| Root boiler | 721,390.8 | units |
| Allen boiler | 1,178,404.5 | „ |
| Phleger boiler | 378,371 | „ |
| Lowe boiler | 692,055 | „ |
| Blanchard boiler | 268,707 | „ |
The same Bulkley pyrometer was used in all the furnaces to indicate the temperature of the escaping gases. On Tuesday morning, when my boiler was to be tried, I saw that before my arrival the pyrometer had been set in the brick chimney, where the readings could be conveniently taken by a person standing on the brick surface of the boiler chamber. Its readings averaged 260 degrees Fahrenheit. I did not believe this to be true. At about half-past two o’clock, when seven readings had been taken, one each half hour, having got ready some bricks and mortar and tools, I pulled the pyrometer out and filled up the hole. I then knocked a hole in the side of the brickwork at the bottom, in front of the flue, and set the pyrometer there. The reading rose to 405 degrees, which was the temperature at which the gases then entered the flue, and averaged about 385 degrees during the remainder of the sixteen readings. Root’s average was 416 degrees, and Phleger’s (also tubular) averaged 503. Obviously the readings taken before the pyrometer was moved should have been rejected; but the boys who did this kind of work added them all together, and our average temperature is printed 345.87 degrees, giving the boiler more credit than it was entitled to by about 40 degrees. I lost a little by this operation. While I was bricking up the hole the fireman came around and told me I was spoiling his fire. When I got the figures of water evaporated and coal burned, I found that in that half hour I had only 900 pounds (three barrels) credited to the boiler, instead of 1800 pounds (six barrels) during every other half hour, being a loss of about .023 in water weighed in the barrel, 38,400 pounds, instead of 39,300 pounds, while, curiously enough, the coal burned was rather increased.
The point of interest in this incident was the fact that the gases had lost 125 degrees of heat in traversing a distance in flues and chimney of less than 20 feet. This seems difficult to believe, but they did. There was no leakage as the excellent draft clearly proved, nor any other way of accounting for the discrepancy. The length of the pyrometer tube exposed to the heated gases was the same in both positions. The heat had been lost by radiation through the brickwork. I have been waiting ever since for a chance to turn this knowledge to useful account, but it has not come yet. I will content myself with suggesting to somebody else the idea of facing the boiler setting, flues and chimney, not only outside but inside also after leaving the furnace, with white encaustic tiles, which will neither absorb nor radiate heat appreciably. This will pay in maintaining the temperature in a large degree to the top of the chimney, so increasing, perhaps doubling, the strength of the draft. An enormous amount of heat must be lost through the extended surface of the brick boiler setting. It is always observed that the hotter a boiler-room is kept the greater the efficiency of the boiler becomes. This is a slight indication of the great gain which might be effected by the plan I propose.
Before this boiler trial we had lost Mr. Allen. He had conceived the idea of the pneumatic riveter and the high-speed air-compressor to furnish this riveter with power. In the latter he utilized the inertia of the reciprocating parts, including two pistons, the steam and the air piston. This he did with my cordial consent, and indeed there was nothing patentable about that feature anyway. Mr. Allen thus became the originator of the important system of pneumatic riveting, in its two methods, by percussion and by pressure. Mr. Allen sold out his stock in the engine company to Mr. Hope and Mr. Smith, and built a shop in Mott Haven for the manufacture of the riveters and compressors. He took the boiler in the fair in part payment, and sold it directly to a party who had erected a wood-working shop at some point on the Harlem River.
The Croton water which had been fed to the boiler contained no lime, but some sediment. Mr. Allen had the boiler taken down and brought to our shop for inspection and cleaning. I determined to improve the opportunity to observe the effect of the circulation on the deposit of sediment, and the result of the examination proved most interesting. Each inclined tube had been provided at the end with a brass plug, by removing which it could be cleaned by the running out of the water which it contained. This had not yet been done.
I took out the tubes on one side of one section, ten in all, five over the furnace and five behind the bridge wall, and planed them in two longitudinally, and had the following revelation: The tubes over the furnace were entirely empty. In those back of the bridge wall a deposit of sediment appeared, only about an inch deep in the first one, and increasing regularly to a depth of 18 inches in the last one, which was not the tube receiving the feed-water. So the water fed into the last tube of each section deposited its sediment most largely in the first tube it reached, in which the circulation was least active, and had deposited it all before reaching the tubes over the furnace. The remaining long tubes were then cleaned, the tubes cut in two were replaced by new ones, and the boiler delivered to Mr. Allen. The next stage in its history was very funny. The purchaser, to save the cost of Croton water, fed his boiler from the Harlem River, and within a month it was found to be filled solid with salt. What was done about it I never heard.
I thought I could sell the boilers where, as in New York City, they could be fed with water free from lime, and I made a few such sales, but the inspiration which led me to employ the second drum for superheating the steam had deserted me.
I came to the conclusion that by making the first drum a large one, and not extending the nipples into the drum to trap a puddle of water, as I had done, I could superheat the steam in one drum. That was a blunder. I had underestimated the furious circulation, which carried a large amount of spray into the drum. I was misled by the quiet position of the water-level, as always shown in the glass gauge. Instead of superheated steam, I found the boiler to give very wet steam. That fault, of course, I could have remedied by returning to my first design. But I was discouraged by other things. The first, of course, was the impossibility of removing scale by any mechanical means. The most serious discouragement was a cracked header. The inclined tubes, on any plan for their use that I could then design, made cast-iron headers necessary. I had taken great pains to obtain perfect castings, making them of the best iron in baked molds in iron flasks, of uniform thickness, ⁵⁄₈ in., and ³⁄₄ in. where threaded, with cores held perfectly central and remarkably well vented, and felt that I could rely on their soundness; but this defect showed that I could not. So reluctantly I abandoned the manufacture of the boiler.
I believe, however, that there is yet a future for the inclined boiler tube, with independent circulation in each tube, the whole made entirely from forged steel; and that better results will be obtained from it than any other form of boiler has as yet given. I have been told by Chief Engineer Melville that all water admitted to the boilers in the United States Navy is made pure enough for pharmaceutical purposes. If this can be done in the navy, where sea water and the mud of harbors have to be used, it can be done anywhere. Cooling towers make it practicable to return all water to the boiler even from non-condensing engines. Then only the waste needs to be made good, and any water can be purified for this purpose. Oil or grease with the feed-water is readily avoided. Only electrolysis remains to be provided against, which can be done by avoiding the use of any alloy of copper in contact with the water. We may then have boilers of the most durable character and safe to carry any desired pressure.
The following incident near the close of my experience in Harlem would be too ridiculous to print except for its consequence. One day Mr. Smith sent me word that he would like to see me in his office. When I entered he asked me, “What do you pay for the castings of your governor arms and balls?” Of course he knew perfectly well, as he had the bills and the books, but that was his way of introducing the subject. I replied, “Forty cents a pound.” He held up both hands in affected amazement, and exclaimed, “Forty cents a pound! Well, sir, I can assure you of one thing, no more of this company’s money is going to be squandered in that way.” I overlooked his insulting language and manner, and said quietly, “Are you sure, Mr. Smith, that you have all the information you need to form a correct judgment in this matter?” “I am sure,” he replied, “what the market price is of copper and tin, and that I can get castings made from our own metal at a price that will bring the cost to not more than 25 cents a pound.”