Among the most prominent diamonds of earlier times are several that are noted for their color.

Florentine Diamond.-This stone is of a lemon-yellow color and weighs 133 3-5 carats. It was at one time the property of Charles of Burgundy, who wore it in his helmet. In the battle of Granson, on Neufchatel Lake, he lost it. A Swiss soldier picked it up and sold it to a priest. Pope Julius II. finally obtained it for 20,000 ducats, and eventually it was acquired by the Austrian crown, where it is to-day.

Dresden Diamond.-A very handsome green diamond is owned by the Saxon crown, and is preserved in the Green Vaults at Dresden. The color is a bright green with a bluish tinge; its weight 314 carats.

Hope Diamond.-Banker Hope, of Amsterdam, possesses a fine blue diamond of 41⁄2 carats. It is cut in brilliant form, and closely resembles a deep blue sapphire in color. Formerly a blue diamond of 67 carats was among the crown-jewels of France, but it disappeared during the revolution.

Within recent years the two largest diamonds have been found in Brazil and Africa respectively.

Star of the South.-This diamond was found in Brazil in 1853, by a negress. Its original weight was 2471⁄2 carats, but by cutting it was reduced to 125 carats. The Star of the South" has a slight pink tinge.

Star of South Africa.-About ten years ago this diamond was purchased from a native, and sold at once for 56,000 dollars.

Cutting. It is evident that a large proportion of the value of a diamond depends upon the preparation it undergoes, in order to develop its beauty. No evidence is on hand to show that any of the ancient nations, East Indians and Chinese excepted, were acquainted with the art of diamond-cutting. From its very superior hardness, it is natural that it can be cut by no other material. In 1373 there was an association of "diamond-polishers" at Nuremberg, in Germany, but not until 1456 was cutting and polishing carried on as an art. Louis van Berquen, in Holland, at that time proceeded to rub two diamonds together, and finally produced a gray surface. The French word equivalent to our "cutting" is "égriser "—to make gray-based upon the first experiments. For a long time Holland had the entire monopoly of cutting diamonds, but finally other nations entered

into competition. In 1660, during the reign of Louis XIII, Cardinal Mazarin had the first diamonds cut for the French crown. Within late years the machinery for cutting diamonds has been greatly improved, so that the Ko-hi-noor was re-cut in the space of thirty-eight days, while the cutting of the Regent had required two years.

Two styles of cutting are employed in shaping the diamond, the rosette and the brilliant. The foundation for the former is the number two multiplied by three, for the latter the number four. A complete rosette cut will cover the entire diamond with faces of equal, triangular shape, while the brilliant presents a flat surface, surrounded by facets and a deep pyramidal or conical body. Numerous combinations of faces are added to increase the action of refraction. As will readily be seen from the most usual forms of crystallization of smaller diamonds, the brilliant cut can be executed with the least loss of material. It certainly presents the stone to best advantage.

Turning aside from the historical associations of the diamond, we have yet to consider its chemical and physical properties.

Among all minerals the diamond is by far the hardest. Next to it are the various corundum species, ruby, sapphire and others. This alone, to a mineralogist, is sufficient to distinguish it. Its specific gravity is 3.5295, about the same as topaz. The index of refraction is 2.439. Expressing the power of refraction in a more tangible manner, we may say that if we have a glass lens of certain dimensions which magnifies five diameters, an equal lens of diamond would magnify eight diameters. Upon being rubbed the diamond exhibits vitreous electricity. By passing an electric spark over a diamond, the stone may be rendered phosphorescent, and retains this quality for a short time. This fact, probably, has given rise to the popular supposition that all diamonds must "shine" in the dark. When looking at a cut diamond it is a good plan to have a dark back-ground, as the brilliancy of the flash thereby becomes more prominent.

Diamond crystallizes in the isometric system, and shows numerous combinations. Most frequently occurring is the octahedron with many combinations. Dodecahedra are found simple and in combination. Perhaps no other mineral exhibits so many different forms belonging to the isometric system as this one. Twins and hemihedral crystals are frequently found. Char

acteristic of the diamond we may regard the curving of the crystalline faces. This occurs to so great a degree, that not unfrequently the specimens are nearly spherical.

Physically, we may distinguish three varieties of diamond: the crystal, the carbon and the anthracitic diamond. As seen above, the specific gravity of diamond is 3.52, while that of carbon is 3.01 to 3.40, and that of anthracitic diamond only 1.66. They show slight impurities, as compared with the crystals, but are chemically diamonds as also in their hardness. The carbon is put to practical uses, on account of its comparatively low price and great hardness. Instead of being colorless it is black, or gray, translucent only in very thin slabs.

