maker. He considered that at least 20 per cent. of fuel was wasted by the carbonic oxide passing off by the chimney. The Ebbw Vale Iron Company saved a large quantity of fuel, by collecting the carbonic oxide from the coking furnaces, and using it for calcining the mine and lime, and for raising steam, &c. The mere evaporation of water was considered to be a fallacious test. In the Heron,' owing to the smallness of the heating surface, the experiments were commenced with the water in the tender at a high temperature; this had vitiated the truth of the result, as the difference of bulk, due to the temperature of the water, had not been taken into consideration. The pres sures in the boilers of the two engines, in the trial against the new engine, had not been noticed, but he presumed they were worked up to as high a pressure as they would bear.

Mr. BIDDER said, he must repeat his previously expressed opinion, that to enable a correct opinion to be formed, all the circumstances of the experiments should have been given. He had analysed the statements given in the table of "Actual Working Results, &c." and had shown them to be deficient in accuracy. It was not enough to suppose the two engines to have done their best, the absolute pressures should have been given.

Mr. D. K. CLARK argued, that the proof of the practically complete combustion of coke in the fire-box, founded on the observed evaporative performance of the fuel, and the heatproperties of the gases of combustion, was as valid, and certain, as any that could be derived from a chemical analysis of the gases.

The expansion of the water in the tender, when steam was blown back, would never, in his opinion, amount to more than one-half per cent. at 90°, of the volume at 60°, and about one per cent. at 120°. It was, therefore, practically unimportant. The measurement by volume, of the water in the tender, might, consequently, be relied on, at all ordinary temperatures. As to the fluctuations of the water in the tender, while the measurements were being made, he believed that the mean level might be closely approximated to, by observing the extent of the fluctuations, and that the average of a great number of such observations must be substantially correct.

With regard to marine and stationary boilers, he had not

asserted that the formula, as it stood, would apply; but he believed, that an adjustment of the co-efficient was all that was necessary, to render it capable of this extended application. He wished it to be particularly understood, that in the construction of the formula, he did not insist on one proportion of surface to grate, more than on another. A heavier boiler might work as economically as a lighter one; but inasmuch as it was heavier, it was clearly inferior, as it was desirable to combine compactness, lightness, and power, in locomotive engines.

If, as had been asserted, 20 per cent. of the coke passed off as carbonic oxide, the evaporation, with ordinary boilers, could not exceed 7.2 lbs. of water, per pound of coke; and in Mr. McConnell's new Express engines, where the temperature in the smoke-box was said to be from 1100° to 1200° Fahr., the evaporation could not exceed 5 lbs. of water, per pound of coke. These conclusions were, however, so at variance with the bestascertained facts, that the hypothesis must be incorrect. Though the evaporative performance of coke, in locomotive boilers, was liable to be vitiated by priming, the results given in the Paper, were checked by the measurement of the steam passing through the cylinders, thus showing, by comparison with the water consumed from the tender, that there had been no material amount of priming.

He then referred to a recent experiment with an engine on the Caledonian Railway, in which the area of the grate was reduced by brickwork from 10 square feet to 9 square feet. It was found, that while an engine of the same class (with 10 square feet of grate surface) evaporated 122 cubic feet of water per hour, at the rate of 6.8 lbs. per pound of coke, the engine with the grate reduced to 9 feet, evaporated 132 cubic feet per hour, at the rate of 8 lbs. per pound of coke; showing that the smaller grate raised more water per hour, and evaporated a greater quantity per pound of coke.

Throughout the discussion, the formula and the reasoning in the Paper had been the chief points touched upon. But it was satisfactory to him that not one of the whole mass of facts he had accumulated, nor the deductions from them, had been fairly impugned. The qualities of the engine had been constantly mixed up with those of the boiler; whereas the Paper treated of boilers, exclusively. Now unless the boiler and

engine were carefully distinguished, the peculiar necessities and qualifications of each for efficiency could not be determined. The conditions of excellence should be found first, for the boiler, secondly, for the engine, thirdly, for the carriage, and lastly, the final duty would be to harmonise and adjust the respective conditions, for the efficient action of those elements, so as to produce the best joint result. Unless such a progressive course of investigation were followed, it was considered impossible to arrive at a final satisfactory conclusion. It was his desire, on subsequent occasions, to follow up the course of this inquiry.

