47" ^ De/cription of an Bydroflatic Lamp, 



partition, F D. Now the fall in A A, may be rendered very fmall by enlarging the diameter 

 of the veflel at that part, and at 13 B j and the elevation of E above A, and confequentljp 

 the infulation of the radiant flame may be governed at pleafure by prolonging the inter* 

 Tal DC. 



It is poflible in the manipulation of this lamp that fome oil or pieces of fnuff may faU 

 into the fpace A A, and float upon the liquid. This efFeft is to a certain extent beneficial, 

 becaufe the covering of oil prevents evaporation : but if this (hould require to be remedied, 

 it is eafily done by pouring the whole contents of the lamp into a bafon, and after a few 

 moments repofe or (training, returning the liquids again into the lamp at E by a fyphon or 

 funnel, in which they will take their proper places by means of their relative weights. 



We may recapitulate the good qualities of thjs lamp in a few words, i. It is capable of 

 any defired form or apparatus for the burners. 2. It prefents no obftacle to intercept the 

 emitted light; and 3. As it raifes the oil by the mere gravitation of a non-elaftic fluid it 

 cannot in any cafe, like the fountain lamp, raife more than is wanted*. 



XI. 



RffleBions on the Decompojilion of the Muriate of Soda by the Oxide of Lead. 



By CiT. Fauq,ueli}{. 



V-yiHEMISTS agree that the oxide of lead decompofes the muriate of foda; and this, 

 as is well known, is one of the methods which have been propofed to obtain foda 

 from this fait ; but the manner in which this decompofitlon is efFefted ftill remains without 

 a fatisfadlory explanation. In reality all the explanations which have been given imply a 



• On the relative confumption and expence of tallow and oil promifed (at p. 365 of our prefent volume) 

 to be rcfumcd, I may here obferve that the manufafturers reckon that the lamp of Argand, of the common 

 fize, having the mean diameter of the channel containing the wick, =: o, i, inch, will require half a pint of 

 good whale oil to give its maximum of light for feven hours; and that I found by the method of ftiadows, 

 Tome years ago, that/uch a lamp gives as much light as eight tallow candles of the fize, called the middling 

 fix, fielh fnutfed. The average light of a candle, allowing for the negleft of fnuffing, is much lower; but 

 on the other hand the combuftion is complete in this lamp, but not fo much fo in this candle as in thofe of 

 fmaller fize. It would be an ufefol refearch to determine the economy of the produflion of light by equal 

 weights of candles of all the different fizes. To return, however, to our c»mparifon, I am difpofed on the 

 whole to eftimate the lamp upon our prefent knowledge as equal in duration and effeil to one pound of 

 candles; and to conclude, that the quantity of light will follow that of the oil, in all lamps, with thijj. 

 wicks. And hence, as oil fells at feven fliillings and fix-pence per gallon, and tallow candles at ten-pence 



h alf-penny the pound, the expence of light by oil will be to that by tallow, as 8 to zi; Or if the candle 

 would illuminate, during four hours for a penny, a lamp would at the fame expence in oil give equal light 

 for ten hours and a half.— -N. 



• Read to the French National Inftitute, on the firft Priarial, and in the year 7, (May »o, 1799.) Inferted 

 in the Annals de Cbimie, xxxi, p. 2. 



3 manifeft 



