neutralized by either chemical, galvanic, or electric combinations, or actions.

But there are methods of locating flues and tubes, or even fire-boxes and stays, in boilers, that cause more trouble, damage and expense than anything chargeable to elementary causes. The badly designed and proportioned boiler, clean or unclean, will seriously interfere with the generating of power, independent of all other conditions.

When tubes, or flues, are placed so near to each other, or to the shell of boiler, that they actually prevent circulation, and the separation of the steam and its free passage from the water, we have a mechanical difficulty before us insurmountable.

We do not wish to make an unreasonable statement, but we really believe that two-thirds of the boilers in use to-day have their tubes and flues too near together-too many of them for the diameter of shell; tubes too small in diameter for their length, where natural draught is depended on; while in fire box, or internally fired boilers, the water spaces are not only too narrow, but it is utterly impossible to clean them.

We will look at the arrangement of tubes first. The diameter of horizontal tubular boiler shells, now-a-days, varies from 30" to 96", and the lengths run from 10 feet to 24 feet. The tubes used are from 2" to 5" outside diameter. fire, of course, passes through the tubes.

The

A boiler with a 66" diameter shell is generally 16 feet long, and contains about sixty-six (66) 31⁄2" tubes-too many tubes by twelve, and too. long by 2 feet, for the best results. The diameter of tubes for the shell is all right.

It is not proper, by reason of natural causes governing the transit of heated volumes of gases, etc., to make tubes proportionate in length to their area. For example, a 5" tube should not be double the length of a 31⁄2" tube simply because it is double the area of the small tube.

Experiment and observation have taught us that, in doubling the area of a tube, the advance in length can only be 50 per cent., with economy in view, so that a boiler with a shell 96" and tubes 5" diameter should be 21 feet long-no more, no less-for the best steaming duty. In all boilers, tube or flue style, the tubes or flues must never be nearer the bottom of shell than Io", while the side rows of tubes should clear side of shell at least 4" (we are now speaking of boilers over 48" diameter). They cannot be cleaned unless this rule is observed.

In designing a 66" x 14 ft. tubular boiler 31⁄2" tubes, we would place the lower course of tubes 13" from the bottom of shell, and the side tubes 41⁄2" from shell. Tubes 13/8" apart measuring on a vertical line, and 15%" apart measuring across the horizontal. The top course is entirely above the centre of boiler; no steam drum, but a liberal

sized inside dry pipe, short, and placed near the front end of boiler; boiler inclines toward the front 3". A boiler constructed after the above design, properly set and mounted, will generate steam for an 80 H. P. engine without the slightest signs of priming, and there will be no more than fifty-four (54) tubes, and fifty-two (52) will give the power noted above; and the water can never be driven away from the bottom and sides. The tubes should never be staggered.

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Some of the steam drums placed on steam boilers are certainly ludicrous in the extreme. They are not only useless in preventing priming, but they act as condensers, render the boiler weak from the mode of attaching them, and are ungainly and a nuisance in handling. As generally constructed, they are about as useful as an ordinary quart measure would be in their place. A boiler that has enough water and steam space in its shell requires no steam drum, and it never will prime, to a noticeable degree, unless sadly overworked.

Priming is, we believe, caused, to a large extent, by a reduction of pressure and increased ebullition under that point of the boiler whence the steam is drawn. By this means, water is . carried into the very top of steam drums, and we have seen cases where the inside of a drum would be plastered with mud two inches thick, and not a particle of it on the tubes, or inside of

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shell, except, perhaps, a little in the immediate locality of the drum. A steam drum cannot be protected or jacketed so as to prevent the reduction of temperature and pressure below that of the boiler shell proper.

MAN-HOLES, STAYS, HAND-HOLES, SIDE SEAMS, CAULKING, ETC.

The use of cast iron man- and hand-hole frame, and plates should be discontinued. Our rolling mill engineers can do almost anything in the line of irregular forms at this date, and there is no excuse for using a metal entirely unfit for the details mentioned. About one-fifth of the boiler explosions almost daily occurring, can be traced to the use of cast iron in construction. We have seen man-hole frames on boilers carrying 80 lbs. pressure, that if actually tested, with a view to rupture, would break at 130 lbs. distributed in the same manner as the steam load. Let all builders adopt wrought iron for the parts here under consideration, discountenance this dangerous practice, and the record of boiler explosions will surely be smaller. When wrought iron is used for frames and plates, two man-holes can be placed above the tubes, in shell, with as much safety as one, each one say 11" x 15". The hand-hole in front head under tubes should never be less than 7" x 10", on a 66" shell boiler we would make it 9" x 12", the common

size hand-hole is of very little use in cleaning, never being larger than 5" x 7", the majority 4" x 6".

The head stays above the tubes should be continuous in design, with eye sockets and pins at the heads, the rods or bars separated in their length at the centre, and coupled and drawn together with taper keys, wired in position, to prevent displacement. The stays can then be taken out and examined when cleaning, an item of as much importance as any other part of boiler inspection. The bolts and clamps, or guards, for holding plates in position, must be large, the threads of bolts of the half V style to resist hard usage, while the clamps should be faced on feet and hubs. All boilers should be double riveted on the horizontal seams. Even with this precaution in construction, they are not as strong at the point of riveting as in the solid portion of sheet.

As for caulking, Connery's concave system will be of as much service in boiler making, in the matter of saving material and preventing accident, as any invention introduced within the last twenty years. Hundreds of good boilers have been ruined in caulking, and many a boiler maker has repaired his own work, knowing, after examination, that his caulkers were responsible for the damage. Machine tools must be used in preparing sheets, such as straightening, bending, flanging, drilling and scarfing, or planing,