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tion to this matter that would be desired. My assistant, Mr. Allbright, has continued the work faithfully, until he was called away to Chicago about two weeks ago. The work has been well done, I believe, and it has been confined mainly to a continuation of the same experiments that had been made at the time of the last Report; but, among other things, we have taken up the matter of the lubricating machines. We had a new machine made, differing somewhat from the former, and it was put into operation; but we found that the amount of power required was so great, that it would be necessary to wait until we could bave the whole power of the engine to use, instead of depending upon what little could be spared from the use of the other machinery. The machine was tried to a small extent; but it proved, as far as we did try it, to present no advantages over the old one. Another machine, which we had at the time of making the last Report, had not been mounted and tried; but we afterwards mounted and tried it, and it has proved unsatisfactory. Mr. Allbright tried it very faithfully; and then, in order to make sure that no points were overlooked that ought to be attended to, I sent him on to the manufacturer to learn from him, or rather from his assistant, just how they had used the machine, and what their results amounted to. I told him, when he went on, that I wanted him to stay there until he got three results with the same oil on one day that agreed with each other, and une result on a different day that would agree with one of those three, at least, or with the three. I told him to stay there until that could be brought about. He stayed something over a week, and saw no signs of bringing it about, and came home. I thought that a machine which was good for any thing, or good for much, should at least give three results with the same oil that agreed pretty nearly: we did not, of course, expect a precise agreement in figures. He obtained no new light upon the subject. He simply found that the manufacturer had made the machine on a theory. He had never actually tested it, to see whether his theory was absolutely correct. We could use the machine and get results; we could get figures very easily : but we are not satisfied with that. We want to get results which will be worth something in reconciling our experiments. The machines, so far as we have tried them, and we have tried three, do not give any results which can be depended upon at all. We get merely figures, nothing else. They do show one thing, perhaps, in a very rough way, - that, the more fluid the substance is that is used for lubrication, the more favorable are the results; and, in fact, with water, we got better results than with any other liquid that we used. I desire to say that this is a principle which holds in practice, — that the thinner the lubricant, the better would it be, if we leave every thing else out of account. But we must recollect that the thinner it is, the more rapid will be the evaporation, and the less time it will last. If we use water, we must keep up a continual supply; and if we use a thin oil, which is volatile, of course we must keep up a full supply of that. If the oil is thin, and volatilizes pretty rapidly, we must use a very large quantity. Hence we must take a medium between something which is very fluid and something which will not evaporate. Those things which will not evaporate are those things which are usually thick. If we take the mineral oils, which have a very high flashing-point, and which evaporate less than five per cent, on the exposure I have mentioned, we find they are very thick. They can be thinned by the use of a thinner animal oil, and I believe the best thing for the thinning of these thick, heavy mineral oils, is either sperm or neat's-foot.
We have not reduced the results to any scientific proposition, and we have no positive direction to give; but that seems to be the general result of all the trials that we have made so far. The vegetable oils are more prone to oxidize : they have a higher specific gravity ; they are not so thin, as a general rule, as animal oils. Sperm oil is the thinnest: neat's-foot comes next to it. Sperm oil has a special advantage, in that it does not oxidize so readily as neat's-foot and other animal oils; and, when either of these thin oils is mixed with a thick petroleum oil, we get something which has a reasonable degree of thinness. And yet the petroleum tends to retard oxidation: it retards it very much indeed; so that a mixture of equal parts of sperm oil and heavy mineral oil will of course have very low evaporation and a very high flashing-point. A mixture of that sort is probably the same, as far as oxidation goes, as a mineral oil. A very small quantity, even ten per cent, of mineral oil, tends to retard spontaneous combustion; and, of course, as spontaneous combustion results from the tendency to oxidation, we may say fairly that even ten per cent will retard oxidation in animal oil, so that there will be hardly any tendency to gum.
Then, as the result of our examination of the mineral oils that are in the market, so far as they have been sent to us, we find that most of them are very good oils indeed. We find once in a while one that has a low flashing-point of 240 or 250, and which will evaporate, say nine, eight, or seven per cent, on the exposure for twelve hours to 140° Fahrenheit. Any thing that has over five per cent, so far as evaporation goes, we think is not to be recommended. I think it will be understood, from what was said in the former Report, that neat's-foot oil, sperm oil, and other animal oils, have no tendency to evaporate when they are exposed to high temperatures. There is a slight increase in weight, owing to the oxidation: there is no evaporation whatever. In other words, these animal oils contain no volatile substance, whereas all the petroleum oils are volatile; but, when we come to those that are very thick, we have them volatile at so exceedingly high temperatures, that practically they are the same as fixed oils.
