CXL. 8S. H. BARRACLOUGH. 
amount of steam consumed. On the other hand, Mr. Bryan 
Donkin in the paper already quoted, states that a coating of 
varnish distinctly lessens the condensation waste, and although 
his experiments were carried out on a specially constructed 
apparatus and not on an engine cylinder, the results are comparable 
with those obtained from an engine test. It is thus evident that 
the precise effect of the condition of the clearance surface is at 
present not known. 
(f) Clearance Volume. It is to be regretted that no systematic 
and extensive series of experiments on the relationship between 
clearance volume and cylinder condensation, have as yet, been 
reported. That the economy of an engine is greatly affected by 
the amount of clearance volume is generally admitted, but the 
precise relationship is undetermined. 
(g) Thermo-dynamic condensation. Rankine and Clausins 
independently demonstrated about 1850 that when steam expands 
adiabatically a portion of it is liquefied. This liquefaction is not 
very large, except in the case of high pressures and large ratios 
of expansion, and its amount can be computed in a perfectly 
straightforward manner. It is not of course to be considered as 
a waste in the ordinary sense, since it is the result of the useful 
work done by the expanding steam against the resistance of the 
piston, but it has however sometimes been regarded as exerting 4 
very important indirect effect in that the presence of the water 
mist caused by the thermodynamic liquefaction would produce 
‘Increased condensation of the entering steam. Experiment has 
however never shown any essential connection between the two. 
(4) The quality of the steam, or the percentage of dry steam 
in the entering mixture of steam and water has not been the 
subject of very much experimental investigation, as regards its 
influence on the amount of initial condensation. An excess of 
entrained water in the steam is of course practically objectionable, 
but, at any rate in the case of the particular types! of engine ee 
Sear eat 
** Experimental aphni“a of i ihe effect of water in steam on the 
chit of the steam engine.”—Trans, Am. tg Mech. Engrs., Vol. *¥- 
