426 
MR. F. OSMOND AND PROFESSOR ROBERTS-AUSTEN 
Between Classes 0 and 1 : pure gold, alloyed with Bi, Zr, Pdi, Pd, Zn. 
,, ,, 0 „ 2 : alloys with Tl, Sb, Se. 
,, ,, 0 „ 3. ,, ,, K. In. 
,, „ 1 „ 4: ,, ,, Li, Al. A large portion of the alloy with 
aluminium belongs entirely to type 4. 
Fig. 3. 
a \ 
This more or less accentuated development of a secondary crystallization is, in 
itself, interesting in connection with the phenomena observed by 
one of us* in the curves which represent the solidification of 
gold (fig. 3). In the presence of small quantities of lead, or of 
certain other bodies, the horizontal portion of the curve, which 
represents the actual solidification of the metal, is not sharp at 
its angles as shown in the line a, b, but is rounded as at c, d, 
and is often inclined at an angle to the datum line. This points 
to the existence of a transitory pasty state which may facilitate the secondary crys¬ 
tallization.! 
It may be asked whether the small crystals above-mentioned, and their aggregates 
do not represent an allotropic form of gold.}; Some explanation may thus be afforded 
of the mechanical properties of the alloys of gold with. 0‘2 per cent, of aluminium, 
and of gold with 0'2 per cent, of lithium, which are, at the same time, the most 
tenacious and the most perfectly-crystallized of the entire series. But, on the other 
hand, this same kind of crystallization connects the alloy of gold and bismuth, for 
instance, with the alloy of gold and rhodium, these being the members of our series 
which are very wide apart from the point of view of tenacity and extensibility. 
It must be admitted, moreover, that the influence of the secondary crystallization 
on the mechanical properties of the alloys, supposing it exists, is at least greatly 
complicated by some other more powerful influence. 
IY. It only remains for us to consider the relations which result from the associa¬ 
tion of contiguous grains or crystallites, that is to say, from their surfaces in contact, 
or joints. The general crystalline orientation of the paste on both borders of the 
joint is not the same, and the elementary crystals belonging to two different groups 
may not be as firmly united as they would be in the interior of a homogeneous 
group ; a joint, therefore, becomes a surface of weakness (sometimes passing pro¬ 
gressively into a fissure), which etching by a reagent enlarges and renders visible. In 
fact, all our etched surfaces are divided by a network of joints, which correspond with 
the outlines of the grains and crystallites. 
The joints revealed by the action of sulphuric acid are simple furrows, which occur 
* ‘ Proc. lust. Mecli. Engineers,’ Oct. 1891, p. 558-564. 
t Secondary crystallization is at a minimum in the case of pure gold. 
+ Compare the notes of H. Louis on “The Allotropism of Gold,” and “Further Experiments on 
Amorphous Gold,” ‘Trans. Amor. Inst, of Mining Engiueei’S,’ vol. 24, pp. 182 and 705, 1894. 
