136 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
of the metals, or of a definite compound of the two, are seen enveloped 
in a second constituent, which is generally the eutectic alloy, containing 
both elements in a very finely divided state. The composition of the 
eutectic mixture remains constant, whilst the amount of isolated crystals 
varies with the percentage composition of the alloy. The limiting cases 
of a pure definite compound or metal, and of a pure eutectic mixture, 
may be grouped with these alloys. 
‘ £ Eutectic alloys vary in appearance according as they have been 
cooled slowly or quickly. In the latter case, the surface is uniformly 
striated, but the crystals or crystallites are so small that it is difficult 
to obtain satisfactory photographs of them. When the solidification is 
slow, however, the separation into lamellae is strongly marked, especially 
when viewed under high powers, and this structure is highly character- 
istic of eutectic alloys, being easily traced in any of them whatever the 
Fig. 10. 
Fig. 11. 
Alloy of silver, 66 per cent. ; antimony, 
34 per cent. 
Alloy of tin, 90 per cent. ; antimony, 
10 per cent. 
metals in the alloy may be. It is well shown in fig. 10, which represents 
an alloy containing silver 66 per cent., antimony 34 per cent., magnified 
500 times ; the metal has been treated with sulphuretted hydrogen, 
which has blackened the silver and left the antimony unchanged. In 
the same figure some straight edges can be seen, in which the ramifica- 
tions end, and which sketch out shapes resembling those of crystals of 
antimony. The presence of these crystallites or incipient crystals in 
eutectics constitutes one of the resemblances between them and the 
micro-felsitic basis observed in many igneous rocks, and it seems likely 
enough that if light transmitted through these alloys could be examined, 
it would show that they are on the borderland between crystalline and 
amorphous matter. 
“ Besides the normal type of binary alloys, in which eutectics are ob- 
servable, there is a second type consisting of alloys of metals which form 
