The late ingenious Mr Bramah, had a patent for various modes of conveying and drawing off beer and other liquors, in which he describes a filtering apparatus which he pro posed to place in the pipes to conduct the liquor. This was a cylindrical vessel, made of copper, tinned within, or of any other materials; the upper end was closed by a lid screwed on by a Haunch, and the lower end terminated in a cone ; a pipe was introduced to the vessel near the lower part to introduce the liquor, and from nearthe upper end a similar pipe proceeded to convey it away. Between these two was fixed the filtering floor, consisting of flannel, sand in bags, sponges, or other similar substances, which were spread upon a horizontal plate pierced full of small holes, and fix ed in the cylinder above the filtering substance ; another similar plate was fixed and screwed down to confine it. The liquor was introduced by the lower pipe by means of a pump or otherwise, and ascending through the filtering floor, and passed oil' in a clarified state : the impurities which are separated collect in the conical bottom of the cylindrical vessel, whence they can be drawn off by a cock. This contrivance is adapted to give a slight filtration to a great quantity of liquor, such as beer.
In 1791, Mr Peacock took out a patent for a method of filtering water in the large way, for the service of towns, &c. His principle was to cause the water to ascend through the filtering medium, instead of descending; and the ap paratus, except as to dimensions, very nearly resembled lit Bramah's, being a vessel divided in two by a horizon tal grate or partition, upon which the filtering medium was spread in layers, and the lower division had a communica tion with a more elevated reservoir, from which the water flowed and rose through the filtering bed. Mr Peacock proposed to use for this, sandy gravel, sand, broken and pul verised glass or pottery, &c. These were to be prepared by repeated washings, and then sorted by sieves into a num ber of .different sizes ; these are to be spread in different layers, beginning with the largest and spreading the small er particles over these, in a regular gradation, until the finest is at the top. This arrangement is better than that we have before spoken of, when the water first passes through the finest, being less liable to chock up.
Professor Parrot of Paris, invented a filter with sand, acting both by the ascent and descent. It is described in the Philosophical Journal to consist of a bent tube, like an inverted syphon. It is curved to nearly a semicircle; this is filled with sand, and the water being introduced into the longest or upper leg of the tube, filters through the sand, and passes off. At the top of the lowest leg, it is recom mended to have three inches of differen e between the level of the two surfaces of the water, and eighteen inches of pure sand for the water to pass through. When the sec tion of the tube was four incite by two, that is eight square inches, it would pass six Paris pints of pure water every hour.
Mr John Isaac Hawkins has contrived a filtering appa ratus, which we consider as better adapted for domestic purposes than any which we have seen. It consists of a vessel pierced with holes, and placed over another, into which the filtered water is to be received. A layer of pounded charcoal is spread in the bottom for the water to filter through ; the lowest part of the layer is to be com posed of charcoal, pounded as fine as coarse sand ; and above this, other pciccs increasing in size, till the largest, which are as large as pease; the whole is covered with a board pierced with holes to admit the passage of the water, but, at the same time, to prevent the charcoal being dis turbed when the water is ponied in. Another form of the
apparatus is very well adapted for the use of a ship's com pany. It consists of a cask divided by a vertical partition, which does not quite reach the bottom, but leaves a space for the passage of the water. The bottom of the cask is filled with powdered charcoal, so as to reach some inches above the space at the bottom of the partition. The foul water being poured into one of the divisions of this cask, is filtered in passing to the other, by being obliged to de scend through the charcoal on one side, and ascend through the timer. This machine affords a great quantity of water ; and the known antiseptic quality of the charcoal is of great consequence in removing any taint with which water is of ten affected, and which is not easily removed by any other filter, unless indeed it is made very fine, such as a thick filtering-stone, and this will permit the water to pass but very slowly.
The most simple filter for experimental inquiries is made by a piece of blotting paper, rolled up to form a co nical funnel, and twisted tight at the point, so that the fluid cannot pass, except through the pores of the paper. This funnel is to be placed in the neck of a bottle, and filled with the liquor, which will filter through the pa per, and drop slowly from the point of the cone in a very pure state.
Another method, which is still more delicate, is per formed by capillary attraction as well as filtration. For this purpose, a glass is filled with the fluid nearly to the brim, and a bunch of coarse cotton threads, such as are used for the wicks of lamps and candles, is hung over the edge, so that one end of the bunch is immersed in the li quor, and the other hangs over a small bottle or other ves sel destined to receive the clear fluid. In this way it will be drawn up on one side, and conveyed through the cotton, from the ends of which it mill drip very slowly, but in a most perfect state of purity from all extraneous mixtures. It is scarcely necessary to mention, that the cotton must be wetted with the liquor, or the ascent will not begin when it is first put in action. A piece of thick flannel, if it is doubled three or four times, will answer the same purpose particularly well.
A very ingenious filtering apparatus has recently been invented by Mr James limes of Edinburgh. A piece of wood is placed within a cylinder, containing the water, which is forced through the pores of the wood by the pres sure of a forcing-pump. Mr Lines has employed this sim ple machine for purifying oil and other fluids.
For an account of Amy's filtering machines, see Mem. Acad. Par. 1745, Hist. 82; 1748, Hist. 121 ; and Machines Approuvees, torn. vii. p. 280; Hempel, Repertory of Arts, vol. ii. p. 230; Collier, Tilloch's Phil. Magazine, vol. vi. p. 240 ; Peacock, Repertory of Arts, vol. xi. p. 221 ; Har man and Dearn, Nicholson's Journal, vol. viii. p. 126 ; Par rot, Nicholson's Journal, vol. ix. p. 40 ; Sir H. Englefield, Nicholson's Journal, vol. ix. p. 95. See also Repertory, vol xiii. p. 140 ; and Gilbert's Journal der Physik, vol. xiii. p. 108. (J. F.)