tures of combustion in oxygen of different kinds of carbon :
°c.
Condensed vapour of carbon...........650
Carbon from sugar, heated in an electrical
furnace ........................660
Artificial graphites, generally..........660
Graphite from ordinary cast-iron.......670
Carbon from blue ground, of an ochre
colour .........................690
Carbon from blue ground, very hard and
black ..........................710
Diamond, soft Brazilian ..............760
Diamond, hard Kimberley ............780
Boart from Brazil ...................790
Boart from Kimberley ...............790
Boart, very hard, almost impossible to
cut ............................900
Hardness
Diamonds vary considerably in hardness, and even different parts of the same crystal differ in their resistance to cutting and grinding.
90
