The lutes for lining furnaces will be de scribed when treating of flumaces.
The junctures of vessels which Ire to be ]rated to each other, most previously be accurately and firmly fitted, by intro ducing between them, when necessary, short bits of wood or cork, or, if the dis proportion be very great, by means of a cork fitted to the one vessel, having a cir cular hole bored through it,- through which the neck of the other vessel or tube passes. After being thus fitted, the lute is either applied very thin, by spreading it on slips of linen or paper, and securing it with thread, or, if it is a paste lute, it formed into small cylinders, which are successively applied to the junctures, taking care that each piece be made to adhere firmly and perfectly close in every part, before another is put on. Lastly, the whole is secured by slips of linen or bladder. In many cases, to permit the escape of elastic vapours, a small hole is made through the lute with a pin, or the lute is perforated by a small quill, fitted with a stopper.
Beat and Fuel. As caloric is an agent of the most extensive utility in the chemi cal operations of pharmacy, it is necessa ry that we should be acquainted with the means of employing it in the most econo mical and efficient manner. The rays of the sun are used in the drying of many vegetable substances, and the only atten tions necessary are to expose as large a surface as possible, and to turn them fre quently, that every part may be dried alike. They are also sometimes used for promoting spontaneous evaporation.
The combustion of different substances is a much more powerful and certain source of heat. The substances employ ed for this purpose, are either fluid or solid. Alcohol, oil, tallow, wood, turf, coal, charcoal, and coke, are all occasion ally employed. Alcohol, oil, and melted tallow, fluid inflammables, must be burnt on porous wicks. These act merely me chanically, by drawing up a portion of the fluid to be volatilized and inflamed. They are therefore burnt in lamps of various constructions. -But although commonly used to produce light, they afford a very uniform, though not very high tempera ture : it may, however, be increased by .increasing the number of the wicks, and their size. Alcohol produces a steady heat, no soot, and, if strong, leaves 110 re sidumn. Oil gives a higher temperature, but on a common wick produces much smoke and soot. These are diminished,
and the light and heat increased, by mak ing the surface of the flame bear a large proportion to the centre, which is best clone by a cylindrical wick, so contrived that the air has free access both to the outside and to the inside of the cylinder, as in Argand's lamp, invented by Alm Boulton of Birmingham. In this way, oil may be made to produce a considerable temperature, of great uniformity, and without the inconvenience of smoke.
Wicks have the inconvenience of being charred by the high temperature to which they are subjected, and of becoming so clogged as to prevent the fluid from rising in them : they must then be trimmed, but this is seldomer necessary with alcohol and fine oils than with the coarser oils. Lamps are also improved by adding a chimney to them : it must admit the free access of air to the flame, and then it in creases the current, confines the heat, and steadies the flame. The intensity of the temperature of flame may be in creased astonishingly, by forcing a small current of hot air through it, as by the blow-pipe.. Wood, turf, coal, charcoal, and coke, solid combustibles, are burnt in grates and furnaces. Wood has the ad vantage of kindling readily, but affords a very unsteady temperature, is incon venient from its flame, smoke, and soot, and requires much attention. The heavy and dense woods give the greatest heat, burn longest, and leave a dense charcoal. Dry turf gives a steady heat, and does not require so much attention as wood ; but it consumes fast, its smoke is copious and penetrating, and the empyreumatic smell which it imparts to every thing it comes in contact with, adheres with great ob stinacy. The heavy turf of marshes is preferable to the light, superficial turf. Coal is the fuel most commonly used in this country : its heat is considerable, and 'sufficiently permanent, but it produces much flame and smoke. Charcoal, espe cially of the dense woods, is a very con venient and excellent fuel : it burns with out flame or smoke, and gives a strong, uniform, and permanent heat, which may be easily regulated, especially when it is not in too large pieces, and is a little damp ; but it is costly, and burns quick ly. Coke, or charred coal, possesses simi lar properties to charcoal; it is less easi ly kindled, but is capable of producing a higher temperature, and burns more slowly.