Klaphake: Air Wells
[ Special thanks to Dr Klaus Neumann,
for retrieving & sharing? this article ]
See also: Air Wells, Dew Ponds & Fog Fences
Proceeding of the Society of
Chemical Industry of Victoria (Australia), 36: 1093-1103 (1936)
for Condensation of Water from the Atmosphere
by Wolf Klaphake, D. Ph, A.A.C.I.
When air is saturated with water
vapor, it rains, and one should be inclined to think that the air is saturated,
when it cannot take up any more water. This conception is wrong, for air
can contain almost any amount of water, providing it is presented to it
in the right form. Air, having a vapor pressure of 31.8 mm of mercury,
is said to be saturated at 30 C, but we can add water drops of a very small
diameter, and they are taken up and transformed into invisible water vapor
until the pressure amounts to several times the initial pressure.
It is said that air is saturated
with water vapor when the air is above a flat surface of the same temperature,
and when the same number of water molecules leave the surface as return
to it, but when the surface of the water is convex towards the air —
as it is in water drops — the saturation pressure is higher. There is
no condensation, even at a great supersaturation, unless there are some
solid or liquid nuclei, on which combination of the vapor molecules can
Dines mentions on one of his papers
that the water content of the air above Europe would yield a rainfall less
than one inch per day. The high rainfall of that continent is due to the
ascending air currents, for a current saturated at 50 F, ascending at a
speed of 1 m/sec, would produce a rainfall of one inch per hour. Such an
air current carries with it water drops formed on nuclei, until these drops
are big enough to fall quicker than the current rises. This is, however,
only one factor in rain-making.
Others are connected with the electric
potential of the air, of the earth, of the drops, and of the nuclei.
Considering the conditions on the
surface of the earth, condensation there takes place in the form of dew,
and the circumstances are very similar to those in higher regions. Dew
is condensed humidity and is deposited chiefly on objects which are good
radiators, and at the same time bad conductors of heat. The humidity of
the air is given either (1) as relative humidity, i.e., the proportion
of the quantity of water vapor which the air contains, to that which it
would were it saturated; or (2) as absolute humidity, i.e., the weight
of the water vapor existing in one cm or one cu ft, given in grams or grains,
respectively. Since the relative humidity depends on the temperature as
a rule, the absolute one is used.
For a longtime the question as to
whether the dew rises or falls was difficult to answer. Aristotle was the
first who asked it, and, according to him, the dew fell — a view which
was taken for granted until the end of the 18th century, when Charles Wells
made his careful experiments, which he described in his “Essays on Dew”
in 1814. His experiments showed clearly that the dew fell, and though later
many scientists worked on this question, nothing was added until John Aitken
(1) showed, in 1880, that the formation of dew was not quite so simple
as Wells had thought, but a complex phenomenon. Aitken proved that the
following conditions are favorable to the formation of dew: good radiating
surface, still atmosphere, warm moist ground or some other supply of moisture
in the surface layers of the earth. The first four conditions he considered
to be necessary, the fifth important to obtain a copious deposit. The formation
of dew over a moist soil may be of great practical importance, for it can
protect plants against night frost. As long as a distillation between the
earth and the plant goes on, the water, condensing on the leaves would
tend to keep their temperature high, but if this heat lost by radiation
were compensated by condensation from the air, then the cooling process
It was Aitken who called attention
to the water drops on the leaves, which one can see glistening in the morning
sun. These drops are regarded as the most striking example that dew has
been deposited. He is of the opinion, however, that these drops are not
condensed from the air but exuded from the pores of the plant. Aitken is
usually referred to as the man who proved that dew rises or falls, or travels
in both directions, as the conditions may be.
Generally speaking, dew is formed
when the dew point curve and the dry bulb cut at the surface of the earth;
if they cut above the surface, mist will be formed, and if below, a distillation
between the layers of the earth takes place, and thus considerable quantities
of water are transported, a process of which our knowledge is still very
There is an important difficulty
regarding apparatus measuring the amount of dew per unit area of surface,
the drosometer as it is called. The recorded measurements are never absolute,
but relative, representing the phenomenon of condensation from the air.
Thus the figures for the annual depth of water fallen as dew differ considerably.
