PURIFICATION OF WATER.

Sir,-Knowing that your scientific publication is open to every subject connected with public utility, I could wish to address you concerning an invention which has of late attracted my attention. Last summer I heard much of a design proposed by an ingenious and scientific foreigner for purifying the water of the metropolis by means of filtration, on a plan of far greater magnitude than has hitherto been attempted. He has succeeded beyond all doubt in demonstrating the reality of his plan, and evinced by experiments, made in the presence of approved judges, the practicability and sure success of his invention. But just when every thing appeared in train for the realization of his magnificent project, the matter seems to have been laid aside. Whence does this arise? Is the obtaining of pure water a matter of such trivial importance that it can be viewed with indifference, especially too, in this water-drinking age? It has been justly said that "water is so essential both to the animal and vegetable creation, either for aliment or other purposes, that its importance probably surpasses that of every other substance amongst the great exuberance bestowed by the beneficent Author of nature. The health, comfort, and enjoyment of mankind, constantly require a plentiful supply, and therefore if utility be a just criterion of value, the inventions and operations to furnish it readily and abundantly in a clear and salubrious state, would seem to be entitled to peculiar attention." Is it the additional expense that makes the companies fear to adopt any plan which must necessarily lead to the augmentation of the water rate? If the plan suggested involved any large addition to the rate already imposed, that might furnish a plausible reason for delaying to adopt this valuable invention; but I am told that the scientific projector proposes so small an augmentation that, even in these economical days, it ought not to induce a moment's demur. Some will say that the quantity of pure water absolutely requisite in families is but small, the greater part of what is received being used for domestic purposes, as cooking, washing, &c. But would our cookery be less agreeable for being assisted by water purified from all the extraneous matter, which, owing to various causes, will inevitably become

mingled with it? And where is the good housewife who would not prefer water pure and clear, for the purposes of washing, cleaning, &c., rather than the brown or yellow muddy stuff which some. times presents itself under the name of water? Do we not hear continually such complaints as these, "The water is so bad we cannot drink it"-" The water is so muddy it is not fit for use." I think, therefore, when means are proposed by which those inconveniences might be avoided, they ought to be seriously and properly attended to, and if proved to be as excellent in practice as in theory, general utility and comfort require that they should forthwith be rendered available.

Trusting that this letter may be the means of directing attention to the subject, I am, Sir, Your very obedient servant, BARTLE CANHAM.

London, May 31, 1842.

[We recollect having heard some very surprising accounts of the system of filtration alluded to by Mr. Canham about a year ago, but from nothing coming of it, we were led to set it down in our minds as one of those nine days' wonders of which the arts and sciences are so notoriously prolific. If there be really any merit in the invention, and the present enquiry should happen to meet the eye of the inventor, we shall be happy to assist him in bringing it once more under the notice of the public. The purification of the water of the metropolis is still a great desideratum.-ED. M. M.]

POWER WITHOUT STEAM.

Sir,-Nearly all men are agreed that the power of steam will some day be superseded by a newly applied expansive force, such as condensed air can supply. The usual question has been-" by what power will you condense the atmosphere independent of human labour or steam ?" and my reply was usually-" by some ingenious application of the force of gunpowder, or the materials of which it is compounded." But I was never able to indicate in what manner that force could be applied mechanically. It has long been employed for murderous purposes and overwhelming cruelty in a horizontal direction, but there appears to be no reason why its agency now should be so limited. A worthy friend of mine has, in

tendency of water or moisture to interrupt or destroy the current; and so strong has this impression been, that the chief difficulty, as well with those who have busied themselves with the application of electricity to telegraphic purposes (Messrs. Cook and Wheatstone, for example, hitherto the most successful experimenters in this line,) as with those willing to avail themselves of it, has been the great expense of providing such tubingamounting to from 250l. to 300l. per mile. Messrs. Wright and Bain having recently turned their attention to the subject of electro-telegraphic communication, began very philosophically with questioning the truth of this assumption of the non-conductible or dispersive properties of water and moisture; and have ended with proving, beyond all dispute, that it is altogether fallacious! Another remarkable instance this of the serious practical blundering into which the vicious habit of taking things for granted, is apt to betray even the most learned of men. As in the infancy of the railway system, nobody imagined that smooth wheels would ever run on smooth rails, and nobody thought of trying whether they would or no; so in the infancy of electro-telegraphic communication, every one has been subscribing to the absolute necessity of protecting the wires from contact with moisture, and many have been the ingenious devices and contrivances for the purpose, whereas, the first persons who try to do without any such protection, find to their agreeable surprise that nothing is less needed!

The fact, that water, in its natural state, possesses in a high degree the property of transmitting the electric current (as well as when in the acidulated state, in which it is used in voltaic batteries,) was first distinctly ascertained by some experiments made by Messrs. Wright and Bain, at the Polytechnic Institution. But desirous of proving it on a larger scale than that Institution admitted of, they applied for, and obtained permission from the Duke of Sussex, the Ranger of Hyde Park, to make the experiments on the Serpentine River, to which we before alluded, and which we shall now proceed briefly to describe.

