bellows, in order to absorb from the air any carbonic acid which that air may contain, and which may be very effectually done by continuing the operation of blowing with the bellows. Wherefore,

as fast as the air in the confined place is contaminated by carbonic acid, which is formed by the breathing of the persons who are shut up in such confined place, the air so contaminated being, by action of the bellows, drawn into them, and then forced out from them down into the liquid, will, by the contact therewith which results from the air re-ascending in bubbles through the liquid, have all the said carbonic acid absorbed from the air by the caustic potash and lime, or by the lime; and the air which rises up from the surface of the water will be in a respirable state, as respects freedom from contamination by carbonic-acid gas.

"The operation aforesaid may be carried on during some hours before the absorbent property of the liquid mixture will become so much diminished as to require a renewal of the liquid. With the proportionate quantities of potash and lime and water (or of lime and water) already mentioned, the liquid will last for four hours. The capacity of the vessel wherein the liquid mixture is contained, should be at the rate of about two gallons for each person. The bellows should be of such capacity, and should be worked with such rapidity, as to pass at the rate of about one cubic foot of the air per minute for each person, through the mixture. And note that for each candle, or ordinary lamp, which is to burn in the air contained in the confined place, nearly as much should be allowed of each of the proportionate quantities, hereinbefore mentioned, as would be required for the breathing of one person.

For replenishing with oxygen, places deficient in that vital element, Dr. Payerne proposed to adopt any of four different methods. 1st. To supply it from vessels containing oxygen gas in a high state of compression, in the same way as the Portable Gas Company supplied at one time inflammable oil gas for purposes of lighting. 2nd. To throw from time to time fragments of peroxide of potassium into water, when the extra portion of oxygen contained in it would become disengaged. 3rd. To subject chlorate of potash, or a mixture of chlorate of potash and peroxide of manganese,

or peroxide of manganese by itself, to heat, when a like disengagement of oxygen would take place. Or, 4. To fill vessels, as in the first case, with many atmospheres of common air, and to let it out from time to time as wanted. Of these agencies, that of peroxide of potassium seems to have been most in favour with Dr. Payerne; and it was this, we believe, which he made use of in his experiments at the Polytechnic Institution.

We come now to the improvements contemplated under Dr. Payerne's second patent and specification.

And first, as regards the purification of vitiated atmospheres. The means formerly used for this purpose were, as the reader has seen, wholly of a chemical character, with the exception of the mechanical contrivances employed to bring the vitiated air into contact with the absorbent mixtures; but Dr. Payerne now proposes, to cause the air to pass also through certain filters or sieves, by which its purification will be still more effectually accomplished. And both these means he has combined together in a new apparatus of his own invention, which is stated to have been used with admirable effect in several of the large hospitals in Paris. A sectional elevation of this apparatus is given in fig 3 of the accompanying engravings; and the following is Dr. Payerne's description of it:

"I employ an apparatus of the description represented in fig. 3, which is a side elevation in section of the same. A is a box divided into two chambers of unequal size, a1 a2, by the partition b, both Fig. 3.

the chemical reagents destined to purify the air are either dissolved or mechanically suspended. B is a pipe, by which the air to be purified is introduced into a1, the larger of the two chambers of A; it terminates in a float, C, which rests on the surface of the water in a1, and is composed of fine wire-cloth, through the meshes of which the air, divided into a multitude of thread-like streams, finds its way into the water. D is a bent pipe of two legs, the one of about twice the diameter of the other. The larger leg fits closely upon, and covers an orifice in, the top of the chamber a1 of the box A; and the smaller one is inserted through a like orifice in the top of the smaller compartment, a2, and is prolonged till it terminates in a second float, D2, similar to C. The pipe D consists of six different flanged pieces, marked 1, 2, 3, 4, 5, 6, which are firmly secured together by bolts and nuts; the pieces 1 and 6, which abut immediately on the top of the box A, being secured thereto in like manner. All the joinings of this pipe are, besides, well luted, so that no air may escape through the sides. At the bottom of the larger leg, as also at the joinings 2 and 3, there are inserted gratings or sieves of copper or iron wirecloth, rendered, by galvanization or otherwise, as little liable as may be to oxidation; and each of these gratings or sieves is covered, to the depth of an inch or two, with moss, interspersed with small pieces of quicklime, or any other substance which is of a like absorbent quality, and not of a nature to generate of itself any gases of a noxious description. At the joinings 6, 5, and 4, of the smaller leg of the pipe D, there are inserted gratings or sieves of fine platinum wire-cloth; and each of these gratings or sieves is covered all over with pieces of spongy platinum. The vitiated air entering, by the pipe B, into the float of the larger chamber a1, of the box A, and thence into and through the water therein, is there purified to a large extent by the chemical reagents which are dissolved or suspended in the water. It then rises into the upper or vacant part of that chamber, and thence into the pipe D, and through the various metallic gratings, and layers of moss, quicklime, and spongy platinum placed thereon, whereby it is desiccated, and

