22 
Proceedings of the Royal Society 
octahedral form, also present in a fairly large quantity ; and thirdly 
a quantity of a brownish substance probably amorphous carbon or 
a carbide of silver, which occurs in little flocks. It would appear 
from this that dissolved carbon, on crystallising slowly, takes the 
graphitic form in the hexagonal system in preference to the octa- 
hedral form of the diamond. I judge tliis from the fact of its 
occurring in so much larger a quantity. By washing this mixed 
powder by decantation, and then treating it first with hydrofluoric 
acid and then with ammonia, and further with caustic potash, the 
greater portion of the brown flocculent substance is thus got rid of, 
leaving the graphitic and adamantine carbon behind, and thus much 
more easy to examine. 
These crystals then are found after the above treatment to have 
the following properties, viz. : — 
1. They are unacted upon by ordinary acids and alkalies. 
2. They remain unattacked even after boiling with hydrofluoric 
acid and being treated with it for some days, (these 
crystals were left under hydrofluoric acid from Friday 
morning until Monday morning). 
3. They are extremely hard, and scratch glass and quartz quite 
easily, and I believe also the saphire • but being so minute 
it is not possible at present to speak absolutely on this 
point, though I am under the impression that scratches 
were certainly made. 
4. When heated in a platinum crucible before the blowpipe, 
under a stream of oxygen they quickly glowed away. 
Such are the properties of this powder. 
It has already been stated that the larger proportion of the powder 
consisted of graphite, and of this it is not necessary to say more 
here ; but to turn again to the other crystals, on making a closer 
examination under the microscope we find them to consist of two 
different kinds, some being dark-coloured whilst others are perfectly 
transparent ; we will examine each of these two kinds of crystals 
separately. 
First, the dark-coloured crystals, which are in most cases black, 
have a perfect octahedral form with curved edges, or in other words 
have the crystalline form peculiar to the diamond, and to that 