1. An electric current was first transmitted from a small Grove's battery across the river from bank to bank, through two copper wires immersed in

the water, and left quite bare and unprotected. The success of the operation was perfect.

2. A single wire was then laid along one bank of the river from the bridge, to near the south east end, a distance of about half a mile, with both ends dipping in the water. The rest of the galvanic circuit was supposed to be completed by the water, that is to say, it was predicated that the water, indifferent conductor as it has been hitherto considered to be, would of itself serve the purpose of the second wire-the immense bulk and extent of the body of water notwithstanding. Bold as this hypothesis was, we had the pleasure of witnessing its complete verification. The current was transmitted through the partly liquid and partly metallic circuit thus formed, with the same instantaneousness as if it had consisted entirely of metal; reversed, too, at pleasure; and this, times without number. Passing an electric current through such small jars of water as one is accustomed to see used in galvanic batteries is a comprehensible enough performance; but to transmit in an instant, the product of a tiny pocket apparatus through a jar half a mile long, a quarter of a mile broad, and containing many million millions of gallons, is, it must be confessed, a thing passing all comprehension. We can but record the fact and wonder.

3. A wire-single wire as in the last case, was finally laid with one end in the river, and the other in a well about 300 yards from it. The electric current was passed through this circuit, with the same facility and success as in the other experiments. Here there was a triune circuit formed, consisting of the wire, water, and earth.

What the limits are to this conducting power of water, or whether there are any limits at all, remains yet to be ascertained. All that Messrs. Wright and Bain seek to deduce from their experiments at present is, the important fact that the wires of electro telegraphs do not, as has been imagined, require to be insulated from damp, and that the expense of enclosing them in pipes, need therefore be no longer an obstacle to their general introduction.

VENTILATION OF MINES. [From the First Report of the Children's Employment Commission, 1842.]

COAL MINES.

The best mode of ventilating mines hitherto discovered is that by means of two shafts sunk near each other, perhaps from 12 to 20 yards apart. A stream of air is made to descend one shaft, called the down-cast shaft, and a corresponding stream of air to ascend the other, called the up-cast shaft. The air is set in motion by means of a fire which is kindled in the up-cast shaft. A portion of the air in contact with the fire in this shaft, undergoing the ordinary chemical change which takes place in atmospheric air in the process of combustion, is decomposed: the nitrogen is separated, and the oxygen uniting with the carbon of the fuel, forms carbonic-acid gas. Both these gases, as well as the portion of atmospheric air which remains undecomposed, being heated are expanded, and occupy a proportionally larger space than the same weight of common atmospheric air, and in obedience to the laws of all fluid bodies, are borne upwards, consequently a strong current of air ascends this shaft; but if a free communication has been established below between the two shafts, an equal current must at the same time necessarily descend the second shaft to fill up the partial vacuum which has been made in the first.

Here then a power is generated capable of forcing a current of fresh air far beyond the distance to which any mine extends. The great generator of this power is the fire, and this power will act with a force and steadiness proportionate to the degree of heat steadily maintained at the bottom of the upcast shaft.

After two shafts have been sunk in a coalfield, the first operation is to establish a communication between them by digging out the coals from the one to the other. The next is to carry forward a mainway from the foot of each shaft, and then to make a road from the extremity of one mainway to the extremity of the other. If a door be now placed in the road which leads directly from the foot of the one shaft to that of the other, the air cannot then pass that way, but must go round along the one mainway across to the other, and thus to the foot of the shaft in which there is the fire, up which shaft the current must ascend.

To whatever distance we suppose the mainways, the sideways and all the other works of the mine to be carried, communications may thus be made between them, and by means of doors properly placed, the circulation of the air may be conducted and guided through them to any extent and in any direction that may be desired. A very

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simple diagram, showing the principle of these arrangements for ventilation, without the intricacy attaching to a plan of all the ways in an extensive pit, is subjoined from Mr. Fletcher's Report, § 20: App. Pt. II. p. 822. A is the upcast-shaft. B the downcast shaft. The arrows indicate the course of the air through the underground passages from the downcast to the upcast shaft; and the lines drawn from one pillar to another, show the trap-doors or partitions which prevent the current of air diverging to the upcast-shaft before it has swept the more dis tant workings.

As the fresh air that descends the downcast-shaft passes along the various roads through which it is directed, it not only affords the means of healthy respiration to the workpeople, but in its course collects and carries with it every heterogeneous matter which it can hold in solution, or which is capable of being mixed with it, which it conveys out of the mine through the upcast-shaft into the air above. The various matters which are thus conveyed out of a coal-mine in this ascending current are atmospheric air, car bonic-acid gas, nitrogen gas, carbureted-bydrogen gas, moisture, and animal effluvia.

