80 BULLETIN tel, U. S. DEPARTMENT OE AGRICULTURE. 
live steam from the boiler and the boiler capacity can be reduced 
practically one-half with a corresponding reduction in fuel, to sa.y 
nothing of the lessened strain placed on the- boiler -through forcing 
and the extra labor required in firing. By feeding the boiler with 
water heated by exhaust steam, expansion and contraction strains are 
greatly lessened, the fuel consumption is reduced as well as the work 
of firing, and the capacity of the boiler is increased in proportion to 
the temperature to which the feed water is heated. Where there is 
use for the heat in the exhaust steam from the engine, pumps, and 
other steam-driven machinery the power 'developed becomes a by- 
product of the heating system, and hence costs but little. In a milk 
plant or creamery in which pasteurization is practiced steam power 
is, generally speaking, the cheapest, for it is necessary to provide a 
boiler to furnish steam for the pasteurizing and as there is about 85 
per cent of the heat in live steam at 70 pounds' gauge pressure remain- 
ing in the exhaust steam from the engine, it is economy to use the 
steam first in the engine to produce, the required power for oper- 
ating the machinery and then for the purpose of pasteurizing, heat- 
ing water, and heating the building. 
The size of boiler will be approximately the same whether it is 
used for pasteurizing only or for furnishing steam first to the engine 
and then employing the exhaust steam in the pasteurizer. Especially 
is this true if the engine is operated only a few hours daily, as it is 
necessary to raise steam for pasteurizing and after the boiler is once 
fired up but little additional fuel is required to furnish steam for 
power purposes for. say, three or four hours. 
There are certain conditions, however, in which it is more eco- 
nomical to install a boiler for heating and a gas engine or electric 
motor for power. For instance, in nonpasteurizing plants where 
only a comparatively small quantity of heat is required for heating 
the wash water, a small boiler may be used for generating low-pres- 
sure steam for heating, and a gas engine or electric motor for run- 
ning the machinery. The advantages in employing a gas engine or 
electric motor are that it is ready for instant use and that power 
costs cease with the stopping of the machine, TTith a steam-engine, 
however, time is required to raise steam in the boiler and firing must 
be continued while the engine is in use. Furthermore, it requires 
about 10 pounds of coal per horsepower capacity of the boiler for 
raising steam. That is, a 20-horsepower boiler requires about 200 
pounds of coal for heating the walls of the setting and raising steam 
to a pressure of 70 pounds' gauge pressure. In some oases the appa- 
ratus requiring power is operated intermittently throughout the 
day. in which case it may not be advisable to use a steam engine, as 
