ated. Table 16 gives the amount of lime and soda
required per 1000 gallons for each grain per gallon of the various
impurities found in the water. This table is based on lime containing 90
per cent calcium oxide and soda containing 58 per cent sodium oxide,
which correspond to the commercial quality ordinarily purchasable. From
this table and the cost of the lime and soda, the cost of treating any
water per 1000 gallons may be readily computed.

Less Usual Reagents--Barium hydrate is sometimes used to reduce
permanent hardness or the calcium sulphate component. Until recently,
the high cost of barium hydrate has rendered its use prohibitive but at
the present it is obtained as a by-product in cement manufacture and it
may be purchased at a more reasonable figure than heretofore. It acts
directly on the soluble sulphates to form barium sulphate which is
insoluble and may be precipitated. Where this reagent is used, it is
desirable that the reaction be allowed to take place outside of the
boiler, though there are certain cases where its internal use is
permissible.

Barium carbonate is sometimes used in removing calcium sulphate, the
products of the reaction being barium sulphate and calcium carbonate,
both of which are insoluble and may be precipitated. As barium carbonate
in itself is insoluble, it cannot be added to water as a solution and
its use should, therefore, be confined to treatment outside of the
boiler.

Silicate of soda will precipitate calcium carbonate with the formation
of a gelatinous silicate of lime and carbonate of soda. If calcium
sulphate is also present, carbonate of soda is formed in the above
reaction, which in turn will break down the sulphate.

Oxalate of soda is an expensive but efficient reagent which forms a
precipitate of calcium oxalate of a particularly insoluble nature.

Alum and iron alum will act as efficient coagulents where organic matter
is present in the water. Iron alum has not only this property but also
that of reducing oil discharged from surface condensers to a condition
in which it may be readily removed by filtration.

Corrosion--Where there is a corrosive action because of the presence of
acid in the water or of oil containing fatty acids which will decompose
and cause pitting wherever the sludge can find a resting place, it may
be overcome by the neutralization of the water by carbonate of soda.
Such neutralization should be carried to the point where the water will