Dilatation of Gases under different Pressures, determined by the method of Constant Pressures. (V.)

ATMOSPHERIC AIR. CARBONIC ACID.

HYDROGEN.

SULPHUROUS ACID.

Pressure Volume at Pressure Volume at Pressure) Volume at Pressure

Pressure Volume at at 100100-.

760

1-36706 760 1.37099

2525 2620

760 1.36944 2520 1-38455 2545 1-36964

1-36613 760-00 760-00 1:39020 1-36616 982-73 987-64 1·39804

The general conclusions of this memoir are as follows:

1st. The coefficient of dilatation of air, 0.375, heretofore admitted by philosophers from the experiments of M. Gay Lussac, is much too great for dry air under the ordinary atmospheric pressure.

The coefficient 0-3645, which is the mean of the experiments published by M. Rudberg, is too small.

When the coefficient of dilatation of air is deduced by calculation, from the changes of elastic force which the same volume of gas undergoes when carried from 0° to 100°, its value is 0.3665.

But when this coefficient is deduced from the changes of volume of the same mass of gas in passing from 0° to 100°, its elastic force remaining constant, we find a value rather higher: that is-0-3670.

2nd. The coefficients of dilatation of the different gases are not equal, as has been hitherto admitted; they present on the contrary, notable differences, as may be seen by the numbers before cited.

There is often obtained for the same gas, very different values for its coefficient of dilatation, according as this is deduced immediately from the observation of the change of volume which the same mass of gas undergoes between 0° and 100°, its elastic force remaining the same, or calculated from the variation in the elastic force of the gas between 0° and 100°, its volume remaining constant.

3rd. The air and all other gases, except hydrogen, have greater coefficients of dilatation in proportion as their density increases.

4th. The coefficients of dilatation of the different gases approach. nearer equality, as their pressures are lighter; so that the law which is thus expressed, "all gases have the same coefficient of dilatation," may be considered as a limiting law which is applicable to gases in a state of extreme dilatation; but which is farther from the truth in proportion as the gases are more compressed, or, in other words, as their molecules are brought nearer together.

(To be Continued.)

New Arrangement for Gas Burners, by M. MACCAUD.

We find in the Bulletin of the Society for the Encouragement of National Industry, for February, 1847, a report by M. Payen, from a committee of the society, appointed to examine a new arrangement of gas burner, invented and submitted to the society by M. Maccaud, of Lyons.

The modification consists in an envelope of wire gauze, through which the air which is to support the combustion passes. This envelope produces two useful effects: the heat acquired by the wire gauze is transmitted to the air, and augments the light of the lamp; and at the same time the flame becomes more regular. The lamp submitted by M. Maccaud was an argand gas burner of twenty tubes; the gallery which supports the glass chimney is fitted with a wire gauze which surrounds the base of the chimney, and is prolonged downwards in a funnel form to the bottom of the burner. It was compared with another similar argand burner without the wire gauze, each giving a light equal to that of a Carcel lamp, burning 14 oz. of oil per hour-where it was found that the expense per hour of the Maccaud burner was to that of the other lamp as 110 to 123, or as 100 to 111.8.

The use of the wire gauze renders the flame steady even when exposed to strong currents of air, so that when a window or door was suddenly opened, the flame remained unaffected, while that of the common lamp became red and smoky.

The committee also examined the behavior of these lamps as contrasted with that of ordinary gas burners in the open air, and especially in doorways and staircases, where the lamps were constantly exposed to draughts, and found that the flame of the Maccaud lamp was always unaffected, while that of the ordinary lamp was so much affected that the glass chimneys were constantly broken by the sudden deviations caused by the currents of air.

In certain particular cases, and where the lamps are to be constantly exposed to very strong currents of air, M. Maccaud covers the upper part of the glass chimney with a conical cap of wire gauze, which prevents the wind from driving the flame downwards; the wire gauze which he uses contains from 40 to 80 wires to the inch.

The invention above described is so simple that it seems incredible that it should never have been invented before. The high authority of the society from which the report emanates, as well as the known personal reputation of the reporter of the committee, are sufficient guarantees for the accuracy of the facts. As to the utility of it, it is unnecessary that we should dwell upon it in this climate where our houses are all open on summer nights, and not unfrequently the wind blows with such violence as to render it impossible to keep a common gas-light burning. When furnished with the cap, it will also prevent insects from accumulating upon the burner. The principle is also manifestly applicable to our street lamps, and would much benefit them in stormy nights. Bull. Soc. Enc. Ind. Nat.

