All About Engines
Forfatter: Edward Cressy
År: 1918
Forlag: Cassell and Company, LTD
Sted: London, New York, Toronto and Melbourne
Sider: 352
UDK: 621 1
With a coloured Frontispiece, and 182 halftone Illustrations and Diagrams.
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James Watt: The Man and his Work 39
steam could exert, he fixed a small syringe to the top
of a closed vessel filled with water and heater (a
Papin’s digester) and placed a weight on the top
of the piston. The piston was only J inch in
diameter, yet the steam lifted a weight of 15 lb.,
representing a pressure of more than 150 lb. per
square inch! Here was force enough, if only it
could be utilised. But when he had proceeded so
far he had to put his experiments on one side in
order to undertake work that was more profitable.
The Newcomen model (see Fig. 15) arrived in
1763, and gave Watt plenty of food for reflection.
It had a cylinder 2 inches in diameter, with a stroke
of 6 inches, and the boiler was about as large as a
kettle. The engine would only make a few strokes,
and then stopped, as though there was no more
steam. Yet according to the dimensions of larger
engines the boiler was of ample proportions for such
a small cylinder. By experiment and calculation he
ascertained the weight of steam necessary to fill the
cylinder and the weight of steam produced by the
boiler in a given time ; and he found that the boiler
was capable of supplying more than enough steam
for the engine.
There was evidently some source of loss here,
and it gradually dawned upon him that the cold
walls of the cylinder condensed most of the steam
that entered. This would be more serious in a small
engine than in a large one, because the surface of
cylinders of different size decreases far less rapidly
than the volume. The cooling effect of a small