respects.

The valve wearing down by its own weight, does not cause a leak over the top; water in the cylinder can find its way back into the steam chest; change of temperature does not affect the fit, and wear may be compensated for by reducing the packing strips.

This valve in its main feature is old, but is new in so far as using loose strips is concerned, and in another very important point. In use this valve showed one marked peculiarity, and one that has been noticed years without any one accounting for it. The four faces of the valve seat and the two outer faces of the cover plate remained perfect, the two inner face of the cover plate at once took on a different appearance, and after some months' use appeared cut away, and would sooner or later leak steam. Investigation revealed the cause. The exhaust steam leaving the cylinder dashed directly against these faces on its way to the exhaust port. A simple remedy has been found in casting the two projecting ledges in the valve itself.

One other point used in the construction of this valve is practiced which adds to its durability. All the edges of the valve and ports are left just as they come from the sand, special care being taken not to disturb the scale of the iron. While I believe no worse use of time and money was ever made than dressing out the ports of steam engines, the necessity for such work is less in this than in most others, as the throw of the valve is greater. About this valve and others working on the "mechanical-fit " principle, there is a feature not commonly thought of, and one that may be pretty generally denied. I make the statement, however, and feel free to maintain it, it is this: that the valve will work with a less consumption of power if worked a certain long distance than if a certain short

one.

The elements in this combination that contribute toward the reduction of friction are a free-running piston and cross head, frictionless piston and valve rods, perfect running journals and crank bearings, a governor that consumes no power, and a frictionless valve.

Against this it may be claimed that we have nothing but a shifting eccentric, a single valve, and, consequently, an imperfect distribution of steam.

While this is true, it is not true to the extent likely to be imagined. Because with this valve motion the worst defects of the shifting eccentric are avoided, and with the free running and extra large double port valve we are able to use it in an unusual manner.

It is usual to give a valve lead that is to admit steam to the cylinder before the crank has arrived to within 5° or 10° of its dead cen

ter. This is to insure smooth running, and to get the steam into the cylinder by the time it can begin to produce rotation, which can not possibly be until the crank has passed from 5° to 10° past the dead center. With high compression, which is necessary for economy, and unavoidable when cutting off short with a single valve, we secure smooth running, and with a large valve and double port we are able get all the steam required without opening in advance.

That is, instead of opening the valve before the crank has got within 14" of the dead center, we do not open it until it is 1" past, and, with this advantage, other things being equal, both exhaust and compression will not take place until the crank has made 11⁄2′′ more of its journey, thus increasing the area of the card at both ends of the stroke.

When one

Of all of this there is not so very much that is new. is groping his way in a field of inventions that has been traversed, by from one to ten thousand people, a hundred years or more, he is not likely to stumble upon a forest of novelties; but all of what I have claimed to be new or useful, I expect to be called upon to back up or back down from.

DISCUSSION.

Prof. Robinson-I would like to raise a query in regard to the occurrence of sediment of dirt in the steam chest, under these side strips which relieve the valve of the back pressure. It has occurred to me, as I have examined these arrangements, that there is a possible chance of sediment getting under as the engine is just starting, the water being forced out of the cylinder and lifting the valve out of its seat, and in that way depositing sediment under these strips. I would like to inquire whether there has been any difficulty met with in that respect.

Prof. Sweet-I think, from reading the reports of the discussions of the papers among the English societies, that it is usual for the one who reads a paper to wait until all remarks upon it have been made, and then to reply to them all at once. Whether that is the best way or not I do not know. I think it has been the practice with the Mining Engineers. I have no objection, however, to answering any questions that come up. I would ask, though, which practice it is desired to pursue in this Society?

The President-We have no precedent as yet, Professor. should say the best way would be to take them as they come. Prof. Sweet-Then I would say, in answer to Prof. Robinson's question that we have not had sufficient experience to know that it cannot take place.

Mr. Porter-I observed by the drawing that the back plate seemed to be held by a screw through the cover.

Prof. Sweet-Not by a screw-by a spring.

Mr. Porter-Well, it is held in contact, unless suddenly lifted for a moment. I do not suppose that the difficulty has ever been encountered, practically, of solid matter lodging upon those surfaces. We have never known anything of the kind.

The President-Do you never get any grit between those surfaces? Mr. Porter-It does not get on those surfaces. There is not only the spring, but when the engine is in motion the pressure of the steam is on the back of the plate, and I fancy that it can hardly be lifted so as to expose the surfaces of the strips in such a way that anything can be deposited upon them.

Prof. Robinson-I think it is claimed by some that in many cases of the pounding of engines, in starting, due to water in the cylinder, the head of the cylinder might be forced off except for the possibility of the valve rising. Take engines with no variability to the stroke of the valve, and then at the same time having a cushion, it strikes me that this must often occur. If we should take the case of an engine where we have a bored-out cylinder and plug valve running in that, I think that we should find a marked difference in the starting of the engine.

Mr. Porter-In case of water in the cylinder, of course this plate will momentarily lift and the cylinder be relieved by the water rushing into the steam chest; but, practically, I never heard of any deposit on those surfaces. My own construction is similar to that. The same liability to have solid matter deposited on those surfaces would exist. But I have never known anything of the kind in practice. I am quite sure it is not to be apprehended.

