Popular science has penetrated too deeply now to render necessary any
refutation of the old popular fallacy which attributed the bursting of
water-pipes to the thaw following a frost; everybody now understands
that the thaw merely renders the work of the previous freezing so
disastrously evident. Nevertheless, the general subject of the action
of freezing water upon our dwellings is not so fully understood by all
concerned as it should be. Builders and house-owners should understand
it thoroughly, as most of the domestic miseries resulting from
severe winters may be greatly mitigated, if not entirely prevented,
by scientific adaptation in the course of building construction.
Now-a-days tenants know something about this and select accordingly.
Thus the market value of a building may be increased by such adaptation.
Solids, liquids, and gases expand as they are heated. This great
general law is, however, subject to a few exceptions, the most
remarkable of which is that presented by water. Let us suppose a simple
experiment. Imagine a thermometer tube with its bulb and stem so filled
with water that when the water is heated nearly to its boiling point
it will rise to nearly the top of the long stem. Now let us cool it.
As the cooling proceeds the water will descend, and this descending
will continue until it attains the temperature marked on our ordinary
thermometer as 39°, or more strictly 39-2/10; then a strange inversion
occurs. As the temperature falls below this, the water rises gradually
in the stem until the freezing point is reached.
This expansion amounts to 1/7692 part of the whole bulk of the water,
or 100,000 parts become 100,013. So far the amount of expansion is
very small, but this is only a foretaste of what is coming. Lower the
temperature still further, the water begins to freeze, and at the
moment of freezing it expands suddenly to an extent equalling 1/15 of
its bulk, _i.e._, of the bulk of so much water as becomes solidified.
The temperature remains at 32° until the whole of the water is frozen.
Fortunately for us, the freezing of water is always a slow process,
for if this conversion of every 15 gallons into 16 took place
suddenly, all our pipes would rip open with something like explosive
violence. But such sudden freezing of any considerable quantity of
water is practically impossible, on account of the “latent heat” of
liquid water, which amounts to 142½°. All this is given out in the
act of freezing. It is this giving out of so much heat that keeps the
temperature of freezing water always at 32°, even though the air around
may be much colder. No part of the water can fall below 32° without
becoming solid, and that portion which solidifies gives out enough heat
to raise 142½ times its own quantity from 31° to 32°.
The slowness of thawing is due to the same general fact. An instructive
experiment may be made by simply filling a saucepan with snow or broken
ice, and placing it over a common fire. The slowness of the thawing
will surprise most people who have not previously tried the experiment.
It takes about as long to melt this snow as it would to raise an equal
weight of water from 32° to 174°. Or, if a pound of water at 174° be
mixed with a pound of snow at 32°, the result will be two pounds of
water at 32°; 142° will have disappeared without making the snow any
warmer, it will all have been used up in doing the work of melting.
The force with which the great expansion due to freezing takes place is
practically irresistible. Strong pieces of ordnance have been filled
with water, and plugged at muzzle and touch-hole. They have burst in
spite of their great thickness and tenacity. Such being the case, it
is at first sight a matter of surprise that frozen water-pipes, whether
of lead or iron, ever stand at all. They would not stand but for
another property of ice, which is but very little understood, viz., its
_viscosity_.
This requires some explanation. Though ice is what we call a solid,
it is not truly solid. Like other apparent solids it is not perfect
rigid, but still retains some degree of the possibility of flowing
which is the characteristic of liquids. This has been shown by filling
a bombshell with water, leaving the fuse-hole open and freezing it. A
shell of ice is first formed on the outside, which of course plugs up
the fuse-hole. Then the interior gradually freezes, but the expansion
due to this forces the ice out of the fuse-hole as a cylindrical stick,
just as putty might be squeezed out, only that the force required to
mould and eject the ice is much greater.
I have constructed an apparatus which illustrates this very strikingly.
It is an iron syringe with cylindrical interior of about half an inch
in diameter, and a terminal orifice of less than 1/20 of an inch in
diameter. Its piston of metal is driven down by a screw. Into this
syringe I place small fragments of ice, or a cylinder of ice fitted to
the syringe, and then screw down the piston. Presently a thin wire of
ice is squirted forth like vermicelli when the dough from which it is
made is similarly treated, showing that the ice is plastic like the
dough, provided it is squeezed with sufficient force.
This viscosity of ice is displayed on a grand scale in glaciers, the
ice of which actually flows like a river down the glacier valley,
contracting as the valley narrows and spreading out as it widens, just
as a river would; but moving only a few inches daily according to the
steepness of the slope and the season, slower in winter than in summer.
Upon this, and the slowness of the act of freezing, depends the
possibility of water in freezing in iron pipes without bursting them.
