POT of time to which llirir operation is to be extended, cannot fiiil of doing frequent mischief. POST, a stnke, or piece of tim- ber, which is lixed in the ground. Posts are used both for the pur- poses of building, and of fencing; but, as the strength f)f the fabric, or tjf the fence, depends greatly on "their nature or solidity, various ex- pedients have been adopted, with a view to season, or prevent them •from rotting. Among these, burn- ing of the lower or subterraneous part, lias been recommended as an excellent preservative ; besmearing them with tar, pitch, &c. has like- wise been found veiy serviceable ; but the most elTeftual method is tiiat employed in the count)' of Durham. — It consists in indenting, pr punCiuring the stake at right angles, to the heart or pith, by means of an instrument, somewhat i"c»emb]ing ti;e cnulking-irons of ship-carpenters ; and which is fur- nished with one, two, or three rows of teeth. Tlic wood ought previously to be well seasoned, warmed, and, lastly, coated with pitch or coal-tar ; which will pe- netrate as far as its centre. By this operation, the strength and durability of timber will by no means be diminished ; on the con- trary, it will thus be better enabled to withstand the injuries of the weather. POT-ASH, denotes an alkaline salt, or, with more propriety, a compound of different salts, ob- tained by reducing large (juanti- (ies of wood to aslies : this process is termed, by chemists, inc'mera- linn. The ashes are next boiled in water, so as to form a strong ley, which, after being strained, is eva- porated in an iron vessel almost to dryness j the matter, which re- POT [4-3 1 mains at the bottom, is then put into a crucible, liquefied over an intense heat, and poured out on iron plates, where it spetdily'coo's, and assumes the form of solid pot- ash. Such is the method generallv practi;;ed in making this alkaline salt ; l)ut ingenious chemists have contrived various modes of prepar- ing it, with a view to prevent the exportation of the large sums an- nually paid to Russia, America, Sweden, and other northern coun- tries. Hence, we shall state only the method followed by Dr. Peu- civAL, for procuring pot-ash from the putrid water which runs from dung-hills ; as being entitled to particular attention. His process is very simple : it consists in eva- porating the fluid part, and in cal- cining the impure salt, till the foul or extraneous ingredients are al- most entirely dissipated by the fire. From 2-1 wine-pipes of such li- quor. Dr. P. obtained nine cwt. and 40!bs. of saleable pot-ash, which was valued at 2l. 2s. per cwt. ; the expence of the who'i; process amounted to 41. 9s. The salt, thus procured, has a greyisli- white appearance; and is, whea broken, of a hard, spongy texture : it is slightly afl'eeted by moist air; but, if it be kept in a dry apartment, near the tire, a powder is formed on its surface. — Lastly, tl;is species of pot-ash contains, according to Dr. P.'s chemical analysis, such a proportion of pure alkali, as amounts to one-third part of its weight ; while that imported from Rus.sia, yields only one-eighth. In the year l/pO", a patent was granted to Mr. Ho.kesi.ey, for his method of making IJritish pot- ash ; for the supply of all manu- fa^lures, in which the foreign salt or
