DIACOPR. 



DIANCHORA. 



X'l 



DIA'COPE, a fNttna of Fishes belonging to the section Acanlho- 

 jrfrrymi and family Ptrdda, and belonging to that aection of tin- 

 family in which the specie* have less than seven branchiostegous 

 rayn, and an interrupted lateral line. 



This genus is allied to Strrmtu, but may be distinguished by there 

 being a notch or emargination in the lower part of the preoperculum, 

 into which is fitted a projecting tubercle. 



Many Urge and beautiful specie* of this genus inhabit the Indian 

 eaa. Dieeofi oetoUiuala, a very beautiful species, caught off the 

 eoast of the Mauritius, is of a brilliant reddish-yellow colour, shaded 

 into white on the belly, and is adorned with four longitudinal blue 

 stripes on each aide of the body ; these stripe* are margined with 

 black. It U about 10 inches in length. 



Some of the species are known to have attained the length of 

 3 feet and upwards. 



DIADE'LPHIA, the seventeenth class in the Linnasan system of 

 arranging plants. Strictly speaking it ought to contain no genera but 

 those which have their stamens united into two equal or unequal 

 parcels; but as it consists principally of Leguminous genera it is 

 customary to place in it all the Papilionaceous plants which have 

 united stamens, whether in one parcel or two. This and similar 

 plans render the Linneean system more natural, but destroy its use as 

 an artificial guide to the determination of the name of a plant. 



DIADEMA. [CIRRIPEDIA.] 



DIALLAGE. [AooiTK.] 



DIAMOND, a crystalline gem, which, on account of its high lustre 

 and extreme hardness, has always been regarded as the most valuable 

 of the precious stones ; the former of these qualities arises from its 

 great refractive power, and on account of its hardness its lustre 

 remain* undimimshed. It is commonly colourless or grayish, but 

 sometimes green, yellow, red, brown, blue, and black ; the two last- 

 mentioned colours are the rarest. Its lustra is adamantine ; refrac- 

 tion single ; transparent, but sometimes rendered opaque by foreign 

 matter. Hardness 10, exceeding that of any other, and scratching 

 every other substance ; owing to its hardness it can be cut, or rather 

 worn down, only by rubbing one diamond against another, and it is 

 polished by the friction of portions of the gem itself reduced to 

 powder : it is broken without difficulty. The specific gravity of the 

 diamond is from 3'48 to 3'55 ; streak grayish ; fracture concboidal ; 

 cleavage parallel to the planes of the regular octahedron, which is its 

 primary form, subject however to numerous varieties, and the faces 

 are frequently curvilinear. When rubbed it phosphorises, and 

 becomes positively electrical, and is therefore a non-conductor of 

 electricity. When heated, without the contact of air, it suffers no 

 change, but if ignited in contact with it, it is totally converted into 

 carbonic acid gas, proving that it is carbon in a state of purity. 



For ornamental purposes diamonds are cut into two shapes : 

 namely, Rose- Diamonds and Brilliants, the former being, for the most 

 part, made out of the octahedral crystals, and the latter from those 

 with curvilinear faces. The weight and consequently the value of 

 diamonds are estimated in carats, each of which is equal to 3'1 66 groins. 

 In the formation of either a brilliant or a rose-diamond so much is 

 out away that the weight of the polished gem is not more than half 

 that of the rough crystal out of which it was formed. 



Newton, considering the fact that transparent bodies which are 

 uninflammable refract light nearly in the ratio of their density, while 

 those which are inflammable have refractive powers that are greater 

 than their density, was led to conclude that the diamond, on account 

 of this great refractive power, was ' probably an unctuous substance 

 coagulated." 



In 16U5 experiments were made at Florence, which proved the 

 diamond to be dissipated by intense heat in the focus of a burning 

 lens. Several chemists proved that diamonds lost no weight when 

 heated without the contact of air, and on the contrary, that they 

 were dissipated when heated in it; but it was first shown by 

 Lavoisier that carbonic acid was obtained by the combustion of the 

 diamond, and he concluded that it contained carbon, and had great 

 analogy with this combustible body. 



Thee* researches were not however sufficient to afford complete 

 proof of the nature of the diamond ; but this was accomplished by 

 the succeeding experiment* of Smithson, Tennant, Guyton Morveau, 

 Allen and Pepya, and Davy, who all arrived at the same conclusion, 

 which is, that although there exist* in many respect* so great a 

 difference between the properties of the diamond and charcoal, they 

 are identical in their chemical nature. Thus, whenever by combus- 

 tion pert* of charcoal, or an equal weight of diamond, are combined 

 with oxygen, the quantity of oxygen absorbed always amounts to 

 14 part*, and the result of their combustion is 22 parts of carbonic 



Diamonds occur in India in the district between Oolconda and 

 Mamlipatam, near Patina, in Bundelcund, also on the Mahanuddy, and 

 in Ellnre. They have been obtained in Borneo, on the west side of 

 the Ratoo* Mountain, with gold and platina. The Brazilian mines 

 were first discovered in 1728, in the district of Serra do Frio, to the 

 north of Rio de Janeiro. The largest diamonds are procured on the 

 river Jeuuitiuhnnha, which is called the Diamond River, also Rio 

 Pardo. In the Ural Mountains diamond* were detected in 1820, by 

 Humboldt and Roes, in their journey into Siberia. In the fnited 



State* the diamond has been met with in Rutherford county, North 

 Carolina, and Hale county, Georgia. They have been found on the 

 river Qinul, in the province of Constantine, in Africa. They have 

 also been discovered in Australia, and of such size as to render it 

 probable they may add yet more to the mineral treasures of that 

 country. 



