ly a mechanical action which may occur
in neutral waters, is intensified by acidity.

Foaming--This phenomenon, which ordinarily occurs with waters
contaminated with sewage or organic growths, is due to the fact that the
suspended particles collect on the surface of the water in the boiler
and render difficult the liberation of steam bubbles arising to that
surface. It sometimes occurs with water containing carbonates in
solution in which a light flocculent precipitate will be formed on the
surface of the water. Again, it is the result of an excess of sodium
carbonate used in treatment for some other difficulty where animal or
vegetable oil finds its way into the boiler.

Priming--Priming, or the passing off of steam from a boiler in belches,
is caused by the concentration of sodium carbonate, sodium sulphate or
sodium chloride in solution. Sodium sulphate is found in many southern
waters and also where calcium or magnesium sulphate is precipitated with
soda ash.

Treatment of Feed Water--For scale formation. The treatment of feed
water, carrying scale-forming ingredients, is along two main lines: 1st,
by chemical means by which such impurities as are carried by the water
are caused to precipitate; and 2nd, by the means of heat, which results
in the reduction of the power of water to hold certain salts in
solution. The latter method alone is sufficient in the case of certain
temporarily hard waters, but the heat treatment, in general, is used in
connection with a chemical treatment to assist the latter.

Before going further into detail as to the treatment of water, it may be
well to define certain terms used.

_Hardness_, which is the most widely known evidence of the presence in
water of scale-forming matter, is that quality, the variation of which
makes it more difficult to obtain a lather or suds from soap in one
water than in another. This action is made use of in the soap test for
hardness described later. Hardness is ordinarily classed as either
temporary or permanent. Temporarily hard waters are those containing
carbonates of lime and magnesium, which may be precipitated by boiling
at 212 degrees and which, if they contain no other scale-forming
ingredients, become "soft" under such treatment. Permanently hard waters
are those containing mainly calcium sulphate, which is only precipitated
at the high temperatures found in the boiler itself, 300 degrees
Fahrenheit or more. The scale of hardness is an arbitra