26 
Proceedings of the Royal Society 
persive power, so as to be easily visible even when mounted in 
Canada balsam. They appear to be of octahedral form, but so far 
none of them seem to possess curved edges like the dark ones. 
Unlike the diamond they have a small action upon polarised light ; 
this might, however, be caused by their too rapid cooling. What 
these crystals are I cannot at present say. 
Finally, let me now call attention to the accompanying sketches 
which I have prepared to show the colour and perfect crystalline 
form of these different crystals : — 
No. 1 is a crystal of very perfect octahedral form with curved 
edges, it is almost black, and is magnified about 520 
diameters. 
No. 2 is another crystal of the same form but not quite so 
dark in colour, being more brown; it is magnified to the 
same amount as the first one. 
No. 5 is another of the same, only in this crystal the third 
edge can be distinctly seen. 
No. 4 is a crystal of perfect octahedral form but without the 
curved edges ; it is also magnified as the others. 
No. 3 is a fragment of a crystal which exhibits a number of 
scratches in its surface, most likely caused by the curved 
edged crystals rubbing against it. It is magnified some 
7 8 times. The scratches were seen by reflected light. 
No. 6 is a sketch of one of the transparent octahedral crystals 
as already described, and shows its perfect crystalline form 
and truncated corners ; it is magnified some 520 diameters. 
It was mounted in Canada balsam, but its high refractive 
power rendered it easily visible. It had a slight action on 
polarised light. 
In conclusion, I may state that a friend who has to deal with large 
quantities of gold and silver has kindly offered me the opportunity 
for making experiments on a large scale with 300, 400, or 500 
ounces of metal at a time, so this method of production will shortly 
be put to a practical test. On the completion of these experiments 
I will bring any further results before the Society. 