The rocks in which the diamond occurs in Brazil are either a 

 ferruginous quartzose conglomerate, or a laminated granular quart* 

 called Itacoliimiie. The latter rock occurs in the Urals, and diamonds 

 have been found in it ; and it is also abundant in Georgia and North 

 Carolina. In India the rook U a quartzose conglomerate. 



In most instances diamonds are obtained from alluvial washings. 

 In Brazil the sands and pebbles of the diamond streams are collected 

 and washed under a shed by a stream of water passing through a 

 succession of boxes. A negro washer U stationed at each box. When 

 a diamond is found weighing 17J carats the negro is entitled to his 

 liberty. 



" The largest diamond of which we have any knowledge is men- 

 tioned by Tavernier as in the possession of the Great Mogul It 

 weighed originally 900 carats, or 2769'3 grains, but was reduced by 

 cutting to 861 grains. It has the form and size of half a hen's egg. 

 It was found in 1550, in the mine of Colone. The diamond which 

 formed the eye of a Brahminican idol, and was purchased by the 

 empress Catharine II. of Russia from a French grenadier, who had 

 stolen it, weighs 193 carats, and is as large as a pigeon's egg. The 

 Pitt, or Regent Diamond, is of less size, weighing but 136'5 carats, 

 or 41 Uj grains ; but on account of its unblemished transparency and 

 colour it is considered the most splendid of Indian diamonds. It was 

 sold to the Duke of Orleans by Mr. Pitt, an English gentleman, who 

 was governor of Bencolen, in Sumatra, for 130,0002. It is cut to the 

 form of a brilliant, and is estimated at 125,0002. Napoleon pi 

 in the hilt of his sword of state. The Raja of Mattan has in his 

 possession a diamond from Borneo weighing 367 carats." (Dana.) 



The great diamond mentioned in the above extract as in the posses 

 sion of the Great Mogul appears to be the identical diamond which, 

 under the name of Koh-i-Noor, excited so much attention at the Great 

 Exhibition in 1851. Some doubt is thrown on Tavernier' a statement 

 of its being cut. This precious gem has seen a variety of fortunes. 

 Its early history is mythical. From the Great Mogul it passed into 

 the possession of the reigning family of CabuL When Shah Suja 

 was driven from Cabul he became the nominal guest and actual 

 prisoner of Runjet Sing, who spared no means to obtain possession of 

 the precious gem. In this he succeeded in 1813. After the death of 

 Kniijut the diamond was preserved for a while by his successors. It 

 was occasionally worn by Khunuk Sing and Shire Sing. Aft<-r the 

 murder of the latter it remained in the Lahore treasury until the 

 supercession of Dhuleep Sing and the annexation of the Paujab by the 

 British government, when the civil authorities took possession of 

 the Lahore treasury, under the stipulation previously made that all 

 the property of the state should be confiscated to the East India 

 Company, in part payment of the debt due by the Lahore government 

 and of the expenses of the war. It was at the same time stipulated 

 that the Koh-i-Noor should be surrendered to the Queen of England. 

 It arrived in this country on the 30th of June, 1850, and on the 3rd 

 of July was presented to her Majesty. Since its public exhibition in 

 1851 it has been submitted to the process of cutting, which has much 

 enhanced its beauty and value. 



The diamond U cut by taking advantage of its cleavage, and also 

 by abrasion with its own powder, and by friction with anoth 

 mond. It is a process of great labour, and many hours are spent in 

 producing a single facet. Diamonds were first cut iu Europe in 1456 

 by Louis Berquen, a citizen of Bruges. 



The diamond is used for cutting glass. [DIAMOND, in ARTS AKD 

 S< . 1 uv.l It is also employed for the lenses of microscopes. It has 

 but little chromatic aberration, but the frequent irregularity of iU 

 structure is a drawback to its employment for this purpose. 



(Dana, Manual of Mineralogy ; Cotalu'jue of Great Exhibition of 

 1851, Class xxiii.) 



DIAMOND-BEETLE. [CuBCOLio.] 



IHAX.'KA. [AflaJUMmj 



DIA'NCHORA, a Fossil genus of Conchiftra allied to Spontlyliu, 

 established by Mr. Sowerby in his ' Mineral Conchology.' It has the 

 following characters : Shell delicate, adherent, regular, symmetrical, 

 equilateral, sulwuriculated, inequivalve ; one valve hollowed within, 

 convex without; the other flat Hinge consisting of two distant 

 condyles. 



Cuvier ('Rogno Animal') places the genus between Pachytai and 

 Podoptit, M. de Blainville between Playioiloma and Podoptis, and 

 M. It img between Pecttn and Pedwn. M. Deshayes, in his edition of 

 Lamarck, after observing that Pachylet had been funned at the 

 expense of Plarfioitoma, states that his examination of the iqwcies had 

 satisfied him of the identity of the genera, and that the same exami- 

 nation instituted with regard to IHnnchora had convinced him that 

 the characters of the last-named genus were identical with those of 

 I'achyta and Podopiit. A further inquiry terminated in the conclu- 

 sion that the so-called genera, Podojait, Dianchora, and Pachyttt, 

 were only Spondyli, whose internal lamina had been dissolved, and 

 had left naked the external or conical lamina. [SPONDYLUS.] The 



