(See Engel.) It is well known that vessels made of a particular kind of porous stone are employed as filtering basins for freeing water, intended to be drunk, from various kinds of impurity. In sea voyages such filtering basins must be highly useful; and they are frequently found useful at land where no water can be had but from stagnant pools, or springs flowing through clay. The stone, however, of which they are made is not every where to be found; and therefore different persons have endeavoured to employ the art of the potter to supply their place.

In the year 1790 a patent was granted to a female potter, for her invention of the following composition for this purpose; viz. four equal parts, out of nine equal parts, of tobacco-pipe clay; and five equal parts, out of nine equal parts, of coarse sea, river, drift, or pit sand; these two materials, in the above proportions, are sufficient for the purpose of making small basins, and other vessels, to contain a quantity not exceeding one gallon of water, or other liquid. But the composition, when confined to these two materials, and in these proportions, often flies or cracks in the fire, if larger basins, or other vessels, are attempted to be made with it. She, therefore, in the second instance, composes her filtering basins of equal parts of tobacco-pipe clay and coarse sea, river, drift, or pit sand; in the third instance, of three equal parts, out of nine equal parts, of tobacco-pipe clay; one equal part, out of nine equal parts, of Stourbridge clay, or clay from the surface of coal-mines, or any other clay of the same quality; one equal part, out of nine equal parts, of Windsor, or other loam, of the same quality with Windsor loam; and four equal parts, out of nine equal parts, of coarse river, sea, drift, or pit sand. Or, in the fourth instance, of four equal parts, out of eight equal parts, of tobacco-pipe clay; three equal parts, out of eight equal parts, of coarse sea, river, drift, or pit sand; and one equal part, out of eight equal parts, of that burnt ground clay of which crucibles are made.

If the lady who invented, or pretends to have invented, these basins, have a right to her patent, far be it from us to wish our readers any description to intrude upon it; but as the use of the materials of which her basins are made was known to potters before she was born, they may certainly compound these materials in proportions different from hers, without doing her any legal injury. As she varies her own proportions so much, we think it probable that some proportion differing a little from them all, may answer the purpose of filtering vessels equally well; and it is almost needless to add, that with this precaution any potter may make such vessels, for which he would undoubtedly have a great demand.

A patent has likewise been granted to Mr Joshua Collier of Southwark for a very ingenious contrivance for filtering and sweetening water, oil, and all other liquids. Of this contrivance, which combines the application of machinery with the antiseptic properties of charcoal (See Chemistry No. 34 Supplement), we shall give a detailed account.

Fish-oil is one of the liquids which he had it particularly in view to free from all its impurities in smell, taste, and colour; and the chemical process employed by him for this purpose consists in pouring a quantity of any species of fish oil, or a mixture of different sorts of fish oil, into any convenient vessel, which is to be heated to the temperature of 110 or 120 degrees of Fahrenheit's scale, and then adding of caustic mineral alkali, of the specific gravity commonly described as 1.25, or of such strength that a phial containing 1000 grains of distilled water will contain 1250 grains of these lees, a quantity equal to four parts of the 100 by weight of the quantity of oil; the mixture is then to be agitated, and left to stand a sufficient time for the salts and sediments to subside; it is then drawn off into another vessel, containing a sufficient quantity of fresh burnt charcoal, finely powdered, or any other substance possessing antiseptic properties, in a powdered or divided state, with an addition of a small proportion of diluted sulphuric acid, sufficient only to decompose the small quantity of saponaceous matter still suspended in the oil, which appears by the oil becoming clear at the surface; the contents of this vessel are also agitated, and the coaly saline and aqueous particles left to subside; after which the oil is passed through proper strainers, herein after described, and is thereby rendered perfectly transparent and fit for use.

The principle of the improved strainers, or filtering machines, consists in the means applied to combine hydrostatic pressure, which increases according to the perpendicular height of the fluid, with the mode of filtering per aeternum, thereby procuring the new and peculiar advantage that the fluid and its sediment take opposite directions. A great advantage attending this invention is, that the dimensions of the chamber in which the sediment is received, may be varied, while the filtering surface remains the same. To adapt the machines not only to the purposes of families, workhouses, hospitals, public charities, the navy, or the merchant service, but also to all the purposes of oil-men, of distillers of the laboratory, the brewery, &c., chambers of various capacities must be provided for the sediment and precipitated matter. With respect to the oil-trade, the space required is very great, especially for spermaceti, or Brazil bottoms. In the various purposes of the laboratory, no limits can be fixed, but all dimensions will be occasionally required: in distilleries and breweries they may be smaller in proportion; and in that designed for water and for domestic use, a very small chamber will be sufficient. When water is to be sweetened, or freed from any putrid or noxious particles, it passes, in its way to the filtering chamber, through an iron-box, or cylinder, containing charcoal finely powdered, or any other antiseptic substance insoluble in water, the water being forced into it by hydrostatic pressure, through a tube of any sufficient height. This box has two apertures to receive and deliver the fluid, and these are opened and closed by cocks, or screws, or any other method used for such purposes, and being affixed to the machine by other screws, may be easily detached from the frame. Thus, whenever the charcoal begins to lose its antiseptic properties, the box is removed and heated till it is red hot; by which means the foreign matter escapes through the small apertures, after which the box is cooled, and the charcoal becomes sweet, pure, and equally fit for use as at first, though the process be ever to often repeated.

