having decided by experiments the superior strength, and conceived the probable utility to the public and to themselves that would result from this novel combination of primary strands; they, similarly to the practice of many others who have invented useful combinations, applied for and obtained his Majesty's Letters Patent. I have purposely used the word combination, because by much the major part of inventions are new combinations, and nothing more; whether in machines which are necessarily formed of wheels, screws, &c. which have individually and conjointly been used various ways; or in manufactured articles, which are formed of wood, iron, hemp, flax, wool, &c. all of which have been used individually and conjointly.

I conceive that no invention is entitled to public protection but on the basis of utility. The obtaining of any end to which the public are in possession of an equivalent would defeat itself, because no one would be induced to pay for its adoption. If, on the other hand, an improvement has been granted to an inventor, I conceive that any small deviation to obtain the same end only would be a piracy; but, if it either be to obtain one more valuable, or to shorten the process, and reduce the quantum of materials, without adopting any part of the other than what is common, then the invention is obviously a new one; and on this ground the patent for strand belts has been found to stand conspicuously, particularly at this period, when hemp is so much wanted for the purposes of our navy both military and commercial.

Exclusively of the circumstances peculiar to the thing itself, I conceive there is both novelty and utility in performing the operation of combining strands or other pli

able

able substances together by a locomotive machine, because it admits of the operation being performed when the separate parts are extended at length and equally stretched, which is of great importance; as, from the want of this circumstance, flat ropes have been found to break their stitches when exposed to sudden jerks, which has occa sioned their disuse at some collieries in Northumberland and Durham. Consequently, this part of the invention also is supported on the basis of utility, and not a mere evasion; which neither necessity nor inclination would have led the parties to have had recourse to. If I have placed this subject in a new light, no other merit is due to me than that which necessarily arises from a combination of practice and theory.

I am, Gentlemen,

Yours, &c.

Newcastle, May 4, 1808.

WM. CHAPMAN.

Description of a cheap Apparatus for filtering and purifying Water, invented by Mr. J. I. HAWKINS, of No. 79, Titchfield-Street,

Communicated by him in a Letter to the Editors.

GENTLEMEN,

AGREEABLY to the intention announced in the ac

count of the Museum of Useful and Mechanical Inventions, inserted in your last number, I now send you the description of another of the articles there deposited for public exhibition,

A cheap Apparatus for filtering and purifying Water. This apparatus consists of a vessel of wood, metal, earthen-ware, or other convenient material, having holes

G 2

holes in the bottom, covered with a piece of thick flannel, on which powdered charcoal is laid, about two inches high. This vessel is placed over another of rather larger diameter, having an aperture near the bottom furnished with a cock; the water to be purified and filtered is poured on the charcoal, through which it gradually passes, and drops perfectly sweet and clear, into the lower vessel; from whence it is drawn off by the cock for use.

The charcoal should be made about as fine as sand, either by being pounded in a mortar, or ground in a -coffee-mill; which last plan is the best, since it leaves the particles more nearly of one size; it must of course be broken into small pieces, before the mill can receive it.

Saw-dust may be burnt into charcoal, and would at once be fine enough for the purpose, if cut from hard wood; but if from soft, it must be pulverised a little

more.

Some little attention is necessary in putting the charcoal into the vessel; a portion of the charcoal, say about half an inch high, must be well damped, and laid in that state on the flannel; then a second portion of about the same quantity, wetted to the consistence of mortar, is to be put on the first; afterwards a third quantity, wetted still more, should be added; and lastly, the remainder, mixed with so much water as to be easily poured on; after standing a quarter of an hour to settle down, water should be poured on, a little at a time, till it begins to drop, which, if proper care has been taken, will be quite clear and sweet, but having a slightly dusty taste, that will go off after a few hours, Should, however, the first running be a little black, it

will not be necessary to disturb the charcoal, because that blackness will soon cease, if water be kept passing through it; and when it once runs clear, will continue to do so for many months, and perhaps years. But although it acts as a filter for so long a time, and will separate whatever of foulness is merely mixed with the water, yet it soon loses the power of attracting that putridity which is in a state of solution; and consequently will not purify more than a given quantity of

water.

The following are the results of my experiments on this point.

One quart of powdered charcoal, purified;

One gallon of water, taken from the macerating tubs of an anatomical laboratory, where it had been used for many months without being changed, to soak the flesh from the bones; it was the most offensive water that could possibly be procured. The charcoal rendered it perfectly sweet.

Six gallons of green stagnant water from a pond.

Ten gallons of the worst water found in the casks on a long sea voyage.

Two hundred gallons of such water as is usually drank on a three months voyage; and,

Five hundred gallons of river water taken opposite a large city.

It must be noted, that when charcoal is wanted to purify, it must be fresh burnt; but if only to filter, that precaution is not necessary. When it has lost its purifying quality, it may be recovered again, by being heated red-hot in a crucible, or iron pot, or even an earthen one, over which a piece of tile or plate of iron is loosely laid,

In taking the charcoal out of the filtering vessel, a layer of about half an inch should be left on the flannel, because in that case, much less care will be required in returning it into its place again; and the water that first runs, will not have that dusty taste, which it would have if the whole of the charcoal were replaced by that which is fresh burnt.

In pouring on the water, great care must be taken not to disturb the charcoal to any considerable depth below the surface, lest the water should pass too rapidly for complete filtration. This accident may be avoided by laying a piece of paper, or cloth, or even a piece of thin board over the charcoal, to pour the water on.

The size of the apparatus must of course depend on the quantity of water wanted; that now in my Museum is eight inches diameter, and the same depth, and it filters from six to seven gallons every twenty-four hours; the holes in the bottom are about one-eighth of an inch in diameter, and distant from each other about half an inch.

1. The flannel is of that stout kind, usually made for ironing cloths.

The purifying nature of charcoal has been known for a considerable time; but a simple and convenient way of using it, has not, I believe, yet been laid before the public; nor has its filtering property been at all taken notice of. It has been supposed necessary to use sand or some other substance to filter the water, after charcoal has purified it; but on trying a great variety of substances for filtering, I found powdered charcoal by far the best; it suffers a greater quantity of water to pass in a given time, and renders it more clear; and certainly no filtering apparatus can be made cheaper than this. It is

also