DISCUSSION.

Mr. Chas. E. Emery.-I consider this paper a valuable contribution to our knowledge on the subject. It has been common for many of us to test the quality of steam by looking at an issuing jet from a gauge cock or other outlet, and it has been supposed that a comparatively small quantity of mist in the steam will change the character of the jet, but what that quantity was definitely we have had no means of determining before. It is a source of gratification to know that it is so small as practically to make it unnecessary to use a calorimeter when the test shows that the steam is dry. I feel grateful to Prof. Denton for having settled the question in so satisfactory a manner, and trust that the photographs presented may be framed and hung in the society's rooms where they may be consulted. The illustrations are good reproductions but the originals are necessarily more clear.

I will only add that many have observed that a very small quantity of refrigerating surface will cause inconvenience from water of condensation. I recollect that in the expansion experiments under the government we had the indicator set with exposed pieces of brass pipe only about eight inches long, but there was trouble all the time with water blowing out around the piston and wetting the paper, which was overcome by simply felting these short pieces of pipe. Referring to the remarks in regard to entraining water, I have of late years found that water lodging in the pockets of steam pipes will be carried along by currents of much lower velocity than I thought possible in former years. The Madison Avenue steam pipe in New York was 10 inches in diameter and about half a mile long, and run up a hill from the boiler house at a steep grade. In starting it to supply less than half a dozen houses I at first placed a trap only at the bottom of the hill, expecting that, with the very low velocity of steam which would be required at first, the water would all run back under the current of steam, but this action did not take place. On the contrary, the water would accumulate ahead of the current of steam until it blocked the pipe, so as to be periodically forced into one of the buildings at the end of a line on a side street, completely disarranging the apparatus, and it became necessary in that half mile of large pipe to put in two additional traps, which remedied the difficulty. I was also annoyed in one of the very large buildings supplied by the company with the statement that water occa

sionally came into the pumps and caused annoyance. It did not seem possible, but on examining the grade of the long pipe running through the basement to the rear it was found that the men had carelessly allowed it to sag in the center about an inch, and although the pipe was 10 inches in diameter and large enough to have carried steam satisfactorily for four times as much apparatus as there was in the building, the water in this little pocket would periodically be carried forward causing the annoyance referred to. (Applause.)

Prof. C. H. Peabody.-I would like to ask Professor Denton how much experience would be required in making tests of this sort in order to be able to judge the quality of the steam from the appearance of the jet? If it would be possible with a small amount of experience to determine whether the steam was nearly dry or whether it contained one per cent. or two per cent. of moisture?

Mr. W. H. Weightman.--If so small an amount as one per cent. of moisture is apparent in the discharged steam, I should like to ask the author of this paper what would be the effect of carrying on the experiment in a moist or humid atmosphere? Would such humidity have any marked effect upon the results or upon the appearance of the steam? Would the projected steam hold a condition and appearance of its own independent of the surrounding atmosphere, or would it be affected at once?

Mr. Geo. H. Babcock.-We are greatly indebted to Professor Denton for this paper, because it establishes with a sort of mathematical exactness certain things which we have heretofore assumed a priori; but we need to keep in mind that steam expanding from a high pressure into a lower, without loss of heat, becomes superheated, and that there would be a difference in the appearance of this issuing jet according to the pressure from which it is allowed to escape; that is, the higher the pressure the more the superheating, and therefore the drier it would appear at the point of issue. We could not therefore say that the same appearance which shows dry steam with 150 lbs. pressure would be required as proof of dry steam at 50 lbs., because there would be more superheating with the first, as is shown by Professor Peabody's paper on the calorimeter. In some of the earlier experiments with the Babcock & Wilcox boiler at the Calvert Sugar Refinery in Baltimore, Mr. Stillman used to take much pride in showing that the steam was dry. His method was to open a petcock and allow

the steam to escape, the jet being quite invisible for about two inches. He would then take a common match and light it by the heat of the steam in this invisible space, holding that there was no better proof of the steam being absolutely dry. It seems by Professor Denton's statement that that must have been dry steam; but it is also probable that it must have been slightly superheated or it would not have lighted a match; but that boiler had no superheating surface, and the steam in the boiler could not have been superheated.