Chemically, the diamond is carbon. At a high temperature it will burn, and be completely consumed, giving off carbonic acid gas. In an atmosphere of pure oxygen it will burn on, if once ignited. Between carbon points of a heavy battery, the diamond will become spongy, and turn to coals. In 1694 the first experiments of burning it were made. This was accomplished by means of a very powerful lens, concentrating the sun's rays. Much speculation became rife as to the behavior of diamonds under the action of great heat. Emperor Francis I, of Austria, conceived the brilliant idea of converting or melting a number of small diamonds together into one large one. In 1750 he placed a quantity of them, and some rubies, into a crucible, and subjected them to intense heat for twenty-four hours. After cooling, the rubies were found to be intact, but of the diamonds not a trace remained. Shortly before the French Revolution a Parisian jeweller asserted the possibility of exposing diamonds to a very high degree of heat without injuring them. He made his experiments before the famous chemist, Lavoisier. Maillard, the jeweller, had carefully surrounded his diamonds in the crucible with pulverized charcoal, and they withstood the fire perfectly. So long as the oxygen of the atmosphere can be excluded, the diamond cannot burn, and the only harm that might befall it would be a cracking from the heat. This, however, occurs comparatively rarely. Lavoisier, fully convinced by the demonstration, first offered a correct explanation of the phenomenon.

Impurities in diamonds are partly of a physical, partly of a chemical nature. Among the former must be classed cracks and cavities. The latter generally manifest themselves in discoloration

unequally distributed. Yellow, green, brown and gray are the colors most frequently observed. According to Brewster, many of the diamonds showing cavities under the microscope afford evidence, upon polarization, of having been subjected to pressure near these cavities at the time the diamond was crystallized. Such cavities, and slight accumulations of coloring matter were at first erroneously designated as chlorophylloid substances.

Yellow and brown diamonds owe their color probably to a very minute percentage of hydrated ferric oxide. It is an expensive amusement to analyze a quantity of diamonds sufficiently great to determine this point, so we are forced to base an opinion upon other than analytical proof. In the beginning of the nineteenth century a Parisian jeweler heated a brown diamond for some time, and, upon taking it out of the crucible, found that it had burned pink. This color, however, only lasted for about ten days, when the stone turned brown again. Since that time the experiment has been repeatedly tried, often with the same result. The chemical action in this instance consisted simply in driving off the water, so that the iron was contained in the diamond as ferric oxide. This imparts a pink color. Upon exposure to ordinary atmosphere, the original hydrated ferric oxide was again formed.

Green diamonds probably owe their color to an indefinitely small quantity of ferrous oxide. Whether the Dresden diamond is colored by the same material may remain an open question. The shade of green it exhibits is not one that would probably be produced by ferrous oxide. Possibly some organic salt of iron may produce the effect of color.

Gray diamonds usually owe their lack of transparency to the presence of innumerable microscopic cavities.

Hope diamond may be can
From analogy we know that

What the coloring matter of the scarcely more than be guessed at. certain salts of iron, organic matter and cobalt produce the same color. Which of these it is will most likely remain a secret. At a venture, the salts of iron might seem the most probable, considering the uniformity of coloring and the shade of the blue.

Regarding the formation of diamonds much has been said and written, and many well-conceived experiments have been made. More than any other agent, heat has been employed to reproduce these treasures of nature's laboratory. Thus far all experiments have failed to attain any available result. Some of the most emi

nent chemists of the present century have expressed the opinion that diamonds owe their genesis not to the action of heat, but to an organic process. Newton, when studying the optical qualities of diamond, came to the conclusion that it must be a "coagulated oil." By means of electricity very minute crystals of carbon have been obtained, but all efforts to reach greater size have been baffled. Liebig regarded the formation of diamond as the result of organic decomposition. Though this view may not be perfectly tenable, it commends itself to the poetical mind from its allusion to the rejuvenated phoenix rising from his own ashes. With an ever-increasing knowledge of chemistry and the constant improvement of mechanical appliances, we may yet, some day, be able to produce diamonds that will compare favorably with those fashioned by the skillful hand of nature.

Practical uses of Diamonds.-Dependent upon its physical properties, the diamond is put to various uses. Perhaps the most prominent is that of drilling. The comparitive cheapness of "carbon" makes it possible to utilize this material for such purposes. Diamonds with sharp, crystallized edges are used for cutting glass and small fragments, and splinters are used to arm graver's tools. Dust is employed in cutting other stones as well as the diamond. itself. Wherever a substance of very great hardness is required, diamond answers best. On account of its high power of refraction, diamond-lenses were formerly prepared, for the use of very high power instruments. The application of diamonds for purposes of personal or artistic ornamentation, may perhaps be considered a practical one in a certain sense. For such use the total absence of color and the high degrees of refraction and dispersion of light, place the diamond in the most prominent position among all precious stones.

Imitations. It is natural that a stone so valuable as the diamond should frequently be imitated. Pastes are manufactured to-day, which only a very experienced eye can detect as frauds Admixtures of lead and, recently, thallium, impart to paste a high angle of refraction, thus producing "flashing" effect very near that of the diamond. Colorless quartz crystals and topaz are frequently cut and are destined to simulate diamonds. Zircon, if heated for a short time, turns colorless from a bright blood-red, and is cut. This too, in smaller settings supplies the place of the diamond.

Quartz and Zircon can readily be detected by the difference of specific gravity. The former is 2.65, the latter 4.30, while