a rivet gets red hot under a steam boiler. In reading this paper I thought the main object of the author was to settle a long dispute between the fire-tube and the water-tube boilers, as to which of the two boilers had the more heating surface. Another thing he wanted to impress upon our mind is that it is necessary for a manufacturer to know the heating surface of a boiler before he can know what he is getting for his money; and one would infer that the man who buys a boiler with the greatest heating surface gets the most for his money. Now I differ from the general way of looking at these things, that the heating surface of a boiler is everything that is required to show its merits, and I want to tell a little story in connection with this which will make my reason plain. A little boy who lived on a farm took a great interest in raising chickens. His parents encouraged him in this, built him a chicken coop, gave him some eggs and hens to start with. One day there was quite a fuss in the chicken coop, and the boy's mother looking over the fence saw Johnny was in the act of setting a hen upon some eggs. His mother said, “What are you doing, Johnny?” He replied, "I am trying to set this old hen." Why, Johnny," said the mother, "you've got too many eggs. Let me see; you've twentyfour there; why, thirteen are enough." "I know that," said Johnny, "but I want to see the old hen spread herself." Now, there was a larger heating surface in the twenty-four eggs than in the thirteen, but of what use was that, seeing that the heating capacity of the hen was only equivalent to thirteen eggs? and I believe that boiler men are running somewhat riotous in the direction of heating surfaces of boilers, and not paying as much attention as they should to the heating surface that can be applied to a boiler. It is results that manufacturers look for, and one of the most economical things I know of in this direction, that of obtaining results from a boiler, was what I saw on the other side of the water, where they had a heating furnace applied to a boiler (one of our well-known water-tube boilers). They fired this furnace by hand, and the results they obtained were as follows: weighing the amount of coal they consumed and the quantity of water they evaporated, they found they evaporate eight pounds of water to one pound of coal; and the boiler gave its full rating as to horse-power capacity, and at the same time heated the material in proper shape to roll. This I think is the basis upon which boilers should be bought.

Mr. Suplee. I think Mr. Baker is in error as to the small value of circulation. The ordinary method in the laboratory of determining specific heat is to heat a piece of metal and put it in water. We heat a piece of metal of a definite and known weight. We plunge it into the water and we note the rise of temperature of the water. Now it is utterly impossible to get correct results in determining specific heat in that manner unless you have an agitator; and the laboratory instrument for that purpose is made so that the water can be agitated rapidly and the temperature can be noted to rise until the water has circulated and practically every particle of water has come in contact with the metal. Lately Mr. Yarrow has made a number of experiments which were presented, I think, before the Institute of Naval Architects in London, concerning the effect of circulation on his water-tube boilers, and there, by the introduction of diaphragms in the lower drums and delivering the water into the outer rows of tubes under pressure, he succeeded in increasing the evaporation very materially by forcing the circulation. I think the figures rose to three, four, possibly five per cent. in the result, according to whether he assisted the circulation or allowed it to work out its own salvation.

Mr. W. W. Bird.--With regard to the question of the temperature of that part of the shell of a boiler which is exposed to the fire, I would say that from observations made in connection with experiments with various devices for preventing smoke, we have concluded that not only is the surface of the shell on the outside at about the temperature of the inside, but that there is a film or layer of gas in contact with this surface which is also at a comparatively low temperature. A small rod was introduced through a piece of pipe which protected the rod so that only the end was exposed at the desired point, and in this way a rough estimate was made of the temperature in different parts of the furnace, with the conclusions as stated.

Mr. LaForge.-There seems to be one view of this matter which has been left out of the discussion altogether. It is a well known fact that a water tube boiler, or a plain horizontal tubular boiler, will run but a very short time before the upper side of the water tubes is covered with a certain amount of ash, and the lower side of the return fire tubes are carrying a certain amount of ash in the bottom. Now, what proportion of

these tubes is it proper to consider as heating surface? In illustration of this point, I will state a little experience that I have had with a Hazleton boiler, which may be of interest. The boiler was running under about 125 pounds of steam, when a six inch nipple blew out of its upper head. After the boiler had cooled down, I found that the water showed in the bottom of the glass water gauge, but on examination I found that the water had been out of two or three of the lower rows of tubes, the bottom side being burned, but where the ashes lay on them they seemed to be all right.

