The diamonds imported are divided by the bureau of statistics statements into two groups, namely: °Diamonds uncut, including miners', glaziers', and engravers', not set,D and °Dia monds cut, but not set?' The value of diamonds uncut, including miners', glaziers', etc., imported in 11 months ended with May has grown from $2,500,000 in 1898 to $10,000,000 in 1910, while that of diamonds cut but not set has grown from $4,000,000 in 1898 to $29,500,000 in 1910, these figures being in each case for the period of 11 months. This inference that the cutting of diamonds is becoming an important industry in the United States is strengthened by the fact that the census statistics of °lapidary work* show that the total value of production of lapidary work in 1905 was over $7,600,000 against less than $500,000 in 1890, and that the value of the materials used in this work in 1905 was over $6,200,000 against less than $250,000 in 1890.
It is indeed worthy of note that although the largestpercentage of diamonds is cut outside of the United States, and all of them mined in other countries, the most improved machinery and many of the patented devices for mining and cutting have been the products of American ingenuity. Even Gardner F. Williams is an American born and bred.
Although the annual production of diamonds has increased more than 1,500 per cent in the last 30 years, and though there are • roduced at the present time more than 3,000,111 carats annually as against 200,000 before the discovery in South Africa, the changed condition has come about in such a manner that the stone has not been cheapened in value, has been fixed on a more even market basis, and has that much enriched the world.
The cutting branch of the industry has almost doubled in the past eight years, and now keeps employed between 700 and 800 men. Nearly five-sevenths of the diamond cutting of the world is done in Amsterdam and Antwerp, though New York has recently begun to make its influence felt in that direction. There are a number of cutting establishments in New York and Brooklyn, employing from 40 to 80 men each, and although the wages paid to American workmen are much higher than those paid in Europe, the advantage of better ma chinery in this country averages the cost of cutting. This is especially true in regard to large stones, though not always so with respect to stones running below an eighth of a carat.
Details of the artificial manufacture of dia monds in an electric furnace by Prof. Henri Moissan, at the University of Paris, were pub lished in June 1903. His experiments were begun after his finding of microscopic diamonds in nature, in the °blue earth° from the Cape, in the sands of Brazil, and in several meteorites. His researches showed that if carbon was pro duced at low temperatures it was always ob tained in the amorphous condition and no crys tals were found. The details of the manufac ture are thus described: For his experiment, Professor Moissan utilized the pressure which is produced in iron when it passes from the liquid to the solid state. It is known in fact that solid iron is less dense than when in fusion, as is shown by the fact that pieces of the metal will float on the melted bath, and it thus resembles water in this respect. He melts the iron in the elec
tric furnace and, saturates it with carbon, and to carry this out 200 grammes of Swedish iron cut ipto cylinders half an inch long and two fifths inch diameter were placed in a carbon crucible and completely covered with powdered charcoal. The crucible was placed under the arc and heated during three to six minutes with a current of 350 amperes at 600 volts. The cover of the furnace was removed and the crucible seized with a pair of tongs and plunged quickly into a bath of cold water. The crucible and metal remain red for a few moments, giv ing off gases which come to the top, then the whole cools off. It was not without appre hension that the experiment was made for the first time, as it was feared that an explosion would be produced when the melted mass at 3,000 degrees came in contact with the cold water. But no bad effect is produced by the meeting of the hot mass and the liquid; and during the first period the mass is cooled rather by a rapid radiation. In order to cool it by conduction, and thus more quickly, it was placed in iron filings. In this way the diamonds which were obtained were of a peculiar nature, and they contained specks of black carbon. The pressure seems to be less, and the transforma tion of the carbon into the diamond is less com plete. The experiment is, however, highly in structive, as it gives a form of speckled dia mond which is also found in nature. To obtain a more rapid cooling, a bath of melted lead was found the best; it was kept at about the fusing point, or 617° F. The crucible, heated as before, is quickly plunged into the bath of melted lead, which is about six inches deep. The iron, which is lighter than the melted lead, is detached from the crucible in masses which tend to form spheres and rise more or less rapidly to the top. When the iron is saturated with carbon in the furnace, it becomes so pasty that the crucible can be turned over and it will not run out, but when it cools off the metal soon becomes liquid and gives up graphite.
°The smallest spheres, half an inch in diam eter, were solid and sufficiently cool on coming to the top. These spheres gave a good yield of diamonds and the latter were especially clear and brilliant, and the spotted form was absent. Some of the crystalline forms were very sharp. One of the transparent diamonds measured as high as 0.57 millimetre, and had a somewhat triangular form with the angles rounded off. It was perfectly clear. It is curious to note that three months after its formation it split into two pieces; this fact is significant, as some diamonds from .the Cape show an identical ac tion, this being no doubt due to irregularities of pressure at the time of formation. The samples of diamonds obtained by this method were interesting to examine as to their differ ent form. Most of them were smooth and brilliant, while others had a grained surface. All the specimens had the particular lustre which is characteristic of the native diamond. When a ray of light is sent into the interior they appear to become luminous. Some of the specimens are cubes and octahedra, with rounded angles.° See DIAMOND.