t to be 0.45 per cent.

[Illustration: Fig. 16. Compact Throttling Calorimeter]

There are many forms of throttling calorimeter, all of which work upon
the same principle. The simplest one is probably that shown in Fig. 14.
An extremely convenient and compact design is shown in Fig. 16. This
calorimeter consists of two concentric metal cylinders screwed to a cap
containing a thermometer well. The steam pressure is measured by a gauge
placed in the supply pipe or other convenient location. Steam passes
through the orifice A and expands to atmospheric pressure, its
temperature at this pressure being measured by a thermometer placed in
the cup C. To prevent as far as possible radiation losses, the annular
space between the two cylinders is used as a jacket, steam being
supplied to this space through the hole B.

The limits of moisture within which the throttling calorimeter will work
are, at sea level, from 2.88 per cent at 50 pounds gauge pressure and
7.17 per cent moisture at 250 pounds pressure.

Separating Calorimeter--The separating calorimeter mechanically
separates the entrained water from the steam and collects it in a
reservoir, where its amount is either indicated by a gauge glass or is
drained off and weighed. Fig. 17 shows a calorimeter of this type. The
steam passes out of the calorimeter through an orifice of known size so
that its total amount can be calculated or it can be weighed. A gauge is
ordinarily provided with this type of calorimeter, which shows the
pressure in its inner chamber and the flow of steam for a given period,
this latter scale being graduated by trial.

The instrument, like a throttling calorimeter, should be well insulated
to prevent losses from radiation.

While theoretically the separating calorimeter is not limited in
capacity, it is well in cases where the percentage of moisture present
in the steam is known to be high, to attach a throttling calorimeter to
its exhaust. This, in effect, is the using of the separating calorimeter
as a small separator between the sampling nozzle and the throttling
instrument, and is necessary to insure the determination of the full
percentage of moisture in the steam. The sum of the percentages shown by
the two instruments is the moisture content of the steam.

The steam passing through a separating calorimeter may be calculated by
Napier's formula, the size of the orifice being known. There are
objections to such a calculation, however, in tha