[ 3° 1

the middle division alone may be made to suffice ; for, onaccount of its width, the sinking of the oil will not beconsiderable in several hours burning. In either cafe,however, it is expedient to renew the wicks every twoor three days ; oftener or seldom er, according as the oilis more or less foul j for its impure matter, graduallyleft in the wicks, occasions the flame to become moreand more dull. For the more convenient renewing ofthem, there should be two of the perforated plates; that,when one is removed, another, with wicks fitted to it,may be ready to supply its place.

One of the black lead pots, described at the beginningof this paper, makes a proper furnace for the lamp. Ifone is to be fitted up on purpose for this use, it requiresno other aperture than one in the bottom for admittingair, and one in the side for the introduction of the elbowof the lamp ; the reservoir stands on any convenient sup-port without the furnace. The stopper of the side aper-ture consists of two pieces, that it may be convenientlyput in after the lamp is introduced ; and has a round holeat its bottom fitting the pipe of the lamp. By thesemeans, the furnace being let upon a trevet or open foot,the air enters only underneath, and spreads equally allround, without coming in streams, whence the flameburns steady. It is not advisable to attempt raising theheat higher than about the 450th degree of Fahrenheit’sthermometer, a heat somewhat more than sufficientfor keeping tin in perfect fusion. Some have proposedgiving a much greater degree of heat in lamp furnaces,by using a number of large wicks; but when the furnaceis so heated, the oil emits copious fumes, and its wholequantity takes sire. The balneum, or other vessel in-.cluding the subject-matters, is supported over the flameby an iron ring, as already described in the sand bath

and