36 
Proceedings of the Royal Society of Edinburgh. [Seas. 
VI. — Note upon the Structure of Ternary Alloys. By G. H. 
Gulliver, B.Sc., A.M.I.Mech.E., Lecturer in Engineering in the 
University of Edinburgh. (With One Plate.) 
(MS. received November 27, 1911. Read January 22, 1912.) 
In a simple class of ternary alloys the solid phases are the three component 
metals, each holding in solution a relatively small proportion of the other 
two. Any one of the three phases may be present as a separate constituent, 
any two may be associated together as a binary eutectic, and the three 
together form a ternary eutectic. The structural constituents of such a 
ternary alloy are — 
(1) Primary crystals- of one phase, 
(2) Binary eutectic of two phases, 
(3) Ternary eutectic of three phases. 
In general the alloy contains all three constituents, but there are certain 
limiting compositions at which any one or any two of the constituents 
may be absent. In what follows it is supposed that three structural consti- 
tuents are always present. Since there are three possible kinds of primary 
crystals, three binary eutectics, and one ternary eutectic, there are six 
different types of alloys when classified according to their constituents. 
The lead-tin-bismuth alloys furnish an example of a ternary series of 
the above kind. Charpy has studied the structure of certain members of 
this series, and has found features which apparently correspond with the 
three constituents.* He has published a section of an alloy containing 
5'5 per cent, of lead, 20 per cent, of tin, and 74 # 5 per cent, of bismuth, 
which, according to the equilibrium conditions determined by the same and 
by other investigators, should consist of primary crystals of bismuth (con- 
taining a little lead and tin in solution), together with a binary eutectic of 
bismuth and tin, and the ternary eutectic of bismuth, tin, and lead. In 
Charpy s figure can be seen three primary crystals of bismuth, each sur- 
rounded by a deep fringe of what he calls bismuth-tin eutectic ; the dark 
ground mass is the ternary bismuth-tin-lead eutectic, of which the structure 
is not resolved. 
The purpose of this note is to call attention to the structural arrange- 
ment of a binary eutectic in a ternary alloy. If Charpy’s section be 
* Charpy, Comptes Eendus , 1898, cxxvi. 1645. 