Loesche estimates the amount of dew for a single night on the West African
coast at 3 mm, equal to one-eighth of an inch. On the Desertas, uninhabited
islands near Madeira, dew falls so heavily that sometimes rivulets run
down the mountain slopes. Dr Marloth, of Cape Town, showed that, from December
1902 to February 1902, Iin56 days, on the Table Mountain, moisture condensed
equal to nearly 80 inches of rain; thus, during the dry season about 150
inches of water fall, exclusive of rain. These experiments were doubted,
and he made further investigations near Maclear’s beacon (3500 ft), and
found that, in January 1904, 1.44 inches of rain fell, but his dew gauge
collected 48.42 inches of water. In the same month at Woodhead Reservoir
(2500 ft), 1.83 inches of rain and 13.73 inches of dew were registered.
The amount of dew collected by different
materials is largely due to their nature. W.C. Wells gives a list of materials
according to their capacity for collecting dew. By far the highest effect
was found with swan’s down, then flax and cotton, followed by silk, paper,
straw, wool, earth, charcoal, glass-sand, river-sand, chalk powder —
a list which runs roughly parallel to the specific heats of the materials
However, it is improbable that the
humidity of the air is only condensed on the surface of the earth; it certainly
is absorbed in great quantities, too. Beside the plants, which are able
to absorb water from the air with their leaves, the soil absorbs it as
well. Ginestous (2) has shown that in the northern part of the Sahara desert
the moisture of the regularly blowing north-easterly wind gradually decreases
with the distance from the sea. At Sousse, the humidity is 17 gr/cm, at
Metlauli 10 gr, and at Tamanrasset, which is about 200 miles distant from
the sea, 2.5 gr in the summer. In this distance of 200 miles the air loses
14.5 gr water per cm, or about 30 tons of water per square mile, assuming
the velocity of the air current to be 3 cm/sec. Ginestous is of the opinion
that this water is absorbed by the soil, this giving the necessary moisture
to the plants during the rainless season, for it is worth mentioning that
the humidity of the air is much greater in the summer than in the winter.
In the Nullarbor Plain, at the border
between South and Western Australia, the atmospheric conditions are very
similar to those described above. There, too, a regular wind carries moisture
from the sea inland; but, unfortunately, there are very few meteorological
As already mentioned, nuclei are
essential for the condensation of water from the air, either in form of
dew or of rain, but it is no0t yet clear how a nucleus is to be understood
and how it works. Aitken invented a simple apparatus by means of which
the nuclei present in the air could be counted, and which showed that their
number is not increased by blowing coal, coke, or ordinary dust into the
Sometimes a difference is made between
solid dust particles and hygroscopic substances in the air, but one cannot
see why, e.g., a calcium chloride particle suspended in more or less humid
air should be more hygroscopic than a carbon particle under the same circumstances.
One would rather attribute a different effect of a nucleus and an ordinary
particle to a different electric potential. However, this will not be further
discussed at present.
Is it possible to make rain? Everybody
has heard of the attempts to produce rain by firing shells against the
sky, by exploding dynamite, by blowing sand or chemicals, with or without
electric charges, into the clouds, and these methods may be effective under
appropriate atmospheric conditions; but they certainly are highly expensive
and economically unsound. A different method was employed by Graham Balsillie,
who experimented in Australia during the Great War. It happens, especially
in the inner parts of Australia, that clouds cover the sky day and night,
but no rain falls and the clouds dissolve over some other part of the country.
Balsillie tried to break these clouds up by using electric waves in order
to enlarge the particles, so that rain might fall. He claimed to have caused
exceptionally heavy dews, whereas the Weather Bureau proved that there
were similar large condensations in districts remote from the place of
the experiments. This says nothing against the attempts, and it would be
worthwhile to go further into this matter, for it seems probable the water
particles could be enlarged by electric power.
One process of making rain may be
mentioned, because it is not well known, and is supposed to be effective,
though it has not been studied scientifically. Some of the northern parts
of Mexico consist of desert-like plains, partly overgrown with cacti. Under
certain conditions, which appear to be great heat, no wind, and a cloudless
sky, the Indians set the cacti afire, thus creating a tremendous heat.
After a very short time a downpour of rain sets in, which lasts for a few
minutes only. This is the description given to the author, and if true
the explanation may be that the heat of the fire pushes wet layers of the
air higher up, that they get cooled beneath the dew point and drop their
water in the form of rain.
Thus the prospect of rain-making
is not too encouraging, though there are many places in the world where
mankind has made use of the humidity of the air by condensing it, and a
number of processes have been developed to draw liquid water from the air.
On the Canary Islands a very primitive
way of obtaining water is employed, by shaking the trees in the morning
and collecting the dew condensed on the leaves.
