In all well-regulated boiler shops, whether the plates are manufactured on the ground or bought from the steel makers, the tenacity of every plate used is known, and the number of that plate registered. Provision is also made for obtaining the analysis of the cast from which those plates were made if necessary. Generally the facilities offered by plate makers for testing and examining surfaces are adequate. The author has known the plates for 200 locomotive boilers to be delivered, and every plate worked up. The plates rejected during inspection for high tenacity, short elongation or bad surfaces were comparatively few.

The quality of the plates used in the boiler practice of to-day is that known as the "best mild steel," of an ultimate tenacity of not less than 26 tons per square inch nor more than 30 tons per square inch, with a minimum elongation of 20 per cent, on an 8-inch bar. Generally the tenacity of plates made by well-known firms ranges between 27 and 29 tons per square inch, and 25 to 32 per cent, elongation, although plates are known with a minimum of 24 tons per square inch with an elongation of 32 per cent.; the above results being upon teat bars taken from the direction of the rolling. The tests from the opposite direction may, and often do, approach the lengthway for tenacity and elongation; but an average of fifty crossway tests, taken at random over a period of six months, gave 27.25 tons per square inch, and an elongation of 25 per cent, on 8 inches.

Regarding the chemical analysis, the plates must be free from silicon, sulphur and phosphorus. The analysis is generally found to be: - Carbon, about .16 to .18; silicon, .01 to .018; sulphur, .03 to .05; phosphorus, .02 to .04; and manganese, .25 to .48. All plates must be rolled truly to a uniform thickness, and both sides must be free from pitting, scale, dirt, lamination or other defects. After shearing, boiler plates must be annealed, and in no case must they leave the mill floor until all buckling is taken out, and they are sufficiently level and true for machining. A boiler shop is never absolutely free from this, lifting and transit always causing unevenness in plates, which is dealt with later on. The maker's name and test number must always be stamped upon the plates about 12 inches from each edge, at one corner, and to facilitate inspection this is encircled with a white paint mark. From the appearance of the surface and the edge of the plates it can be seen at a glance whether they have been annealed or not. Test strips, after being heated and cooled in water at about 80° F., should bend to a curve, the inner radius of which is one and a-half times the thickness of the plate. It is generally found that the majority will more than satisfy this test, bending down flat upon themselves. Drifting tests are made periodically upon strips 3 inches wide, in which ⅝ inch holes are punched, and afterwards drifted cold until they reach l« inch diameter. Some specifications stipulate that the plates are to he made from ingots hammered upon all sides, which gives a more homogeneous material, cogging being equally good.

The modern boiler shop is replete with first-class tools, and the template is used throughout, consequently the finest material is used to its best advantage, and the modern boiler is almost a perfect work of accuracy. Angle iron, etc., is nearly dispensed with, being replaced by hydraulic flanging; circular flanges are turned and the edges of all plates are planed. Almost all the rivets are closed by hydraulic pressure, and are of the best quality. It is generally admitted that rivet steel should be of the toughest material, so that test specimens should bend through an angle of 180°, and close down upon themselves when cold, without showing a crack or flaw. The tensile strength should be from 24 to 28 tons per square inch, with 25 per cent, elongation on 8 inches, and 45 per cent. contraction of area, and showing good tough silky structure. A tenacity of 26. 5 to 27 tons per square inch is sufficient, because the mechanical work put into the material in making the rivet, will increase its tenacity in some cases from 2 to 4 per cent. The metal must further be capable of going through the various processes of manufacture without serious abrasion and cracking. It should flow well in riveting, and the heads of test samples should admit of being hammered down to ⅛ inch in thickness without fracturing the edges when hot. The carbon should not be more than .15 per cent, and the phosphorus .04, although some American specifications admit of phosphorus .07.

Whenever the term "best iron" is used, it must be understood to be a well-known brand, and the qualification "best mild steel" infers an established firm; although, perhaps, lately the testing machine has done much to show up the good quality material made by small firms. Whenever the word "or" appears, it is to be distinctly understood that only one or the other item would appear in a specification. A modern shop may be conveniently built in three bays, the one containing the various drilling, planing, punching, shearing and bending machines, suitably situated in order to carry work forward as much as possible. The larger machines, at which heavy work is done, are provided with jib and lifting tackle. The second, or central division may be devoted to the marking of plates, the fitting together of the sheila, and the general erection of boilers; whilst the third hay may take the general repairs. The angle smiths and hearths for welding internal flues, domes, etc., are placed in a smithy immediately adjoining the boiler shop. The hydraulic riveters attached to jibs of various rake, should be conveniently placed for the work they are required to do, as also the pumps and accumulators. The shops should also be fitted with the necessary pressure and return piping from the accumulator to the various hydraulic machines, whilst a narrow-gauge tramway should serve the machines and heavier portions of the work. Convenient pits should be made for certain machines, to facilitate drilling flanges and foundation rings, although the specially designed flange-drilling machine has rendered them less necessary. Pits are also required for certain punching machines, multiple drills, riveting, etc, and are convenient for fullering the foundation ring and fitting on the roof bars. Each hay should be traversed from end to end by a 12 or 15-ton rope-driven crane. The rivet fires may be placed between columns, etc, wherever required.