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much superior to the other machine in this respect. You can take out this box, put on a very small quantity of oil, — a measured quantity or a weighed quantity,—and then put it on again, and run the machine till it begins to show an increase of friction. But suppose there is a little inequality:- the metals will then soon come in contact, the oil being crowded aside. In order to test fairly the lubricating quality of oils, we must have a simple friction of the oils themselves, and no rubbing of the bare metals on each other. We should have two perfectly fitting surfaces, and keep the oil between them. It is desirable to have something which represents the circumstances that prevail in practice; and at first sight this arrangement appears to be such. Here we have a shaft and a bearing, as usual; only the bearing in this case is made of hard metal, rarely used in actual practice.

Now, it seems to me to take up one other point-that the harder the journal is, and the softer the box is, or the greater the difference between them, the better it will be, because then they will soon wear equal, and tend to stay so. Of course there is a practical difficulty there. If we could, in fact, use mere tallow for a bearing, or something which is very soft indeed, it would do very well; but tallow would soon crush and leave no support. We all know that wood makes a pretty good bearing, if we have pretty hard wood: it adapts itself to the metal very well; but it will wear out after a while. Babbitt's metal is sometimes used, and it is certainly a very good thing. We have, in a Babbitt's metal box and an iron shaft, a very great difference in the two bearing surfaces. If there is any inequality in the shaft itself, it will soon be compensated for by the actual scraping out of the softer metal; and the tendency is to wear to a true fit. There are softer metals, like lead, which yield too much, and are, so to speak, too viscous; that is, while being abraded, they catch on the iron of the shaft, and cause a dragging. They are somewhat like resin, which catches and sticks to rubbing surfaces, and increases friction. Babbitt's metal is soft enough and brittle enough to be scraped to a fit by the harder iron, and yet it is firm enough to bear up against a pretty strong pressure, and hence comes its great utility for lining boxes.

One thing we should observe in this connection, and that is, the tendency to cohesion between metals in contact. Any thing which tends to cleanse metallic surfaces tends to make them

stick together. You know, when we want to solder tin or copper or zinc, we must have perfectly clean surfaces, or else the solder will not adhere. We scrape the surfaces to be united, and use chloride of zinc, or resin, to keep them clean till the solder unites with both. If we use a lubricating oil that is a little bit acid, and therefore tends to dissolve the coating of oxide on shaft or bearing, we get something which makes the metal bite. Any thing which is acid, which tends to dissolve metallic oxides, or tends to bring two perfectly clean metallic surfaces in contact, tends to bring about exactly the right conditions for their absolutely adhering together. We want, therefore, to get something free from acid, something that will not dissolve metallic oxides; and we want metals whose oxides have little affinity for oils, or for acid in the oils. Copper and brass are acted on by animal and vegetable oils. Iron is not. Babbitt's metal is not. Brass and bronze are objectionable on this account. I am glad to say that the experiments we have made, on the mineral oils received by us, show that most of them are entirely free from acids. The vegetable and animal oils develop by exposure more or less oleic and stearic acid, and this is an objection to the use of such oils unmixed.

I think some of you may remember the time when it was proposed to use the dead oil of coal-tar as a lubricant. It became pretty well known that dead oil rather tended to make bearings bite than otherwise. Dead oil contains carbolic acid; and probably the biting was on account of its tendency to clean the metal surfaces, and bring them in closer contact. What we want is to have no metallic surfaces in actual contact; we want large surfaces to distribute the pressure, and we want them true, so that the oil may receive the pressure uniformly throughout the whole extent. If there is one point of metal in contact with another, we are no longer getting the full benefit of the oil. The machines that I have here have failed in this, that we can never get more than one or two points of bearing; and of course, as the prominent points of the metals soon come in contact, you can tell very little about the oil. We ought to have something which continually tends to wear true. Now, if instead of cylindrical surfaces we have disks, the chances of compensation are much better. To be sure the little brass disk-machine that we have tried is too small and too simple, and it has not proved quite satisfactory. But the true principle is to have disks,

