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Instead of the numbers in the table, a tolerably near approximation to the true temporary elongation corresponding to each observed elasticity of the bar in minutes, might have been obtained by multiplying the number of minutes by .000847 inches, the length of one minute on the arc of a circle, the radius of which is 2.914 inches. This would give a result sensibly correct, especially for all numbers of minutes under sixty.

Sources from which the materials were obtained.-The materials on which the committee have performed the experiments detailed in this report, were procured from various sources, a considerable quantity having been collected previous to their appointment by one of its members, then making arrangements for a private course of investigations on several scientific and practical points relating to tenacity. Other specimens were voluntarily offered, or kindly supplied at the request of the committee by the different manufacrers, or other persons to whom application was made for that purpose. In several instances, more specimens of the same iron were furnished than will be found mentioned in the tables as derived from the same quarter; the whole number obtained being about 250, and the number tried about 150. As the aim of the experiments was the establishment of such practical truths as might be found generally useful in regard to the manufacture and employment of materials for steam boilers, it was not deemed necessary to enter into a minute comparison of the merit of different manufacturers from whom the materials were received, nor to limit the inquiry to any given number of specimens, or of trials on those. derived from each source. The reader will, however, be able to nstitute such comparisons as his curiosity may dictate, the tables

Observed elasticity.

Extension and recoil,

in inches.

furnishing all the facts, (as well as the name of the manufacturers when known,) which have been obtained by the committee, in regard to the origin and manufacture of the different specimens.

Among the names of those from whose manufactories specimens have been received are Messrs. Mason & Miltenberger, H. S. Spang & Son, Barnet Shorb, H. Blake & Co., and Shoenberger & Son, of Pittsburg; J. E. H. & P. Ellicott, and E. T. Ellicott & Co., of Baltimore; the Salisbury Iron Company, of Salisbury, Connecticut; Messrs. Yeatman & Woods, of Nashville, Tennessee; Mr. Massey, of Maramec, Missouri; R. Lukens, of Coatesville, Chester county, Pennsylvania; George Pennock, McWilliamstown, in the same county; Messrs. Grubbs, Lancaster county, Pennsylvania; Hardman Phillips, Esq., Clearfield county, and Messrs. Valentine & Thomas, Centre county, Pennsylvania. To Messrs. A. & G. Ralston, the committee were indebted for specimens of boiler, bolt, and railroad iron, of English manufacture, which served as means of comparison between the foreign and the domestic material; and from other importers they procured those of Russian and Swedish manufacture, for the same purpose. All the samples of American iron thus far mentioned were manufactured by the aid of charcoal. A single specimen furnished by Mr. P. Ritner, of Carthouse's Place, on the west branch of Susquehanna river, was made by smelting. with coke.

The specimens of boiler copper tried by the committee were obtained from the establishment of John McKim, Jr., & Son, of Baltimore. To the above and several other gentlemen, who were active in procuring the materials, and otherwise forwarding the objects of this inquiry, the committee are bound to offer their grateful acknowledgments.

Preparation and gauging of the specimens.-The experiments were made on materials in several different forms; and as the results are in some measure dependent on the circumstances now referred to, it seems proper to describe those several conditions, together with the method of obtaining the areas of transverse sections at the points of fracture.

As the greater number of experiments was, of course, made on materials manufactured expressly for steam boilers, the mode of preparing these is of most importance. The strips were in general cut, by shears, from the plates, about two or two and a half feet long, and one inch wide; and, with a view to determine the tenacity in different directions, they were cut either lengthwise, crosswise, or diagonally of the direction in which the plate had been rolled.

The tables will be found to indicate, in all cases where rolled iron is under consideration, the direction of the slitting.

On specimens of this kind trials were made in three ways. First, by finding and measuring the area of the smallest section, as the strip came from the shears, and placing it in the machine, applying force till that or some other section gave way. When not broken at the smallest section, the actual area of the point of frac

ture was ascertained approximately by measuring, after fracture, at a short distance on each side of the broken part, taking care to keep just outside of the constriction or part sensibly diminished by the strain. After thus determining the area, previous to trial, a portion of the bar was replaced and other fractures made, until the specimen had been used up. Fractures on bars tried in this manner are referred to in the tables as made at original sections. But as the slitting of bars in the manner described necessarily caused some diminution of strength along the edges, and as from accidental causes this diminution was often very unequal, it was apparent that the irregularity in the strength might frequently be greater than that in the breadth of a strip. To ascertain the mean effect of the shears on bars of this breadth, the second method of trial was adopted.

This consisted in filing away a section of the metal on each side of the strip, in the form of the segment of a circle. At different points these sections were filed to different depths, with a view of ascertaining how far beneath the surface the metal had been effected. The scale of oxide was also in some cases filed from the surface; but, in most instances, where the rolls had left the iron. tolerably smooth, it was thought best to take the measurements of thickness, as they must be taken in practice with the surface in its natural state. In some instances it will be found that the fractures did not occur in the filed section, even when a considerable portion of the whole material had been filed away. In general, however, about one-eighth of the breadth of the bar being removed by the two opposite sections, the sound part of the metal was attained, and gave results nearly proportionate to the areas of the remaining sections.

