sectional area required for each stay will be found as follows: 18,200 x 850,000 = 2.9 sq. in., and the diameter will be found as follows: 2.9+.7854 = 3.69, which is the square of the diameter, and the square root of 3.69 1.9 in., or practically 2 in. The same methods of calculation are applicable to the staying of the heads below the tubes, also for stay bolts in fire box boilers.

=

Strength of Unstayed Surfaces. A simple rule for finding the bursting pressure of unstayed flat surfaces is that of Mr. Nichols, published in the "Locomotive,' February, 1890, and quoted by Prof. Kent in his "Pocket-book." The rule is as follows: "Multiply the thickness of the plate in inches by ten times the tensile strength of the material used, and divide the product by the area of the head in square inches." Thus,

5/8 x 55,000 × 10+ 3,421 = 100, which is the number of pounds pressure per square inch under which the unstayed head would bulge.

If we use a factor of safety of 8, the safe working pressure would be 100 ÷ 8 = 12.5 lbs. per sq. in., but as the strength of the unstayed head is at best an uncertain quantity it has not been considered in the foregoing calculations for bracing, except as regards that portion of it that is strengthened by the flange.

In all calculations for the strength of stayed surfaces, and especially where diagonal crow foot stays are used, the strength of the rivets connecting the stay to the flat plate must be carefully considered. A large factor of safety, never less than 8, should be used, and

the cross section of that portion of the foot of the stay through which the rivet holes are drilled should be large enough, after deducting the diameter of the hole, to equal the sectional area of the body of the stay.

Dished Heads. In boiler work where it is possible to use dished, or "bumped up" heads as they are sometimes called, this type of head is rapidly coming into use. Dished heads may be used in the construction of steam drums, also in many cases for dome-covers, thus obviating the necessity of bracing. The maximum depth of dish, as adopted by steel plate manufacturers April 4, 1901, is % of the diameter of the head when flanged, and if the tensile strength and quality of the plate from which the heads are made are the same as those of the shell plate, the dished head becomes as strong as the shell, provided the head has the same thickness or is slightly thicker than the shell plate.

Welded Seams. A few boiler manufacturers have succeeded in making welded seams, thus dispensing with the time-honored custom of riveting the plates together. A good welded joint approaches more nearly to the full strength of the material than can possibly be attained by rivets, no matter how correctly designed the riveted joint may be. The weld also dispenses with the necessity of caulking, and a boiler having a perfectly smooth surface inside, such as would be afforded by welded seams, would certainly be much less liable to collect scale and sediment than would one with riveted joints. But in order to make a success of welded seams the material used must be of the best possible quality, and great care and skill are required in the work.

The Continental Iron Works of Brooklyn, New York, exhibited at the St. Louis World's Fair in 1904

a welded steel plate soda pulp digester without a single riveted joint. The dimensions of this vessel, which may be likened to a cylinder boiler without flues, were as follows: Thickness of plate, 3/4 in.; diameter, 9 ft.; length, 43 feet. The heads were dished to the standard depth. The safe working pressure was 125 It appears not only possible, but probable, that the process of welding boiler joints may in time supplant the older custom of riveting.

lbs. per sq. in.

CHAPTER II

CARE OF THE BOILER

Washing out the boiler-Duties of the boiler washer-How to pre pare a boiler for washing-How to clean and inspect the inside of a boiler-Fusible plugs-Advantage of manholes, giving free access to top and bottom of boiler-Responsibility resting upon the boiler washer-Necessity of keeping water column clean-Scraping the flues-Fire cracks and how to deal with them-Firing up and how it should be done-Danger in too sudden heating up of a boiler-Advantages of filling a recently washed out boiler with warm water-Connecting with the main header and the safest method of procedure.

Washing Out. In order to get the best results from the burning of coal or any other fuel in a boiler furnace it is absolutely necessary to keep the boiler as clean as possible, both inside and outside. In large plants the boiler washer and his helper are detailed to look after this part of the work, and while the job is by no means a very desirable one, it is at the same time a very responsible one, and much depends upon the thoroughness with which the work is done. In small plants, consisting of one or two boilers, the engineer generally has to attend to the details of the work himself, and no matter whether the plant be large or small, the engineer in charge is the man above all others who should be most interested in seeing that thorough work is done, not only as a matter of safety, but for the sake of his reputation as an engineer. The boiler that is to be washed out should be allowed to gradually cool for ten or twelve hours. It will then be in a condition which will permit a man to go inside of it

and do effective work, and no boiler can be thoroughly cleaned and inspected unless the boiler washer does go inside.

These remarks apply, of course, to horizontal tubular or flue boilers and water tube boilers having drums large enough for a man to crawl into. Some types of internally fired boilers are provided with man-holes, but the majority of them have only hand-holes into which the hose for washing out may be inserted.

After the water has been allowed to run out, the first step in washing out a boiler is to remove all the loose mud and scale possible by means of a steel scraper fitted to a long handle and introduced through the man-hole in the bottom part of the head. This will prevent the scale from getting into the blow-off pipe and stopping the flow of the water used for washing the boiler. If there is a man-hole on top, the next thing in order is to take the hose in through it and give the sides of the shell and also the tubes a good cleaning.

Sometimes it happens that where an exhaust heater of the open type is used, oil will find its way into the boiler and, mixing with the mud, will form a thick pasty-like substance on the sides of the boiler along the water line. This should be carefully scraped off and removed, as any matter containing oil or grease is a very dangerous thing to have inside a boiler.

After cleaning the upper part of the boiler, it should be inspected for loose braces or rivets. This can best be accomplished by tapping the parts with a light hammer. A solid rivet will give a clear metallic sound, and a little practice will enable one to easily detect the sound of a loose brace or broken rivet.

Signs of corrosion or pitting of the shell along the