103
THE NEW ZEALAND GAZETTE.

which steampipes are constantly surrounded by
the sea water to be operated upon, and which
thus becomes heated by them. The steam is
procured on board of steamers directly from
their boilers, and, consequently, at a trifling cost;
in sailing-ships it is obtained from a small
boiler, which may or may not be connected
with the hearth, galley, or caboose.

The steam of the above-mentioned pressure
being of course hotter than ordinary boiling
water, serves to convert a portion of the water
contained in the evaporator into ordinary or
on-pressure steam, which, as it reaches the
condenser, is resolved therein into fresh water.

By thus evaporting water under a slight pres-
sure, one fire performs double duty, and thus
the first condition, that of economy, is com-
pletely fulfilled, for whilst, in the usual way,
1tb of coal evaporates 8 or 9tbs. of water, the
same quantity of coals is thus made to evaporate
16 or 18tbs of water. In fact, I am in a posi-
tion to prove by actual experiment, that from
the same amount of steam or of coals employed,
the machine which I have just described will
produce double the quantity of fresh water that
can be obtained by simple or ordinary distilla-
tion, and I may say, that with an apparatus
constructed on the same principle, and which
was sent to Copiapo, in Chili, not less than
30,000 gallons of fresh water per diem are ob-
tained from the sea.

The steam issuing from the evaporator, and
which is condensed by the water in the conden-
sor, imparts, of course, its heat to the sea water
in it, and as this water is admitted cold at the
bottom, whilst the steam of the evaporator is
admitted to the top of the condensor, the water
therein becomes hotter and hotter gradually as
it ascends, and when it finally reaches the top,
its temperature is about 208° Fahr.

I have already stated that water begins to
part with its air at a temperature of about
130° Fahr., therefore, the greater portion of
the air contained in the water which flows con-
stantly and uninterruptedly through the con-
densor is thus separated, and led through a
pipe into the empty space left for steam room
within the evaporator, when it mixes with the
steam.

Now, as about six gallons of sea water must
be discharged for every gallon of fresh water
which is condensed, it follows that the steam in
the evaporator, betore it is finally condensed,
has been in contact with twice as much air as
water can take up, the result being a produc-
tion of fresh water to the maximum of aeration
that is, containing as much air as in pure rain
water, whilst, the upper part of the condensor
being open to the atmosphere, all pressure is
thus removed from the apparatus.

This aeration of the water is a condition of the
utmost importance, and, in fact, is a condition
which, were it not accomplished, would render
the apparatus comparatively useless, even
though the other desiderata were fulfilled.
When the natural waters supplied to our habi-
tations are obtained from impure sources, as is
unfortunately too often the case, the evils re-
sulting from their use may in some degree be
remedied by putting in practice the recommen-
dation which has been sometimes made of boil-
ing such water previous to employing is as a
beverage; unfortunately, the water being
thereby deprived of air and of carbonic acid is,
like distilled water, though in a less degree,
unpalatable, and vapid, and heavy; it is, in fact
of difficult digestion; but there is something
worse than that; water which has been boiled,
or which has been distilled, by reason of its con-
taining no air, has a great tendency to absorb
or to take air from the media where it is kept,
so that if distilled water, which contains no air,
be kept in a ship's hold, or in an impure and con-
fined place, it will absorb precisely the quan-
tity of air which it can absorb, namely, 15 cubic
inches per gallon, and if that air be loaded with
organic particles or impure emanations, it will
soon become fetid and putrid. Thus water,
though distilled, if kept in tainted rooms, will
soon become foul. The empyreumatic odour
and taste which distilled water always possesses
and retains for a considerable time, is in fact
due to the destructive action, of the heated sur-
face of the vessels in which the water is boiled,
on the organic substances which are always
floating on the air, on those indescribable parti-
cles of dust which are seen playing or moving
about in a sunbeam, and which have been dis-
solved or taken up by the water before its distil-
lation. That water has the power of absorbing
and dissolving organic matter in this way is, of
course, well known, but it may be illustrated in
a very simple manner, as follows:-If water,
from whatever source, be distilled, the distillate
will, of course be fresh water, pure fresh water,
but it will have a peculiar, nauseous, and empy-
reumatic taste and odour, stronger in propor-
tion as the heat applied to evaporate it has been
more elevated; it is that smell and taste which
render it undrinkable for a while. If, when it
has become sweet again by long standing,
which period may be hastened by agitation in the
atmosphere; if, I repeat it, that distilled water
be then redistilled, the distillate will be found to
have acquired again the same empyreumatic
taste and odour as when it was first distilled.
How is this? Because it will by standing or
agitation, have re-dissolved a portion of the air in
the room in which it was kept, and along with that
air it will have absorbed whatever substances were
present, dissolved or suspended in it, and those
substances by their contact with the heated sur-
faces of the still, yield an empyreumatic product,
which taints the distillate. The only condition
necessary for distilled water not to become putrid
or offensive is to saturate it with pure air, because
in that case there is no room left for other gases
to impregnate it, at least practically speaking,
and in the ordinary conditions of domestic or
of ship economy. On board ships, the water
which is stored in for the use of the crews in the
usual way, in the course of about a fortnight
becomes putrid and almost undrinkable, because
the organic matter which that water contains is
undergoing a course of putrefactive fermentation.
But about a month or so afterwards the water