Prof. Robinson-I might remark that I had supposed from the appearance of the piston presented on the sketch, that Mr. Porter would be inclined to make a point of the light piston. This, I understand, is to be a high-speed engine. The question might arise why Prof. Sweet does not introduce the heavy piston. I would like to hear this marked difference explained, if there is a good reason for the light piston.

Prof. Sweet-The difference between Mr. Porter and myself, so far as I have gone, is, that I put the weight in the cross head instead of in the piston.

Mr. Babcock-The action of surfaces of different materials rubbing together under steam pressure, I think ought to be considered. It is quite common in this country to-day to use cast-iron on cast-iron, but it is not uncommon in this day to find engineers using brass piston rings, and even in some cases brass valves. I do not know that any one has published any information in regard to the action of such surfaces under steam. But some ten years or

more ago, in making some experiments on this subject, I found that there was a very marked difference; that the friction of brass upon iron under steam was exactly the opposite in its results from what it was when they were put together under ordinary lubrication. Instead of reducing the friction it vastly increased it. The friction of brass upon iron, under steam pressure, is double that of iron upon iron.

Mr. Woodbury-I could not see by the drawing that there was any packing on the piston.

Prof. Sweet-We use small rings sprung in grooves.

Prof. Thurston-There were two or three points which I no ticed, as this paper was being read, in regard to which I wish to ask some questions, with the view of suggesting a line of debate. The writer opened his paper with a statement that he would rather secure an economy of ten per cent. friction, than of ten per cent. steam. I saw some time ago some statistics of locomotive expenses, which I have not with me, but which, as nearly as I can remember, were as follows: The running expenses of the engine were seventeen cents per train mile. Of the seventeen cents, three and one-half cents only went for fuel; six and one-half cents went for cost of attendance, including the engineer, his firemen and cleaners, and three and one-half cents more were for the miscellaneous expenses incurred in the shop, the remaining item being cost of repairs. And it occurred to me, that possibly that distribution of expenses might indicate a direction in which we are to look for economy. In considering economy in the handling of steam engines, we have usually forgotten the fact that economy of steam and economy of fuel are by no means the most important of all economies, and the measures, in the direction of economy, taken by railroads, point to this fact; the doubling of the work of engines-keeping them running day and night, seems to indicate that this matter of the economy of fuel is a matter that is not of primary importance. At least, it is not the matter to which we are looking to-day, but towards decreasing friction, decreased cost for repairs. and decreased expenses in a thousand-and-one other directions which would go to make up the other portion of the seventeen cents. I thought that would perhaps suggest a line of argument. I also wish to ask Prof. Sweet how he secured himself against the tendency of the two parts of his counter-balance to spring the shaft.

Prof. Sweet-They spring the shaft to a less extent than if the wheels were outside. If you put counter-weights in the two wheels to equal the weight of the reciprocating parts, and the wheels outside the frame, the inertia of the reciprocating parts acting in one direction, and the centrifugal force of the counter-weight acting

opposite, both tend to bend the shaft in the boxes; whereas, if the wheels are inside the frame, the two forces neutralize each other, or, at least, their lever arm is greatly reduced.

Prof. Thurston-I was at one time in charge of a heavy engine in which there was an overhanging crank, and although the engine was designed by one of the most distinguished engineers in the country, and was carefully run, it was found impossible to keep the journal cool. Nor could we get a journal under that shaft that would obviate the difficulty of springing the shaft. I want to ask a question that bears upon one point already brought up. Prof. Sweet has not had difficulty from grit getting upon the piston rod? Prof. Sweet-We have not so far.

Prof. Thurston-I never had any trouble, in my own experience, with grit on rods.

Prof. Sweet-We take great pains in getting out the sand from our small engines before we start them.

Prof. Thurston-I did not understand whether the Professor intended simply to assert that the longer the traverse of his valve the less work it did.

Prof. Sweet-That is a point on which I suppose that I may have to defend myself. I have come to that conclusion from experimenting with surface plates. If you take one surface plate and lay it upon another, and move it a small distance slowly, it will only work a few times before it will stick and bind. If you keep it moving sufficiently fast and run it a long distance, it will run all right. If slow and a short distance, you have it in contact. If the surface plates be kept in motion, they will keep apart. If they traverse slowly for a short distance, they will come together.

Prof. Thurston-There was another matter that seemed to me of great importance. A remark was made that, by avoidance of lead, friction could be avoided. Rankine, you remember, went so far as to say that the advantage of a compound engine was very largely due to the avoidance of friction on the crank pin. But the avoidance of friction on the crank pin is effected most efficiently by this very plan of avoiding lead and using compression.

Prof. Sweet-I cannot see any object in putting an intense pressure on the crank pin, for about ten or fifteen degrees, when it could not produce rotation to any appreciable extent. I suppose, if there was no pressure there, it would be quite as well.

Prof. Robinson-In regard to the scoring, if we take into consideration the overhanging crank, it strikes me that the scoring of the bearing, near the crank, can avail but little, from the fact that at a distance from the crank, there will be the same flexural strain exerted, although there may be a slightly greater flexion for the