ROA 



metals. In expelling the volatile parts from lime-done and 

 gypfum, the procefs is termed burning, and in the latter 

 fometimes boiling. The term roafting is principally con- 

 fined to iron, and other ores abounding with fulphur and 

 arfenic. 



The iron ores of this country are roalled for the purpofc 

 of expelling fulphur, water, and carbonic acid. The former 

 would probably injure the quality of the iron in fmelting ; 

 the latter would contribute to an expenditure of the heat 

 of the furnace. The procefs is conducted in the open air, 

 by piling the iron-Hone and fmall coal in alternate ftrata, 

 allowing the mafs to burn till the coal is confumed. The 

 iron-Hone, by this means, becomes of a red colour, and 

 lofes much of its weight. In fome iron-works the procefs 

 is performed in kilns, fimilar to thofe employed for burning 

 lime-ltone. 



The ore from which zinc is obtained is generally blende, 

 which is the fulphuret of that metal. It is expofed to the 

 itrong heat of a reverberatory furnace, by which the fulphur 

 is expelled, and the metal oxydated. 



When the metals or their oxyds are themfelves volatile, 

 and are combined with fulphur, roafting is not practicable : 

 recourfe mud then be had to fome other agent, which will 



ROB 



which back forms one fide of the fmoke chimney. This 

 arrangement is fufficient for diltnbuting all the difpofabV 

 heat equally on every fide of the roalter. We (hall next 

 point out the contrivance for difpofing of the fmel] above 

 alluded to. The door of the oven is cafed with wood, a 

 piece of thick paper, Iteeped in a folution of alum, a'nd 

 (beared with clay, being placed between the wood and the 

 iron, to prevent the wood from being charred. The door 

 extends below the bottom of the oven about three inches. 

 This, when the door is open, expofes a plate three inches 

 deep, and the width of the oven, and which conftitutes the 

 front of the cavity under the oven. At one fide of this 

 plate is a hole at the entrance of the tube, which extends 

 to the other end of the cavity, where it is bent, and returns on 

 the other fide of the cavity, and opens into another cavity 

 formed by a double plate, which conftitutes the iron part of 

 the door. The firft entrance of this tube correfponds with 

 an opening at the bottom of the door, fo that when the 

 door is (hut, cold air can enter the tube. In its pafTage it 

 becomes heated, and then enters the oven at the top, from 

 the cavity in the door. It now pail'es over the meat, and 

 efcapes through a tube in the back plate, which extends fo 

 :h as to reach above the fmoke damper. By this means 



combine with the fulphur, and feparate the metal itfelf. the roafter is'conltantly cleared of any difagreeable vapour 

 Such is the cafe with cinnabar and arfenic. See the refpective by a force equal to the draft of the chimney. 



metals 



R.0 'STING, in Dome/Ik Economy. When that change by 

 heat which animal food undergoes to render it lit for digef- 

 tion is brought about by a temperature capable of partially- 

 changing the furface, the procels has been termed roafting ; 

 a limilar change in vegetable food, Inch as bread, pud- 

 dings, and pies, being termed baking. The moil ancient 

 method of roafting, which is (till the general practice, is by 

 turning the meat before the fire ; and it is ilill hippofed, 

 without any good reafon, that meat cannot have its proper 

 flavour when roaded in any other way. It is true that 

 roajlcrs or ovens of the common conftruction are apt to give 

 the meat a difagreeable flavour, arifiugfrom the empyreumatic 

 oil which is formed by the decomposition of the fat, expofed 

 to the bottom of the oven. This evil has been completely 

 remedied in two ways, iirll by providing againft the evil of 

 allowing the fat to burn, and lecondly by carrying off by a 

 itrong current of heated air the empyreumatic vapours. 



The roafter ufed in the Derby Infirmary, and in many 

 private houfes in the neighbourhood, is not on any account 

 objectionable, but it is particularly valuable in an economical 

 point of view. This is principally effected by calling 



A Aiding rake is made, fo as to fit the top and fides of 

 the oven, that the whole furface becomes perfectly fcraped 

 by one motion. 



ROATO, in Geography, a town of France, in the 

 department of the Tanaro ; ten miles N.W. of Afti. 



ROB, in Pharmacy, the infpiffated juice of any fubltance, 

 ufually boiled up to the confidence of honey. 



There are robs made of quinces, floes, cherries, mulber- 

 ries, elderberries, barberries, goofeberries, and other fruits, 

 for various difcafes. The juice of grapes, thus prepared, 

 is more particularly called rob, or fapaftmplex ; this is almolt 

 of the conlifteuce of honey. 



When only one-third of the humidity is boiled away, it ia 

 called defrutum ; and when only boiled to the confidence ol 

 a foft electuary, a re/in. 



The word rob is pure Arabic ; and fignifies originally a 

 juice dried in the fun, or over the lire, that it may keep 

 the longer without damage. 



Sometimes it alfo denotes a compofition of fome juice 

 mad.' up with honey or fugar, in which fenfe it is confounded 

 with loche or lohoc. 



The rob is a form now much out of ufe, though there 



. r 1 j: o._j • .1 11 ■•/- 6 . 



the heat entirely upon tli ■ object of roafting, iuilead of are feveral directed in the college difpenfatorv ; as robs of 



fending th ol the heat up a capacious chimney, 



and iteif part of the remainder upon the 



con 1 ., and the walls and furniture of the kitchen. 



The roafter abov - alluded to is made of Iheet iron, of the 



ftrcngth ol about one pound to the fquare foot : its form 



I a parallel pip I i t, about twenty-five inches high, 



black cherries, of floes, of quinc-s, of elder, Sec. 



It is poffible that great improvements might be made, bv 

 introducing the ufe of this form among the malt-diftillers. 

 The great inconvenience attending that art being, that the 

 malt being of a large bulk, in proportion to its faccharine 

 part, and requiring a larger proportion of water to extract 



tadth. The lire is put that faccharine part, many large vcflels, fuch as malh-tubs, 

 under it; bul one COUrfe of brick, is placed immediately coolers, fermenting backs, &c. at lary j and the ne 



over the !: hove this a cavity of five inches deep 



between the brick roof and the oven bottom. The flame 

 of the lire pafleta little lo the right and left, and riles per- 

 pendicularly up the lull of thereafter, freely communicat- 

 ing with th top of the fame. By this mean; the flame 

 and hot . ipo ir will be the hotted at the top of the oven, 

 bccaulc ol it» greater levity, and its not being allowed to 



efcape at this point, according to the comn tij Vfter 



the hot vapour has bellowed its heat on the fuperior part, 

 it now deicends and enters on each fide the cavity under 

 the oven, from whence it pallcs up the back of tie' fame. 

 Vol. XXX. 



ceffary labour on the fubjedt is increafed, and the commodity 

 red dearer. The remedy of this lhouhl feem the intro- 

 ducing a new art fubl'ervient to that of the malt-diftiller, and 

 confining itfelf to the boiling down ol' malt-wort to a rob, 

 lo a; to fupply the malt-ftiller with his fubjedt, in the fame 

 manner a the fine-ftillers are fupplied with treacle from the 

 i- B) thi an thi bufinefs of the malt-ftiller 

 would be reduced to a great degree of Gmplicity, and the 

 fpirit pn duced would be alfo much liner than at prefent, 

 bccaulc thi fubj et would come tolerably refined to 

 hands, and purged oi its grofs, mealy, and huflty matter, 

 Z Z which 