Even iron yields a little before bursting, but ordinary qualities not
sufficiently to bear the expansion of 1/15 of their contents. What
happens then? The cylinder of ice contained in the tube elongates as
it freezes, provided always the pipe is open at one or both ends.
But there is a limit to this, seeing that the friction of such a
tight-fitting core, even of slippery ice, is considerable, and if
the pipe be too long, the resistance of this friction may exceed the
resistance of tenacity of the pipe. I am unable to give any figures for
such length; the subject does not appear to have been investigated as
it should be, and as it might well be by our wealthy water companies.
We all know that lead pipes frequently succumb, but a little
observation shows that they do so only after a struggle. The tenacity
of lead is much less than that of iron (about 1/20 of that of ordinary
wrought iron), but it yields considerably before breaking. It has, in
fact, the property of viscosity similar to that of ice. At Woolwich the
lead used for elongated rifle bullets is squirted like the ice in my
syringe above described, powerful hydraulic pressure being used.
This yielding saves many pipes. It would save all _new_ pipes if the
lead were pure and uniform; but as this is not the case, they may burst
at a weak place, the yielding being shown by the bulge that commonly
appears at the broken part.
From the above it will be easily understood that a pipe which is
perfectly cylindrical—other conditions equal—will be less likely to
burst than one which is of varying diameter, as the sliding from a
larger to a smaller portion of the pipe must be attended with great
resistance, or a certain degree of block, beyond what would be due to
the mere friction along a pipe of uniform diameter.
Let us now consider the relative merits of lead and iron as material
for water-pipes in places where exposure to frost is inevitable. Lead
yields more than iron, and so far has an advantage; this, however is
but limited. As lead is practically inelastic, every stretch remains,
and every stretch diminishes the capacity for further stretching; the
lead thus stretched at one frost is less able to stretch again, and has
lost some of its original tenacity. Hence the superiority of new leaden
pipes. Iron is elastic within certain limits, and thus the iron pipe
may yield a little without permanent strain or “distress,” and if its
power of elastic resistance is not exceeded, it regains its original
size without becoming sensibly weaker. Add to this its great tenacity,
its nonliability to be indented, or otherwise to vary in diameter, and
we have a far superior material.
But this conclusion demands some qualification. There is iron and
iron, cast-iron and wrought-iron, and very variable qualities of each
of these. I need scarcely add that common brittle cast-iron is quite
out of the question for such purposes, though there is a new kind of
cast-iron or semi-steel coming forward that may possibly supersede all
other kinds; but this opens too wide a subject for discussion in the
present paper, the main object of which has been a popular exposition
of the general physical laws which must be obeyed by the builder, or
engineer, who desires to construct domestic or other buildings that
will satisfy the wants of intelligent people.
The mischievous action of freezing water is not confined to the pipes
that are constructed to receive or convey it. Wherever water may be,
if that water freezes, it must expand in the degree and with the force
already described. If it penetrates stone or brick, or mortar or
stucco, and freezes therein, one of two things must occur—either the
superfluous ice must exude at the surface or to neighboring cavities,
or the saturated material must give way, and split or crumble according
to the manner and degree of penetration. To understand this, the reader
must remember what I stated about the little-understood _viscosity_ of
ice, as well as its expansion at the moment of freezing.
Bricks are punished, but not so severely as might be anticipated,
seeing how porous are some of the common qualities, especially those
used in London. They are so amply porous that the water not only finds
its way into them, but the pores are big enough and many enough for
the ice to demonstrate its viscosity by squeezing out and displaying
its crystalline structure in the form of snow-like efflorescence on
the surface. This may have been observed by some of my readers during
a severe frost. It is commonly confounded with the hoar-frost that
whitens the roofs of houses, but which is very rarely deposited on
perpendicular wall faces.
The mortar most liable to suffer is that which is porous and
pulverulent within, but has been cleverly faced or pointed with a
crust of more compact material. This outer film prevents the exuding
of the expanding ice crystals, is thrust forth bodily, and retained by
ice-cement during the frost, but it falls in scales when this temporary
binding material thaws. Mortar that is compact throughout does not
suffer to any appreciable extent. This is proved by the condition of
the remains of Roman brickwork that still exist in Britain and other
parts of Europe. Some of the old shingle walls at Brighton and other
parts of the south coast, where the chalk for lime-burning was at the
builder’s feet, and where his mortar is so thickly laid between the
irregular masses of flint, also show the possible duration of good
mortar. The jerry builder’s mortar, made of the riddlings of burnt
clay ballast and dust-hole refuse just flavored with lime, crumbles
immediately, because these materials do not combine with the lime as
fine siliceous sand gradually does, to form an impermeable glassy
silicate.