In England two different processes
are to be found. In Cornwall, the rustics smooth the surface of the slop
of a mountain by means of clay, thus preparing an area of about 40 sq ft,
which they surround with a small wall. This are is covered with a thick
layer of straw. During the night the straw collects dew as grass does,
but the former is said to be more effective. As the climate of Cornwall
is damp and the night temperatures in the mountains low, the process works
quite well, but the straw has to be renewed frequently as it putrefies
quickly, being moist day and night.
The best known process is that of
the English dew ponds, mostly in the Midlands and the South of England,
which are characterized best by saying that they do not fail to give water
when other ponds at low levels have dried up. This fact is indubitable,
for many observers, from Gilbert White onward, have confirmed it. The name
of dew pond has been used since the beginning of the 19th century, but
it appears to be purely a scientific expression, for most of the farm laborers
in Sussex, when questioned about dew ponds, rejected the name and called
them mist ponds.
It is easy to get information about
the construction of these ponds, as many know how to build them, thought
there are many different varieties. Generally, such a pond consists of
a saucer-shaped mould covered with a layer of straw, on top of which a
layer of puddled clay is rammed, the latter being frequently protected
by stones or chalk. Martin has given a minute description of the structure
of the different ponds. For ramming the clay carefully, and puddling the
surface, the rustics used to drive horses round and round and through the
pond for a whole day. Martin speaks of a man who remembered that, as a
boy, he knew a pond which sometimes contained a little water. When this
was so he obtained permission to drive the horses on the way home through
the pond in order to cleanse their hoofs. After having done it frequently,
the pond commenced to hold more and more water, showing that it ceased
to leak by the stamping hoofs of the horses.
The base of dew ponds is covered
with grass, and most of them are surrounded by trees or bushes. IF ther
is no grass, the pond dries up regularly. Martin has, to a certain extent,
put an end to the discussion about dew ponds, by proving that they are
not replenished by dew falling on their water surface, as, with few exceptions,
the water is warmer than the air, and no dew could be deposited on them.
Consequently, either mist condenses on the water as Martin believes, or
the grass collects dew which flows towards the center, forming a pond.
Both explanations are probably true. Dew ponds are typically English, as
they rely on the English climate, and there are very few known in other
parts of the world. To give some idea of the amount of water collected
in such ponds, Gilbert White may be quoted. He says that a pond near his
house at Selborne, west of London, which was never more than three feet
deep in the center and not more than 30 feet in diameter, contained about
15,000 gallons of water and was never known to fail, though it afforded
drink for 300 sheep and 20 head of cattle every day.
In the Libyan Desert, Northern Africa,
the Italians have endeavored, since the Great War, to create a water supply
from the atmosphere. They have built high walls of mud bricks with sloping
sides, both of which they covered with smooth, condensing surfaces. At
the bases of either side, troughs or channels are fitted running the whole
length of the alls. Though the desert is arid and barren, the wind carries
moisture from the sea towards the land, and water is deposited in the inner
parts of the walls. A similar process has been used in Spain for centuries,
and the thick walls of stone which are so common in Dalmatia undoubtedly
retain a great deal of water.
The so-called Foggaras of the Sahara
Desert are elaborate constructions, consisting of subterranean passages
many miles long. They are dug by hand into the slopes of the mountains,
and are big enough for a man to walk through upright. They are connected
with the surface of the earth by an air tube at every 75 ft distance. Some
of the foggaras are built on the surface and collect the humidity of the
air, whereas those underneath certainly are fed by seepage, too.
These are the processes for condensing
water from the atmosphere, as they are known and used today; they are not
frequently employed, but the old literature shows that, in the times before
the creation of the Roman Empire, whole townships relied on water condensed
from the air, and many descriptions are given in old books. And it was
by reading Maimonides that the author received the idea of thus condensing
water. He was a Spaniard who lived roughly 1000 years ago, and wrote, besides
philosophic books, a description of Palestine and its people in the Arabic
language. This book contains some hints regarding such a condensation of
water as used there.
Shortly after the war experiments
on dew were carried out, and, the study being a hobby, it took a good many
years to come to a conclusion, for the question was not to condense water
from the air simply by cooling it artificially (as this was too easily
solved), but to construct a highly effective building which condenses water
without or with very low running costs. Gradually it was found that the
knowledge of erecting buildings for water condensation from the air was
spread all over the world, but that the old Greeks seemed to have had the
best knowledge of the process. The usual description of these buildings
in our archaeological literature runs like this” Covered troughs or channels
were found leading up the slope of a mountain right to the top, where ruins
of a great vault were detected, which seemed to have contained water. It
is not known how the water got there, but certainly the town possessed
a very great supply of water from sources which disappeared”. Such descriptions
were found for about 50 towns, which obtained their water in this way,
and most of which belonged to the sphere of Greek influence, but the old
Incas used the same principles and the mystic buildings on some of the
Pacific Islands may have served this purpose, too.
