The name is absent

280 Science and Human Welfare

matter what part of the world it is in. And at some of the
places they say that the water “is so hard that it bounces.”
New detergents, containing soaps which do not give insoluble
precipitates with hard water, have been developed. These
soaps produce a perfect lather no matter how hard the water
may happen to be.

Even though the excess hardness has been removed by the
municipal water-treating plant, the industrial plants, es-
pecially those in which scale may be formed due to concen-
tration or heating, must have even softer water. For the past
fifteen years the trend has been to higher steam pressures in
commercial boilers. This is advisable in order to improve the
plant cycle efficiency. The high pressures of former years,
like 5∞ pounds per square inch, are giving way to pressures
of 1200 or more. At high rates of heat absorption, even a
scale o.oi inch thick may cause failure due to burned-out
tubes. When solutions which contain salts whose solubilities
increase with an increase in temperature are concentrated
beyond their saturation value, these substances deposit as
sludge. If their solubilities decrease they form scale. The
formation of scale occurs in situ, that is to say, these con-
stituents deposit directly upon the heat-transfer surface as
scale. Sludges remain in suspension and are constantly re-
moved from the boilers by the blow-down.

At low pressures sodium carbonate may economically be
added to the feed water in order to cause precipitation as
sludge, of calcium carbonate, not of the chief scale-former,
which is calcium sulphate. At higher pressures with asso-
ciated higher temperatures, phosphates are added. They do
not decompose and yet, as in the case of the carbonates, they
form precipitates whose solubilities increase with tempera-
ture; and consequently they form sludge—not scale.

For the successful operation of a boiler it is just as im-

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