596 



NATURE 



{April 1 8, 1889 



SOCIETIES AND ACADEMIES. 

 London, 



Royal Society, Mirch 28.— "On certain Ternary Alloys. 

 I. Alloys of Lead, Tin, and Zinc." By C. R. Alder Wright, 

 D.Sc, B.Sc, F.R.S., Lecturer on Chemistry and Physics, and 

 C. Thompson, F.C.S., F.LC, Demonstrator of Chemistry in 

 St. Mary's Hospital Medical School. 



It is well known, that quite apart from a tendency to separate 

 more orless completely intodifferent mixtures during solidification, 

 certain mixtures of molten metals show a tendency to separate into 

 two alloys of different densities on standing fu^ed for some time. 

 Lead and zinc and bismuth and zinc have been shown by 

 Matthieson and V. Bose to form two such mixtures ; the authors 

 find that aluminium and zinc or aluminium and bismuth also 

 behave in the same way ; in each case two different alloys are 

 formed, one consisting of the heavier metal with a little of the 

 lighter one dissolved therein, the other of the lighter metal 

 containing a small quantity of the heavier one. 



On the other hand, tin will alloy indefinitely in all proportions 

 with any of the four metals, lead, bismuth, zinc, or aluminium, 

 the mixtures exhibiting no particular tendency to separate into 

 two different alloys on simply remaining at rest in a fu-ed con- 

 dition, although in certain cases more or less separation is apt I 

 to occur dtmng solidification, owing to partial formation of 

 eutectic alloy. Various other metals, e.g. cadmium, antimony, 

 silver, &c., appear to behave like tin in this respect. i 



It seemed to be of interest to examine the behaviour under i 

 similar conditions of ternary mixtures where two of the ingre- 

 dients are not miscible together in all proportions (like aluminium 

 and lead), whilst the third is miscible indefinitely with either of 

 the other two (like tin). It might be expected that with certain 

 proportions a single stable alloy would result, whilst with others 

 the mass would divide into two different ternary mixtures. In 

 point of fact this is precisely what occurs. I 



For a variety of reasons the authors selected the alloys of lead, i 

 tin, and zinc for their first experiments. 1 



These led to the conclusion that the greater the proportion of i 

 tin present (provided it does not exceed the limiting amount ! 

 beyond which no separation takes place) the more zinc is con- ! 

 tained in the heavier alloy, and the more lead in the lighter one ; 

 but that the distribution of the tin throughout the entire mass is 

 by no means uniform, the lighter alloy containing the greater 

 percentage when the proportion of tin in the total mass is low, 

 and vice versa when it approaches towards the limiting amount ; 

 so that with a particular proportion of tin in the total mass 

 uniform distribution as regards weight percentage occurs, but 

 with no other proportion. 



The authors next attempted to find out whether a moderately 

 large variation in the temperature at which the mass kept molten 

 had any great influence on the end result ; for if not, obviouslymuch 

 laborious work would be saved. Two series of compound ingots 

 (forty in all) were accordingly prepared, one at a temperature close 

 to 565° C, the other at near to 689° C. From the analytical 

 results obtained, three noteworthy curves are deducible— 



(a) When the tin percentages in the heavier alloy are plotted 

 as abscissa and the zinc percentages as ordinates, 



{b) When the tin percentages tin the lighter alloy are plotted 

 as abscissse and the lead percentages as ordinates. 



{c) When the tin percentages in the heavier alloy are plotted 

 as abscissse and excesses of the percentage (-1- or -) in the 

 lighter alloy over those in the heavier one as ordinates. 



These three curves respectively represent approximately the 

 solubility of zinc in lead containing tin, that of lead in zinc 

 containing tin, and the relative distribution of tin in the two 

 alloys formed simultaneously. The three curves obtained from 

 one series are practically identical with the corresponding 

 curves from the other series, so that it may be fairly concluded 

 that the effect of variation in temperature from 565" 10689° is 

 negligible as compared with the experimental errors, more 

 especially those due to imperfect separation by gravitation of 

 the two alloys from one another. 



The curves representing the tin distribution are remarkable. 

 As long as the tin percentage in the total mass is less than about 

 sixteen the lighter alloy contains more tin than the heavier one ; 

 at about this point (representing some 14 percent, in the heavier 

 and 18 per cent, in the lighter alloy) the difference becomes a 

 maximum, after which the difference diminishes, until at about 

 28 per cent, the same percentage of tin is contained in both 

 alloys. After this the heavier alloy contains moie tin than the 

 .lighter, the difference continually increasing. 



