LoppEr.—On Compound Engines. 149 
then the same quantity of coal to evaporate the same number of pounds of 
water (same as in the first-example) this will give a consumption of 8-9, or say 
9 cwt. per hour, with an increase of power equal to 143 horse-power more 
than in the preceding example, and the consumption would be 1-2 lbs. per 
indicated horse-power per hour. 
Taking this then as a purely comparative statement, it shows an increase 
of power and at the same time nearly 50 per cent. saving of fuel. It must 
not be taken to mean that these caleulations which leave out many sources of 
loss of heat and force, are likely to be attained in practice in any altered 
engines, but the least result of 1-2 Ibs. Pata imdicsted o per hour has 
been surpassed by compound engines. 
It has been stated by some that eqhally good results could be obtained 
with using high-pressure steam in single cylinder engines, and cutting of at a 
fractional portion of the stroke. There are objections to this plan ; for instance, 
in expanding the steam say 6 to 1, asin the other cases, the terminal pressure 
would be very great, and totally lost as far as exerting any power is con- 
cerned, unless it was a very long stroke, and this for screw-engines is imprac- 
ticable ; besides, the vacuum would not be nearly so good, and there would be 
‘more loss by condensation than with compound engines. 
š The compound engine uses the steam down to its very lowest pressure, 
and none is lost, except a little by condensation, and this can be reduced to 
about 1:5 lbs. 
From what lias been advanced it will be seen that there can = little 
doubt of the superiority of the compound engine in point of economy over the 
old system with low pressure steam and jet condenser. There is not such a 
low consumption per indicated horse-power with the “Star of the South’s” 
engines as is stated to be got on the trial trips at home from some of the large 
boats, but the surest test is, when knowing the consumption and speed of a 
certain vessel with the old system to compare the obtained results after 
conversion, as has been done in the “Star of the South’s” case, and a saving 
in fuel proven, of 42:1 per cent., after six pseonthe running, with no diminution 
., as shown by the above tables ; and 
no doubt even a better result would bb ‘obtained with new compound engines 
in speed, but an increase of one per 
than by converting old. 
If we consider the two theoretical examples given we find a very small 
consumption per indicated horse-power. There is no doubt but a very great 
saving could be effected in a vessel of the class selected. 
We now come to some of the disadvantages of using surface condensers 
and high-pressure steam ; and first, with regard to priming, it is one of the 
phenomena of ebullition, and occurs more or less in all boilers using surface 
condensers, whether with high or low pressure steam, irrespective of the kind 
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