before and cause C to rise, while at the same time the cocks d and e permit the steam between C, and C to be exhausted into the calorimeter. Then that part of the heat supplied by E (119.19 heat units), which in Experiment II. was directly dissipated against the atmosphere, will be collected as heat in the water of the condenser or calorimeter, F, as in Mr. Barrus' experiment. But this fact does not deny the law that the heat which has been spent in making the upward stroke of piston, C, is p1 V1. We temporarily collect a portion of this p1 V1, equal to the work of back pressure, in a mass of water, long enough to measure it, but it is immediately thereafter dissipated to the atmosphere, as in Experiment II.

Mr. W. M. Barr.-I should like to ask Mr. Emery a question -perhaps it lies outside of the paper-and that is in regard to the relative cost of power between compound engines and triple expansion engines; that is to say, whether there is a difference in econony in making a compound engine (non-condensing or condensing, as you like) in which the same ratio of expansion, beginning, we will say, with 150 pounds of steam pressure and expanding down to the atmosphere, and doing the work in two cylinders instead of three. The development of the triple expansion engine is brought about by a number of conditions which cannot be entered into here. In the first place, the favorite type of marine engine is three cylinder engine; the reason for the engine being made with three cylinders is separate and apart from questions of economy, and antedates the modern triple expansion engine; it was originally designed with three cylinders so as to give a smooth motion to the ship. The same conditions would obtain very nearly in the case of a pumping engine having three cylinders instead of two. Now what I cannot get at exactly-because I do not know of any comparative experimental data on the subject in which the relative efficiencies of the two forms of engines are set forth, both using the same initial pressure, both doing the same quantity of work, and both expanding down to the same low pressure-is a comparison of the two types, the two cylinder and the three cylinder; or to re-state the question, Is the triple expansion under the same range of expansion any more economical in cost of power than a two cylinder compound? What I mean by cost of power is the amount of power developed for a given quantity of coal consumed.

Mr. Jerome Wheelock.-I would like to inquire of Mr. Emery if the type of engine he experimented with was similar to the one with which Prof. Denton experimented, and also what influ

ence the Professor found that steam jacketing with exhaust steam exercised in his experiments.

Prof. Denton. That was not touched upon, sir. I could not re-build the engine.

ments.

Mr. C. E. Emery.-Mr. Chairman: It is not possible to answer the various questions raised by Mr. Denton without more knowledge of the condition of the engine and of the details of the experiHe acknowledges that the engine was leaky, which fact should vitiate all experiments on a strictly scientific basis. As hinted by Mr. Wheelock, the Buckeye engine used is of peculiar construction, being provided with a great valve with the live steam inside it and surrounded by exhaust steam. The method of balancing and general construction are such as to invite leakages of sufficient amount to vitiate the results of experiments with small consumptions of steam, and it is possible that the relative changes of temperature between the steam and exhaust under different conditions of working may make a difference in the shape of the valve, thereby varying the amount of leakage. The small engine used in the experiments by myself had an ordinary slide valve, which was scraped carefully to its seat and run until it was absolutely tight, as proved by experiments again and again. The cylinder ports were on the side and inclined toward the valve, so that every drop of water in the cylinder was carried out with the exhaust at each stroke, a condition of things secured in some engines nowadays, but by no means in all. The piston was also made tight, so that its movements were absolute measurements of the quantity of steam used under the particular conditions. The results obtained with the Buckeye engine, constructed in the peculiar way it is, and leaking when standing more than sufficient steam for one horse power, cannot properly be compared with the experiments from an absolutely tight engine presented by myself. Prof. Denton's experiments are interesting, and can properly be studied to see what changes take place in the use of a peculiarly constructed engine as compared with that of more ordinary type. When his experiments are plotted in the same form as those presented by myself it will be seen that the disagreement in the general shape of the curves is not great. The results substantiate the remarks given in the latter part of my paper (page 20), to the effect that the cost in some cases remains substantially the same through a large range of expansion. Some of the experiments show the effect also of a constant leak which operates to greatly increase the relative cost of