or something equivalent to disks. Suppose two flat surfaces brought together with an eccentric rotary movement. These will tend to wear true; and, if there are any inequalities in them, they will wear spiral grooves, and by continual intercrossing the grooves will soon be effaced. The true principle of a lubricating machine, which I think will yet be developed, would be to have the motion of the painter's muller, and never to have precisely the same parts opposed to each other in any two successive revolutions. If we could have a machine of that sort, it would be a practical lubricating machine; but we have not been able to conceive of any way of bringing that about as yet. But if we have to use a simple rotary motion, as perhaps we must in order to get great speed, instead of a disk we must have a flat ring working against a plain surface. The objection to this is that the outer portion of the ring is moving at a greater velocity than the inner portion, and of course the constant wear is greater at a greater distance from the centre. The tendency would be to wear down into the disk next the outside direction; and on the other hand, when the inner portion gets a little high, that wears down. So I think there might be a very slight, but inappreciable, inequality produced. But perfection is to be aimed at; and there is one way in which we can restrict the difference in velocity between the outer part of the ring and the inner, and that is by making a conical ring bearing on a hollow cone, the proper angle being determined by experiment. The books on mechanical engineering give us, however, the exact form of bearing-surfaces which will wear exactly true. The question would seem to be between a disk-machine, which will move eccentrically somewhat, and a cone-machine. A cone-machine has been devised by Mr. Whiting, and he has favored us with the drawing which is here exhibited. A cone-machine, if it could be well mounted, would be a very good thing; but there is one point to be considered. If we have a cone, it would hardly do to have a sharp edge. It should be made rounding, and the corresponding edge of the cup should also be cut rounding, so that both cup and cone will wear off just alike.

It is essential, in order to get a machine which will indicate in a few minutes, or even in a few hours, the lubricating power, that the oil be in some way or other well distributed. Any of these things which rub together, with large surfaces, tend to work the oil out all the time. There ought to be some way by

which it should be retained where it is needed. I think this might be brought about. I use a good many "might be's," because it costs a good deal to build a machine; and, although we have a great many ideas, we cannot afford to carry out those ideas, until we get one which seems to be pretty nearly perfect.

Suppose we have a ring, which is rubbing round on a flat surface; of course there is a tendency all the time to rub out the oil. Now, I think if the face of the ring were spirally grooved, remotely like the stones of a grist-mill, the effect would be to overcome centrifugal force, which is all the time throwing the oil outward. This requires a good deal of nice adjustment, but with grooves in curves of the right form, and with rounded edges, the machine would distribute the oil evenly and retain it where it is wanted. It requires much study to get up a machine which will distribute the oil well and will wear equally, and I cannot say that we are prepared as yet to recommend any form as perfect in all respects.

QUESTION. Why not submerge your upper cone in oil?



Professor ORDWAY. That would be a very good thing if we could run it long enough; but the idea with most of these machines is to take a small quantity of oil, and run the machine ten or fifteen minutes; of course, if we took a large quantity, we should have to run it two or three days. We must either take a small quantity of oil and use it up, — that is, run for twenty minutes, or even twenty hours, until it has a chance to oxidize and impair its lubricating quality, and then consider the time that it remains efficient, or else we must use a larger proportion, and depend upon the heat evolved. If we could measure the heat very nicely, that would do very well. This machine pretends to measure the heat. Here is a little thermometer, which is supposed to register the heat which is developed by friction. If you look at it, you will see the utter absurdity of the thing. In the first place, the bulb of the thermometer is surrounded by confined air; there is a space between it and the bearing, and heat is communicated to it very slowly, as confined air is one of the best non-conductors of heat. The bulb ought to be immersed in water or mercury. This thermometer is of very little use. It gives an indication that bears no exact relation to the amount of heat produced. Then, in the second place, we have a very great mass of metal to take


and dissipate the heat. Here is a great box, and here is a great journal, that, in an ordinary experiment, produce a very small amount of heat. Still, that would be all very well if they were insulated so that we could measure what heat there is; but instead of being insulated they are in contact with this great mass, say fifteen pounds of metal, and the heat is being conducted and radiated away all the time. Thus the heat is diminished to such an extent that the thermometer will not indicate more than a tenth of what is actually produced. Then there is another thing: here is this other bearing very close to the one which is being tested. It is producing heat all the time, and there is nothing to show how much of the temperature indicated is due to it. The heat of all the bearings is communicated from one part to another, and spreads all through the machine in every direction. Moreover, when the machine is moving with a high velocity, the air is rapidly impinging against it all the time, and tending to cool it.

To make a friction-machine capable of acting as a calorimeter, we must surround the rubbing disks or cones with wool or eiderdown, and keep in the heat. This looks easy enough; but, in practice, a calorimeter of that sort requires a great many little contrivances before it can be made complete. What we want is disks, which should be insulated by wooden connections; and not only that, but the disks should be cut off from radiation, conduction, and the convection of the air; and then we might get indications philosophically correct. But with such a machine as either of those before us, there is nothing definite to go by. We find, in the first place, that there is a lessening of friction. Why? It is because heat is produced, that warms up the oil and makes it thinner, and then there is less friction. You come after a while to a balance; but the first effect, immediately after starting, is a diminution of friction. At the first start, when the oil is cold, of course the pendulum of one of the machines is drawn up a considerable distance. After a while it begins to come back again, because the oil is getting thin. By and by you get to a poise, and then, after running twenty or thirty minutes, it begins to come up again. If we could take off the box, put on more oil, and get the same result again, it would be very well; but that we have never been able to do. I don't think it is for want of care in the operator; I think it is owing to a defect in the machine, and I have more

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