in pharmacy and chemistry, the reducing hard and ponderous bodies to an impalpable powder, by grinding them on a porphyry, or in a mill. See CHEMISTRY, p. 590.
A new method of reducing powders to a great degree of fineness has lately been invented by means of a fanner. This has the advantage over the other methods, in being much more expeditions, and attended with less trouble and expense; the degree of fineness to which they are reducible being thus also in a manner unlimited. The construction of the fanner employed for this purpose is different from that employed for winnowing corn; the blast not being collected into a small compass as in the latter, but diffused over a considerable space, lest a violent blast should hurry off both coarse and fine together. For this purpose, the leaves of the fanner are made as long in the direction parallel to the axis as can be done conveniently. In the other direction projecting from it, they differ not from the ordinary length, nor do they in the general situation with respect to each other. Before the leaves is a wooden partition reaching half way up, to prevent the coarse powder from falling in among the leaves, which reaches about half way from bottom to top; and about two feet or less from this, according to the size of the fanner, is another partition in a sloping direction, reaching from the bottom of the box to near the top. The whole is inclosed in a large box six or seven feet long, having in the end farthest off from the leaves a slit equal to the space left betwixt the top of the box and the sloping partition already mentioned. On the top of this is another box, extending from the farthermost end of the former to the hopper which holds the coarse powder, with a hole in the end nearest to the fanner; and upon this another box, Levigation box, &c. as long as it is found that the air carries off with it any quantity of powder. This will be best understood from the following description of the figure.
A represents the fanner itself, having a hole in the case for the admission of the air, as usual.
B, The first wooden division, to prevent the return of the powder upon the leaves of the fanner.
C, The second division, reaching not quite to the top of the box. Its use is to direct the current of air produced by the fanner obliquely upwards; thus it strikes the powder, falling down from the hopper, in the same oblique direction, and carries off the fine parts, first through the aperture a; after which some of them are lodged in the box D; the still finer particles are carried through the aperture b into the second box E, where part of them are lodged: they next pass through the aperture c into the box F, and through d into the box G; the powder becoming still finer and in smaller quantity as it ascends into the higher boxes, until at last the waste becomes so trifling, that the air may be allowed to pass off entirely through the aperture b in the fourth or some other box, as is found most convenient.
Thus it is evident we may obtain powders of every degree of fineness, and such as neither sieve nor levigating mill could equal. Winnowing over with water may indeed produce powders equally fine; but the length of time requisite for settling, and the trouble of drying them again, must decidedly give the preference to the fanner; especially when we consider, that there is not any occasion for taking out the powder in small quantities, as is the case in sifting, washing, or levigating; but it may be allowed to remain till as much is collected in the boxes as we desire.
The principal difficulty in the construction of this fanner is the letting down the powder in a proper manner, so that the stream of air, which ought not to be very strong, may freely pass through it. For this purpose, the hopper must not let it fall in a large body, as in winnowing of corn, but in a long and thin sheet, which can easily be pervaded. The best method seems to be to make the hopper extend the whole breadth of the box, having a narrow slit at bottom. Close on the under part of this slit, a fluted roller ought to turn, which shutting up the aperture exactly, cannot allow any powder to pass but what does so in consequence of the hollow flutes of the roller; for a smooth round one would allow nothing to pass. It would be proper also that the flutes be but small, that a thin and nearly continued stream of powder be always descending; for this will contribute greatly to the fineness of the produce: and on this account the powder ought, before it is put into the hopper, to be passed through a lawn sieve. In the figure, e represents the hopper, and f the fluted roller. Motion is easily communicated to the latter by means of a wheel fastened on the axis of the fanner.
The coarse powder is kept back by the partition C, and descends through a slit i in the bottom of the lowermost box, into a receptacle k, which may be removed occasionally. All the joints and seams of the machine must be very close, for the fine powder is very penetrating; for this reason also the hopper ought to have a lid.
LEWDNESS. See Fornication.—Lewdness is punishable by our law by fine, imprisonment, &c. And Mich. 15 Car. II. a person was indicted for open lewdness, in showing his naked body in a balcony, and other misdemeanors; and was fined 2000 marks, imprisoned for a week, and bound to his good behaviour for three years. 1 Sid. 168. In times past, when any man granted a lease of his house, it was usual to insert an express covenant, that the tenant should not entertain any lewd women, &c.