The machinery designed by the author for this industry was described. A sixteen horse-power direct-acting winding engine was introduced for hauling up loads at the rate of about one thousand feet per minute, and a twenty-five horse-power geared engine, for hauling up heavier loads at the rate of from six hundred feet to seven hundred feet per minute.
Water was dear, and water-heaters were fitted to each engine, by which thirty-three per cent. of the water was again used, thus saving one third. The boilers were of the locomotive type, mostly of steel, to save weight, and thus reduce the cost of transit. The fire-boxes were also made of steel of very soft and ductile quality. A semi-portable engine was made for driving the wash mill. The engine was so arranged that it might be removed from the boiler and placed separately. The boiler was made to work at a pressure of 140 pounds per square inch. Automatic cut off gear was fixed to each engine, and the governors were provided with a spiral spring for adjusting the speed. A screen, or cylinder wash mill and elevator, were used for dealing with the diamantiferous soil, and were described. Standing wires were fixed at the back of the machinery, and passed over a frame fixed at the top of the mine, the end of the mine being secured to strong wooden posts. After the blue soil had been blasted and collected into trucks, it was placed in tubs, which ascended the standing wires. It was then emptied into the depositing box. The yellow soil might be put into the wash mill direct, also that portion of the blue which had passed through the screen fixed over the depositing box. The remainder of the blue, which was spread out to a thickness of four inches or six inches on the depositing ground, some distance from the mine to dry, was delivered into the upper part of the screen. The return water from the elevator, with a portion of fresh water, was also discharged at this point, and operations were thus greatly facilitated, the soil becoming thoroughly saturated, and passing more easily down the shoots. The large pieces which would not drop through the meshes of the screen were discharged into trucks at the lower end and carried away. The smaller pieces with water, in the form of sludge, fell through into a shoot, and thus were conveyed into the wash mill pan, and there kept in constant rotating motion by agitators. The diamonds and other pieces of high specific gravity sank to the deepest part of the pan, and the remainder of the sludge was forced over the inner ledge to the elevator. The sludge was then lifted and thrown upon an inclined screen and down the shoot over the side of the bank. The residue left in the pan at the end of the day's work was passed through a pulsator, in which, by the force of water, the mud and lighter particles were carried away, leaving behind the diamonds, agates, garnets, and other heavy stones. It was the practice occasionally to put a few inferior stones in the soil, to test the efficiency of the machinery.
In 1881 the author paid a visit to Kimberley, and found the industry a large one. The Post Office return showed the value of diamonds passed through the office in one year to be 3,685,000l. Illicit diamond traffic had hitherto been a source of great trouble at the fields. It was a question whether this industry would ever cease; in any case there was no doubt but that it would last for over a century. It was believed that the main bed of diamonds had not yet been reached, and that the mines in operation were merely shafts leading to it. Now that the water works were finished, with a bountiful supply of water, coupled with the great boon of railways to the Fields, and the advantage of a law recently passed for the prevention of illicit buying, a great and prosperous future was in store for the Diamond Fields.
SPONGES AT THE BAHAMAS.
Within the last few decades the sponge industry of the Bahama Islands has increased at such a rate that to-day it is the second in importance on the island. Although the product is not of such excellent quality as that from the Mediterranean, it sells well and is in demand both in England and in America.
For sponge fishing little boats of ten tons burden are employed and manned by from six to twelve men. The sponges that are washed upon the rocks and reefs are taken with iron rakes fastened to long poles, or are brought to the surface by divers and spread out on the deck of the vessel. This kills their soft, slimy organisms, which are black as tar. The sponges are then repeatedly beaten with sticks to remove this black slime, and afterward well washed.
The sponges are then sorted and softened for several hours in lime water, dried in the sun, and bleached. They are finally pressed by machinery into 100 lb. balls and then packed for shipping.
A rich and very extensive "sponge field" was recently discovered near Eleuthera, but as the water there has a considerable depth, five or six fathoms, fishing is attended with difficulty. In fact, it is rendered impossible wherever the "segler" or sailor fish are found, for the mud which these tiny creatures stir up completely veils the sponges from the eye of the fisherman.