ON THE STRUCTURE OF METALS. 
425 
complicated sutures analogous to those in cranial bones. This tendency is still more 
marked in the alloys with indium and antimony, especially in the interior, but it is 
visible in the prisms at the periphery (photo. 14). The alloy with potassium is a 
curious mixture of little grains, of perfectly defined crystallites, and of mixed forms 
(photo. 11). The appearance of certain portions of the alloy with aluminium approaches 
that of the alloys with lithium and selenium, but the bulk is rather crystalline. 
III. The interior paste, whether it be in grains or crystallites, is certainly crystalline, 
as might have been anticipated from the fact that the colour of the grains varies with 
the incidence of the light. When examined, after etching, under an enlargement of 
1000 diameters, this paste presents three aspects :— 
(a) Clear vermicular structures on a dark ground. 
(b) Parallel grooves. 
(c) Pointed crystals of the same orientation, in lines nearly parallel. 
The photographs 21, 9, and 10 show these different aspects, which, it must be 
remembered, do not correspond with true differences of structure, but with different 
sections of a single structure. As far as it is possible to judge, it is a question of files 
of little crystals penetrating each other, the general orientation of which remains 
constant in the area of each grain. 
In this paste, resrdting from primary and rapid crystallization, which constitutes the 
principal mass of the greater part of our alloys, some small secondary crystals separate 
themselves with relative distinctness. These are probably small cubes, the diameter of 
which is about 2'5 p, ; they have a tendency to range themselves in groups and pass 
progressively into crystallites by a series of intermediate stages, which it is easy to 
follow through the whole series of the specimens, and thus to connect one with another. 
During the course of this secondary crystallization five stages or classes can be 
distinguished, and each can be designated by a number : 
0. Absence of little crystals (photo. 10, pure gold ; 1000 diameters). 
1. Small detached crystals isolated indiscriminately. 
2. Small crystals in rows at regular intervals (photo. 14, in which the magnifica¬ 
tion is 150 diameters, and 17, 500 diameters). 
3. Small connected crystals, often joined in parallel lines, in which they may 
lose their individuality, and are illustrated by the same photos, as in 
Class 2. 
4. The parallel lines thus formed become aggregated crystallites (photo. 13, Al, 
150 diameters). 
None of the specimens belong exclusively to a single class, as one part of a section 
represents a certain class and the rest of it another, but in a given section the secondary 
crystallization attains certain limits which it does not exceed, and among these five 
classes our thirteen specimens are distributed as follows:—• 
MDCCCXCVI. —A. 3 I 
