Part 28 (1/2)

CHAP IV

_Of Mechanical Operations for Division of Bodies_

SECT I

_Of Trituration, Levigation, and Pulverization_

These are, properly speaking, only preli the particles of bodies, and reducing them into very fine powder These operations can never reduce substances into their primary, or elementary and ultiation of bodies; for every particle, after thethe original mass from which it was divided The real chemical operations, on the contrary, such as solution, destroy the aggregation of bodies, and separate their constituent and integrant particles from each other

Brittle substances are reduced to powder by means of pestles and1; of lass, Fig 4; of agate, Fig 5; or of porcellain, Fig 6 The pestles for each of these are represented in the plate, i, and are lass, porcellain,to the nature of the substances they are intended to triturate In every laboratory, it is requisite to have an assortment of these utensils, of various sizes and kinds: Those of porcellain and glass can only be used for rubbing substances to powder, by a dexterous use of the pestle round the sides of the mortar, as it would be easily broken by reiterated blows of the pestle

The bottoht to be in the forree of inclination as to make the substances they contain fall back to the bottom when the pestle is lifted, but not so perpendicular as to collect theet below the pestle, and prevent its operation For this reason, likewise, too large a quantity of the substance to be powdered ought not to be put into the et rid of the particles already reduced to powder, by means of sieves to be afterwards described

The ation is by7 of porphyry, or other stone of similar hardness, upon which the substance to be reduced to powder is spread, and is then bruised and rubbed by a muller M, of the same hard materials, the bottoe sphere; and, as the muller tends continually to drive the substances towards the sides of the table, a thin flexible knife, or spatula of iron, horn, wood, or ivory, is used for bringing thee works, this operation is perfore rollers of hard stone, which turn upon each other, either horizontally, in the way of corn- upon a flat stone In the above operations, it is often requisite to moisten the substances a little, to prevent the fine powder fro off

There are many bodies which cannot be reduced to powder by any of the foregoing methods; such are fibrous substances, as woods; such as are tough and elastic, as the horns of anium, &c and the malleablereduced to powder For reducing the woods to powder, rasps, as Pl I

Fig 8 are employed; files of a finer kind are used for horn, and still finer, Pl 1 Fig 9 and 10 for h to powder under the pestle, are too soft to be filed, as they clog the file, and prevent its operation Zinc is one of these, but it may be powdered when hot in a heated ironit with a small quantity of mercury One or other of thesea blue flarains, by pouring them when melted into water, which serves very hen they are not wanted in fine powder

Fruits, potatoes, &c of a pulpy and fibrous nature11

The choice of the different substances of which these instruments are made is a matter of importance; brass or copper are unfit for operations upon substances to be used as food or in pharmacy; and marble or metallic instruments must not be used for acid substances; hence ranite, or glass, are of great utility inand Washi+ng Powdered Substances_

None of thebodies to powder is capable of producing it of an equal degree of fineness throughout; the powder obtained by the longest and e of particles of various sizes The coarser of these are reeneous particles by12 13 14 15 of different finenesses, adapted to the particular purposes they are intended for; all the powdered er than the intestices of the sieve reain subh The sieve Fig 12 is auze; and the one represented Fig 13 is of parchment pierced with round holes of a proper size; this latter is eun-powder When very subtile or valuable materials are to be sifted, which are easily dispersed, or when the finer parts of the powder15 is made use of, which consists of the sieve ABCD, with a lid EF, and receiver GH; these three parts are represented as joined together for use, Fig 14

There is apowders of an uniform fineness, considerably more accurate than the sieve; but it can only be used with such substances as are not acted upon by water The powdered substance is itated ater, or other convenient fluid; the liquor is allowed to settle for a few moments, and is then decanted off; the coarsest powder remains at the bottom of the vessel, and the finer passes over with the liquid By repeated decantations in this rees of fineness; the last sedied suspended in the liquor, being the finest This processsubstances of different degrees of specific gravity, though of the sa, for separating the heavier hter earthy matters hich they are lass or earthen ware are e the liquor without disturbing the sedi 11 is used, which may be supported by means of the perforated board DE, at the proper depth in the vessel FG, to draw off all the liquor required into the receiver LM The principles and application of this useful instrument are so well known as to need no explanation

SECT III

_Of Filtration_

A filtre is a species of very fine sieve, which is perh which the particles of the finest powdered solids are incapable of passing; hence its use in separating fine powders from suspension in fluids In pharmacy, very close and fine woollen cloths are chiefly used for this operation; these are co 2 which has the advantage of uniting all the liquor which drains through into a point A, where it e phar is streached upon a wooden stand, Pl

II Fig 1

For the purposes of chemistry, as it is requisite to have the filtres perfectly clean, unsized paper is substituted instead of cloth or flannel; through this substance, no solid body, however finely it be powdered, can penetrate, and fluids percolate through it with the greatest readiness As paper breaks easily et, variousto circue quantity of fluid is to be filtrated, the paper is supported by the fra a piece of coarse cloth stretched over it, by means of iron-hooks This cloth must be well cleaned each time it is used, or even new clothi which can injure the subsequent operations In ordinary operations, where moderate quantities of fluid are to be filtrated, different kinds of glass funnels are used for supporting the paper, as represented Pl II Fig 5 6 and 7 When several filtrations9 supported upon stands C and D, and pierced with round holes, is very convenient for containing the funnels

Some liquors are so thick and clah paper without some previous preparation, such as clarification byht to boil, and, entangling the greater part of the impurities of the liquor, rises with them to the surface in the state of scum