PHYSICAL AND CHEMICAL PROPERTIES OF THE DIAMOND
NEED scarcely say the diamond is almost pure carbon, and it is the hardest substance in nature.
When heated in air or oxygen to a temperature varying from 7600 to 8750 C, according to its hardness, the diamond burns with production of carbonic acid. It leaves an extremely light ash, sometimes retaining the shape of the crystal, consisting of iron, lime, magnesia, silica, and titanium. In boart and carbonado the amount of ash sometimes rises to 4 per cent, -but in clear crystallised diamonds it is seldom higher than 0-05 per cent. By far the largest constituent of the ash is iron.
The following table shows the tempera^