CXXXIV. 8. H. BARRACLOUGH. 
heat, H, supplied to any engine that can theoretically be used. 
Hence it is perhaps rather a misnomer to talk of a thermodynamic 
waste. It might possibly be more correctly termed the thermo- 
dynamic disability of the heat engine. Supposing, for instance, 
steam were introduced into the cylinder at a pressure of 90 bs., 
corresponding to a temperature of 320° F., and that it was rejected 
to the condenser at, say 100° F., then the maximum possible 
efficiency would be given by 
320-100 220 
320+ 461 781 
or, in other words, out of 100 heat units passing through the 
cylinder, only 28 could possibly be turned into available work. 
The ordinary cycles adopted in steam engine cylinders are me 
completely reversible, as it is impossible to secure the adiabatic 
compression necessary to bring the working fluid back to = 
initial pressure before the succeeding cycle begins, and on -~ 
account the possible thermodynamic efficiency of the actual engine 
is lower than that indicated by the above: equation. This fact 
has given rise to a controversy! as to the correct standard cycle 
with which to compare the steam cycle in any particular engine. 
The question is one to which there seems no finality, but in the 
author’s opinion few satisfactory reasons have been advanced 
against the adoption of the original Carnot cycle as a standard, 
rather than one of the more recent cycles that have been proposed. 
It is a cycle of maximum efficiency and of definite value, towards 
which all engines should be made to approximate, even though 
they might never actually attain to it. 
_ B. The mechanical or frictional wastes depend almost entirely 
on the structural form of the engine, and are capable of easy and 
approximate computation, In some engines of exceptionally 
mechanical design and construction the frictional waste is redu 
to 5Y of the total power developed in the cylinder. For good 
general practice, however, a more usual figure is 10%. AS first 2 
__ } Proe. Inst. C.E., Vol. CXXV., p. 182. 