Dr. LYON PLAYFAIR said, that the question under discussion must be resolved by experiment, as it was not yet in a condition to be closely examined by chemical theory. It was no doubt true that the carbonic acid,-the normal product of combustion, -did seize an equivalent of carbon, from the incandescent coal, or coke, and took it away, as carbonic oxide, in which form no available heat was developed. If this carbonic oxide could be advantageously used, it would doubtless be productive of economy of fuel. But the practical question rested on other grounds. There was still a wide difference between the theoretical calculations of chemists, and the practical results arrived at by engineers. Thus, one pound of coal was supposed, theoretically, to be capable of raising 10 or 12 millions of pounds of water, one foot in height; whereas the results of the best Cornish engines, showed the practical effect to be only about 1 million pounds. Again, by theory, one pound of coal should evaporate nearly 14 lbs. of water, whilst practically, under favourable circumstances, only about 11 lbs. were evaporated. Whilst this discrepancy between theory and practice existed, it was useless to examine the question otherwise than practically.

Mr. P. M. PARSONS, through the SECRETARY, said, he believed the question of the economical use of steam in the locomotive engine afforded a wider field for increasing the efficiency and economy of the machine, as a whole, than by confining the discussion to the boiler alone. Mr. Parsons thought that the expansive action of steam had, as yet, been applied in a very partial and disadvantageous manner to locomotive engines. The steam was either worked with its full pressure throughout the entire stroke, or nearly so, or it was worked expansively, to a limited extent, by the common D valve and ordinary link motion, or, in

a more extended and perfect manner, by means of a separate expansive valve and gear; but in all cases the driver had to accommodate the rate of expansion to the work the engine had to perform. When the engine was exerting its greatest power, and using probably twice, or three times the quantity of steam that it did when exerting its least, the steam was not worked expansively. It was only when the engine was exerting a less power, that any advantage from expansion was obtained. He considered that increased economy would result from substituting larger cylinders for those usually employed, and fitting them with an expansive apparatus, giving a fixed rate of expansion at all times. These conclusions had been arrived at by observing the working of several engines, under various circumstances, both with and without variable expansive gear. He found that the fixed expansive gear was about 21 per cent. inferior to the variable expansive gear, when the engine was doing a small amount of duty; but when that duty was doubled, the fixed expansive gear had an advantage of about 36-77 per cent., and that its superiority was in proportion to the increased duty and the higher pressure of steam used.

A simple method of applying a fixed expansive apparatus to cylinders placed together, with their slides back to back, was to add two cut-off valves, on the backs of the ordinary D valves, and to connect the expansive valve of one engine with the D valve of the other, and vice versa. It would then be found, that the D valves, being adjusted so as to open and shut the steam and exhaust ports in the most advantageous manner, without expansion, the expansion valves would cut off the steam at 1, 4, or of the stroke, according to the adjustment, the one by its inner, the other by its outer edges, in reversing. The back eccentrics should be adjusted to cut off the steam by the D slides at about half stroke, as the expansion valves did not then come into play.

Mr. R. STEPHENSON, M.P., V.P., explained, that the Institution of Civil Engineers could not, by its regulations, take the initiative in any trials, but if the results were submitted to a meeting, they would doubtless undergo that candid consideration, and fair discussion, which all questions had hitherto received. Many of the results, already attained, were new and strange, and receiving them as facts, they induced careful re-consideration of previous impressions and accepted data, and from the attention

thus directed to a most important subject great results might be anticipated. The profession was greatly indebted both to the Author of the original Paper, for the clear and definite views he had laid down, and to the designer of the new boiler and engine, for the statement of the results which had been produced. He hoped that they would both continue their observations, and again meet in the Institution, for the comparison and discussion of the results.

INDICATOR CARD FOR ASCERTAINING THE PRESSURE ON THE PISTON OF A STEAM ENGINE.

After the meeting, Mr. Hulford, of H.M. Dockyard, Woolwich, exhibited an instrument of his invention, for ascertaining from an indicator card, the steam pressure on the piston of a steam engine.

The indicator card being placed on the board, so that the atmospheric line coincided with the marks on the retaining springs, the triangular scale was placed at the bottom of the figure, and the side roller made to revolve, until the spiral line on it intersected the edge of the scale, in which position the roller was fixed. The distances between the steam and vacuum lines were taken, by sliding the scale along the figure, and ten, or twenty divisions might be taken, according to the degree of accuracy required; the sum of the distances, divided by their number, gave the mean pressure on the piston.

A great saving of time, in the measurement of all irregular figures, resulted from the use of the instrument, and its simplicity and low price were also points in its favour.

March 15 and 22, 1853.

ROBERT STEPHENSON, M.P., Vice-President,
in the Chair.

The discussion upon the Paper No. 887, "Experimental Investigation of the Principles of the Boilers of Locomotive Engines," by Mr. D. K. CLARK, having been renewed, was continued to such a length as to preclude the reading of any communication.