Certain irregularities were observed due to the existence 

 of some cause interfering with the proper separation by gravita- 

 tion of the heavier from the lighter alloy : this was ultimately 

 traced to convection currents set up through unequal heating of « 

 the walls of the containing vessel at different levels, and it was M 

 found that the imperfect separation could be almost completely ^ 

 obviated by so heating the mass as to avoid this inequality of 

 temperature. This was finally effected by employing crucibles 

 very long in proportion to their diameter (large test-tubes 

 moulded on a core from a plastic mixture of fireclay and syrupy 

 silicate of soda, diluted with about three times its weight of 

 water), heated by immersion in a bath of molten lead some 6 or 

 7 inches deep, contained in an iron cylindrical vessel (the lower 

 two-thirds of a mercury bottle), surrounded by a concentric clay 

 jacket and heated by a number of bunsen burners playing into 

 the annular interspace. Several series of compound ingots were 

 thu^ prepared, containing lead and zinc in ratios different for 

 each series (2 to i, i to i, i to 2), some at a temperature near to 

 650"", others at about 750°. From the results of the analysis of J 

 upwards of 130 different alloys thus obtained, the following 9 

 conclusions are drawn : — '^ 



When a mixture of lead, tin, and zinc in the molten condition 

 is well stirred ud by mechanical means and then left to itself 

 for some hours at as nearly as pos-ihle a uniform temperature, a 

 single homogeneous alloy results if ihe proportion of tin present 

 is not less than three-eighths of the whole ; but if materially less 

 tin than this is present, the mass divides itself into two different 

 ternary alloys, lead predominating in the heavier one and zinc in 

 the lighter one. This phenomenon is entirely distinct from the 

 segregation of alloys during solidification, in consequence of 

 formation of eutectic or other differently fusible alloys. 



If there is little or no inequality of temperature at different 

 parts of the mass, separation by gravitation only is complete in 

 a few hours, at any rate when tolerably pure metals are employed ; 

 but if the mode of heating is such that convection currents are 

 set up, the separation is greatly interfered with, and in extreme 

 cases almost entirely prevented. 



The heavier alloy is a saturated solution of zinc in lead contain- 

 ing tin, and the lighter one a similar solution of lead in zinc con- 

 taining tin. No matter what the relative proportions between 

 lead and zinc in the original mass, the two alloys always 

 correspond to two conjugate points on the solubility curves of 

 zinc in lead-tin and of lead in zinc-tin. 



But little, if any, difference in the way in which a given mass 

 divides itself is noticeable, whether the temperature which the 

 molten' mass maintained is below 600° C. or above 700° C. 



The tin contained in the mass does not distribute itself equally 

 in the two alloys except when present in one particular pro- 

 portion, which varies with the ratio of the zinc to the lead in the 

 entire mass. With less tin than this the lighter alloy, and with 

 more the heavier one, takes up the higher percentage of tin. 



Curves drawn representing the tin present in the heavier alloy 

 as abscissas, and the ( + or — ) excess of tin in the lighter alloy 

 over that in the heavier one as ordinates, are found to differ with 

 the ratio of zinc to lead in the entire mass. They always possess 

 the same general features, viz. rising from the origin to a 

 maximum elevation, then sinking down again to the base line, 

 and crossing it so as to become negative ; but the position and 

 height of the maximum, the crossing point, and the general 

 dimensions of the curve, vary with the ratio of zinc to lead in 

 the mass. 



As a result of this, whilst an indefinite number of different 

 mixtures may be prepared, each one of which will give the same 

 heavier alloy, the lighter alloy simultaneously formed will be 

 different in each case ; and conversely. 



When no tin is present, lead dis-olves zinc to such an extent 

 as to form an alloy containing 1-24 per cent, of zinc, and zinc 

 dissolves lead forming an alloy containing i "14 per cent, of lead ; 

 the higher values found by previous observers being slightly 

 incorrect through imperfect separation. 



Nothing abnormal appears to characterize the solubility curves 

 of zinc in lead-tin and of lead in zinc-tin ; in each case the 

 amount of one metal dissolved by the other increases as the 

 quantity of tin present increases, in such a way that the curves 

 are somewhat concave upwards. 



Royal Society, April 4. — " On the Magnetic Inclination, 

 Force, and Declination in the Caribee Islands, West Indies." 

 By T. E. Thorpe, Ph.D., F.R.S. 



The following determinations of the magnetic elements 

 among the Caribees cr Windward Islands were made iri 



