cylinder of the dimensions of the condensing engine cylinder using saturated steam with an expansion of nearly eight times. By an indirect method, with the data obtained during the series of experiments made on the condensing engine by the committee of experts for the Industrial Society of Mulhouse, the condensation in the cylinder during experiments B and C hereinbefore referred to, was determined to be 29.6290 per centum of the steam evaporated in the boiler. (See page 435 of the last June number of this journal.) One of the most important causes of that condensation is the difference of the extreme temperatures of the cylinder during a double stroke of the piston. In the condensing cylinder, the initial steam pressure being 70-9 pounds per square inch above zero, and the minimum back pressure, say, 3 pounds per square inch above the same, the temperatures corresponding to which are 303-62 degrees Fahrenheit and 141.67 degrees, this difference is 161.95 degrees. In the non-condensing cylinder, the initial steam pressure being 78-744 pounds per square inch above zero, and the minimum back pressure 15.9 pounds per square inch above the same, the temperatures corresponding to which are 310-76 degrees Fahrenheit and 215.10 degrees, this difference is only 95.66 degrees. And besides this cause of greater condensation in the condensing cylinder, there was the greater refrigeration produced by the greater measure of expansion with which the steam was used in that cylinder, than in the non-condensing cylinder. The net horse-power, representing the portion of the total horsepower developed by the engine that was commercially useful, was obtained for the consumption of 31707·0685 Fahrenheit units of heat per hour with the condensing engine, and of 32091.6077 Fahrenheit units with the non-condensing engine; and if a very small allowance be made in favor of the latter for the greater economic vaporization in its boiler per pound of fuel, owing to the slower rate of combustion, the cost of the net horse-power in both cases will be equal ; showing that a non-condensing engine with an unjacketed cylinder of the experimental dimensions, using saturated steam of 70 pounds boiler pressure per square inch above the atmosphere, with an expansion of nearly 43 times, gave the same commercial result-that is to say, the same net power for the same quantity of fuel per hour—as a condensing engine with a two and a quarter times more capacious unjacketed cylinder using saturated steam of 663 pounds boiler pres sure per square inch above the atmosphere with an expansion of nearly 8 times. Hence, under the experimental conditions, no economy would result from the employment of a condenser and air-pump, when the boiler pressure was not less than 70 pounds per square inch above the atmosphere. If the engine works with a variable load,. this must be taken for the lower limit of pressure-not the average pressure-giving equality of economic effect. Of the total pressure in pounds per square inch above zero with the condensing engine, there were utilized as net pressure 80-6420 per centum; and with the non-condens 23:4890X100 ing engine ( comparing as ( 39.8365 ) = 58.9635 1:36766 to 100000 or very nearly the 1-35127 to 1·00000 found as the ratio of the heat cost of the total horse-power in the two cases; so that the less fraction of the total horse-power utilized as net horse-power with the non-condensing engine just balanced the less heat cost of its total horse-power, enabling the net horse-power to be obtained for the same heat cost in both cases. The correctness of these facts was confirmed some years ago at a large flour-making mill in New York City, which was operated by several non-condensing cylinders of moderate dimensions, unjacketed, and using saturated steam of about 90 pounds boiler pressure per square inch above the atmosphere, with a considerable measure of expansion. The proprietor was persuaded to add a surface condenser and an air-pump, and a variable cut-off, expanding the steam sufficiently more to retain the same mean cylinder pressure with the same boiler pressure, the expectation being that a marked difference in the weight of fuel consumed per hour to grind and dress the same number of bushels of wheat would result; and such indeed was the case, but in the opposite direction to the expectation, the power actually costing so much more fuel that the condenser and air-pump were removed and the original conditions restored. The foregoing results are true for only the precise experimental conditions, and they will be modified by any of the causes which diminish cylinder condensation, as, for example, steam-jacketing the cylinders, super-heating the steam, employing larger cylinders, etc., for there is a greater economic gain possible by them for the condensing than for the non-condensing engine, as the former has the most cylinder condensation to be reduced. Consequently, therefore, just in proportion as the cylinder condensation is lessened by steam-jacketing, steam-superheating and larger cylinders, must the boiler pressure be increased for the non-condensing engine to sustain its equality of economic performance, gaining by the resulting increase of the fraction which the net power is of the total power, what it loses in decrease of relative cylinder condensation. It is probable, however, that with a boiler pressure of from 95 to 100 pounds per square inch above the atmosphere the non-condensing engine would give the net power with fully as much economy of fuel as the condensing engine using the same steam pressure with the measure of expansion found to produce the greatest economy, even with steam-jacketing, steam-superheating and cylinders of the largest dimensions in both cases. For marine engines, the use of high pressure steam is important, because it lessens proportionally the dimensions of