724 RUM 



* 



the new alkalis, M. Bunsen examined the water of a large number of German saline 

 springs, and in almost all he found caesium and rubidium in quantities more or less 

 minute. The solid sources of rubidium are much more prolific ; several varieties of 

 lepidolite, in particular, containing it in notable proportions, so that from this mineral 

 it may now be prepared by the pound. Dr. Struve, the well-known manufacturer of 

 artificial mineral waters, is now selling (at six thalers per kilo.) the residue from the 

 preparation of lithia, which residue contains about fifteen per cent, of chloride of 

 rubidium. M. Grandeau of Paris tested many of the French mineral waters for the 

 new metals, and with very frequent success. The waters of Bourbonnes-les-Bains, in 

 particular, proved to be rich in rubidium and caesium ; ten litres of the water having 

 yielded M. Grandeau no less than two grammes of the double chlorides of the new- 

 metals and platinum. M. Grandeau has likewise shown that rubidium occurs in the 

 mother-liquor left after the extraction of the alkalis from beet-root vinasses. From 

 one kilogramme of the mother-liquor M. Grandeau obtained no less than 4 - 7 grammes 

 of chloride of rubidium, or exactly 0-47 per cent. Hence it appears that rubidium is 

 a notable constituent of certain soils ; so that the question arises whether the new 

 alkalis take part, like potash and soda, in the nutrition of plants ; and if so, whether 

 :is merely accidental or substitution constituents of ash, or (in certain cases) as 

 essential ingredients thereof. (Hofmann.) For the salts of rubidium, see "Watts's 

 ' Dictionary of Chemistry.' 



RUBIRETINE. See MADDER. 



RUBY. A beautiful and favourite gem. The true ruby is a red sapphire, an 

 almost pure form of alumina. (See SAPPHIEE.) This extremely valuable gem is 

 found chiefly in the kingdom of Ava, and is frequently known as Oriental Ruby, in 

 order to distinguish it from the commoner stone called Spinel Ruby. 



Ruby spinel, or Spinel ruby, is of a light or dark red, and, if held near the eye, a 

 rose-rod colour. Its hardness is 8 ; specific gravity 3 '523. Its fundamental form is 

 the cube or hexahedron, but it occurs crystallised in many secondary forms, such as 

 octahedrons and tetrahedrons. Fracture conchoidal ; lustre vitreous ; colour red, 

 passing into blue and green, yellw, brown, and black ; and sometimes it is nearly 

 white. Pure spinel is a compound of alumina and magnesia, usually in the pro- 

 portions of about 28 magnesia and 72 alumina, although we sometimes find the 

 magnesia partially replaced by lime, and the alumina by oxide of iron. Vauquelin 

 discovered 6'18 per cent, of chromic acid in the red spinel. The red varieties exposed 

 to heat become black and opaque ; on cooling, they appear first green, then almost 

 colourless, but at last resume, their red colour. 



Pleonaste is a black variety which yields a deep green globule with borax. 



Balas ruby. Pale red or rose-red spinel, with sometimes a tinge of brown or violet. 



Rubicelle. Yellow or orange-coloured spinel. 



Almandine ruby, which is of a violet-red colour. 



Crystals of spinel from Ceylon have been observed embedded in limestone, mixed 

 with mica, or in rocks containing adularia, which seem to have belonged to a primi- 

 tive district. Other varieties, like the pleonaste, occur in the drusy cavities of rocks 

 ejected by Vesuvius. Crystals of spinel are often found in diluvial and alluvial sand 

 and gravel, along with true sapphires, pyramidal zircon, and other gems, as also with 

 magnetic iron ore, in Ceylon. Blue and pearl grey varieties occur in Siidermannland 

 in Sweden, embedded in granular limestone. Pleonaste is met with also in the diluvial 

 sands of Ceylon. Clear and finely -coloured specimens of spinel are highly prized 

 as ornamental stones. When the weight of a good spinel exceeds 4 carats, it is said 

 to be valued at half the price of a diamond of the same weight. M. Brard has seen 

 one at Paris which weighed 215 grains. As a gem, the ruby is cut in the same form 

 as the diamond, and may be set with a foil of copper or gold. 



RUBY, ORIENTAL. The red sapphire. See RUBY. 



RUBY SILVER. See PYBABGYBITK ; SILVER. 



RUBY, SPXXTEIi. See BUST. 



RUE (Ruta graveolens) produces a yellow colouring-matter similar to that obtained 

 from BUCKWHEAT, which see. 



RUM is a variety of ardent spirits distilled in the West Indies from the fer- 

 mented skimmings of the sugar-waste, mixed with molasses, and diluted with 

 water to the proper degree. A sugar plantation in Jamaica or Antigua, which 

 makes 200 hogsheads of sugar, of about 16 cwts. each, requires for the manufac- 

 ture of its rum two copper-stills ; one of 1,000 gallons for the wash, and one of 

 600 gallons for the low wines, with corresponding worm-refrigerators. It nlso 

 requires two cisterns, one of 3,000 gallons for the lees or spent wash of former 

 distillations, called dunder (quasi redundar, Span.), another for the skimmings of 

 the clarifiers and teaches of the sugar-house, along with twelve or more fermenting 

 cisterns or tuns. 



