[2] Mr. Paterson called “limey stuff” what is now termed “blue ground.” It was also formerly called “marl stuff,” “blue stuff,” and “blue clay.”

[3] The original name for the Kimberley Mine. It was also sometimes known as “Colesberg Kopje.”

[4] Diamonds and Gold in South Africa. By T. Reunert. Johannesburg, 1893.

[5] According to Gardner Williams the South African carat is equivalent to 3·174 grains. In Latimer Clark’s Dictionary of Metric and other Useful Measures the diamond carat is given as equal to 3·1683 grains = 0·2053 gramme = 4 diamond grains; 1 diamond grain = 0·792 troy grain; 151·5 diamond carats = 1 ounce troy.

Webster’s International Dictionary gives the diamond carat as equal to 3? troy grains.

The Oxford English Dictionary says the carat was originally ¹/₁₄₄ of an ounce, or 3? grains, but now equal to about 3? grains, though varying slightly with time and place.

The Century Dictionary says the diamond carat is equal to about 3? troy grains, and adds that in 1877 the weight of the carat was fixed by a syndicate of London, Paris, and Amsterdam jewellers at 205 milligrammes. This would make the carat equal to 3·163 troy grains. A law has been passed in France ordaining that in the purchase or sale of diamonds and other precious stones the term “metric carat” shall be employed to designate a weight of 200 milligrammes (3·086 grains troy), and prohibiting the use of the word carat to designate any other weight.

[6] Artificial tribo-luminescent sphalerite:—

Mix with distilled water and dry at a gentle heat. Put in luted crucible and keep at a bright red heat for from two to three hours.

[7] Sir James Dewar, in a Friday evening discourse at the Royal Institution in 1880, showed an experiment proving that the temperature of the interior of a carbon tube heated by an outside electric arc was higher than that of the oxy-hydrogen flame. He placed a few small crystals of diamond in the carbon tube, and, maintaining a current of hydrogen to prevent oxidation, raised the temperature of the tube in an electric furnace to that of the arc. In a few minutes the diamond was transformed into graphite. At first sight this would seem to show that diamond cannot be formed at temperatures above that of the arc. It is probable, however, for reasons given above, that at exceedingly high pressures the result would be different.

[8] The silica was in the form of spheres, perfectly shaped and transparent, mostly colourless, but among them several of a ruby colour. When 5 per cent of silica was added to cordite, the residue of the closed vessel explosion contained a much larger quantity of these spheres.

[9] A pressure of fifteen tons on the square inch would exist not many miles beneath the surface of the earth.

[10] There are abundant signs that a considerable portion of this part of Africa was once under water, and a fresh-water shell has been found in apparently undisturbed blue ground at Kimberley.

[11] The water sunk in wells close to the Kimberley mine is sometimes impregnated with paraffin, and Sir H. Roscoe extracted a solid hydrocarbon from the “blue ground.”

[12] Chemical News, vol. lxi, p. 209, 1890.