cylinders required for a given power, the dimensions for high powers having now become inconveniently large, and because it allows the removal of the airpump and appendages. A surface condenser would still be required to furnish the boiler with distilled water, but the quantity of surface could be seriously reduced, the reduction being due not only to the fact that about one-tenth less heat is to be taken out of the exhaust steam, but that owing to the greater difference of temperature on the opposite sides of the condensing surface, a unit of this surface is proportionally more efficient for condensation. Less than nine-tenths of the refrigerating water would also be used because the difference between its initial and final temperatures in the condenser would be very much greater, so that a portion of the power required for pumping this water with condensing air-pump engines would be saved. The power expended in working the air-pump and the circulatingpump in marine engines is much greater than in land engines, because of the greater resistance against which they discharge, due to the height of the outboard column of water and to the greater tortuousness of the discharging pipes. The advantages of the non air-pump engine are, of course, for the cases in which a uniform power is employed, as for merchant steamships. For naval steamships which are engined for the development of high powers during short periods at long intervals, their principal steaming being done with very low powers, the condensing air-pump engine preserves its economic superiority. DISCUSSION Of the Papers of C. P. Sandberg on "Rail Specifications and Rail Inspection in Europe," of C. B. Dudley on the " Wearing Capacity of Steel Rails in Relation to their Chemical Composition and Physical Properties," and of A. L. Holley on "Rail Patterns," at the Philadelphia Meeting of the American Institute of Mining Engineers, held at the Franklin Institute, February 17th, 1881. (Continued from page 118.) C. E. STAFFORD, Steelton, Pa.: I must confess my high appreciation of Dr. Dudley's conscientious and painstaking work, and of his scientific methods in obtaining the data; but with his method of handling these results and with his conclusions drawn therefrom I cannot agree. The reasons for this difference of opinion I will endeavor to explain. It is apparent on inspecting his Plates 6 and 7 that the majority of the slower-wearing rails are from the north track, and generally have a longer "time of service," a greater average tonnage per rail, and a smaller average tonnage per year per rail than the faster-wearing, the majority of which are from the south track, and generally have a shorter "time of service," a smaller average tonnage per rail, and a greater average tonnage per year per rail. Have these facts any significance ? Have these differences of conditions to which they are subjected any bearing on the relative wearing capacity of these rails? I venture to say they have. I think, after a study of Table I, (an arrangement of lines 17 and 18, Plate 8,) in connection with Plates 6 and 7, we will find that the slower wear of the 32 best rails is only partly due to qualities inherent in the rails themselves, but is principally due to external conditions favorable to slower wear. In regard to the north and south track, we know that over the south track come the loaded cars from the West, and that over the north track these cars return, most of them empty. It is evident that this means for the north track a less average tonnage per rail per year; or, in other words, a lower wheel-tonnage. When the load per wheel is less, the resistance and consequently the wear must, necessarily, be less, other things being equal. "Time of service," also, has an important bearing on the question in hand. It has been only within the last five or six years, as Dr. Dudley has pointed out, that the roadbed of the Pennsylvania Railroad has reached its present admirable condition. Before this time the roadbed was more elastic, more yielding (and probably not uniformly so) than at present. These circumstances might cause a softer rail to be more durable than a harder one, owing to the fact that it would yield more or less to the bending force of the passing load and would thus get a bearing on each cross-tie. The harder rail, on the other hand, being stiffer and more unyielding, would not have this bearing uniformly, and would thus, to a greater or less degree, be subjected to the same conditions as a beam under shock, vibration and a rapidly moving load. Under such conditions, I believe, a harder rail would crush, break and perhaps wear out more easily and quickly than a softer rail. This agrees with Dr. Dudley's statement: "With the improvement in maintenance of way, during the last five or six years, the removal of rails from track from the first two of these causes has quite notably diminished." Under conditions as they now exist on the Pennsylvania Railroad, I believe, the harder rail will give the slower wear. With the ballast comparatively solid and unyielding, as at present, the rail, having a more nearly perfect and uniform bearing, and acting less the part of a beam than that of an anvil must, in my opinion, be a hard one to withstand the pounding of the locomotive and the abrasion due to combined rolling and sliding friction. Viewed in this light, a hard or soft rail would be respectively preferable as the maintenance of way has become more or less practically perfect. Of the seven rails, in track seven years or less, included in the slower-wearing division, and whose phosphorus units average 40.95, there will be found but one showing, under the same conditions, a slower wear for the softer rail. As these rails were put in track during and after the improvement in maintenance of way they tend to confirm the proposition that with a well-ballasted track |