268 
MESSES. C. T. HEYCOCK AND F. H. NEVILLE 
The upper line, or liquidus, ABCD, was taken from our previous memoir (‘ Phil. 
Trans.,’ A, 1899). The solidus begins at A, the freezing-point of gold, and the first 
branch ends at a, with 13 atomic per cents, of gold, or, in our notation, at A1 13 ; 
it continues horizontally to b, then probably follows the line be, and is continued 
horizontally through C to a point d , which lies nearly under the summit D of the 
liquidus. It is, perhaps, unnecessary to say that at points below the solidus all 
alloys are wholly solid. 
The diagram deals with three substances—the solid solutions alpha and beta, which 
are of variable composition, and with a third substance, D, which is the sole 
constituent of the alloy A1 28 at the summit D of the liquidus. D may very well be 
the compound Al 3 Au 8 ; it is very constant in appearance in all the alloys from A1 18 
to A1 28, in which we have studied it, and from the fact that second freezing-points 
occur along the line C d to a point almost under the summit D of the liquidus it does 
not appear probable that D is a solid solution. 
The diagram ends at 400° C., and all alloys considered in it are supposed to have 
been melted, cooled to a temperature not below 400° C., and chilled. This limitation 
is important, as alloys cooled below 400° C., even if afterwards heated, generally 
require another diagram, 