But as neither the rolling nor the hammering of iron can give a perfect uniformity of structure, and as, consequently, the results on very deeply filed sections would not always prove uniform in their indications of strength, it became necessary, in order at once to remove the irregularities proceeding from the slitting, and to compare the advantage of different modes of manufacture and different kinds of metal employed, as well as to ascertain the maximum and the minimum strength of the same bar at various temperatures, to employ the third method of preparation, that of filing away the edges of the inch bars until they were reduced to three-quarters of an inch in width throughout their whole length, and also removing completely the scale from both faces, and rendering the thickness as nearly as possible uniform throughout. The bars treated in this manner were next divided through their whole length into spaces of one inch each, marked across with a steel point, numbered at every inch, and subsequently gauged at every mark, both in breadth and thickness. In these measurements, as well as those applied in the two other methods of preparation, the gauging was carried to thousandths of a lineal inch in both directions, giving the areas true to millionths of a superficial inch.

Plate II. represents the apparatus used for this purpose and a

portion of a bar prepared for gauging. C is a pair of proportional callipers of brass, pointed at a a with steel. S is a screw head projecting half an inch above the face of the instrument, and is onethird of an inch in diameter, being a trifle less in length than the thickness of the two arms of the callipers. The distance St is ten times that of S a, so that the space between the points a a is read in tenths, hundredths and thousandths, when that between t ton the diagonal scale D is found in inches, tenths and hundredths.

Specimens of hammered iron, and of iron formed into bars by rolling and slitting, were tried with a view to certain comparisons, and in these cases, all the three modes of preparation applied to specimens of boiler iron were likewise employed.

In a few instances specimens were received from the manufacturers in a form which required no alteration before trial; but in the majority of cases they were to be either slit, or hammered and filed, to adapt them to the purpose of these experiments. In the treatment of boiler iron, heating before trial, was, with few exceptions, avoided. The tables will be found to contain a few experiments on up-setting, annealing, and hammer hardening. They will also exhibit a very limited number of trials on cast iron and steel; but as these materials enter sparingly into the composition of steam boilers and as their tenacity has been, formerly, much more extensively examined than that of boiler plate, it was not considered within the purpose of the present investigation to do more than present a few verifications of the correctness of those results on which practical men commonly rely.

The bars of cast iron were tried as they came from the mould, or with very little filing to remove the irregularities of the surface. The specimens of copper were all reduced, by filing, to a good degree of uniformity, and gauged as already described.

At the foot of each column of original areas in each bar, gauged throughout its length, will be found the mean area; and under areas of "sections of fracture" are the mean areas of the points. broken.

Apparatus for high temperatures.-The general arrangement of the parts of apparatus, expressly designed for experiments at the highest temperatures, is represented in plate I., where F is the portable furnace for charcoal, suspended by an iron ring which is fastened on near its upper edge, and attached by means of pins on the opposite sides to the two ends of a semi-circular fork on one arm of the lever x. The weight of the furnace and its contents is counterpoised by the weight c. About the centre of the lever is a slit 6 or 7 inches long, through which passes the end of a screw suspending rod. The nut belonging to this screw is furnished, on its upper surface, with an elevated ridge, serving the purpose of a knife edge, which applies, at pleasure, to any one of several transverse notches on the under side of the lever along the slit. This serves, for the time, to fix the lever, and to prevent its sliding endwise, unless when lifted from its bearing.

As this nut revolves freely on the screw, a horizontal motion about the screw as an axis is readily given to the lever, while to

raise or lower the furnace in order to regulate the temperature, the knife edge on the nut affords ample facility. The top of the furnace rises between the two guide rods s, s, and between the two iron blocks b' and b', within which the bar to be tried is confined. When not in immediate use the furnace is swung round beneath the beam of the frame M, and placed under the cap H, the pipe of which is supported on the end of the crane R, adapted for its reception, and passing into a chimney at g. The thermometer t, suspended from an arm projecting beyond one of the uprights which support the pulley p, is lowered when in use, into a bath of hot liquid, through which the specimen under trial passes, as described below. The details of the arrangement are seen in plate III., where a plan is given of so much of the machine as may be necessary to comprehend the manner of fixing the bars and applying the heat. In plate IV. a vertical section through the length of the bar is exhibited; the references in both these plates being, so far as they apply to common objects, the same as those in plate I. Thus in plates III. and IV., i', i', and i", i", are the straps of iron connected with the blocks b' and b", which by means of their projecting arms repose on the two guide rods s, s. F is the furnace, t the thermometer seen immersed in the bath of hot liquid B, and x is the lever supporting the furnace. The bath is composed of an elliptical copper or sheet iron cup, 4 inches long, 3 wide, and 4 inches high, with two lips or channels in the direction of its shorter diameter, each one inch deep and the same in breadth, to admit the passage of the bar through them, and to contain the packings w, w, adapted to retain the hot liquid, and cause it to cover the bar a. These channels extend each about one inch beyond the sides of the cup, affording room for the straps y, y passing beneath them and rising on each side, near the tops of which are placed two cross heads c, c, and through these pass the tightening screws n n, employed in pressing down the packings w, w. The manner in which the bars are held by the blocks b', b" is seen at w, w', where the dove-tailed form of the holes into which the wedges pass, and the arrangement of teeth on the steel face of each wedge are particularly indicated. In adjusting the bars in their place for these experiments, it became necessary to form perfectly secure joints at w, w, where they pass through the channels beforementioned.

In most of the experiments below 600 degrees, this was effected by means of loosely spun cotton wrapped about the bar, for an inch at each point where the screws were to be applied. For temperatures above 600°, a packing formed of fibres of iron scraped from wire in the manufacture of weavers' reeds was adopted. This being formed into mats and rolled in a powder of oxide of tin, constituted an impervious barrier to the melted metal, particularly after being duly settled and condensed intò place, and then firmly compressed by the screws.

Below 600°, the fluid commonly employed was olive oil, and for higher temperatures, a mixture of tin and lead. In some cases,

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