the power when the amount of the power is small. The engines that he experimented with developed, at the longer points of cutoff, very much more power than the experimental engine referred to in my paper, so that the saving due to increased power for a given amount of surface shown in my formula applies to reduce the relative cost of the power under such conditions. This explanation will also undoubtedly largely, account for the difference found in the use of a vacuum. The paper states that with the low power and small engine used no gain was found by using a vacuum. With, however, the greater cylinder development at low powers and the greater actual power developed at other times in the Denton experiments, it is evident that the removal of the back pressure should make a great difference, as shown by his experiments. It is not possible to trace out all the irregularities shown in the experiments presented by Prof. Denton. Many of them must be considered mere puzzles due to abnormal conditions. On the whole, there is no contradiction in general results when the variations in conditions provided for in the formula are all considcred. A series of formulæ applicable to condensing engines would not be nearly as simple as those presented, but it is understood that we at this time only attempted the non condensing branch of the subject. We would again call attention to the fact that the formulæ do not depend on the experiments in the small engine. Such experiments furnished mere starting points by showing the condensation under the particular conditions in that particular engine. A large number of other experiments were also considered and formed guides, by means of which the curve F was originally located on curves No. 2, but still other experiments were available at the time this paper was written, locating the curve for non-condensing engines of medium size below that, and showing, when compared with the theoretical curve-as has been stated distinctly-that the margin of saving with non-condensing engines is very slight.

Mr. Barr will please excuse me if in answering him I simply give some references on the subject. A full answer to the question would require going over the whole subject of compound and noncompound engines. He will find published in the Journal of the Franklin Institute, six or eight years ago, a series of tests made in vessels of my design under direction of Mr. Loring, of the navy, and myself, covering the same points he speaks of. There were three boats of the same size and same boiler power, but the engines were different. One was a high pressure condensing engine,

another was a low pressure condensing engine, and another a compound engine. The relative cost of the work done by each is set forth in that paper, and abstracts of it can be found in various publications. The results have, in fact, gone into current literature largely abroad.

In regard to the triple compound engine, there is plenty of information to be found in scraps through the technical journals abroad, but none where there is a direct comparison in such way as to show conclusively the exact saving by their use, separated from that due to other improvements. In discussing this subject at the Washington meeting, I simply worked back to the triple compound engine from the compound, in an article on the subject of "Cylinder Condensation," etc. By examining the results of the experiments, as published in Engineering and in the Journal of the Franklin Institute at the time, in connection with the articles more recently appearing in our own transactions, the information asked for by Mr. Barr will be found approximately.

I will add that even in non-condensing engines operated at high steam pressures, the increased cylinder condensation due to the differences of temperature, referred to in the paper above mentioned on "Cylinder Condensation," will undoubtedly take place, and therefore, as stated in the paper under discussion, it will probably be necessary as the pressure is increased to increase also the number of cylinders, making double-cylinder compound, triple compound, and even quadruple compound engines, as the pressures are raised more and more, so that the back pressure of the atmosphere has less and less influence on the result.

*The discussion of Prof. Denton, as sent for publication, contains much new matter which it is not practicable to examine closely at this time. It also includes replies to features of the discussion at the meeting which emphasize some of the conclusions stated in my original response. This is particularly the case with respect to the arrangement of the main valve of the Buckeye engine in a chest surrounded by exhaust steam. Prof. Denton concludes that since the difference of temperature between the live steam and the exhaust is less than between live steam and the air, the economy of the exhaust jacketed system should not be inferior. The fact is, that the difference of temperature is but one of the elements to be considered. The resistance of a metal plate, even though it be of cast iron and suitably thick, is comparatively small and the quan

* Added since the meeting, under the rules.

tity of heat carried off is very nearly proportioned to the weight of refrigerating fluid which passes over the cooling surface. This was sufficiently proved in Prof. Richards' experiments with steam coils for heating currents of air, and the general result is familiarly known in many applications. It follows, therefore, that the quantity of heat which would be absorbed and carried away by currents of air moving with the velocity due to the differences of temperature about a steam chest would be very small compared to what would be carried off by a current of exhaust steam containing par ticles of water in suspension with an enormous capacity for heat. The oversight in the Professor's statement is evident on its face without lengthy discussion.

In response to the Professor's request for further details of the experiments with the small engine, I would call attention to the statements in the paper as to the way the experiments were plotted, and to the fact that all the customary data may be obtained from the curves except the speed of revolution, which was, on the average, 55 revolutions per minute. The general method of making these experiments is given in "Topical Discussions," page 375, Vol. VII., Trans. A. S. M. E., and there is also given there the cost of steam power in the small engine at different speeds of revolution when the engine was operated with a vacuum. I do not find that as complete a series was made on this point without a vacuum. The results of two experiments made without a vacuum, as given below, have, however, a direct bearing on the subject.

The statement that there was no economy in the use of a condenser with a small engine was a general one. A careful compilation of the various experiments would show what is stated generally in the above discussion, that economy should be secured as the cylinder development or power is increased. Evidences of this will be seen by comparing the results of the experiments above given with those in the "Topical Discussion" referred to. The experiments with the higher powers show some economy due to the vacuum, while those of lower powers do not. With larger engines or still larger powers in the same engine undoubtedly a vacuum would show economy in all cases.