A very simple method of freeing water from its impurities by means of the capillary attraction of fibrous substances is represented in the annexed engraving, a is the reservoir, b the lower compartment, c an open tube soldered into the bottom of the reservoir, in which is put a wick of cotton or wool, (the latter is best,) with one end immersed in the bottom of the reservoir, whilst the other end hangs down a little below it, forming a kind of syphon. The water in rising by the capillary attraction between the filaments deposits the gross matter floating therein, and descends in a comparatively pure state into the vessel b, or into a jug placed therein.
The figures represented in page 502, are a portion of Mr. Suwerkrop's apparatus for filtering and heating water. Fig. 1 shows a side elevation of the vessels in question; and Fig. 2 is a vertical section of the same. The letters have reference to similar parts in each figure. The water is supposed to be conveyed by the pipe a from a reservoir situated upon a higher level than the cask b, which is divided by the partition c into two equal parts, forming thereby a double filtering machine. In each of these divisions, the filtering substances and the arrangement of them are the same. As the water flows from a higher level, it will of course ascend through the filtering substances, and flow out at the upper part. The first substance which it has to pass through is a circular mat d, made by coiling up and sewing together a rope of platted horse-hair, which detains the grossest of the impurities; from this it passes through a floor or false bottom of wood, e, pierced throughout with numerous small holes; upon the wooden bottom is laid first a stratum of coarse gravel or small pebbles, over this is put a layer of finer, then a layer of finer still, and lastly, a bed of sand f, about six or seven inches thick; from this the water rises in a tolerably pure state; if not sufficiently purified, instead of drawing it off for use, it may be allowed to pass through the curved pipe h into the upper division i of the cask.
The water continuing to rise, then percolates successively through the horse-hair mat j, the perforated floor k, and the various strata of the sand and gravel l, finally flowing out of the cask, and through the pipe m, into the heating vat n. The vat is constructed with a furnace o, and flue p p inside of it, all made of copper, except the grating for the fuel, which is made of cast iron as usual; copper being preferred for the flue on account of its oxidating less rapidly than iron or other cheap materials. The heated air or gases first rise up the neck q into the hollow sphere r, which becomes soon occupied with intensely heated air, from whence it has little disposition to descend and escape by means of the spiral tubes, which finally become flues for the grosser products of the combustion; as these tubes, however, make a long circuitous course through the tub of water, the heat is almost wholly absorbed by it. The furnace and flues are supported and kept in their positions by stays fixed to the sides of the vat, as shown.
The three closed apertures in the cask b, Fig. 1, are for the several purposes of washing the bottoms of the horse-hair mats, by passing water through them downwards; and for taking out and refreshing the layers of sand and gravel when they have become foul by deposition from the water.
The engraving on the next page represents an apparatus contrived by Messrs. Williams and Doyle, for the purpose of separating the salt from sea-water, by merely causing it to percolate through a body of sand under mechanical compression, and thus to render it fresh. Could this object be obtained by such means, the invention would doubtless be one of the utmost importance to navigation, as it would render a store of fresh water unnecessary, thereby affording additional stowage for provisions or cargo; but we are not aware of any experiments proving that substances dissolved, and chemically combined with a liquid, can be separated by filtration; we therefore apprehend that the apparatus would be ineffectual for the object the inventors had in view, although it may prove very efficient in freeing water from any impurities floating or suspended in it The following description of the engraving (which represents one of the several modes of construction proposed by the inventors), is derived from the specification of their patent, a is a part of the cask supposed to contain sea water; b a tube descending therefrom, made fast by bands c c c to the filtering apparatus d d, which is a strong square trunk of wood, lined internally with sheet lead, which are cemented together to prevent the interposition of water.
This part of the apparatus is given in section, that the construction and arrangement may be seen at one view; e is the lower chamber, where the water is first received; f is a strong stool of open frame work, supported on five stout legs, g. A plan of this stool is given in a separate figure F, the situation of each of the five legs being marked with a g. Over this short frame is nailed a plate of copper, pierced with numerous small holes; this plate is also shown by a separate figure H. Over the perforated plate are several layers of woollen cloth, or woven horse-hair i, and above these a body of sand k, filling up the entire trunk; on the top is placed a sliding cover lf which is operated upon by a strong screw m, working through a fixed nut n, which is supported by curved iron arms, extending from opposite sides of the trunk. The sand having been compressed, by the agency of the screw, into a more dense and compact mass, is prevented from rising by the pressure of the water, which percolating through the minute interstices to regain its level, deposits its salt, and runs out by the pipe o in a fresh state into a vessel p placed to receive it.
When the sand has become saturated with salt, it is to be removed by taking out the screw and the pressing board l; the man holes r r may then be opened by unscrewing the plugs, when the other materials may be easily sifted. These matters being completed a fresh quantity of sand may be taken from the ballast of the ship, and the process of filtration continued as before.
We shall close this article with a description of a very convenient apparatus for filtering liquids out of contact with the atmosphere, invented by Mr. Donovan. By means of this arrangement, alkalies can be preserved in their caustic state, the absorption of carbonic acid by the alkali being prevented, a is a bottle of green glass, with a funnel-shaped end inserted into another bottle b, the junction being luted or ground to fit closely; the neck d of the upper vessel has a cork tightly fitted to it, perforated in the middle for the reception of the glass tube c, which being bent downwards, enters the branched neck e of the lower vessel, thus connecting them together, and opening an air passage between them. The funnel-shaped end of the upper vessel has a piece of linen, loosely rolled up, placed in it, for the purpose of filtering, but for the corrosive acids a stratum of pounded flints should be employed instead of the cloth. To charge the upper vessel with the alkaline solution, the tube c must of course be removed, and the first droppings should be allowed to run to waste previously to the apparatus being fitted together, that no absorption of carbonic acid may take place in the filtered liquor When the whole is properly closed, the filtration will proceed without the possibility of absorption.
Now it is evident that no liquor can fall from the upper vessel without an equal volume of air entering it, and that none can enter the lower without an equal bulk escaping from it. Both these conditions are fulfilled by the connecting tube c, the air being driven from the lower into the upper vessel at every dropping of the filtered liquid. The whole process is therefore conducted without the access of more air than the vessels at first contained, and in the most cleanly and perfect manner. The utility of this contrivance is very extensive. The most volatile liquids, as ether, alcohol, ammoniacal liquors, volatile oils, etc. may be filtered without loss, as the vapours cannot escape during the operation; and by the exclusion of the atmosphere in the filtration of a variety of fluids, other injurious effects to which they are subject by the common process, may be entirely obviated.