Prof. Denton.-Answering Prof. Peabody's question I would say that I think a departure of one per cent. of steam from dryness cannot fail to be recognized by anybody whose attention is once called to this method. One per cent. will unquestionably show a decided difference between dry steam and a steam with that amount of moisture. But I have stated in the paper that when we go beyond two per cent. the method fails. If it is a fact, as I have allowed myself to assume-and I should like to be verified upon this point by men of long experience who are here-if it is a fact that moisture in steam always shows by irregular flowing, you cannot have priming of any great amount in a boiler without irregularity of action. It has been suspected that boilers give a great deal more moisture than they actually do. The moisture question has been made too much of. I believe that boilers that give a continuous gaseous flow of steam have dry steam. I believe that nine out of ten boilers will be found to give steam very close to dryness if they run regularly at all. If they do not run regularly the test will be off. Nobody will desire calorimeter discriminations to test a boiler that violently primes. The real test is to find when a boiler is doing much uniform work how much heat is to be charged to it. I think the distinctions are going to narrow themselves down to between zero and one per cent. in tests that are of any value.

As to Mr. Weightman's point, it is well raised. If that jet flowed into an atmosphere saturated, I think there would be a difference in its appearance. There generally is not much moisture over a boiler where a jet will be located. But the point is well raised. I have been looking, since the paper was written, for a foggy atmosphere, but when it came I could not use it, and the point is still open. Mr. Babcock's remarks about the superheating were also well taken. Of course, all the energy of flow goes into the jet, and it is superheated. Undoubtedly the difference of

pressure will affect the appearance, as he most correctly states, and for that reason I made the test at 55 pounds and 95 pounds, and showed jets during all conditions at those two pressures, and, as remarked in the paper, the 95 pound jet always tends more towards whiteness. There is a slight departure of the high pressure jets from the absolutely invisible color of the low pressure jets, but I am encouraged to believe from experiments for 55 to 95 pounds that no ordinary pressure would prevent the steam being still gaseous, and quite blue, and that whiteness would never show unless there was absolute moisture added to the steam.

Since writing the paper I have been troubled about one point. In cooling this jet it was all cooled at the surface; all the chilling that was done was done on the steam around the interior surface of the pipe, and of course it all clung to the surface of the jet. By looking at the jet with a magnifying glass this whiteness was a series of lines of white water hanging together and between them would be little strips of gas, the lines being so close together as to present a white appearance. Now, if the water emanated from the boiler, we might have the moisture similarly distributed in the jet; but it seems to be a fact that water in the jet tends to form a stream of its own; all the water tends to cling together.

Referring to Mr. Emery's point as to water being carried along with the steam, I am very glad to have the conclusions regarding Figs. 70 and 71 confirmed by his account. It appears that the velocity in the pipes will carry the water to an engine, and if we get a wet jet at any considerable distance from the boiler, we must not say that the boiler made the water, until it is traced clear back to the boiler.

Mr. Oberlin Smith.-I would like to ask what occurred when that drain cock was shut, and then the throttle valve was shut; did that make any difference in the jet?

Prof. Denton.-I did not try that particular experiment.

Mr. Oberlin Smith.-I should think then that the jet would still show white. If the water ran along the pipe at slow velocity, and was not allowed to escape, it would be carried out of the jet.

Prof. Denton.-I arranged a drum on the outflow pipe similar to that illustrated in the cuts although not large, and the jet was always white, no matter how thoroughly it was drained.

Mr. W. F. Durfee.-I would like to ask Professor Denton, if he has tried this experiment, whether there would be any difference