In looking at the plans of large coal-pits there seems to be great perplexity and much ingenuity in the manner in which the air is conducted to the different parts of the mine, but the great principle in all is the very sim ple one which has now been stated, and at the cost of maintaining a sufficient fire at the foot of the upcast-shaft, and an adequate arrangement for conducting the current of air through the pit, any coal-mine can be perfectly ventilated.

Several of the sub-commissioners have given detailed descriptions of the different modes of ventilation adopted in their res pective districts.

From the evidence it appears that in all the districts there are particular mines in

which, often at great expense to the owners, every precaution is taken which intelligence and skill can devise to render the mine healthy and safe; but that there are great numbers of mines in which both ventilation and drainage are grossly neglected, and in which, as a necessary consequence, there is often a frightful destruction of human life.

COPPER, TIN, LEAD AND ZINK MINES.

(Cornish District.)—In proportion as a mine increases in depth, the importance of ventilation increases, and it becomes at the same time more difficult to effect it thoroughly. As far down as the adit level there is usually a free perflation, and it is only in an end,' a cul-de-sac remote from the shaft, that the air can be materially impure. Farther down, as no horizontal communication with the surface can exist, the interchange of ascending and descending currents of air affords the only natural supply; and by making the levels of large size, and establishing free communication between them by the short levels, called winzes, aëration (considered sufficient) is effected even in the deepest mine in Cornwall, without the use of air machines. In fact, those which have been hitherto commonly adopted are much more advantageously applied in the shallower mines or parts of mines. (Dr. Barham's Report, § 30, 31: p. 738). To ventilate ends not relieved by winzes, resort is had to air cylinders, a current being forced through wooden pipes, and to falls of water from one level to another.

An analysis of eighteen samples of the air from different places in which the men are employed, shows an average composition of oxygen 17.067, carbonic acid 0.85, and nitrogen 82-848. The Sub-Commissioner states, "that in one instance the quantity of oxygen was reduced to 14.51, and in another the quantity of carbonic acid was raised to 0.23. These results exhibit a lessening in the proportion of the vital ingredient of the air from its usual per centage 21, and an increase in a directly noxious ingredient, carbonic acid gas, from 0.05, its ordinary amount, calculated to produce effects sufficiently injurious to those who, for hours together, inhale such a fluid. But the proportion of deleterious gases occasionally present where the miner must labour (whether of sulphuretted hydrogen and sulphurous acid, which are very rapidly absorbed by the water lying in the levels, or of carbonic acid, which accumulates, like water, where there is no drainage), is much greater than that detected in the analyses here reported. It is then that the distinctly poisonous effects of these agents are produced, and loss of life, either at once or more remotely, has

often been the consequence. Carbonaceous particles from the candles and from blasting, and mineral-dust from the working of the strata or veins, are also suspended in the air which the miner inspires, and give a peculiar character to his expectoration: copper has even been detected by analysis in notable quantity in such air (Ibid. § 30: p. 738).

No method hitherto introduced is adequate to maintaining the air in the places in which the miners work in anything like a state of purity; and even in those parts in which ventilation keeps up a fair supply of fresh air, there is in almost all mines a constant smoke after the first blasting in the morning; so that the shafts and galleries are not unlike chimneys, often sending out a visible column at the surface. The smoke is sometimes so thick (Evidence, No. 1: App. Pt. 1., p. 822, 1. 3) that the miner can with difficulty see his hand.

From the nature of the case, the most advanced point of the excavation must be a cul-de-sac, and it will often be impossible to establish any communication with parts above or below. Hence it is that almost every miner in the deeper mines is at times exposed to what he himself designates "poor air," by which he means air so impure as to affect him in a noxious way distinctly perceived by him at the time. Of the less marked degrees of impurity he makes no account. Of the deficiency of oxygen, the excess of carbonic acid, the presence of sulphurous acid or sulphuretted hydrogen, he is not aware, and of smoke, however dense, he seldom takes any notice. (Ibid. § 32, 33: pp. 738, 739).

(Alston Moor District.)—At his place of work, however remote, says the Sub-Commissioner for this district, the under-ground labourer has no air except what comes from the level by which he has entered. There is nothing to make a current. Yet some levels in this district are half a mile in length, some a mile, and one called the First Force Level is nearly five miles in length. In such a situation "only slowly, and very slowly, can the air about him, merely by the effect of a difference of temperature wind its way upwards, and make room for other air which may penetrate to take its place."

Means may be taken to diminish an evil which cannot be removed. Sometimes a body of air may be forced in by a fall of a stream of water from the top surface of the hill. An opening is made for it to descend down to the level, which it does with great violence, driving a body of air before it, and then it runs out along the bottom of the level from the mine.

Machines, or fanners, are also used, being