PHARMACY. 



and suspended by a funnel. It is of ad- 

 vantage to introduce glass rods, or quill- 

 barrels, between the paper and tunnel, to 

 prevent them from adhering- too closely. 

 What passes first is seldom fine enough, 

 and must be poured back again, until, by 

 the swelling of the fibres of the filter, or 

 filling up of its pores, the fluid acquires 

 the requisite degree of limpidity. The 

 filter is sometimes covered with charcoal 

 powder, which is a useful addition to 

 muddy and deep-coloured liquors. The 

 filtration of some viscid substances is 

 much assisted by heat. 

 ^ Expression is a species of filtration, as- 

 sisted by mechanical force. It is piinci- 

 Eally employed to obtain the juices of 

 esh vegetables, and the unctuous vege- 

 table oils. It is performed by means of a 

 screw press with plates of wood, iron, or 

 tin. The subject of the operation is pre- 

 viously beaten, ground, or bruised. It is 

 then inclosed in a bag, which must not be 

 too much filled, and introduced between 

 the plates of the press. The bags should 

 be of hair-cloth, or canvass inclosed in 

 hair-cloth. Hempen and wooden bags are 

 apt to give vegetable juices a disagreea- 

 ble taste. The pressure should be gen- 

 tle at first, and increased gradually. Ve- 

 getables intended for this operation should 

 be perfectly fresh and freed from all im- 

 purities. In general they should be ex- 

 pressed as soon as they are bruised, for 

 it disposes them to ferment ; but subacid 

 fruits give a larger quantity of juice and 

 of finer quality, when they are allowed to 

 stand some days in a wooden or earthen 

 vessel after they are bruised. To some 

 vegetables which are not juicy enough of 

 themselves, the addition of a little water 

 is necessary. Lemons and oranges must 

 be peeled, as their skins contain a great 

 deal of essential oil, which would mix 

 with the juice. The oil itself may be ob- 

 tained separately, by expression with the 

 fingers against a plate of glass. 



For unctuous seeds, iron plates are 

 used ; and it is customary not only to 

 heat the plates, but to warm the bruised 

 seeds in a kettle over the fire, after they 

 have been sprinkled with some water, as 

 by these means the product is increased, 

 and the oil obtained is more limpid. But 

 as their disposition to rancidity is in- 

 creased by it, if possible, this practice 

 should be laid aside, or confined to ex- 

 posing the bruised seeds, inclosed in a 

 bag, to the steam of hot water. 



Despumation is generally practised on 

 thick and clammy liquors, which contain 



much slimy and other impurities, not 

 easily sepnrable by filtration. The scum 

 arises either by simply healing the liquor, 

 or by clarifying it, which is done by mix- 

 ing with the liquor, when cold, whites of 

 eggs well beaten with a little water, 

 winch on being heated coagulates, and 

 entangling the impurities of the liquor, 

 rises with them to the surface, and may 

 be easily removed by a perforated ladle'; 

 or the liquor may now be filtered with 

 ease. Spirituous liquors are clarified by- 

 means of isinglass dissolved in water, or 

 any albuminous fluid, such as milk, which 

 coagulates by the action of alcohol with- 

 out the assistance of heat. Some ex- 

 pressed juices, such as those of the an- 

 tiscorbutic plants, are instantly clarified 

 by the addition of vegetable acid, such as 

 the juice of bitter oranges. 



Fluids can only be separated from each 

 other when they have no tendency to 

 combine, and when they differ in speci- 

 fic gravity. The separation may be ef- 

 fected by skimming off' the lighter fluid 

 with a silver or glass spoon ; or by draw- 

 ing it off by a syringe or syphon ; or by 

 means of a glass separatory, which is an 

 instrument having a projecting tube, ter- 

 minating in a very slender point, through 

 which the heavier fluid alone is permitted 

 to run ; or by means of the capillary at- 

 traction of a spongy woollen thread ; for 

 no fluid will enter a substance, whose 

 pores are filled by another for which it 

 has no attraction ; and, lastly, upon the 

 same principle, by means of a filter of 

 unsized paper, previously soaked in one 

 of the fluids, which in this way readily 

 passes through it, while the other remains 

 behind. 



Mechanical mixture is performed by 

 agitation, trituration, or kneading ; but 

 these will be best considered in treating 

 of the forms in which medicines are ex- 

 hibited. 



Chemical Operations and Results. 



Under this chapter we have to consider 

 the apparatus employed, the changes 

 produced, and the general analyses that 

 ensue. 



The apparatus consists of vessels, fuel, 

 or heat; and the different modes by 

 which such fuel or heat is applied, whe- 

 ther lamps, furnaces, See. 



The vessels must necessarily vary in 

 their form and materials ; upon the first 

 of which it will be more convenient to 

 enlarge, as we proceed to treat of the 

 particular operations in which they are 



