690 
Report on the Trials of Portable 
In what precedes, only the coal consumption of the engines 
under trial has been recorded, whereas, if any discrimination is 
to be made between engine-economy and boiler-economy, it is 
needful to know how much steam each engine used per horse- 
power per hour, and how much steam its boiler made for every 
pound of coal consumed. 
It is quite conceivable, for instance, that a boiler capable of 
evaporating 12 lbs. of water per lb. of coal, may be saddled 
with an engine needing 36 lbs. of steam per horse-power per 
hour; while another, capable of making only 10 lbs. of steam 
per lb. of coal, may carry an engine requiring 30 lbs. of steam 
per horse-power per hour. Three pounds of coal per horse- 
power per hour would be consumed in both these cases, while, 
if the respective engines and boilers changed places, one engine 
would burn 3'6 lbs. of coal per horse-power per hour, while the 
other would only burn 2 5 lbs. of coal per horse-power per hour. 
The total water consumption of each engine, which, for 
reasons given at length in the Engineers' Report, cannot be 
stated with the same accuracy as its coal consumption, was 
ascertained in the following way. 
The water actually supplied to the feed-tub was measured in 
each case. The temperature of such supplied water, together 
with the temperature of the feed-water, was ascertained, and the 
difference between these temperatures being the work of the 
exhaust steam, the weight of such steam requiring to be con- 
densed in order to raise the temperature of the measured 
" supply " water to the temperature of the hot " feed " water was 
ascertained and added to the weight of szipplied water. Finally, 
the condensation in the jackets, not being measurable, was 
estimated from data furnished by experiments upon engines in 
which such condensation was measurable, and the weight of 
jacket- water, so ascertained, was added to the sum in question. 
It will be noticed that, taking the two classes of engines into 
account, some used more than twice as much water as others, 
and, apart altogether from the question of the coal bill, this is a 
matter of the utmost importance. The water supply of farms 
is often scanty, and, almost always, distant from the points 
where motive power is needed. In the case of traction and 
ploughing engines, particularly, that motor is best which, 
besides being economical of coals, puts the least strain upon 
the water cart. 
The Secondary Trials. 
These consisted chiefly, as already stated, in indicating the 
various engines, and in the collection and analysis of the 
smoke-box gases. Efforts were also made to measure, hj 