Stucco is punished by two distinct modes of action. The first is where
the surface is porous, and the water permeates accordingly and freezes.
This, of course, produces superficial crumbling, which should not occur
at all upon good material protected by suitable paint. The other case,
very deplorable in many instances, is where the water finds a space
between the inner surface of the stucco and the outer surface of the
material upon which it is laid. This water, when frozen, of course,
expands, and wedges away the stucco bodily, causing it to come down in
masses at the thaw. This, however, only occurs after severe frosts,
as the ordinary mild frosts of our favored climate seldom endure long
enough to penetrate to any notable depth of so bad a conductor as stone
or stucco. It is worthy of note that water is a still worse conductor
than stone.
Building stones are so various both in chemical composition and
mechanical structure that the action of freezing water is necessarily
as varied as the nature of the material. The highly siliceous granites
(or, rather, porphyries that commonly bear the name of granite) are
practically impermeable to water so long as they are free from any
chemical decomposition of their feldspathic constituents; but when we
come to sandstones and limestones, or intermediate material, very wide
differences prevail.
The possible width of this difference is shown in the behavior of the
unselected material in its natural home. Certain cliffs and mountains
have stood for countless ages almost unchanged by the action of
frost; others are breaking up with astonishing rapidity in spite of
apparent solidity of structure. The Matterhorn, or Mont Cervin, one
of the most gigantic of the giant Alps, 15,200 feet high, is rendered
especially dangerous to ambitious climbers by the continual crashing
down of fragments that are loosened when the summer sun melts the ice
that first separated and then for a while held them in their original
places. All the glaciers of the Alps are more or less streaked with
“moraines,” which are fragments of the mountains that freezing water
has detached.
Our stone buildings would suffer proportionally if some selection of
material were not made. Generally speaking, this selection is based
upon the experience of previous practical trials. Certain quarries are
known to have supplied good material of a certain character, and this
quarry has, therefore, a reputation which is usually of no small value
to its fortunate owner. Other quarries are opened in the neighborhood
wherever the rock resembles that of the tested quarry.
Sometimes, however, materials are open for selection that have not been
so well tested, and a method of testing which is more expeditious and
less expensive than constructing a building and watching the result, is
very desirable. The subject of testing building materials in special
reference to their resistance of frost was brought before the Academy
of Science of Paris by M. Brard some years since.
In his preliminary experiments he used small cubes of the stone to
be tested, soaked them in water, and then exposed them to the air in
frosty weather, or subjected them to the action of freezing mixtures.
Afterwards he found that by availing himself of the expansive force
which certain saline solutions exert at the moment of crystallization,
he could conveniently imitate the action of freezing without the aid
of natural or artificial frost. Epsom salts, nitre, alum, sulphate of
iron, Glauber’s salts, etc., were tried. The last named, Glauber’s salt
(or sulphate of soda), which is very cheap, was found to be the best
for the purpose.
His method of applying the test is as follows: Cut the specimens into
two-inch cubes, with flat sides and sharp edges and corners, mark each
specimen with a number, either by ink or scratching, and enter in a
book all particulars concerning it. Make a saturated solution of the
sulphate of soda in rain or distilled water, by adding the salt until
no more will dissolve; perfect saturation being shown by finding, after
repeated stirring, that a little of the salt remains at the bottom
an hour or two after the solution was made. Heat this solution in a
suitable vessel, and when it boils put in the marked specimens one by
one, and keep them immersed in the boiling solution for half an hour.
Take out the specimens separately and suspend them by threads, each
over a separate vessel containing some of the liquid in which they were
boiled, but which has been carefully strained to free it from any solid
particles. In the course of a day or two, as the cubes dry, they will
become covered with an efflorescence of snow-like crystals; wash these
away by simply plunging the specimen into the vessel below, and repeat
this two or three times daily for four or five days or longer. The most
suitable vessel for the purpose is a glass “beaker,” sold by vendors of
chemical apparatus.
In comparing competing samples, be careful to treat all alike, _i.e._,
boil them together in the same solution, and dip them an equal number
of times at equal intervals.
Having done this, the result is now to be examined. If the stone is
completely resistant the cube will remain smooth on its surfaces and
sharp at its edges and corners, and there will be no particles at the
bottom of the vessel. Otherwise, the inability of the stone to resist
the test will be shown by the disfigurement of the cube or the small
particles wedged off and lying at the bottom of the liquid. Care must
be taken not to confound these with crystals of the salt which may also
be deposited. These crystals are easily removed by adding a little more
water or warming the solution.
For strict comparison the fragments thus separated should be weighed in
a delicate balance, such as is used in chemical analysis.