of writing paper, and _no
excuse_ should be accepted from engineers for permitting a boiler to be
damaged by the accumulation of calcareous deposit.

392. _Q._--What is the temperature at which sea water boils in a steam
boiler?

_A._--Sea water contains about 1/33rd its weight of salt, and in the open
air it boils at the temperature of 213.2 deg.; if the proportion of salt be
increased to 2/33rds of the weight of the water, the boiling point will
rise to 214.4 deg.; with 3/33rds of salt the boiling point will be 215.5 deg.;
4/33rds, 216.7 deg.; 5/33rds, 217.9 deg.; 6/33rds, 219 deg.; 7/33rds, 220.2 deg.; 8/33rds,
221.4 deg.; 9/33rds, 222.5 deg.; 10/33rds, 223.7 deg.; 11/33rds, 224.9 deg.; and 12/33rds,
which is the point of saturation, 226 deg.. In a steam boiler the boiling
points of water containing these proportions of salt must be higher, as the
elevation of temperature due to the pressure of the steam has to be added
to that due to the saltness of the water; the temperature of steam at the
atmospheric pressure being 212 deg., its temperature, at a pressure of 15 lbs.
per square inch above the atmosphere, will be 250 deg., and adding to this 4.7 deg.
as the increased temperature due to the saltness of the water when it
contains 4/33rds of salt, we have 254.7 deg. as the temperature of the water in
the boiler, when it contains 4/33rds of salt and the pressure of the steam
is 15 lbs. on the square inch.

393. _Q._--What degree of concentration of the salt water may be safely
permitted in a boiler?

_A._--It is found by experience that when the concentration of the salt
water in a boiler is prevented from exceeding that point at which it
contains 2/33rds its weight of salt, no injurious incrustation will take
place, and as sea water contains only 1/33rd of its weight of salt, it is
clear that it must be reduced by evaporation to one half of its bulk before
it can contain 2/33rds of salt; or, in other words, a boiler must blow out
into the sea one half of the water it receives as feed, in order to prevent
the water from rising above 2/33rds of concentration, or 8 ounces of salt
to the gallon.

394. _Q._--How do you determine 8 ounces to the gallon to be equivalent to
twice the density of salt water, or "two salt waters" as it is sometimes
called?

_A._--The density of the water of different seas varies somewhat. A gallon
of fresh water weighs 10 lbs.; a gallon of salt water from the Baltic
weighs 10.15 lbs.; a ga