effect
of the fire depends upon the width of the throat of the hopper at _u_,
which regulates the supply of fuel to the grate, and upon the
inclination of the latter. The throat is usually from 6 to 8 inches
wide, according to the nature of the fuel. The inclination of the grate
is 40 to 45 deg. and, in general, should be that which is assumed by the
sides of a pile of the fuel to be burned, when it is thrown up into a
heap. This grate ensures complete combustion of fuel that would fall
through ordinary grates, and that would merely smoulder upon a hearth.
The fire admits of easy regulation, the ashes may be removed and the
fuel may be supplied without _checking the fire_. Not only broken peat,
but coal dust, saw dust, wood turnings and the like may be burned on
this grate. The figure represents it as adapted to a steam boiler.

6.--_Hygroscopic water of peat fuel._

The quantity of water retained by air-dried peat appears to be the same
as exists in air-dried wood, viz., about 20 _per cent._ The proportion
will vary however according to the time of seasoning. In thoroughly
seasoned wood or peat, it may be but 15 _per cent._; while in the poorly
dried material it may amount to 25 or more _per cent._ When _hot-dried_,
the proportion of water may be reduced to 10 _per cent._, or less.

When peat is still moist, it gathers water rapidly from damp air, and in
this condition has been known to burst the sheds in which it was stored,
but after becoming dry to the eye and feel, it is but little affected by
dampness, no more so, it appears, than seasoned wood.

7.--_Shrinkage._

In estimating the value and cost of peat fuel, it must be remembered
that peat shrinks greatly in drying, so that three to five cords of
fresh peat yield but one cord of dry peat. When the fiber of the peat is
broken by the hand, or by machinery, the shrinkage is often much
greater, and may sometimes amount to seven-eighths of the original
volume.--_Dingler's Journal, Oct. 1864_, _S._ 68.

The difference in weight between fresh and dry peat is even greater.
Fibrous peat, fresh from the bog, may contain ninety _per cent._ of
water, of which seventy _per cent._ must evaporate before it can be
called dry. The proportion of water in earthy or pitchy peat is indeed
less; but the quantity is always large, so that from five to nine
hundred weight of fresh peat must be lifted in order to make one hundred
weight of dry fuel.

8.--_Time of excavation, and