Discoveries and Inventions of the Nineteenth Century

In ancient times, and down to a comparatively late period, the only region from which were derived all the diamonds that found their way to Europe, was India, where Golconda was long celebrated for the productive mines in its neighbourhood, and for the high estimation in which fine specimens of their yield were held. In the seventeenth century these mines employed 60,000 persons, it is said; and in other districts of India diamond-seeking has also been carried on from time immemorial. A gradual decrease in the finds of Indian diamonds has long been observed, and the supremacy the East had so long enjoyed as the purveyor of gems was in the earlier part of the eighteenth century transferred to another hemisphere. In 1727 the diamond was first discovered in Brazil; or rather, we might say, was then first discerned there. For the gold-seekers in washing the sands of certain Brazilian rivers had found numberless specimens which they either threw aside as worthless, or, seeing them prettier pebbles than the rest, used them as counters in their card games; their true nature was not recognized, because the rough diamond has by no means the attractive appearance of the cut and polished brilliant flashing with refractive radiance. It must have been these last, and not diamonds in their natural state, that presented themselves to the imagination of the poet when he penned the line— Or deep with diamonds in the flaming mine. The announcement of some diamonds having been found in America had no effect on the prices in the Indian market, but the exports that soon after came from Brazil in great abundance quite changed the conditions of the trade, for in the first fifty years their value was estimated 697at no less than £12,000,000 sterling. As already stated, the presence of diamonds in Brazil was not recognized until 1727, and then by the accident of one Lobo, an inhabitant of the gold district of Minas Geräes, who had been in India and had seen rough diamonds there, observing the resemblance; he took some of the Brazilian stones to Lisbon, where their identity with the products of the Indian mines was established. But the European dealers, alarmed lest this discovery should depreciate the value of their stocks of Indian gems, spread a report that the so-called diamonds from Brazil were but the refuse of the Indian mines that had been sent to Brazil. This had the effect of stopping for a time the sale of the Brazilian diamonds; but the traders in these were not above taking a hint from their rivals—fas est et ab hoste doceri—for they carried their diamonds to Bengal, and there sold them as Indian stones at Indian prices. For nearly one hundred and forty years after this Brazil was by far the most productive diamond region in the whole world, and especially after 1754, when diamond-seekers congregated by thousands in the very rich fields of Bahia, a district of Brazil. Nor have the places above mentioned been by any means the only localities in Brazil where diamond-finders have been at work; but the production has decreased and has lost its relative importance by the South African discoveries that about 1870 caused an entire change in the diamond industry, and the high prices of the Brazilian gems no longer capable of being maintained, the fall in value has rendered the workings less remunerative than formerly. We may now pass over with mere mention, discoveries of diamondiferous districts in North America, Australia, and elsewhere. While rejecting as entirely inapplicable and inexcusable by any stretch of poetic licence the epithet flaming for the diamond mine, we must question whether the word mine, that as the customary word we have continued to use, does not convey an equally false notion of the nature of the workings to which hitherto reference has been made. For these in most cases are nothing more than holes, very much like gravel pits in the side of a hill. The diamonds which have so far been in question are usually found among alluvial sands or gravels, the water-worn fragments of disintegrated rocks. These are in many cases carried down by rivers, and the diamonds under such circumstances are very frequently accompanied by gold; indeed, it is the search for gold that has in many cases led to their discovery. In the dry season of the year, which extends from April to October, the lessened currents of certain of the Brazilian streams are diverted from their course into canals, so as to leave dry the bed of the stream, and here the mud is dug out to the depth of six or eight feet or more, and transported near the washing huts, these operations being continued throughout the dry season. When this is over the digging is necessarily interrupted by great volumes of water that fill the rivers and streams, and the diamond-seekers devote their attention to washing the mud that has been collected. About one cwt. of this is placed in a long trough, and water is made to flow in, while the negro labourer stirs up the mass with his hands, until the water runs off clear, all the particles of mud having been washed away. The residual gravel is then very carefully examined, stone by stone, and any diamonds found are handed to the overseer, who watches all proceedings from an elevated seat. These Brazilian diamonds are mostly of a small size: occasionally, but very rarely, stones of quite exceptional value are found, but perhaps not one in 10,000. Formerly when in the Brazilian fields a negro slave found one 698of 18 carats, or more (18 carats = 72 grains), he not only obtained his freedom, but was rewarded with gifts, and for the finding of smaller stones commensurate rewards were given. The value of a diamond of the larger sizes depends upon so many adventitious circumstances that it would not be easy for any one to state the money’s worth of an 18–carat stone, but, considering too that the price increases in a more rapid ratio