Another part of the invention consists in filtering machines in the form of fills, in which charcoal may be repeatedly burned after any fluid substances have passed through it, for the purpose of freeing them either from putrid or noxious particles, or of discharging their colouring matter; which filtering fills are so constructed, that the fluid may pass through in any quantity, without displacing the charcoal: the part of the fluid remaining interfused among the charcoal, may be driven over by heat, and be employed for many inferior purposes of the arts or manufactures. Lastly, the heat may be raised so as to purify the charcoal, as has been before described in the machines for water. The use of these fills is so constructed that water may be employed to cool them without the loss of time requisite for their gradually parting with their heat to the surrounding atmosphere, so as to be fit for a subsequent operation.

But it was not merely to the purifying of oils and various liquids that Mr Collier turned his attention. To his filtering apparatus are attached instruments for ascertaining the comparative qualities of oils, which depend in part on the principle of their specific gravities; spermaceti oil, contrasted with other fish oils, being as 875 to 920. For this purpose, a glass vessel of any convenient shape, is made use of, furnished with a bubble also of glass, and a thermometer. If the oil is pure, this bubble sinks, when the mercury rises to a certain standard, by the application of the hand, or any other heat to the vessel containing the oil. If the spermaceti oil is impure, the bubble will still float, though it is of the temperature required; and the degree of impure, or foreign matter, will be shewn by the state of the thermometer at which the bubble sinks. To determine what tendency oils used for burning have to congeal in cold weather, a freezing mixture is put in a phial of thin glass, or any other convenient vessel; into this a thermometer is immersed, and a single drop of the oil, under experiment, suffered to fall on the outside of the vessel, where it immediately congeals; as the cold produced by the mixture gradually ceases, it is easy to observe by the thermometer at what point of temperature the oil becomes fluid, and runs down the side of the glass.

A short description of this apparatus will make its principles plain to every reader. A (fig. 1.) is the cistern, into which the water or other liquor to be filtered is put. B B, is a tube opening into the bottom of the cistern A, and bent along the bottom of the machine conveying the fluid into C C C the filtering chamber, which is covered with leather bound down round its circular rim, and through which the water is percolated. D D, the bason rising above the level of the chamber and receiving the filtered liquor. E, The spout by which it runs off into a pitcher or other vessel. F, Another spout furnished with a cock to draw off the foul water from the chamber when necessary. G G G, The air tube, which begins above the level of the chamber, is covered with a button, which saves the leather from being cut, and has a small lateral aperture for the air to be carried off. This pipe passes along the bottom and up the side, and rising above the level of the water in the cistern, is there closed, except a small lateral aperture through which the air escapes. H, A guard or rim with cross bars put over the leather to keep it from being forced up by the water. It is fastened down by means of two notches on opposite sides of the guard, by which it locks into two staples riveted into the bottom of the bason. I, The lid sliding down to cover the water from dust, and suspended at pleasure by means of K K, two springs on each tube for that purpose. L M N O, A cylindrical box containing charcoal, which is connected with the above by means of the tube P, and a continuation of the tube B. L M, The water tube B continued below the charcoal apparatus, so that the fluid may pass through the same into the cylinder, from whence it enters the chambers at P, so as to be filtered through the leather as before described. R R, Collars which may be unscrewed at pleasure, so as to detach the charcoal apparatus whenever the charcoal requires to be purified by heat. S S, Two cocks to direct the fluid through the charcoal cylinder or immediately into the filtering chamber.

Fig. 2. A, A tub or cistern containing the oil to be filtered, and supplying a tube of sufficient height for the hydrostatic pressure to operate. B B, A main tube of wood, tin, leather, or cloth, to which any number of bags, of the size and shape of corn sacks, or any C C, convenient size or shape may be connected. These are bound to D D D, straight double iron bars, furnished with a hinge at one end and a screw at the other, by opening which the bags may be emptied. F, A trough underneath, made to receive the filtered oil from the receivers E E E.

Fig. 3. A, A funnel cask or cistern, into which the fluid is put which passes down. B, A tube fitted into the same, through which it enters. C, An iron fill, or fill of any other substance capable of sustaining heat, full of finely powdered and sifted charcoal, through the head of which the fluid passes into any receiver. D, A fire place of any construction to drive over the fluid remaining interposed among the charcoal, and also to purify the charcoal by an increase of temperature when required. E, A cock to let water into the flues to cool the apparatus for a subsequent operation.

Fig. 4. The trial glass with its thermometer.