LAMP. 



505 



Gr>ctil ob- 

 KrT*tion 



lamps than in condles, it is now necessary to explain 

 these circumstances rather more fully. 



The flame which we employ tor artifici.il light, is 

 produced by the combustion of some gas, which con- 

 tains carbonaceous matter ; and it is most probable, 

 that the matter, while it burns in these pases, is chiefly 

 composed of particles of carbon, in a very minute state 

 or division. Combustion takes place when the carbon 

 combines with the oxygen of the atmospheric air, in 

 the requisite proportion to produce the carbonic acid 

 gas: and if the oxygen is supplied in a less proportion, 

 the oxide of carbon will be produced in the form of 

 smoke or soot. 



The chief circumstance influencing the combustion 



<>f the different carbonaceous matters which are used 



fur producing light, is the decree of temperature which 



require, in order to make them combine with the 



n of the atmosphere, in sufficient proportion to 



produce flame. 



The relative affinities of oxygen and carbon increase 

 or diminish according to the degree of heat which they 

 possess t the' time of union ; and, for this reason, the 

 same carbonaceous matter, which, when properly heat- 

 ed, will combine with oxygen in such a proportion as to 

 produce flame, will only produce smoke, when heated 

 to a less degree ; and that degree of heat, which is 

 sufficient to volatilize the carbonaceous nutter, is not 

 sufficient to create that affinity for oxygen, which will 

 inflame it ; but a higher degree of heat must be ap- 

 plied, or we shall have smoke instead of flame. Thin 

 we see, whenever a lamp burns with the wick drawn 

 up too high, or when a candle burn-, with too long a 

 snuff. The- wick then exposes greater quantity of oil 

 to volatilization than the flame can perfectly consume ; 

 for th beat of the flame is carried off* so rapidly by 

 this volatilization, that it is not sufliricnt to heat all the 

 gas to that temperature which is necessary fur its in- 

 flamioati. '..<!. of thing*, uch a portion of the 



gas J is sufficient combines fully with the 



oxygen, and | imr ; another portion is heat- 



ed sufficiently to combine with the oxygen in that pro- 

 portion which produces soot ; and some small portion 

 will be so little heated, as to escape in the state of va- 

 pour of oil, or tallow, part of which will condense by 

 cold, into an empyreumalic grease. 



The nature of this oily vapour is most clearly exhi- 

 bited when a candle is blown out by a sudden current 

 of air ; this removes the flame sideways from the wick, 

 nd carries off so much heat from it, that the gas which 

 it still continue* to afford, in the form of a thick white 

 moke, will not combine with the oxygen ot the atmos- 

 rce to produce cither soot or 

 Mte smokr, when it ooln, forms a r 

 tallow, a- n in unpleasant oj. ur. Thi- 



is less ob . l^mp, because oil setms to require a 



greater heat to volatilize it than tallow. 



These particulars being understood, we may deduce 

 from them the requisite properties for a perfect lamp. 



d with carbonaceous matter, 



and with oxygen ; 51, It mint convert the former into 



-oous state ; and, .Sd, it must bring the gas, so pro- 



i-t with oxygen, at Mich a temperature, 



that the carbon wil with the oxygen, in the 



t degree, to produce the greatest quantity of flame, 



of oxygen, we have no 



means sufticir. >mmon use, in any great- 



er d.vrec of concentration, Uan a* it exists in atmos- 

 TOU iii. rajrr IL 



pheric air ; hence all that can be attained in lamps is, Lamp, 

 to cause a constant and liberal supply of atmospheric ~~~Y- ' 



air to be given to the flame. General oh - 



TL i < .i i i * i servations 



1 ne proper supplying of oil to the flame, depends on i. lmps . 



principally upon the wick. The best material for a lamp- 

 wick, is coarse cotton thread, very' loosely twisted ; 

 but a coarse article has, of late years, been manufac- 

 tured from the refuse of the tow of hemp and flax. The 

 most common form of a wick, is several threads, put 

 together, and twisted slightly round each other ; this 

 is railed the round wick. It burns well, when of a 

 small size, but does not answer so well for large flames, 

 because the vapour produced from the central part of 

 the wick is not sufficiently supplied with air. 



The best form of a wick, is a flat band, composed of 

 a number of threads, disposed parallel, and united by a 

 weft of very slight cotton. If a very great body of 

 light is required, the flat wick is bent into a cylindrical 

 form, so as to form a circle of flame, and the air is ad- 

 mitted to the inside of the ring, as well as the out- 

 side. 



To make a lamp burn with a clear and steady light, 

 the length of wick standing up above the tube or nozzle, 

 which supports the wick, must be regulated according 

 to its capacity for conducting the oil, otherwise the 

 whole of the oil which it supplies will be volatilized 

 by that portion of flame which surrounds the lower part of 

 the wick. In this case, the upper part of the wick, 

 which is in the centre of the flame, will burn to a char- 

 coal or snuff, which will be an extraneous body in the 

 centre of the flame. This is an unavoidable evil in 

 candles, and must be corrected by the constant appli- 

 cation of the snuffers. In a lamp, a snuff must be avoid- 

 ed, by keeping the wick to a pro|>er height. 



A mull in the centre of the flume, produces a smoke, 

 and a great diminution of light, which it occasions, 

 by increasing the body of the wick ; and as the air can- 

 not have free access to the wick in the centre of the 

 flame, the g:is there produced cannot burn immediately, 

 but must rise upwards, and will inflame when it gets 

 high enough to meet the air, provided it then retains a 

 sufficient heat. This ascent of the vapour before it in- 

 flames, is the cause of the pyramidal form of the flame ; 

 the vapour arising from the central parts of the wick be- 

 ing obliged to rise to a greater height before it can meet 

 with sufficient oxygen to burn. A large snuff to a 

 lamp or candle, occupies the tpace that should be fill- 

 ed with flame, and thereby diminishes the heat; it also 

 divides the flame into seven! small points, instead of 

 being in one pyramid. Tin real \w'ml of the pyramid 

 is wanting ; and great part of the gas which should 

 form this point rises in smoke, for want of sufficient 

 heat to make it bum when it has risen into the open air. 

 Un the other hand, a wick, which is too little raised 

 above tlie nuzzle, or tube which holds the wick, will 

 not volatilize the oil so fast a* it draws it up, because 

 the heated body of wick through which the oil is dif- 

 fused, is too small in proportion to the quantity of oil 

 contained in it : hence the action of the flame is exerted 

 upon too large a quantity at once to volatilize it per- 

 fectly. Still what is volatilized is perfectly burned, and 

 smoke is not produced ; but the flame is diminutive, 

 and liable to be extinguished by any shock or current 

 of air. 



The simple lamp, of which we have spoken, with a 

 flat dish of oil, is very imperfect. The oil is liable to be 

 .spilled, and the oil vessel intercepts a considerable por- 

 tion of the light in one direction. 

 Si 



