OCH 



OCT 



OCEAN, in geography, that vast col- 

 lection of salt and navigable waters, in 

 which the two continents, the first includ- 

 ing Europe, Asia, and Africa, and the 

 last America, are inclosed like islands. 

 The ocean is distinguished into three 

 grand divisions. 1. The Atlantic Ocean, 

 which divides Europe and Africa from 

 America, which is generally about three 

 thousand miles wide. 2. The Pacific 

 Ocean, or South Sea, which divides Ame- 

 rica from Asia, and is generally about ten 

 thousand miles over ; and 3. The Indian 

 Ocean, which separates the East Indies 

 from Africa, which is three thousand 

 miles over. The other seas, which are 

 called oceans, are only parts or branches 

 of these, and usually receive their names 

 from the countries they border upon. 

 For the saltness, tides, &c. of the ocean, 

 see the articles SEA, TIDES, &c. 



OCHRES, in chemistry, combinations 

 of earths with the oxide of iron : they are 

 of various colours, and are principally em- 

 ployed as pigments. 



OCHROIT, in chemistry, an earth dis- 

 covered by Klaproth : the colour of the 

 mineral in which the earth is found, and 

 \vhich is denominated ochroites, is be- 

 tween red and brown. It is compact, and 

 breaks splintering in irregular or angular 

 pieces. Jt is perfectly opaque, and the 

 powder is of a reddish grey. The speci- 

 fic gravity is about 4.6. The earth was 

 called ochroit, from the Greek word 

 a X>% 0< >> on account of the characteristic 

 property which it possesses of acquiring 

 a light brown colour after being heated. 

 The mineral consists of 



Ochroit earth 54.5 



Silex 34. 



Oxide of iron 4 



Water 5 



Loss 



97.5 



, 2.5 



100 



Ochroit earth is capable of combining 

 with carbonic acid, during its precipita- 

 tion from acids by carbonated alkalies, 

 and strongly consolidating a portion of 

 water. It is observed in " Nicholson's 

 Journal," that the ochroit earth bears the 

 nearest relation to ittria, and like that, it 

 forms a connecting link between the 

 earths and the metallic oxides. Like it- 

 tria, it has the property of forming a 



reddish-coloured salt with sulphuric acid, 

 and is precipitable by prussiate of potash; 

 but it differs from ittria, in that it does 

 not form sweet salts ; that it is not solu- 

 ble, or at least very sparingly, in carbo- 

 nate of ammonia; and that, when ignited, 

 it acquires a cinnamon. brown colour. It 

 differs also from ittria, by not being so- 

 luble in borax, or phosphate of soda, 

 when urged upon charcoal before the 

 blow-pipe, wjnch salts easily effect a so- 

 lution of ittria, and melt with it also into 

 a pellucid pearl. See ITTRIA. 



OCHNA, in botany, a genus of the Po- 

 lyandria Monogynia class and order. Na- 

 tural order of Coadunatse. Magnolia, 

 Jussieu. Essential character : calyx five- 

 leaved ; corolla h've-petalled ; berries 

 one-seeded, fastened to a large, roundish 

 receptacle. There are three species. 



OCHBOMA, in botany, a genus of the 

 Monadelphia Pentandria class and order. 

 Natural order of Columniferce. Malva- 

 cex, Jussieu. Essential character : calyx 

 double, outer three-leaved ; anthers con- 

 nate, anfractuose; capsule five-celled, 

 many-seeded. There is but one species, 

 viz. O. lagopus, a large tree, with diva- 

 ricating branches ; the wood is white, 

 tender, and sufficiently light to be used 

 instead of corks for nets; the bark is 

 thick, fibrous, and ash-coloured ; leaves 

 frequently a foot and half in diameter ; 

 flowers on the upper branchlets, on thick, 

 straight peduncles ; calyx greenish red ; 

 petals white, fleshy ; capsule eight or 

 ten inches long. It is a native of Ame- 

 rica. 



OCHROXYLUM, in botany, a genus 

 of the Pentandria Trigynia class and or- 

 der. Essential character: calyx five- 

 cleft ; petals five ; nectary an annular 

 three-lobed gland ; capsule three, ap- 

 proximating, one-celled, two-seeded. 



OCIMUM, in botany, basil, a genus of 

 the Didynamia Gymnospermia class and 

 order. Natural order of Verticillatse. 

 Labiatse, Jussieu. Essential character: 

 calyx with the upper lip orbiculate, the 

 lower four-cleft ; corolla resupine, with, 

 one lip four-cleft, the other undivided ; 

 filaments, the two outer putting forth a 

 reflex process at the base. There are 

 twenty-five species ; these are either 

 herbs or under shrubs, possessing a sweet 

 scent ; their flowers are in whorls, form- 

 ing a loose spike, terminating and axil- 

 lary. 



OCTAGON, in geometry, is a figure of 

 eight sides and angles : and this, when 

 all the sides and angles are equal, is call- 

 ed a regular octagon, or one which mty 



