Page:Popular Science Monthly Volume 69.djvu/277

Rh Lying true color can be determined, but to make the stones marketable abroad where this is unknown, recourse is had to heating them red hot and pouring on a chemical when the crust is consumed and the real color appear-. 1 have seen apparently dirty red, green, brown, blackish and yellow stones after burning turn out to be pure whites and blue whites. Stones so treated lose in weight about one per cent., and those with cracks or defects frequently break to pieces.

The largest authentic Brazilian diamond ever found is the famous 'Estrella do Sul' (Star of the South). It weighed 254.5 carats in the rough, and cut and polished weighs 124% carats, with a value of $450,000. The greater number of diamonds found are less than one carat; the average weight is about two carats, while a stone of 10 carats is a great exception.

Carbons which occur along with diamonds are very ordinary looking stones and would be refused as a present by any one not well acquainted with them. Their history is very obscure. Other than a few small ones found in Minas Geraes, and those are of poor quality, Bahia is the only known place where they occur. They seem to have been known in 1848, when a Frenchman traveling through Bahia bought them for twenty-seven cents a carat under the name of 'ferragens' (iron stones). In March, 1856, Mr. Domingos Gomez, of Boncador, took to London 6,475 carats, which he had bought for sixty cents a carat, and was more than pleased to sell them at $1.25 a carat. At that time their sole use was to be pounded to dust for use in diamond polishing.

The later history of the carbon is the history of the so-called diamond drill which now constitutes their principal use. For this purpose stones weighing from 1 to 4 carats are desired and larger stones have to be broken to these sizes. The drill consists of 6 or 8 carbons set in a crown or cylinder of steel forming the bit. They are set in such a way that they alternately slightly project beyond the inner and outer edge, thereby cutting as they are rotated a core, which is brought to the surface from time to time as desired. Being the hardest known material they will cut the most refractory ores or stones.

As the drill goes around the carbons wear off and have to be from time to time reset, until finally they become so small as to be useless. For this reason, unlike the diamond whose chief use is for adornment, the number of carbons is constantly growing less while the demand is exceeding production. With the perfection of the drill and its great use in cutting tunnels, mines, canals, etc., the price of carbon has steadily gone up from $17 a carat in 1892 to $60 to-day in New York for the best quality of proper size, and the price obtained at the mines has been a fair equivalent.

The average weight of carbons encountered is much larger than