Page:The Kinematics of Machinery.djvu/435

 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.

given here shows wheels of a profile absolutely identical with that of Root's wheels.
 * Clegg, Manufacture of Coal Gas, 5th. Ed., 1868, p. 181. The engraving