RIOE 703 



Erecipitate the baryta. It is then boiled, filtered, and evaporated, first adding to it a 

 ttle nitric acid and then a great excess of sal-ammoniac. The evaporation is carried 

 to dryness at 212, and the residuum is washed with a concentrated solution of sal- 

 ammoniac, which removes all the rhodium. When the washings are no longer 

 coloured, the liquor is evaporated with a great excess of nitric acid, which destroj - s 

 the sal-ammoniac, and when only the salt of rhodium is left, the evaporation is 

 finished in a porcelain crucible. The rhodium salt is now moistened with hydro- 

 sulphide of ammonia, mixed with three or four times its weight of sulphur, and the 

 crucible is heated to bright redness, after which metallic rhodium is left in the 

 crucible. So obtained rhodium may be considered almost pure, after it has been 

 boiled for some time, first in aqua regia, and then in concentrated sulphuric acid. To 

 obtain it perfectly pure it must be melted with four times its weight of zinc. The 

 alloy is treated witli concentrated hydrochloric acid, which dissolves most of the 

 zinc, but leaves a crystalline matter which is really an alloy of rhodium and zinc in 

 definite proportions. This is dissolved in aqua regia, and the solution is treated with 

 ammonia until the precipitate first formed is redissolved. The solution is boiled .and 

 evaporated, by which is obtained the yellow salt, or chloride of rhodium. This is 

 purified by repeated crystallisation, and then calcined with a little sulphur, by which 

 means rhodium is procured absolutely pure. 



Rhodium melts less easily than platinum, so much so that the same fire which will 

 liquefy 300 grammes of platinum only will melt 40 or 50 grammes of rhodium. It 

 is not volatilised, but it oxidises on the surface like palladium. Less white and 

 lustrous than silver, it has about the same appearance as aluminium. When perfectly 

 pure it is ductile and malleable, at least after fusion. Its density is 12-1. 



The alloys of rhodium, those at least which have been examined, are true chemical 

 combinations, as is shown by the high temperature developed at the moment of their 

 formation. The alloy with zinc already described resists the action of muriatic 

 acid, but in contact with air and the acid there is soon a well-marked rose-coloration 

 which reveals an oxidation of the two metals under the double influence of the nir 

 and acid. The alloy with tin is crystallised, black, brilliant and fusible at a very 

 high temperature. 



RHODONITE. A silicate of manganese, sometimes containing iron, magnesium 

 and calcium, found chiefly in Sweden. 



RHOXVXB SPAR. Native carbonate of magnesia. 



RHUBARB (Rheum). Thirteen species of plants have been named as yielding 

 the medicinal rhubarb ; it has, however, been recently determined that the Rheum 

 officinale is the true rhubarb plant. The best rhubarb is called Turkey rhubarb, and 

 only procured by the Russians, at Kiachta, from the Chinese. Several species of 

 Jhubarb are cultivated in this country, for the agreeable acidity of their stems. See 

 Elements of Mater ia Medica, by Bentley and Redwood. 



RHUS. The SUMACH, which see. 



RHUSXIXA. Rhusma turcorum. Used as a depilatory. 



RIABOCCA WOOD, or Kiabocca wood, an ornamental wood obtained from the 

 East Indies. It is not known what tree produces it. It is much used for making 

 ornamental boxes, desks, and the like. 



RIBBON MANUFACTURE. This differs in no particular respect from the 

 manufacture of woven fabrics in similar materials. See SILK, and WEAVING. 



RICE. (Oryza sativa, Linn.) This plant, originally a native of Asia, is now 

 extensively cultivated in India, China, the islands of the Eastern Archipelago, in 

 the West Indies, Central America, and the southern of the United States. Roxburgh 

 informs us that there are above forty different varieties. Carolina and Patna rice are 

 the kinds most esteemed in this country. Braconnot (Ann. Chim. Phys.) has given 

 the following analyses of two varieties of rice : 



Carolina rice Piedmont rice 



Starch 85-07 83-80 



Woody fibre .... 4-80 4-80 



Gluten 3-60 3'60 



Tallowy oil . . . . o % 13 0'25 



Sugar (uncrystallisable) . . 0'29 0'25 



Gum 0-71 0-10 



The inorganic constituents being, as estimated from the ash of the grain, as follows: 

 Potash, 18-48; soda, 10'67 ; lime, 1'27; magnesia, 11-69; oxide of iron, 0'45 ; 

 phosphoric acid, 53'36; chlorine, 0'37; silica, 3'35. 



Rice is used as food by a hundred millions of the inhabitants of the earth, and it is 

 employee! as an agreeable and nutritive diet in various forms by ourselves. 