The principle is a very simple one.
In India and other tropical countries, rooms are found in houses which
have very thick walls and small windows right under the ceiling. These
rooms are remarkably cool, and that is understandable, for the cool air
flows through the windows into the room during the night and is kept there
in the daytime, since it cannot escape through the windows, and as these
rooms are well insulated by their thick walls. If, in such a room, holes
are made near the bottom, so that the cool air can flow out, water condenses
on the walls, for the humidity condenses on the cool surfaces.
This process relies not only on the
humidity of the air, which is everywhere present, but also on the difference
between day and night temperatures — the greater this difference the
more favorable are the conditions — and this is the reason why the buildings
of ancient times were situated on the tops of the hills.
At first the process was tried by
insulating a room of a house and making holes at the ceiling and at the
bottom, but this method did not work very well, as houses in Europe usually
stand in the valleys.
A better method consisted in selecting
a mountain slope, smoothing it with cementitious or other material apt
to make the surface watertight, and covering it with an insulating material,
so that the cover formed over the area a canopy or roof which was supported
by pillars or ridges. The sides of the canopy were closed, whereas the
upper and lower ends were left open by constructing holes or vents to allow
the air to pass under the roof. This construction proved to be very successful,
as the cooling surface of the inner part was highly effective. The disadvantage
was that the structure was very expensive, and so a return was made to
the block house type.
Many types of building were tried,
but that finally adopted was a sugarloaf shaped building, about 50 ft high,
with walls at least 6 ft thick, with holes on the top and at the bottom,
the inner surface being enlarged by a network of walls of a material with
great surface. The outer wall is made of concrete to be able to take up
a great amount of thermal units, the inner surface consists of sandstone
or any other porous material. The building produces water during the day
and cols itself during the night; when the sun rises, the warm air is drawn
through the upper holes into the building by the out-flowing cooler air,
becomes cooled on the cold surface, deposits its water, which then oozes
down and is collected somewhere underneath. It is wrong to think that this
process works only on days with dew, as the inner surface becomes much
cooler than one should expect. In Dalmatia, that day was a rare exception
which failed to produce water.
Nearly all the experiments were performed
in Yugoslavia, most of them on the numerous islands of the Adriatic Sea,
some in the inner parts of Dalmatia. The southern parts of the northeastern
coast of Adria have plenty of rain in the winter, but in the summer rain
falls only occasionally, and, as the soil consists of pervious limestone,
this is one of the dry districts of Europe, though the humidity of the
air is high.
The essential principle in obtaining
water from the air has thus been shown to be — a great water condensing
surface which must be well protected against the heat of the sun and at
the same time it is necessary that the air should pass to the condensing
surface slowly, in order that it may cool properly and so deposit its water.
The conclusion of this is — that a big heap of stones would do the same
thing as the above-described buildings. The last experiments in Yugoslavia
followed this line, where one did produce a small amount of water, though
this work was not completed. This process, too, was used by the old Greeks
for the water supply of the town of Theodosia on the Crimean Peninsula,
where artificial heaps of stones condensed the necessary water on the surrounding
hills, whence pipes ran down to the city. These heaps were about 10,000
ft square and 30 ft high, and each of them yielded more than 500 gallons
of water per day.
This paper would be incomplete without
mentioning that in Paris, Achille Knapen (4) is working on the same line
independently of the author. To dry wet walls of buildings, he has invented
a tube, closed at? one side, which he calls “siphon atmospherique
monobranche”, and it has proven successful, as its use is simple, cheap,
and effective. He transferred the principle of this tube to a building,
shaped similar to the above proposition, and erected a big experimental
“Puits Aerien”, as he calls it, near Trans-en-Provence in Southern
France. He has met with success, though his published results have not
yet been seen by the author.
In conclusion, the author feels confident
that it is possible to use this process under Australian conditions, and
so has decided not to apply for a patent, as this would hinder its application.
It would give him much pleasure if one day this process could be seen to
have helped those living in the outback.
(1) Trans. Royal Soc. Edinburgh
(2) La Tunisie Agricole (18-12-192
(3) “Dew Ponds”, Edward A.
Martin (London, 1917)
(4) Memoire et Compte Rendu des
Travaux de la Societe des Ingenieurs Civils de France, 1928, 1929,
Permission to reproduce by Robert Nelson