JONES, ROOT. 413
It will be seen that the machine is a Pappenheiin chamber-wheel train in which each wheel has two teeth. Eoot made the surfaces of the teeth at first of wood, afterwards of iron. His blower is constructed at various places, and is very extensively used ; there were several at the Vienna Exhibition of 1873. Eoot does not appear, however, to have been the first inventor of this chamber- wheel train, for it was used as a gas-exhauster (made by George Jones of Birmingham) in 185 9 5 * and does not appear to have been new even then. 6d
Fig. 2 is a section of a second form of Eoot's blower, in which
the profiles of the teeth are altered. As in the chamber-wheel
engine of Murdock already mentioned, the teeth have here their
points made with cylindric profiles, nr, so, u w, pairing with the
walls of the chamber. Each of these profiles extends through a
quadrant, i.e. through half the pitch, as does also each section m q,
pt,vx, of the circular profile of the root cylinder with which the
points of the teeth work in contact while crossing the line of
centres, m q therefore slides upon nr, uw on v x and so on.
The profiles pn>mo, &c. of the flanks of the teeth are here curtate
epitrochoids of the rolling pitch circles. The profile m o is described
by the motion of the point n of the wheel b relatively to the wheel
a, these therefore work together as the wheels move as indicated
by the arrows. Eoot does not use exactly the profile thus found,
but a profile falling behind it in the wheel, and this is quite
justifiable. He sacrifices the second point of contact certainly,
but at the same time he avoids the alternate exhaustion and
compression of air which would otherwise occur in the space left
between the two points of contact. The exact profiles are only
shown in the figure for the sake of simplicity. In designing the
wheels they have in all cases to be found, in order to determine
the limits within which the actual profile can be drawn. Of Eoot's
two arrangements the first is the better, for it delivers a uniform
stream of air, which the second, for the reasons mentioned in
connection with Fig. 1, PI. XXXIIL, does not. In both of them
the volume of air delivered per revolution very nearly approximates
to that of the tooth-ring cylinder.
- Clegg, Manufacture of Coal Gas, 5th. Ed., 1868, p. 181. The engraving
given here shows wheels of a profile absolutely identical with that of Root's wheels.
