SMALL SAWMILLS, THEIR EQUIPMENT,. ETC. 21 
and some form of tannic acid as their base. Tannic acid has a slight 
action on the iron of the boiler and is reasonably efficient in prevent- 
ing scale from sticking. 
To prevent scale, or at least to diminish the injury it does to 
boilers, the feed water should be heated by live steam under boiler 
pressure in a separate vessel before going to the boiler. By allowing 
the water to settle for some time, sediment, mud, and dirt will be got 
rid of. Oil from the engine cylinder is particularly injurious to 
boilers, and, when noticed in the condensed steam, should be carefully 
removed. 
STEAM PUMPS. 
If water can not be obtained under sufficient pressure to cause it to 
flow into the intake by gravity, some sort of pump is necessary. 
Usually the pump runs by steam. If the pump runs badly, make sure 
the water valves and water pipes are all right before examining the 
steam end. When the pump is not in use in cold weather open all 
the cocks and drain plugs to prevent freezing. Always see that the 
pump has a full and steady supply of water to work on. Do not take 
the pump apart to see what is inside as long as it does its work well. 
Set a pump on a level solid foundation so as to avoid undue strain on 
the pipes and resulting leaky joints. Long pipes should be larger 
than short ones, to allow for increased friction. All pipes should 
be as short and straight as possible. A foot valve and strainer 
should be attached to the suction pipe. 
Use few elbows, tees, and valves, substituting full round bends for 
elbows, and wyes for tees ; sharp bends greatly increase the friction. 
Care must be taken to guard against leaks in the suction pipe, as a 
very small leak will supply the pump with air to its full capacity, and 
little or no water will be obtained. A suction air chamber made of 
a short nipple, a T, a piece of pipe smaller in diameter than the 
suction pipe and from 2 to 3 feet long, and a cap, screwed upright 
into the suction pipe close to the pump are always useful, and when 
the suction pipe is long, in high lifts, or when the pump is running 
at high speed, it is a positive necessity. Its use insures a steady 
and uniform flow of water through this suction pipe and prevents 
" pounding " or " water hammering." 
Use good cylinder oil, and oil the steam end just before stopping 
the pump. Keep the stuffing boxes full of good packing, well oiled, 
and just tight enough to prevent leakage without excessive friction. 
WATER POWER. 
As a general thing, water power is not practicable for a portable 
mill. It may be found in one location, but not in the next. It is 
cheaper than steam, but the source of power is neither uniform nor 
