PHARMACY, 



done by a cylindrical wick, so contrived 

 that the air has free access hotli to the 

 outside and to the inside of the cylinder, 

 as in Argand*s lamp, invented by Mr. 

 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 tiling it comes 

 in contact with, adheres with great ob- 

 stinacy. The heavy turf of marshes is 

 preferable to the fight, 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. 



When an open grate is used for chemi- 

 cal purposes, it should be provided with 

 cranes, to support the vessels operated 

 in, that they may not be overturned by 

 the burning away of the fuel. 



Furnaces, In all these, the principal 



objects are, to produce a sufficient de- 

 gree of heat, with little consumption of 

 fuel, and to be able to regulate the degree 

 of heat. An unnecessary expenditure of 

 fuel is prevented by forming the sides of 

 the furnace of very imperfect conductors 

 of caloric, and by constructing it so, that, 

 the subject operated on may be exposed 

 to the full action of the fire. The degree 

 of heat is regulated by the quantity of air 

 which comes in contact with the burning 

 fuel. The quantity of air is in the com- 

 pound ratio of the size of the aperture 

 through which it enters, and its velocity 

 The velocity is increased by mechanical 

 means, as by bellows, or by increasing 

 the height and width of the chimney. 

 The size and form of furnaces, and the 

 materials of which they are constructed, 

 are various, according to the purposes 

 for which they are intended. 



The essential parts of a furnace are, a 

 body for the fuel to burn in ; a grate for 

 it to burn upon ; an ash-pit to admit air, 

 and receive the ashes ; a chimney for car- 

 rying off the smoke and vapours. 



The ash-pit should be perfectly close., 

 and furnished with a door and register- 

 plate, to regulate the quantity of air ad- 

 mitted. The bars of the grate should be 

 triangular, and placed with an angle point- 

 ed downwards, and not above half an 

 inch distant. The grate should be fixed 

 on the outside of the body. The body 

 may be cylindrical or elliptical, and it 

 must have apertures for introducing the 

 fuel and the subjects of the operation, and 

 for conveying away the smoke and va- 

 pours. When the combustion is support- 

 ed by the current of air naturally excited 

 by the burning of the fuel, it is called a, 

 wind-furnace ; when it is accelerated by 

 increasing the velocity of the current by 

 bellows, it forms a blast-furnace ; and 

 when the body of the furnace is covered 

 with a dome, which terminates in th6 

 chimney, it constitutes a reverberatory 

 furnace. 



Furnaces, are either fixed, and built of 

 fire-brick, or portable, and fabricated of 

 plate-iron. When of iron, they mus': 

 be lined with some badlv conducting 

 and refractory substance, both to pre- 

 vent the dissipation of heat, and to defend 

 the iron against the action of the fire. A 

 mixture of scales of iron and powdered 

 tiles, worked up with blood, hair, and 

 clay, is much recommended; and Pro- 

 fessor Hagen says, that it is less apt to 

 split and crack when exposed at once to 

 a violent heat, than when dried gradually, 

 according to the common directions, pr 