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still further purified, the moss and lime serving to absorb any excess of humidity, and the platinum resolving into water any hydrogen which may come over into the smaller leg of the pipe D. On escaping from the pipe D, the air undergoes another and final purification by being passed through the water in the smaller chamber a2 of the box A, which holds, in a state either of solution or suspension, chemical reagents of the same sort as the large chamber a1; and rising from out of this water, the air is carried off, in a state fit for respiration, through the pipe Q. P1 P2 are doors through which the water and chemical substances are introduced into the chambers a1 a2; and T T, cocks by which the water or solutions may at any time be withdrawn."

With respect to the sort of liquid solutions to be employed with this apparatus, Dr. Payerne does not claim to have discovered anything new; but he makes the following useful observations on this part of the subject:

"The agents most efficacious for absorbing or neutralizing the deleterious matters which are most frequently required to be counteracted, namely, carbonic acid gas, sulphuretted hydrogen, and ammoniacal gas, are the hydrates or oxides of potassium, sodium, calcium, barium, strontium, lithium, magnesium, &c. It is not necessary, however, that these hydrates and oxides should be in a pure state. A cheap absorbent mixture may be made by combining quicklime with carbonate or sulphate of potash, or with the carbonate of soda, in proportions to be determined from analogy by the following rules. Supposing it is desired to make provision for the absorption of the carbonic-acid gas generated by the respiration of one man in the course of one hour, the mixture in the box A should consist of quicklime 1 oz., carbonate of potash oz., or carbonate of soda oz., and water 1 lb. Or if the sulphate of potash be substituted for the carbonate, then the quantities of water and quicklime should be doubled. In places where the air has become loaded with metallic exhalations which it is necessary to neutralize, as, for example, in smelting works and chemical manufactories, the air must be passed through some liquid acid capable of entering into solid combination with them. Sulphuric acid will generally be

found the most suitable for this purpose, employing it in a more or less concentrated state, according as the product which results from its presence is an anhydrous compound or not. Where the air contains a variety of deleterious matters, requiring different sorts of reagents, the air should be passed through a series of different solutions or mixtures, for which purpose, instead of the two compartments al a2, there must be three, four, or more provided according to circumstances. For example, there may be one compartment containing an alkaline solution to absorb impurities of an acid nature; a second containing an acidulated solution for the saturation of such substances as ammoniacal gas; and a third, containing a mixture of substances of a compound quality, to serve the purpose of double decomposition. In some cases it may be found advisable to have a compartment specially appropriated to the conversion of carburetted hydrogen gas into water and carbonic acid, and that will be best effected by bringing together in this compartment, out of contact with water, the two conductors of a galvanic battery, which ought to consist of some unoxidizable metal, and be divided at their extremities into a number of threads or filaments, which will render their action more prompt and efficient. I have lately made use of a battery for this purpose constructed in the following manner, and find it very powerful and inexpensive. I insert in a glass vessel another of porous earthenware, fill the first and surround the second vessel with a paste composed of concentrated sulphuric acid and peroxide of manganese; and I put into the second vessel pieces of iron or granulated zink, with weak hydrochloric acid. I establish the communication in the same way as in the present batteries, and use the same sort of conductors."

To cause the vitiated air to flow through the purifying apparatus, it is said that " any suitable blowing or exhausting apparatus may be employed;" but in the case of mines Dr. Payerne recommends the use of an apparatus of a particular construction, which he has lately invented, and describes very fully. It is an ingenious, and, we doubt not, efficient machine; but our present limits will not allow of our doing more than thus generally adverting to it.

Secondly, with respect to the reaxy

genating of exhausted atmospheres, Dr. Payerne now recommends, as preferable to all the other substances formerly pointed out, the ferrate of potassium, a new compound lately discovered, we believe, by a M. Fremy, a countryman of his own.

