R H O 



It fhould be remarked, that the odour of the root is 



greatly impaired by culture. 



Miller cultivated a variety of this plant for many years at 

 Chelfea, which was fmaller in all its parts, and had purphlh 

 flowers. 



We can by no means admit Rhodiola Hternata, Loureir. 

 Cochinch. 627, becaufe that author had never feen the 

 female flowers ; and his defcription of its twining ftem, and 

 doubly-compound leaves, renders it in habit fo totally unlike 

 the original Rhodiola. 



R H O 



fait of a rofe-colour, and foluble in alcohol ; with nitre, or 

 the muriates of ammonia or foda, are formed cryltallizable 

 triple falts infoluble in alcohol. 



Nitrate of rhodium is alfo uncryftallizable. It appears 

 not to be decompofable by filver, but is fo by copper, mer- 

 cury, and mod of the other metals. 



The foda-muriate of this metal affords a black powder by 

 digeilion with zinc ; which, when heated with borax, ac- 

 quires a white metallic luftre, but is infufible bv any heat 

 that has hitherto been applied. It is, however, fufible, 



Rhodiola, in Gardening, comprifes a plant of the low either with arfenic or fulphur, and may be again fepa 



herbaceous, odoriferous, fucculent, perennial kind, of which 

 the fpecies cultivated is the common, or yellow rofewort 

 (R. rofea). 



Of which there is a variety, m which the roots are fmaller ; 

 the (talks fmall, and not above five inches long ; the leaves 

 fmall, ending with a purple point ; the petals are purphfh, 

 and the ftamens little longer than the petals. It flowers 

 later than the common fort. 



Method of Culture. — This plant may be increafed by 

 planting cuttings of the (talks in the beginning of April, 

 foon after they come out from the head, in a fh.idy border ; 

 covering them clofe down with a glafs, and keeping them 

 dry, when they moftly put out roots in about fix weeks ; 

 but the cuttings fhould be laid in a dry room at lead a week Platina 

 before they are planted out, otherwile they are apt to rot Rhodium Lignum 

 and be deftroyed. They may alfo be raifed by parting the 

 roots in the beginning of autumn, when the (talks begin to 

 decay ; and when the flefliy parts are cut or broken, they 

 fhould be laid to dry a few days before they are planted. 

 They require a fhady fituation, and a dry undunged foil, in 

 which they will continue many years. They afford variety 

 in the borders, clumps, &c. 



RHODITES Lapis, the Rofe-ftone, in Natural Hipry, 

 the name given by authors to a kind of aitroites, or itar-ltone, 

 in which the figures more represent rofes than ftars ; they are 

 in both owing to coralloide bodies immerfed in the ftone ; 

 which, according to their various fpecies, afford a different 

 figure, when cut tranfverfely, in cutting the (tone into 

 plates for ufe. 



RHODIUM, in Chemijlry, a new metal, found in crude 

 platina, fo called from the rofe-colour of a dilute folution 



rated from thofe fubftances by heat, but it does not ac- 

 quire by this treatment any degree of malleability. It com- 

 bines with molt metals, and with filver and gold forms very 

 malleable alloys, which are unaltered by a high heat, but 

 become encrufted with a black oxyd when flowly cooled ; an 

 alloy of fix parts of gold and one of rhodium differs but little 

 in colour from fine gold, but is much more difficultly fufible. 

 The fpecific gravity of rhodium appears to be fomewhat 

 more than 1-1. That of an alloy confilting of one part rho- 

 dium and about two parts lead, was 1 1.3 ; which is fo nearly 

 that of lead itfelf, that each part of this compound may be 

 confidered as having about the fame fpecific gravity.. Phil. 

 Tranf. for 1804, vol. xciv. pt. 2. See Palladium and 



See Aspalatii. 



Rhodium Marmor, a name given by the ancients to a 

 marble brought from Rhodes ; it was a good white, but in- 

 ferior to the Parian, and was ufed by the Romans in their 

 public buildings, and fometimes in itatuary. 