than the weight, we may to some extent draw an inference from the published values in 1867 of smaller Brazilian brilliants, perfectly white, pure, and flawless, when one of 5 carats (20 grains) in weight was priced at £350. As the rough diamond gives a brilliant of only half its weight, we may from the above assume an 18–carat stone to be worth in its finished state at least £1,000. It may well be asked what are the qualities possessed by the diamond which have caused it to be so highly valued as an adornment all the world over; and here it will be proper to invite the reader’s attention to the chemical as well as to the physical character of the diamond. The most obvious and attractive quality of the cut brilliant is its unsurpassable lustre, which is due to its high refractive power. In a section of our article on light the subject of refraction has been dealt with, and an explanation given of the index of refraction. That of the diamond is the highest known, being 2·50 to 2·75; other precious stones have indices ranging from 1·58 to 1·78; those of glass and of quartz are between 1·50 and 1·57. It follows from the known laws of refraction that the limiting or critical angle is less for diamond than for other substances, as, for example, glass, for the posterior surface of a diamond will totally reflect all the light that falls upon it at any angle with the normal greater than 24°; glass will totally reflect only when the incidence is greater than about 42°: hence the diamond reflects from its farther surface about 64 per cent. of rays that glass similarly situated would allow to pass outwards without reflection. Another property in which the diamond excels all other substances is hardness. It is the hardest substance in nature; for a diamond will scratch every other, but by none can it be scratched, except by another diamond. Not but that by the application of a file the edges of a diamond or brilliant may be notched and broken; but this would be through sheer mechanical force tearing the substance, and would be a test of brittleness, not of hardness. These two properties have not unfrequently been confounded, as when it was foolishly prescribed as a test for the genuineness of a diamond, that it should be placed on an anvil and struck with a hammer. No doubt many good and valuable stones have been sacrificed by this ignorant treatment. The hardness of the diamond does not prevent its being reducible to powder when so required. Again, diamonds are sometimes in such a condition of internal strain that very slight shocks are sufficient to cause them to separate into fragments. We read of diamonds that are suspected to be in this condition being packed for transmission within raw potatoes. The extreme hardness of the diamond secures it from all those accidental abrasions and injuries to which softer materials are liable, so that it does not deteriorate by age or use. It is unaffected also by any chemical substances. In chemical composition the diamond is pure carbon, one of the most commonly diffused of the elementary bodies, as it enters into the constitution of the atmosphere, of all organic bodies, and of a vast number of mineral substances. Carbon in a less pure form also occurs naturally 699as graphite, plumbago or black lead, and in other conditions comes into ordinary use as already explained in our article on Iron. It was only towards the end of the eighteenth century that the composition of the diamond was demonstrated by the celebrated French chemist, Lavoisier, who actually burnt a diamond in oxygen gas, and found the resulting product to be carbonic acid gas, identical with that obtained by similarly burning a piece of charcoal. Soon afterwards another French chemist, Clouet, confirmed Lavoisier’s conclusion by producing steel from pure iron and diamond heated together, an experiment of much significance when considered in the light of the remarkable relation between these substances, which is one of the latest discoveries of our century. It should be observed that Clouet’s result implies a fusion of the diamond as well as of the iron in the act of entering into chemical combination. Like nearly every solid substance of definite chemical composition, this pure carbon takes the crystalline form. The phenomena of crystallization are of the highest interest and beauty, for in them we see shapeless matter fashioning itself into definite and often perfect geometrical solids, as if it had been wrought by the hand of some mathematical artist. Every substance forms crystals of some one shape when the conditions are identical, and one essential condition for any crystallization is that the particles should be capable of free movement in arranging themselves, and this condition can occur only when the substance is in the state of liquid or of gas. Crystals are commonly deposited from solutions when the solvent evaporates or is cooled down; or they are formed when a fused substance solidifies. In either case the crystals are the larger and more perfect as they are allowed the greater time to form. Now, carbon in any of its conditions has been found to be absolutely infusible and insoluble, and therefore the origin of the diamond has long been a puzzle to scientific men, very diverse surmises having been propounded on this subject. Some have thought it was separated from carbonic acid by the action of heat, or of electricity; others, that the carbon had been gasified by subterranean heat; others, among whom were Newton and the German chemist, Liebig, believed that heat had nothing to do with it, but that the crystals slowly separated from vegetable matters (hydro-carbons) in the process of decomposition under some unknown conditions; others, that the diamond crystallized out from liquid carbonic acid, holding under pressure some unknown form of carbon in solution; others, that carbon was ejected by volcanic action in a fused state; and so on. We hope to show that the