Statement of the case.

is larger than the same mass of iron when cold. Now here the molten iron was poured into the mould at the hub. Thence it flowed out through the sand mould of the spokes to the tread. There it came in contact with the chill, and as soon as it touched the chill it was cooled, crystallized, and reduced in volume almost instantly. The metal immediately behind it, on the contrary, being in contact with the sand, parted with its heat more slowly, and remained in a fluid or semifluid state much longer. Thus it happened that the periphery of the tread cooling and shrinking first, reduced its diameter, while the hub and spokes remaining in a fluid or soft state, presented little or no resistance to the contraction of the tread or rim. But as these spokes and

hub subsequently parted with their heat, and passed into the sólid state, an inherent strain began to be exerted between the rim and hub. The spokes were too short. Restoration of so much of their length as had been diminished by the

Statement of the case.

prior cooling and shrinking of the rim was demanded. All parts of the wheel having passed into the solid state, and become comparatively unelastic, the spokes were severed by mere tensile strain before the temperature of the whole mass was reduced to that of the atmosphere. And the same result followed when, instead of spokes, disks or plates were used on the sides of the wheel, as shown in Figure 3.

To obviate this effect, a rude practice was, on the one hand, to uncover and expose to the air the thick parts of the wheel, sometimes, in addition, pouring cold water on them; while, on the other, the thin portions would be covered with burning fuel or hot sand. Still, however, the wheel would always strain, and usually break.

The great matter now was to remove this difficulty. One plan was to divide the hub into sections, as shown in Figures 2 and 3, instead of casting it solid. This, of course, relieved the spokes from the tensile strain they were subjected to when connected with the solid hub; the spokes connected with each of the sections being left comparatively free to contract in length (only, however, it may be added) by carrying the section. of hub to which they were attached with them.

FIG. 4.

To restore the requisite strength to the hub, the spaces between these sections would be subsequently filled with pieces of metal of the exact size of the spaces, and wrought-iron bands would be shrunk on to each end of the hub, so as to hold firmly together all the sections, and the metal fillings or plates between them. Figure 4 illustrates the metal fillings or plates and bands that would be put into and on the hubs.

Wheels of this description were used till 1840. At that date our roads began to be made more substantial, and higher velocities upon them being demanded, the cast spokewheel, thus filled out at the hub, began to show great defects. The expense of filling the spaces between the sections was considerable. There was difficulty in putting the

Statement of the case.

wrought-iron bands on the ends of the hub and of boring out the divided hub so as to make it fit well on the axle and to secure it from becoming loose. Yet if these things were not effectually done, the wheel broke or changed its position on the axle, and the cars were thrown from the track.

FIG. 5.

To avoid these difficulties other means were employed to compensate for the unequal cooling and shrinking of the parts. These were nearly all confiued to making the hub solid, and connecting the hub and rim by a disk or plate, which was generally made double; two plates extending from hub to rim, in form convex, as in Fig. 5, or otherwise curved, so as to be susceptible, as was supposed, of contracting or expanding in diameter as much as would be required by the unequal cooling and contraction before noticed. In one of these forms the hub was also divided, as shown in Fig. 5, it being expected that with the shrinking of the outer disks it would about close up. These wheels, when skilfully made, were an improvement on the spoke-wheel, with

the hub divided into sections, so far as safety was concerned, but they were still faulty.

What, in this obviously not yet perfect art of making castiron car-wheels, was wanted, was some way to make such wheels, having a solid hub, and either spokes, or any desired form of plates, single or double, straight or curved, as represented in Figs. 6 and 7 below, and possessing all the requisites of durability and strength in the respective parts, and yet free from the defects which had attended, up to this time, all wheels yet made; and not requiring the expenditure of special labor upon the mould or pattern before casting, nor upon the finishing of the wheel for use, after it had been cast and cooled; some new and effective device which should eradicate and annihilate the difficulties which have been already imperfectly described, and which were still baffling manufacturers and inventors in this art. A new process

of

Statement of the case.

prolonging the time of cooling, in connection with annealing wheels would, if rightly conceived, secure the desired end.

It was in this state of the art and of its necessity that Whitney made a claim for what he called "a new and useful improvement in the process of manufacturing cast-iron railroad wheels," and on the 25th of April, 1848, obtained a patent for it, for fourteen years.

The specification in his patent was thus:

"My improvement consists in taking railroad wheels from the moulds in which they are ordinarily cast, as soon after being cast as they are sufficiently cool to be strong enough to move with safety, or before they have become so much cooled as to produce any considerable inherent strain between the thin and thick parts, and putting them in this state into a furnace or chamber that has been previously heated to a temperature as high as that of the wheels when taken from the moulds. As soon as they are deposited in this furnace or chamber, the opening through which they have been passed is closed, and the temperature of the furnace or chamber, and its contents, gradually raised to a point a little below that at which fusion commences,

Statement of the case.

when all the avenues to and from the interior are closed, and the whole mass left to cool no faster than the heat it contains permeates through, and radiates from the exterior surface of the materials of which it is composed. By this process all parts of each wheel are raised to the same temperature, and the heat they contain can only pass off through the medium of the confined atmosphere that intervenes between them and the walls of the furnace or chamber; consequently, the thinnest and thickest parts cool and shrink simultaneously together, which relieves them from all inherent strain whatever when cold.

"The figure below represents a vertical cross-section of the FURNACE OF CHAMBER, wherein is shown a pile, of wheels as they

are placed to be annealed. The cover of the furnace, being movable, is raised when the wheels are put in, and then closed and covered with earth, to prevent the too rapid escape of the heat. The damper in the flue leading to the chimney is also closed, after the wheels are put into the furnace, and the opening in the lower wall stopped by an iron plate banked with earth, which prevents the escape of the heat in that direction.*

There were other drawings and descriptions, not given by the reporter.