

CARAVAN TEA CARBON. 



47 



of Moliamnied once at least during his life, caravans 

 of pilgrims go to Mecca every year, from various 

 places of meeting. The leader of such a caravan to 

 Mecca, who carries with him some cannon for pro- 

 tection, is called Emir Adge. Trading caravans 

 choose one of their own number for a leader, whom 

 they call Caravan Baschi. Much information on the 

 subject of caravans is to be found in the travels of 

 Niebuhr, who made many journeys with them, and 

 describes them, as it is well known, minutely and 

 faithfully. For an account of some of the most im- 

 portant routes pursued by the caravans hi Africa, 

 see the article Africa. 



CARAVAN TEA. See Tea. 



CARAVANSARIES, hi the East ; a sort of bin, 

 situated hi countries where there are no cities or 

 villages for a considerable extent, to furnish tra- 

 vellers with a shelter. Some of them are built with 

 much splendour, though they are generally unfur- 

 nished, and the traveller is obliged to bring with 

 him his bed and carpet. In many, the hospitality is 

 gratuitous. It is common for a pious Mohammedan 

 to establish, during his life or by will, one or several 

 of such caravansaries. This kind of benevolence is 

 considered peculiarly agreeable to the Deity, and 

 promotive of the eternal happiness of the founder. 

 Sometimes persons are kept hi these establishments 

 to show the way to the caravans for some distance. 

 See Khan. 



CARAWAY SEEDS (fructus carvi) are a stimu- 

 lant and excitant, the fruit of a biennial plant (cani?n 

 carvi, Linnaeus), a native of Europe, growing parti- 

 cularly in the south of France. 



CARBON. Charcoal, as we are familiar with it 

 in common life, contains hydrogen" and saline and 

 metallic substances. Accordingly, it became neces- 

 sary to mtroduce-a peculiar term for its pure base, 

 and the one adopted by chemists was carbon. This 

 element, besides forming the inflammable matter of 

 charcoal, exists largely in animal substances, and is 

 extensively distributed in the mineral kingdom. The 

 only body hi which carbon has been found to exist 

 in a state of absolute purity, is the diamond. This 

 precious stone has always been esteemed as the most 

 valuable of the gems, a superiority which it owes to 

 its hardness, lustre, and high refractive power. 

 Diamonds are brought from India and from Bra- 

 zil. Those of India, which have been the long- 

 est known, are principally found in the kingdoms 

 of Golconda and of Visiapour. Those of Brazil, 

 discovered at the commencement of the seven- 

 teenth century, belong to the district of Serro-do- 

 Frio. The situations in which they occur are such 

 as to favour the idea of their recent formation 

 since they exist disseminated through a lootfi, 

 ferruginous sandstone, or quite detached hi a sandy 

 soil ; and, in both cases, are situated at no great depth 

 below the surface. In Brazil, the conglomerate in 

 which they exist is called cascalho ; from which they 

 are extracted by washing, hi the same manner as 

 gold. The diamond uniformly occurs crystalized, 

 and presents a great variety of forms ; all of wliich 

 yield readily to mechanical division parallel to all the 

 planes of the regular octahedron, which, therefore, 

 is the form of the primary crystal, and under whicli 

 figure it is sometimes found in nature. The faces of 

 its crystals are very frequently curved, so as to com- 

 municate to them a rounded appearance. They are 

 commonly limpid ; and are either colourless, or of a 

 yellowish, bluish, yellowish-brown, black-brown, 

 Prussian blue, or rose-red colour. Specific gravity, 

 3-5. Its hardness is extreme; so that it can be 

 worn down only by rubbing one diamond against 

 another, and is polished only by the finer diamond 

 lewder. The weight, and, consequently, the value 



of diamonds, are estimated in carats, one of which is 

 equal to four grains ; and the price of one diamond, 

 compared with that of another of equal colour, trans- 

 parency, and purity, is as the squares of the respec- 

 tive weights. The average price of rough diamonds, 

 that are worth working, is about 2 for the first 

 carat. The value of a cut diamond is equal to that 

 of a rough diamond of double weight, exclusive of 

 the price of workmanship ; and the whole cost of a 

 wrought diamond of 



1 carat may be about 3fi dollars, or 8 



2 carats is X 8 = T,2 



3 do. is S* X 8 = 72 



4 do. is 4 X = 128 

 100 do. is 100* X 8 =80,000. 



This rule, however, is not extended to diamonds of 

 more than twenty carats. The larger ones are dis- 

 posed of at prices inferior to their value by that 

 computation. The snow-white diamond is most 

 priced by the jeweller. When transparent, and free 

 from cracks, it is said to be of the first water The 

 following are some of the most extraordinary dia- 

 monds known : one in the possession of the rajah of 

 Mattan, hi the island of Borneo, where it was found 

 about a century ago : it is shaped like an egg, and is 

 of the finest water: its weight is 367 carats, or 2 oz. 

 169 grs. Troy. Another is the celebrated Pitt dia- 

 mond, now among the crown jewels of France, 

 weighing 136 carats ; another hi the sceptre of the 

 emperor of Russia, of the size of a pigeon's egg; and 

 another in the possession of the Great Mogul, wliich 

 is said to weigh 280, and which, hi a rough state, 

 weighed 793 carats. 



From the fact that transparent inflammable bodies 

 refract light hi a ratio greater than their densit es, 

 Sir Isaac Newton conjectured that the diamond might 

 consist of an unctuous matter coagulated. The Flor- 

 entine academicians had rendered its combustibility 

 probable, by exposing it to the solar rays of a pow- 

 erful burning-glass, and observing that it gradually 

 disappeared, or was consumed. Subsequent experi- 

 ments settled the question, by proving, that the dia- 

 mond lost none of its weight when calcined out of 

 contact with the air ; but, on the contrary, that it 

 was dissipated when heated in contact with this fluid. 

 It still remained, however, to be discovered, what 

 was the true nature of the diamond. This was ac- 

 complished by Lavoisier, who enclosed diamonds in 

 jars filled with atmospheric air or oxygen gas, and, 

 after having caused them to disappear by the heat 

 of a burning-glass, examined the air in the vessels. 

 He found it to exhibit precisely the same properties 

 as the air which results from the combustion of char- 

 coal. This experiment was also performed by Mor- 

 veau, who demonstrated the nature of the diamond 

 by still another arrangement. A diamond was en- 

 closed hi a cavity made hi a piece of pure, soft iron ; 

 a stopper of the same metal was driven into it, and 

 the mass was put into a small crucible, which was 

 covered, and this into a second ; the space between 

 them being filled with pure silicious sand. The 

 whole was exposed, for some time, to an intense heat. 

 When examined, the diamond had disappeared, and 

 the iron, with which it had been in contact, was con- 

 verted into steel. Now steel is a compound of iron 

 and carbon; and, as the diamond was not visible, 

 and as there was no source from which the carbon 

 could have been obtained, the conclusion was una- 

 voidable, that the diamond was pure carbon. Yet so 

 different is this mineral from charcoal, that it was, for 

 a time, imagined that it contained some other ele- 

 ment than carbon ; but the numerous and delicate 

 experiments of Sir H. Davy, and several other die- 

 mists, failed 01 detecting any thing else in its compo- 

 sition ; and, although there exists so great a differ- 