Prof. S. W. Robinson.—I think that attention should be called to this matter of strength of red hot rivet heads. In calculating the strength of a boiler we allow certain metal to resist the pressure, but I do not think it is customary to take that resistance on red hot metal. If the metal gets red hot for a considerable distance along a seam it would be very likely to fail, since there is a considerable strain under two or three hundred pounds modern pressure of steam. I think it would be rather dangerous business for people to be around in the neighborhood of a red hot boiler. I think a boiler should be so constructed that the metal sheets will not become red hot, on this score alone, of strength of the shell of the boiler.

Mr. Henning. Those cracks always occur on account of some previous defect of the material, either by punching or drifting, or by caulking the edge, but they do not occur on the water side of the seams except in rare instances, but they occur in a great many cases on the fire side. That is such a well known fact, that if you look into any locomotive boiler (I don't care whether it has been in service two weeks or two years) you will find some cracks. If the boiler is heated up in the shop just for a trial you will find some such cracks. Whether the sheet has been wrinkled or the hole has been drifted or simply punched without reaming, you will always find those initial cracks. I have seen some few on the water side, but that was due to bad workmanship which should not have been tolerated. But the contact of fire with the sheets develops those cracks, and it is such a well known fact that I did not think I ought to bring it up in connection with the present paper, because I was simply talking of the conduction of heat from the surface through the sheet. I did not mean to say that the fire really caused those effects, but the fire simply developed them. But I

do not want it understood that I said that those cracks were initiated by the heat. They are initiated by bad workmanship mainly; sometimes by bad material, and the heat on the fire side of a double seam like that develops them.

Mr.Jas. McBride.-Since the discussion has turned upon cracks, perhaps some of the members would like to know when they do get a crack of that kind how to close it. In a couple of boilers I have, there was great trouble with the fire box sheets cracking. They would crack from the rivet out to the outside edge, run in on the sheet as much as two inches, and leak very badly. Of course it would be very expensive to throw away the fire box, so I repaired it in this way (Fig. 145): I drilled the rivet out, which of course goes through the two sheets. I took the rivet out, reamed the hole out true, and tapped it with three-quarter inch pipe tap. I plugged the hole and drilled another hole here, plugged it with a soft steel plug, and on each side of this, drilled another hole about a quarter of an inch into the first one. I continued that process until I had drilled out all of the crack, out to the edge of the sheet. Those holes all tapped with half

inch pipe tap and a soft steel plug screwed in as tight as it could be screwed, the square head was then sawed off true on the outside. Into each of these plugs I drilled a three-eighth inch hole. I did not drill through the plugs, understand, but nearly through and reamed them, tapering. I then made tapered pins of steel, and drove them into the plugs as hard as I could drive them, and have never had a leak since. I fixed four or five cracks in that way, and they are perfectly tight.

Mr. Henning.-I would like to give a little simpler method of doing that, which is the rule adopted by the French railroads. If you see a crack on the inside of a rivet, drill a little hole at its end and put a little plug in and caulk the crack either side of the rivet. If you can get on the inside, do the same thing there. But it may become necessary to put a patch on the whole business. But the first thing is to stop the crack by drilling a smooth, round hole, and then it won't continue.

Mr. LaForge.-I would like to ask you how much stronger it is after you do that than before.

Mr. Henning. It is not a matter of strength. There is always an excess of strength in the seam, so that that is not the question. Of course a boiler is always weaker when it has cracks. Therefore, when the crack gets very bad a patch is put on it.

Colonel Meier.-I will say that I do not believe any such cracks ever occurred from bad workmanship or from the heat. It was no doubt bad material; for which reason, when I find a number of cracks like that occurring (referring to blackboard), though I think that is a very skillful and very ingenious method of repairing-but I take such a sheet out and condemn it, because I know that the material of the plate is worthless. I do not believe any cracks have ever occurred, even where the sheet is simply punched, where the material was of the right sort, and with the kind of steel that we can get for boilers in the United States, there is no excuse for it. It may be different in

France.

Mr. Henning.-I was talking of Otis steel, which I believe is pretty good.

Colonel Meier.--I think that is a grave mistake to buy steel of any kind by the brand. It should be bought from specifications, and subject to careful tests. I know that unless you test your steel, not only physically but chemically, you are never sure