progressively decrease as mercury is added until the solid amalgam finally becomes merely a lusterless, brittle solid. The addition of 3 per cent mercury to Lipowitz alloy lowers the freezing point about 3' C. Some 9 to 10 per cent of mercury can be added before the alloy becomes unrecognizable as a metal, the freezing point being depressed about 6" to 7" C. Since the nomenclature of tlie alloys has been loosely applied, it is possible that the melting points of mercury alloys have been reported merely under the names of Wood's metal or Lipowitz alloy. An undercooled alloy containing 6 to 8 per cent mercury should solidify a t about 60" C.
Loose Nomenclature
,
113
Siiice tlie iitliiies "Wood'F metal" and "Lipowitz alloy" 1itLve been so loosci~yapplied to Pundry fusible quaternary alloyi, these names have ceased to carry any exact meaning, yct the attempt is made to give the alloys exact melting pointb. diirce both alloy hare the same melting point, the names iiiiglrt be used intercliangeably for any alloy having a melting Imiiit coinciding with that of tlie eutectic alloy. However, 5 ~ ~ ac solution h of tlie problem could \vel1 lead to multiplicity ol naiiies to include alloy- of other compositions melting at the eutectic point. Tlie simplest solution seems to be to drop all names, call the eutectic alloy simply a quaternary eutectic, and state its melting-freezing range and composition. This solution has precedent, since the International Critical Tables give the composition of the eutectic aiid the melting-freezing range, but no name. They do not list tlie alloy composed of 50 per cent bismuth, 25 lead, 12.5 tin, 12.5 cadmium, comnioiily regarded as Wood's metal.
Literature Cited ( I ) Hiiclgw, N. l p . , 1.C / L C WI .d . , 43, 200-3T (1924). ( 2 ) Urii. St:tndnrds, Cut. 388 (1930). (3) Steinmetz, C . P., J . Am. C h n . Soc., 40, 913-100(191s) It~uckxv~cu April 2 , 1985. Preseiited before the Division of Iiidustrial aiid ISiigiueering Clieiiiistry a t the 89th Aieeting of the iliilericaii Clieiiiical Society, Kew Yorlr, N. Y., April 22 t o 26, 1935.
FREDERICK G. STRAUB Chemical Engineering Division, University of Illinois, Urbana, Ill.
Analcite crystals were prepared from aqueous solution at 282" C., and petrographic examination and chemical analyses were made of them. The solubility of analcite was determined at 182' t o 282" C. in water and a sodium hydroxide concentration u p to 3.5 millimoles per liter.
S PART of research on the preveiitioii of silica scale in steam boilers, it became advisable to obtain data relative to the type of silica compounds which would form a t boiler temperatures and to obtain further data relative to the solubility of these compounds at boiler temperatures. Analcite scale (Kaz0.Al2Od.4Si02.2H20) has been found in steam boilers ( 1 ) . Pure analcite was prepared and a study made of its solubility in water aiid dilute sodium hydroxide solutioiis a t temperatures between 182" and 282 O C. In pieparing the analcite, the necessary amounts of the desired chemicals Tiere added to uater in the larger bomb (used in solubility tests 2). The sampling tube and filter inside the bomb were left out, and a 200-mesh copper gauze was put inside of the top. The small upper bomb nas not used. After the bombs had been held at 282" C. for 46 hours, they mere removed fiom the furnace and inverted, and the sampling valve was opened, thus alloiiing the liquid to be forced out and leave the solid behind in the bomb. When the bombs were cool, the solid was removed, washed with Ivater, and dried. The solution added to the bombs mas sodium silicate in which 70 cc. contained 10.8 grams of silica Eight giams of 93.5 per cent solid sodium aluminate (equivalent to 4.6 grams of alumina) were placed in each of six bombs, 70 cc. of the silicate solution \+ere added, and then water was added (40 cc. in bombs 7 and 8,110 cc. in bombs 9 and 10, and 260 cc. in bombs 11and 12). The solids formed in bombs 11 and 12 had larger crystals than in any of the other bombs. Petrographic examination showed that these crystals were analcite in uniform rounded grains about 0.1 mm. in diameter. Table I gives the result of tlie chemical analyses of the crystals formed and shows that tlicy had almost identical composition as natural analcite. A microphotograph of sample 12 is shonn in Figure ld. The crystals mere very hard and could be easily separated from each other in a group by pressing with a spatula. The crystals could not be easily broken. Figure 1B shows a microphotograph of crystals formed in z later test (sample 2 3 ) . Tlie same conditions wrre iiwd a5 in tests 11 and 12, except that 10 grams o i sodium aluminatc.
