CRYSTALLINE ‘STRUCTURE OF GOLD NUGGETS. 77 
In Plate 12 is shown the structure brought out on etching an 
internal horizontal section of the ingot cut parallel with the top 
and base through the plane A.B. Plate 10, in this also the groove- 
like lines seem to be due to the stress of the planing tool. This 
horizontal section was made by planing away the top of the ingot 
down to the median line A.B. 
Next a large ingot, weighing 1,203 ounces, of standard gold 
coinage alloy (22 carat or 11 gold to 1 of copper), was cut 
through, polished and etched; this impure gold, as might be 
expected, showed a much smaller crystalline structure (Plate 13), 
and the crystals only radiate inwards a short way. This particular 
specimen was etched for me by Mr. McCutcheon, Assayer to the 
Sydney Mint, as it was found inconvenient to have such large 
. masses of gold carried between the Mint and the University 
laboratory. It will be noticed that the striz caused by the cutting 
tool, (if they be due to that in the softer and purer ingot) are not 
visible in this harder alloy. Although only two ingots are figured 
and described, several other smaller ones were made and examined, 
with similar results. 
The next, Plate 14, is a collotype of, nominally pure and 
standard gold fillets, of the thickness of a sovereign; the crystal- 
line structure is preserved in spite of the rolling and annealing 
which they have undergone, and in the case of the purer gold, 
Some of the crystals are etched so deeply as to throw the others 
up into such high relief as to yield well defined shadows. It is 
noticeable too, that the large longitudinal crystals (elongated by 
the rolling process) are crossed, practically at right angles, by 
other smaller but well defined crystalline strie. Enlarged two 
diameters, 
Plate I5 represents an etched rolled fillet of Mount Morgan 
gold, assaying 1,000, and supplied to me by the late Dr. Leibius 
of the Sydney Mint, as a specimen of the purest gold he had ever 
made. In this the crystals are still larger. Enlarged two 
diamete ie 
