llon of salt water from the Irish Channel weighs
10.28 lbs.; and a gallon of salt water from the Mediterranean 10.29 lbs. If
we take an average saltness represented by a weight of 10.25 lbs., then a
gallon of water concentrated to twice this saltness will weigh 10.5 lbs.,
or the salt in it will weigh .5 lbs or 8 oz., which is the proportion of 8
oz. to the gallon. However, the proportion of 2/33rds gives a greater
proportion than 8 oz. to the gallon, for 2/33 = 1/16 nearly, and 1/16 of 10
lbs. = 10 oz. By keeping the density of the water in a marine boiler at the
proportion of 8 or 10 oz. to the gallon, no inconvenient amount of scale
will be deposited on the flues or tubes. The bulk of water, it may be
remarked, is not increased by putting salt in it up to the point of
saturation, but only its density is increased.

395. _Q._--Is there not a great loss of heat by blowing off so large a
proportion of the heated water from the boiler?

_A._--The loss is not very great. Boilers are sometimes worked at a
saltness of 4/33rds, and taking this saltness and supposing the latent heat
of steam to be at 1000 deg. at the temperature of 212 deg., and reckoning the sum
of the latent and sensible heats as forming a constant quantity, the latent
heat of steam at the temperature of 250 deg. will be 962 deg., and the total heat
of the steam will be 1212 deg. in the case of fresh water; but as the feed
water is sent into the boiler at the temperature of 100 deg., the accession of
heat it receives from the fuel will be 1112 deg. in the case of fresh water, or
1112 deg. increased by 3.98 deg. in the case of water containing 4/33ds of salt--
the 3.98 deg. being the 4.7 deg. increase of temperature due to the presence of
4/33rds of salt, multiplied by 0.847 the specific heat of steam. This makes
the total accession of heat received by the steam in the boiler equal to
1115.98 deg., or say 1116 deg., which multiplied by 3, as 3 parts of the water are
raised into steam, gives us 3348 deg. for the heat in the steam, while the
accession of heat received in the boiler by the 1 part of residual brine
will be 154.7 deg., multiplied by 0.85, the specific heat of the brine, or
130.495 deg.; and 3348 deg. divided by 130.495 deg. is about 1/26th. It appears,
therefore, that by blowing off the boiler to such an extent that the
saltness shall not rise above what answers to 4/33rds of salt, about 1/25th
of the heat is blown into the sea; this is but a small