•JO ConfruFthti of Cnndlrs. Fnfihility of the pvcral Alateiials. 



conftruiTlcil lamps is more or Icfs liable to be fpilled. When the wick of a Itimp is once 

 acijullcd as to its length, the fljmc continues nearly in the fame ftate for a very confidcrable 

 time. 



It is almoft unneceffiiry to Jtfcribe a thing fo univerfally known as a candle. This ar- 

 ticle is formed of a confilleMt oil, which envelopes a porous wick of fibrous vegetable 

 matter. The cylindrical form and dimenfions of the oil are given cither by calling it in a 

 mould, or by repeatedly dipping the wick into the fufed ingredient. Upon comparing 

 a candle with a lamp, two very remarkable particulars are immediately fcen. In the 

 firft place, the tallow itfelf, which remains in the unfufed llate, affords a cup or cavity to 

 hold that portion of melted tallow which is ready to flow into the lighted part of the wick. 

 In the fecond place, the combuftion, inftead of being confined, as in the lamp, to a cer- 

 tain determinate portion of the fibrous matter, is carried, by a flow fucceflTion, through the 

 whole length. Hence arifes the greater neceflity for frequent fnuffing the candle; and hence 

 alfo the (lation of the freezing point of the fat oil becomes of great confequence. For it 

 has been fhewn that the brilliancy of the flame depends very much on the diameter of the 

 wick being as fmall as poflible ; and this requifite will be mofl attainable in candles 

 formed of a material that requires a higher degree of heat to fufe it. The wick of a 

 tallow candle mud be made thicker in proportion to the greater fufibility of the material, 

 which would otherwife melt the fides of the cup, and run over in ftreams. The flame 

 will therefore be yellow, fmoky, and obfcure, excepting for a fliort time immediately 

 after fnufling. Tallow melts at the 92d degree of Fahrenheit's thermometer ; fpermaceti 

 at the 133d degree; the fatty matter formed of flelh after long iramerfion in water 

 melts at 127°; xht pela* oi the Chinefe, at i4S°i bees-wax at 142°; and bleached wax 

 at 155^. Two of thcfe materials are well known in the fabrication of candles. Wax ia 

 particular does not afford fo brilliant a flame as tallow . but, on account of its lefs fufibility, 

 the wick can be made fmaller ; which not only aflbrds the advantage of a clear perfeft flame, 

 but from its flexibility it is difpofcd to turn on one fide, and come in contaft with the exter- 

 nal air, which completely burns the extremity of the wick to white aflies, and thus performs 

 the office of fnufling. We fee, therefore, that the important objedt to fociety of rendering 

 tallow candles equal to thofe of wax, does not at all depend on the comUudibility of the re- 

 fpetlive materials, but upon a mechanical advantage in the cup, which is afforded by the in- 

 ferior degree of fufibility in the wax ; and that, to obtain this valuable objedl, one of the fol- 

 lowing efl^etls muft be produced : Either the tallow mu(t be burned in a lamp, to avoid tlic 

 gradual progreffion of the flame along the wick ; or fome means mufl be devifed to enable 

 the candle to fnufF itfelf, as the wax candle does ; or, laftly, the tallow itfelf mufl be ren- 

 dered lefs fufible by fome chemical procefs. I have no great reafon to boafl of fuccefs ia 

 the endeavour to efFe£l thefe ; but my hope is, that the fafls and obfcrvations here prc- 

 fcnted may confiderably abridge the labour of other-, in the fame purfuit. 



The makers of thermometers and other fmall articles with the blow- pipe and lamp, give the 

 preference to tallow inflcadof oil,becaufe its combullion is more complete,and does notblackcn 

 the glafs. In this operation, the heat of the lamp melts the tallow which is occafionally brought 

 into its vicinity by the workman. But for the ufual purpofes of illumination, it cannot be 

 fuppofed that a pcrfon can attend to fupply the combuflible matter. Confidcrable diilicultlcs 



• Pcarfon, in the Philofophical Tranfaftions for ^^<j■\. 



arifc 