"In the specification of a former patent, granted to William Revell Vigers, of date the 7th July, 1842, for the invention of a mode of keeping the air in confined places in a pure or respirable state, to enable persons to remain or work under water and other places without a constant supply of fresh atmospheric air,' which invention was communicated by me to the said William Revell Vigers, several means of generating supplies of oxygen for the purpose were pointed out, which included the best with which I was then acquainted; but I have since then found out that the following is a more economical method. Take any given quantity, say twelve ounces, of the sesquioxide of iron of commerce, and lave it with warm water, until the sulphate of soda contained in it is expelled; then dry it, and heat it to a brown or dark red, when a very pure oxide of iron, in a state of most minute division, will be the result. To one part of this oxide of iron add four parts of dry nitre in the state of powder. Then place the mixture in a crucible of double the size required to contain it, and lute the neck of it well, leaving only a few apertures to serve as vent holes, and keep it at a bright red heat for about an hour and twenty minutes. The product will be a porous mass of a deep reddish brown colour, which, while still warm, must be broken into small pieces, and transferred as quickly, and with as little exposure to the air, as may be, into well-stoppered flasks for subsequent use. Persons confined in places which are liable to become foul from loss of oxygen, should provide themselves beforehand with one, two, or more flasks of this ferrate of potassium, according to the length of time they are likely to be excluded from communication with the external atmosphere; and as often as they feel any difficulty of respiration from the waste of the oxygen, all that they have to do is to throw a few pieces of the ferrate of potassium into a little water, when a fresh supply of oxygen will be immediately evolved."

in the case of diving-bells, Dr. Pa

yerne recommends the adoption of both the principal methods before described; and he gives drawings (of which the figures on our front page are copies on a reduced scale) of the way in which a bell 77 may, in his judgment, be best constructed.' The following is the Doctor's description:

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Fig. 1 is a sectional elevation, and fig. 2 a plan on the line Y Z. FF is an outer bell-shaped case, and D D the top cover, with bull's-eye lights, ggg. G is an inner case, of the shape of a frustum of a cone, which is fixed at a little distance from the outer one, gradually diverging towards it from the top, till at the points, h h, it is closely united with it by a horizontal piece, n n. H is a square case, on which the cylindrical and conical parts, F F and G, are placed, and to which they are closely united, so that when the bell has descended to the bottom of the water, the four corners of the square case form open spaces, by which workmen

may penetrate into corners not approachable with bells of the ordinary construction. The whole of the space between the two cases, F F and G, is made perfectly air-tight, for the purpose of containing a body of highly compressed air, by means of which the air in the part which is open to the water may be kept in a state of equilibrium with the column of water outside, even when descending to very great depths. As the bell descends, and the water begins to rise in it, a cock, M, in the compressed air chamber, is to be opened, and as much air let out as may be necessary to keep up a perfect balance between the pressure within and the pressure without. Jis a pipe, through which this chamber is to be filled before descending, with air, to the amount of two, three, or more atmospheres, according to the depth to which it is intended to descend. K is the cock for opening and shutting the pipe I. M is the cock by which the compressed air is to be let off into the inner case as required. I I is a reservoir where a quantity of compressed oxygen gas may also be kept. N is an apparatus for freeing the air, by absorption as before explained, of the carbonic acid gas, and any other deleterious matter with which it may become intermixed."

BLOWING FANS HOW TO MAKE THEM LESS NOISY.

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Sir,-Observing in No. 1044 of your valuable Magazine, a description of an improved blowing fan, which is stated to have been suggested by the unpleasant noise which they generally make, I beg to inform "X. X.," and your other readers, that the method there given, will not, in the majority of cases, prove a remedy. The noise is chiefly caused by the fan not being properly balanced, as every one may readily prove by trying a small model, in and out of balance. Some time ago, a fan was set to work near the place where I reside, which made so much noise as to alarm the neighbourhood, and be considered an absolute nuisance. Persons considered judges of such matters were called in, and stays, props, bolts, &c., were applied to make it fast to the building and the ground. Still, however, the machine continued to make the same noise, so as even to shake the building. At last a gentleman (whose name is not unknown to your readers) was requested to give his opinion. He caused the fan to be taken out, and, as he expected, he found it considerably out of balance. It was thereupon adjusted, put in its place, and all the props, stays, &c., removed, when it was again set to work, without any of those residing near being aware of the fact the noise was gone, and with it their complaints. I am, dear sir, Yours obediently,

:

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Sir,-Many letters have appeared in your useful Journal with reference to the comparative speed of the Isle of Thanet and the Prince of Wales steam-boats, the friends of the latter claiming precedence for their favourite, without (I think) showing cause why such claim should be allowed. My object is to call attention to a challenge made by Mr. Napier, when attacked as to pressure of steam"-"to run against any boat at a less pressure than his opponent.' To conclude, I am sure, Sir, of your acquiescence in an opinion general amongst people who, like myself, are unknown to Mr. Napier, that the total absence of puff in his operations is well worthy of imitation by many who have not done the state such service as He has. I am, yours,&&01;/T -12 A DQUITY READERTON de, Sarovovi Tua osoy mi lendirneob and you hodnolia gino e di und; Ubod