It would be very desirable to obtain a scientifically accurate and precise instrument for testing lubricating oil, as to lubricating power. Whether this is possible or not, I hardly know. Besides the three forms of machine that have been used, there have been others proposed, which, however, rest essentially on the same principle, I believe; and, as I said in the former Report, any machine which has a journal with a box around it, is not a suitable form, from the fact that there will be unequal wear. Two of the machines which have been used for our trials consist of a cylinder and a bearing above it, like that (illustrating on blackboard]. The journal of one is made of steel or iron, and the other of bronze. Now, if we could have this perfectly hard, – that is, incapable of any wear at all, — the tendency of that journal is to wear up into that bearing, so that in time we should have it in this shape. You can never have the machine twice alike, unless you rebuild it, and cut it out at certain points of its wear. But, on the other hand, it is absolutely impossible that we should have any thing which will not wear at all. If we take the hardest steel and have it rub against bronze, the steel will wear; and the result will be, both wearing, and the journal continually growing smaller, and the bearing continually growing larger, so that, instead of the round part touching all around as it ought to, it will, after a time, touch in that way. Of course, this is continually wearing up; but it is continually wearing smaller, and it never can touch except in one line. Well, perhaps that would not signify, if we could always keep this at right angles to the direction of motion; but we cannot. This line will swing round, and of course we have a harsh motion; and it is utterly impossible that any machine of that sort should work with any thing like smoothness; should not vibrate; and any vibration is fatal to a fair trial of the oil.
We have found considerable difficulty with the machines we have tried, in keeping the oil distributed on the bearing. If we have the bearing smooth, and the journal smooth, the tendency of course is for the oil to work out. Now, it is almost impossible to get one of these machines made true: it would cost a great deal of money to have it made absolutely true, and, if we had it, on account of the usual inequalities of the metal, it would be impossible for it to remain so. But suppose we have the journal horizontal, and the bearing over it true, and suppose there is a little hump near the end of the journal. Of course, if there was only that hump, and it did not tend to tip there, that would soon wear down; but the effect of the hump is that it carries the box a little out of the horizontal direction, and the consequence is that the box wears where the hump presses on it, and at the other end where the box presses on the journal; and so it will not hit everywhere exactly alike. There is a tendency to shake; there is a continual vibration, and the effect of the vibration is to cause very rapid wear. It will bring certain points of the opposed surfaces in direct contact, and there will soon be no grease where we want it. We want it on the rubbing points, and those are just the places where we cannot get it to stay. Of course, the longer the shaft and bearing are, the less will be the inequality; and we want to have those very long, not very short, as in the machine before us.
We have run this machine at about twelve hundred revolutions a minute. It consists of a steel journal, which slips on over the free end of the shaft, and is embraced by these brass boxes, which can be tightened by screwing up from below; and any pressure can be brought to bear, according to the strength of the spring inside. There are two or three springs, so that we can put on different pressures. We have tried fifty, a hundred, and two hundred and fifty pounds to the square inch. A screw at the bottom presses up against the spring, and the amount of pressure is shown by the index there. We can make the pressure greater or less. But there you see we have a round box, and that is continually wearing oval. Still it would do tolerably well, if there were vibration only in a plane, at a right angle to the line of the shaft; but there is also a tendency to vibrate in direction of the shaft, which certainly must be objectionable. But the maker says that an oscillation in the direction of the shaft is a characteristic of a rightly working machine. I cannot see it. It seems to me, that, in order to make that machine work right, it should be always true and steady lengthwise of the shaft, and only vibrate in the other direction.
You can easily see what this machine is intended to do. As the journal moves round, of course it produces friction on the box, and tends to swing the pendulum which holds the box; and the amount of motion is indicated by the index here. The scale is supposed to indicate the coefficient of friction. The oil is put into a small hole, running through the upper half of the bronze bearing. Now, we found, on mounting the machine, and running it a little while, that we got a certain coefficient of friction. Then we loosened it a little bit and put it back again, and tried it again, and we did not get the same coefficient. You cannot get the oil to distribute itself well, any way you can fix it. Then, again, this bearing, contrary to what I have already mentioned as essential, is very short indeed: it has a tendency to wear oval, and there is vibration in a direction in which there should be none.
At first sight, it looks as though that machine were very delicate and sensitive; but, when you come to examine into the points I have mentioned, it seems to me that the theory of the machine is decidedly against it, and certainly the practice is very decidedly against it. Suppose there is a slight place that is projecting on either the journal or the bearing : of course, that place must wear down, and, in wearing down, it has a tendency to make a jerking motion all the time. And it will not only wear that spot, but some other spots, and the consequent tendency is to make these bearings always irregular : they never can wear true, any way; they are growing worse and worse all the time.
In using this machine it was proposed to put a definite quantity of oil on the bearings. This whole box with the pendulum can be taken off very easily; it is convenient on that account,