just turn red litmus paper blue. As a preventative of such action
arising from the presence of the oil, only the highest grades of
hydrocarbon oils should be used.

Acidity will occur where sea water is present in a boiler. There is the
possibility of such an occurrence in marine practice and in stationary
plants using sea water for condensing, due to leaky condenser tubes,
priming in the evaporators, etc. Such acidity is caused through the
dissociation of magnesium chloride into hydrochloride acid and magnesia
under high temperatures. The acid in contact with the metal forms an
iron salt which immediately upon its formation is neutralized by the
free magnesia in the water, thereby precipitating iron oxide and
reforming magnesium chloride. The preventive for corrosion arising from
such acidity is the keeping tight of the condenser. Where it is
unavoidable that some sea water should find its way into a boiler, the
acidity resulting should be neutralized by soda ash. This will convert
the magnesium chloride into magnesium carbonate and sodium chloride,
neither of which is corrosive but both of which are scale-forming.

The presence of air in the feed water which is sucked in by the feed
pump is a well recognized cause of corrosion. Air bubbles form below the
water line and attack the metal of the boiler, the oxygen of the air
causing oxidization of the boiler metal and the formation of rust. The
particle of rust thus formed is swept away by the circulation or is
dislodged by expansion and the minute pit thus left forms an ideal
resting place for other air bubbles and the continuation of the
oxidization process. The prevention is, of course, the removing of the
air from the feed water. In marine practice, where there has been
experienced the most difficulty from this source, it has been found to
be advantageous to pump the water from the hot well to a filter tank
placed above the feed pump suction valves. In this way the air is
liberated from the surface of the tank and a head is assured for the
suction end of the pump. In this same class of work, the corrosive
action of air is reduced by introducing the feed through a spray nozzle
into the steam space above the water line.

Galvanic action, resulting in the eating away of the boiler metal
through electrolysis was formerly considered practically the sole cause
of corrosion. But little is known of such action aside from the fact
that it does take place in certain instanc