An Improved Manometer. By M. GALY CAZALAT.

"In the manometer, of which the use is prescribed (in France) by the ordinance of May 22nd, 1843, the glass tube must exceed in height as many times 76 centimetres (30 inches), as the pressure of the steam exceeds an atmosphere.

"In order to shorten the column of mercury, the weight of which balances the force, it has occurred to me to oppose to the pressure of the steam the horizontal end of the rod of a piston, moving without friction, and steam-tight, which, by descending, causes the mercury to rise in the glass tube. According to this arrangement, if the area of the end pressed by the steam be n times smaller than that of the piston pressed by the mercury, this latter will rise in the tube to a height n times less than in the usual manometer."

It will be evident that the only practical difficulty to be overcome in this arrangement, is to render this piston steam-tight, at the same. time that it shall move without friction. This object is attained, however, by the use of diaphragms elastic and impermeable interposed between the ends of the piston, and the mercury or steam.

With these remarks, a glance at the accompanying sketch, with reference to the explanations, will render further description unnecessary.

The moving principle is the brass piston c, on which impinges, and which transmits to the mercury, the pressure which the steam exercises

on the horizontal end of its rod d. For this purpose, the piston rod moves without friction in a central bushing of copper e, attached in

an iron cylinder f, of which the lower face is recessed at g, to receive the disc or piston c. The two ends of this cylinder are each covered with a flexible and impermeable membrane (as, for example, caout

chouc) v, v. These two membranes are confined by the flanch i, i, and the base k, k, which form the cavities 1, m; the upper one is full of water which communicates with the steam from the boiler by the tube d; while the lower is full of mercury by the canal p, with a vertical cylindric reservoir q, in which is attached the gauge tube s; n is a canal to conduct air to or from the upper face of the piston c, at its upper end, the tube terminates in a bulb (not shown) to receive any mercury which may be blown out.

The space in height, occupied by this apparatus, is evidently at the option of the maker; but for locomotives, 4 centimetres (1.57 inches) per atmosphere, is found to be a good scale; in which case, the relation of the two ends of the piston will be as 19 to 1; and for 7 atmospheres the whole height of the tube will be only 11.2 inches.

Method of Closing Glass Vessels Hermetically.

Ibid.

M. Maissiot, of Paris, has proposed the following method of closing glass vessels of every size hermetically.

The mouth of the glass vessel is ground upon the top, and a glass plate ground so as to fit accurately upon it. A quantity of caoutchouc is then melted, (the addition of of its weight of tallow assists the melting and does not hurt the preparation,) the heat must be gentle and carefully regulated, and the matter must be constantly stirred; if the heat be raised too high it will be indicated by thick fumes. As soon as it is nearly fused, slacked and sifted lime is added, little by little, the paste being constantly stirred with a spatula. Immediately the strong smell of caoutchouc diminishes, and soon disappears entirely. It is then replaced by a peculiar odor which indicates that the operation has been well performed, and that the caoutchouc has combined intimately with a portion of the lime. The excess of this alkali plays the part of an inert powder, by which you may give the cement any consistence desirable. When it is as thick and tenacious as you want it, withdraw the vessel from the fire, and the cement is made. This cement possesses a remarkable plasticity, it appears scarcely to dry up; after a year's use, it does not appear to have in the least changed its properties. The property of hardening in time may be given to it by the addition of proper quantities of the compounds of lead. A thin coat of this cement is then spread with a knife over the edges of the vessel, and the cover being applied to it, pressed with the finger in the centre, and turned round for a moment, so as to spread the cement evenly, the joint will be found completely air-tight. The softness of the cement does not prevent it from adhering strongly to the glass. Thus, filling a cylindrical vessel of six inches in diameter, and immediately turning it upside down, the cover was not forced off, nor did the liquid leak. M. Maissiot has enclosed in this way concentrated alcohol with a vacuum over it, which, after many months, remains perfect. This method will be found very advantageous for the preservation of preserves, fruits, and meats, by Appert's process, as well as for anatomical preparations, &c.

Ibid.