uperheated steam, the percentage of gain will be greater
than the figures given above, which are the minimum and are for the most
economical type of large steam turbines.

An example from actual practice will perhaps best illustrate and
emphasize the foregoing facts. In October 1909, a series of comparable
tests were conducted by The Babcock & Wilcox Co. on the steam yacht
"Idalia" to determine the steam consumption both with saturated and
superheated steam of the main engine on that yacht, including as well
the feed pump, circulating pump and air pump. These tests are more
representative than are most tests of like character in that the saving
in the steam consumption of the auxiliaries, which were much more
wasteful than the main engine, formed an important factor. A resume of
these tests was published in the Journal of the Society of Naval
Engineers, November 1909.

The main engines of the "Idalia" are four cylinder, triple expansion,
11-1/2 x 19 inches by 22-11/16 x 18 inches stroke. Steam is supplied by
a Babcock & Wilcox marine boiler having 2500 square feet of boiler
heating surface, 340 square feet of superheating surface and 65 square
feet of grate surface.

The auxiliaries consist of a feed pump 6 x 4 x 6 inches, an independent
air pump 6 x 12 x 8 inches, and a centrifugal pump driven by a
reciprocating engine 5-7/16 x 5 inches. Under ordinary operating
conditions the superheat existing is about 100 degrees Fahrenheit.

Tests were made with various degrees of superheat, the amount being
varied by by-passing the gases and in the tests with the lower amounts
of superheat by passing a portion of the steam from the boiler to the
steam main without passing it through the superheater. Steam temperature
readings were taken at the engine throttle. In the tests with saturated
steam, the superheater was completely cut out of the system. Careful
calorimeter measurements were taken, showing that the saturated steam
delivered to the superheater was dry.

The weight of steam used was determined from the weight of the condensed
steam discharge from the surface condenser, the water being pumped from
the hot well into a tank mounted on platform scales. The same
indicators, thermometers and gauges were used in all the tests, so that
the results are directly comparable. The indicators used were of the
outside spring type so that there was no effect of the temperature of
the steam. All tests were of sufficient duration to sh