The next wheel may have an axle worn little or none. (See Fig. 28)

Now, if these brasses are exchanged, we have the conditions as shown
in Figs. 29 and 30, and we must expect they will heat. The remedy was
simply to keep each brass upon its own journal. To do this the brasses
were fastened to the axle by a piece of small wire, and went with it
to the lathe and press. When its truck was reached, the brass was
there with its journal. Worn-out brasses, of course, could not be put
in, and new ones were substituted. The little trouble from that source
that followed the change showed the efficacy of the remedy.

[Illustration: FIG. 29 and FIG. 30]

The manner in which the tires of engines were to be changed, when the
final day came, was a serious question. The old-fashioned fire upon
the ground could not be thought of. The M. & O. had used a fire of
pine under the wheel, which was covered by a box of sheet iron, so
arranged that the flame and heat would be conveyed around the tire,
and out at an aperture at the top. (Fig. 31.) Many thought this
perfect, while others were not satisfied, and began experiments for
something better. A device for using gas had been patented, but it was
somewhat complicated, as well as expensive, and did not meet with
general favor. A very simple device was soon hit upon. A two inch pipe
was bent around in a circle a little larger than the outer rim of the
wheel. Holes 1/10 in. in diameter and 3 or 4 in. apart were drilled
through the pipe on the inside of the circle. To this pipe was
fastened another with a branch or fork upon it. To one branch or fork
was connected a gas pipe from the meter, while to the other was
connected a pipe from an air pump. With the ordinary pressure of city
gas upon this pipe it was found that the air pump must keep an air