55G Trials of Traction-Engines at Wolverhampton. 
exhaust steam, it follows that the fuel has to supply the difTerence,. 
and that therefore it has not so many units of heat left to evaporate 
cold feed-water, and that thus a little less water is evaporated than 
would have been had not the exhaust mingled with it to heat it 
The benefit of this process, thei'efore, appears in the diminished" 
coal required to produce the horse-power : but it does not appear 
in any extra amount of cold feed-water evaporated, thus differing 
from those cases where the feed-water is heated by passing through 
a pipe jacketed by steam. When this is done, the steam which 
heats the feed-water does not mingle with it, and does not add to 
its quantity, and therefore, with feed-water thus heated, there is 
a greater evaporation per lb. of coal than there is from cold feed- 
water ; while in feed-water heated by actual contact with waste 
steam there is no greater evaporation. 
We have felt it necessary to comment upon this point at some 
little length, because we know that among the exhibitors, and 
indeed among other engineers, there were those who were inclined, 
on first consideration, to hold that if the heating of feed-water 
be the means of obtaining an economy in the production of 
power, it obtains that economy by a higher evaporative duty, and 
that that duty should be shown in the amount of feed-water 
evaporated, forgetting that this would only become apparent if 
the cold feed-water, after having been augmented by the con- 
densed steam, could be measured, and that it cannot become 
apparent if the cold feed-water alone be taken into account. 
On finding the poor evaporative results, we became anxious to 
ascertain the temperature of the products of combustion as they 
issued from the boiler ; but no provision had been made for this, 
and there was not time to drill holes into the smoke-box to intro- 
duce a thermometer. Some rude attempts were made to obtain 
comj)arative temperatures by holding a thermometer over the 
tops of the funnels ; l)ut evidently such attempts must be highly 
unsatisfactory so far as getting anything like an accurate result is 
concerned, because at that point the waste steam is mingled with 
the products of combustion and has cooled them, and the least 
priming makes, as might be expected and as we found, a most 
sensible reduction. We made further trials by lowering down 
the funnels pieces of lead attached to a wire — also a very insuffi- 
cient mode of arriving at the truth. This being so, we feel it 
would be wrong to publish any of the results, and we will con- 
tent ourselves with saying that the tests, rude as they were, 
made it quite clear there were great differences in the tem- 
peratures of the escaping gases from the various boilers, and 
that In the interests of the exhibitors and of engineering progress 
it is most desiraljle on the next occasion of the trials of engines 
by the Society that each exhibitor should be required to provide 
