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ARTICLE II.
COMPARISON OF THE POWERS OF THE OLD AND
NEW PRINCIPLES.
ON the principle of using the steam as an agent to form a vacuum, the power of the engine has never been made to exceed 12 or 15 pounds to the inch area of the piston. The vacuum being imperfect in all cases, the practice falls short of the theory; and the boilers being constructed of such form, as to be only sufficient to bear a power of steam, necessary as the agent, a little exceeding the weight of the atmosphere,* were subject to be blown up by overloading the safety valve; the load allotted being 3 pounds to the inch, it is very easy to double it to 6 or 12 pounds, by accident, when, if the steam does not get vent, the boiler explodes.
But on the new principle of working simply by the elastic
power of the steam, the power may be raised with safety, from 12 to 120
pounds to the inch area of the piston, which makes this engine ten times
as powerful as the other, and because the boilers are constructed of circular
forms, (the best possible form for holding a great elastic power,) and so
as to bear from ten to forty times the load that is generally required on
the safety valve, which is not subject to be laid on by accident, this engine
is by far the safest.
*When we speak of steam equal in power to the weight of the atmosphere (which we call atmospheric steam) we mean, steam produced by the boiling heat under the pressure of the atmosphere. 212 degrees, the boiling heat of water-170 degrees, the boiling heat of spirits of wine.