On Compound Engines for Agricultural Purposes. 665 
what larger than the present one, though in some cases it need 
not bo much larger. 
The steam-boiler, with its furnace, and the water contained 
in it, together with the part of the carriage necessary for sup- 
plying these items, necessarily weigh much more than the steam 
cylinder and its belongings. 
An 8-horse-power portable engine, when empty, weighs about 
4 tons ; of this weight, probably about 3 tons would represent 
the weight of the boiler with its furnace, and the proportion of 
the carriage necessary for supporting these items. 
Probably the average portable engine in regular work would 
use as much as 48 lbs. weight of steam per indicated horse-power 
per hour. 
It is probable that the average consumption of steam under 
similar circumstances, and with the same boiler-pressure, could 
be reduced 25 per cent, by making the engine compound. This 
would allow the weight of the boiler and its share of carriage to 
be reduced to the same extent, viz., from 3 tons to 2 tons 5 cwt. ; 
and if this alteration adds a cylinder with piston and covers 
weighing 5 cwt., the whole engine may be reduced from 4 to 
3^ tons in its weight, when empty ; its cost should be certainly 
no more than before, and the fuel consumption will be reduced 
25 per cent. 
If at the same time the pressure be increased to 120 or 
150 lbs., the extra thickness of boiler plates may make the 
whole engine as heavy as the original, but its fuel consumption 
will be further reduced to two-thirds of its former amount. 
In a traction or ploughing engine, the relative advantages 
will be greater still, as in them the water and fuel have to be 
carried on the engine ; and frequently the cost of conveying 
these commodities is important. 
An 8-horse-power traction engine fully equipped for travelling 
with water and coal weighs about 10 tons, of which probably 
5 tons would represent the boiler and furnace with coals and 
water, and proportion of carriage of these items. 
Suppose now that the average consumption of such engines 
is 48 lbs. weight of steam per indicated horse-power per hour, 
and that this can be reduced 25 per cent., viz. to 36 lbs. by 
adding a cylinder weighing, with all its extra belongings, 5 cwts. 
Then to give the same maximum power, and the same length 
of journey with bunkers and tank full as before, the boiler, coal, 
and water maj', in virtue of the greater economy, be reduced 
from 8 to 6 tons, and the nett gain in the gross travelling-weight 
of the engine will be 1 ton 15 cwts., making it 8 tons 5 cwts. 
instead of 10 tons ; or, with the same weight of coal and water 
as before, the engine will travel a longer distance by one-third. 