RHODIUS, in Geography, a river of European Turkey, 

 which takes its fource N.E. of mount Ida ; and after re- 

 ceiving fome rivulets which flow from the neighbouring 

 mountains, and traverfing a fpace of twelve or fifteen miles, 

 difcharges itfelf into the Hellefpont, by the fide of the 

 cattle of Dardanelles. Its waters, which are far from 

 being abundant in fummer, are kept back and employed in 

 the irrigation of the lands ; but in winter, fwelled by 

 the rains which are frequent in that feafon, it occupies a bed 

 fufficiently large to deferve the name of river. The inha- 

 bitants of the Dardanelles, built on its banks, have con- 

 ftrufted a wooden bridge, at fome diftance from its mouth, 



of the falts containing it, by Dr. Wollaiton, to whofe in- in order to be able to crofs at all times to the left bank, and 

 quiries we are indebted for proof of its exiftence, and an repair to the fields which they cultivate beyond it. Behind 

 account of its properties. This metal is thus procured : the caftle, between the town and the river, is a tolerably ex- 

 fome crude platina being digelted in moderately dilute nitro- tenfive walk, naturally turfed, and (haded by very tall plane- 

 muriatic acid, a brownifh-red folution is obtained ; from this trees. This river waters an extremely fertile valley, formed 



the platina is to be feparated, for the moft part, by muriate 

 of ammonia, and the refidual liquor is to be heated with zinc ; 

 by this treatment a black powder will be obtained, and the 

 fupernatant fluid will confift of the muriates of zinc and iron. 

 This black powder, by digeftion in very dilute nitric acid, 

 will be freed from the copper and lead which it ufually con- 

 tains, and the refidue is to be digefted in dilute nitro-muri- 

 atic acid, till every thing foluble is taken up. To this folu- 

 tion a little common fait is to be added, and the whole eva- 

 porated to drynefs ; after which, by repeatedly warning with 

 warm alcohol, the foda-muriates of platina and palladium will 

 be diifolved, leaving behind a pure foda-muriate of rhodium. 

 This fait is readily foluble in hot water, and depofits on 

 cooling rhomboidal cryftals of a bright rofe-colour. Sal 

 ammoniac occafions no turbidnefs in the folution ; but if a 

 few drops of muriate of platina are added to the mixture, 

 an immediate yellow precipitate is thrown down. Neither 

 pruffiat of potaffi, nor hydro-fulphuret of ammonia, nor the 

 carbonated alkalies, produce any precipitate ; but the pure 

 alkalies throw down a yellow oxyd, foluble either in alka- 

 lies or acids. The muriate of this metal is an uncryitallizable 



by a plain to the eafl of the town. In this town are 

 reckoned fcarcely 4000 inhabitants, Greeks, Muflulmans, and 

 Jews. Its pofition is agreeable, its territory is fertile, and 

 its productions are very diverfified. To the N.E. is a riling 

 ground, covered with vines ; and at the extremity of the 

 fore-mentioned valley are found indications of a volcano ; 

 among others are to be feen confiderable blocks of granite, 

 the quartzofe part of which is almoft converted into glafs. 

 A little farther on is a fertile and circular bottom of imall 

 extent, furroundedby mountains covered with wood. 



In the territory of the Dardanelles are cultivated cotton, 

 feiamum, various kitchen-garden plants, the vine', the olive- 

 tree, and feveral fpecies of fruit-trees. The orange-trees 

 begin to grow here in the open air ; and a tolerable large 

 quantity of grain is collected here. The neighbouring 

 mountain furnifh the " velanida," (fee Queucus JEgilops,) 

 and gall-nut ufed in trade. Olivier. 



Rhodius, in Ichthyology, the Acipenser Sturio. See 



::RON. 

 RHODODENDRA, in Botany, a natural order of 

 plants, named after its principal genu?, (fee the next article,) 



and 



