and analysed with as little delay as possible. The eudiometric process was employed. In all cases the carbonic acid was first absorbed by caustic potash, and averaged one-ninth the total volume operated upon.

30 cubic inches of air from the nearest flue of the

3.01

engine, Tresavean, gave ¤, o3

Ditto, from flue nearest stack, ditto

3.00

Ditto, (a second experiment,) from nearest flue, ditto... 2.98 Ditto, from nearest flue, North Roskear, ditto

3.20

Ditto

ditto

ditto

3.07

Ditto, from end flue, Taylor's United Mines, ditto

2.75

The proportion of oxygen to nitrogen in the atmosphere is about one-fifth: thus we learn the quantity which has entered into combination with carbon and hydrogen, to form carbonic acid and watery vapour, to develope available heat.

A few experiments with charcoal will show that, after its combustion in a close vessel, the air still contains sufficient oxygen to support the combustion of sulphur, and, consequently, that it is not possible to deprive atmospheric air of all its oxygen by ignited coal alone. This accounts for the oxygen found in the flues. The results obtained appear to indicate that the admission of atmospheric air has, in these cases, been so regulated as to produce the best practical effects. If a less quantity had been admitted, the fires would not have burned freely; and if, on the contrary, a larger amount had entered, it would have exerted a cooling influence, and diminished the duty in proportion to the coals consumed. Experience has shown Cornish engineers that the best duty is obtained when all apertures through which strong currents could find their way into the apparatus are closed, and just sufficient air admitted to support a moderate, but not rapid combustion.

ON THE USE OF CONDENSING AND NON-CONDENSING ENGINES FOR MINING PURPOSES. BY T. B. JORDAN, ESQ.

The Cornish method of unwatering mines by the use of large single-acting condensing engines, has been the subject of much able discussion, and has frequently been determined to be unapproachable in its economic results. We will not, therefore, venture to question what has been so often decided by higher authorities, but take a view of the subject which, although it has not formed part of the scientific enquiry, is, nevertheless, important to the owners and managers of mining properties. It is fully admitted that a single-acting Cornish engine is capable of

raising more water from a given depth, with an unit of coal, than any other known machine, but this is only one portion of the question which mine managers have to consider, in order to determine the kind of steam machinery they will employ. The whole question then becomes, By what means can we give a mine a fair trial in the shortest time, and with the smallest possible outlay? We believe that, by the use of comparatively small highpressure non-condensing engines and double-acting pumps, this object may be frequently effected.

The cost of a large Cornish engine, with pit-work, will, necessarily, be considerable; and it is, therefore, a matter of some importance to determine whether a condensing or non-condensing engine shall be used, since in many cases it amounts to deciding whether the property can be proved at a small instead of a large expense; and it not unfrequently happens that a promising piece of ground is allowed to remain untried, on account of the assumed necessity for a large outlay of capital. The great advantage of a non-condensing engine is, that the required power can often be obtained in a tenth of the space and at a tithe of the cost of similar power in the single-acting condensing engine.

The non-condensing engine and its boilers will also produce a higher proportional price, if resold, than the larger machine, since it is just as applicable to every manufacturing purpose as it is to mining; and because its moderate price, and its greater facility of removal, brings it within the means of a larger number of purchasers this may also be said, in some measure, to apply to double-acting pumps. These pumps may be variously arranged, either for drawing or plunger lifts; but in all cases they discharge an equal quantity of water, both in the up and down stroke, and consequently possess the following advantages:-Pumps of half the area of those generally used discharge the same quantity of water, and, therefore, the expense of many tons of pit-work is saved. The water is constantly moving upwards in the column, and much of the inertial force which has to be overcome at every stroke of a single pump is avoided, and less power is required. The engine also makes several strokes in the cylinder to one of the pump, therefore its irregularities are not coincident with those of the resistances in the pitwork, and the entire apparatus can be adjusted to a more perfect balance. The enormous unbalanced weight of pump-rods requisite to make the out-door stroke is likewise done away with, and the excess of strength in the main-rod, necessary to bear the sudden admission of steam on the piston, and to overcome the inertia of the column of water, is no longer required.

It is not intended by the foregoing remarks to attempt to prove

that the present system of employing large low-pressure engines for mining purposes is universally objectionable, but merely to show that cases occur, in which it is more economical to employ a less expensive apparatus, although consuming a somewhat larger amount of fuel in proportion to the power obtained.

DESCRIPTION OF HORIZONTAL NON-CONDENSING ENGINE.

In this machine the cylinder, c, bed-plate, K, parallel guides, D, and the plummer-blocks of crank-shaft, &, are in one casting, which renders it impossible that there should be any error in fixing, since the adjustments are wrought in the fitting-shop, and cannot be altered or deranged. There are two fly-wheels for the purpose of distributing the load more perfectly on the bearings, as well as to render the engine more compact and portable; they may also be used for taking off the power by belts if required, and be used as carriage wheels for the engine itself in transit over difficult roads. These wheels for a 12-inch engine are 5 feet diameter, and 6 inches wide on the rim, and heavy enough to be perfect as regulators without being so cumbersome and difficult to remove as a single larger wheel must be.

In the figure, B is the slide-box, A the handle of governor valve, F is the connecting rod, & the crank axle, H the feed pump, and I the eccentric.

103

SUPERHEATED STEAM.

THE following is an abstract of a "Mémoire" recently presented by our friend, Mr. Hirn, of Colmar, to the Industrial Society of Mulhouse, and entitled "Mémoire sur la Théorie de la Surchauffe dans les Machines à Vapeur, présenté par M. G. A. Hirn, dans la séance du 29 Octobre, 1856.

In this paper the author proposes to investigate the various phenomena taking place in the cylinder of a steam-engine, when, instead of being supplied with ordinary saturated steam, superheated steam is employed. Or, in other words, when, instead of making use of ordinary steam generated in the usual way, such an additional amount of caloric is imparted as to convert it into a gaseous state.

A machine was exhibited by Mr. Wethered, of Baltimore, at the Paris Exhibition of 1856, in which superheated steam was employed; but in that arrangement a mixture of common and superheated steam is introduced into the cylinder.

The experiments of M. Hirn, as detailed in his Mémoire, go to show the advantages to be derived from the employment of superheated steam alone.

This Mémoire is divided into three distinct parts. In the first, the subject is treated in a practical point of view; the apparatus employed described, the nature of the experiments detailed, and the results obtained stated. In the second, the phenomena attending the production of superheated steam, and the effects produced by its employment in steam-engines, are explained and analysed. The third division treats of the modifications introduced by the employment of superheated steam, relative to the quantity of heat which becomes latent during the expansion of the gaseous steam, and the mechanical equivalent of heat.

The boilers supplying the two large engines of Messrs. Haussmann, to which the superheating apparatus to be described has been adapted, possess nothing peculiar in their construction. They are each provided with three boiling-tubes, whilst the smoke and heated air, after having followed these throughout their whole length, enter the flues surrounding the boilers, and finally escape, by the stack, into the atmosphere. Behind the boiling tubes, and immediately below the point where the smoke and heated air leave them to infringe on the surface of the boiler, an aperture, A, is made in the brickwork of the setting, and which, by means of