Scientific American Supplement, No. 803, May 23, 1891Various
Science
Scientific American Supplement, No. 803, May 23, 1891
Various
Science -- Periodicals
It was while at Glasgow University, working under such influences and
in such an atmosphere of intellectual activity, that the accident of
the Newcomen model engine needing repair brought to the mind of Watt
the opportunity which, availed of at once, made him famous and gave
the world its greatest aid, its most powerful servant. The observing
mind of the great mechanic immediately noted its defects, sought their
causes, found their remedy. He discovered, at once, that the quantity
of steam entering the cylinder of the little engine has four times the
volume of the cylinder receiving it: in other words, three-fourths of
that steam must be condensed immediately on entrance. This meant,
evidently, that only one-fourth of the steam supplied was utilized,
and even then inefficiently, in doing its work. The reason of this was
as easily seen, immediately the fact was revealed. As Watt himself
expressed it, the causes of this loss, causes which would obviously be
exaggerated in a small engine, were: "First, the dissipation of heat
by the cylinder itself, which was of brass and both a good conductor
and a good radiator. Secondly, the loss of heat consequent upon the
necessity of cooling down the cylinder at every stroke in producing
the vacuum. Thirdly, the loss of power due to the pressure of vapor
beneath the piston, which was a consequence of the imperfect method of
condensation." This much determined, the next step looked toward the
confirmation of his conclusions and the remedy of the defects.
To meet the first difficulty he made a cylinder of wood, soaked in oil
and baked, a non-conducting and non-radiating material. Then he was
able to determine with some accuracy the quantities of steam and
injection water used in the engine; and a comparison with the original
cylinder and its operation showed that not only four times the
quantity of steam, but also four times the amount of injection water
was used as was necessary, assuming wastes checked. Further scientific
research on the part of Watt gave him measures of specific heats of
the metals and of wood, the specific volumes of steam at various
working pressures, the evaporative efficiency of boilers, the
pressures and temperatures of steam in the boiler under specified
conditions, the quantities of steam and of water required for the
operation of his little condensing engine.
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