F JAN. 5, 1872. THE BUILDING NEWS. 5
to abolish, and which they stigmatised as
sewers of deposit. ‘‘ But look,” said the de-
fenders of these large sewers, ‘‘ at the men who
are regularly employed in them: they look
healthy enough.” Now this notion has
reference solely to the experience of London
and other places where the sewers are un-
usually large. In these the obnoxious gases
are largely diluted with atmospheric air. It
is in the higher and smaller branches, in the
house drains, where the concentration takes
place that isso injurious. These places the
Sewer men never approach. When house
drains have to be repaired, or taken up and re-
laid, itis by another set of workmen altogether
that the work is done, and many of these
have suffered illness and death that have been
traced without doubt to the act of opening a
drain at its upper end, and inhaling the pent-
up gases.
In smaller towns, where there is no parti-
cular set of men working regularly in the
sewers, but where sewers have occasionally
to be opened for the purpose of connecting
branches with them, or for the purpose of
repair, the men who do this work are not
exempt from illness caused by the inhalation
of sewer gas to the same extent that the
other class of menare, but, on the contrary,
itis a very common thing for them to go
home ill after having done their work. It is
all a question of dilution. A given quantity
of poisonous sewer gas largely diluted with
atmospheric air may do no harm, but the
Same quantity breathed in a concentrated
form may be fatal.
On the 12th, Mr. Haywood, engineer to the
City Commissioners of Sewers, answers Mr
Gibbs thus :-— ; Sa
“Tt is popularly thought that a system of sewers
resembles a mine. Now, both are subterranean
cHaeae _but were the resemblance ceases, and in
e conditions affectin eir lati
eaten ate ee g their ventilation they are
‘“ A mine consists of a series of passages ‘ally
of about the same sectional cee WThaiver thew
Jength may be, they are carefully adjusted with the
view specially to transit and ventilation; there is
ordinarily but one entrance to a mine, or if more
the mine is divided so as in respect of ventilation
practically to form distinct mines; and whether the
ventilation be by natural or artificial means, there is
but one downeast shaft for the entrance of air and
one upeast shaft for its exit.
“Whatever, therefore, may be the length of
channel im @ mine, and however much the air
currents in them may be turned, divided, and re-
united (and this is largely done), the quantity of air
Set in motion neither loses ner gains materially on
its passage; practically, that quantity which goes
down comes up, and no more; thus the ventilating
power can be calenlated, and within the limits of
the power the quantity of air can be diminished or
sae according to exigencies.
x © sewerage of a town consists of tubes vary-
ing from three inches in diameter to others a re
dved times that capacity, and in London even from
3 inches to 13 feet in diameter. They are laid with
various directions, inclinations, and levels, and at
every 90 fect at least of their length is agulley, sink-
pipe, water-pipe, or other inlet, all of which must
admit water through them, and most of which at
times do, although they should not, admit air to
escape through them. In 1858, when Dr. Letheby
and myself investigated this subject, we found that
peo the City of London alone there were 260
re ge channel and more than 47,000 in-
““ Under existing conditions sewers, therefore, are
but tubes perforated with air holes at intervals along
their entire length, and the application of air exhaus-
ters would be practically useless, for wherever placed
the air currents would rush in with great velocity
towards them from the nearest inlets, the current
becoming feebler and feebler from other inlets as
the distance increased, until the exhausting power
would no longer operate at all.”
On the same day, ‘“ Paterfamilias ” says :—
“At present our architects and builders appear to
ze to ‘lay on” to every dwelling-house a supply of
ae Sewer gases as carefully as they do water and
il uminating gas. Isitnecessary that thesewershould
be brought into the house at all? I think that it is
Be ony unnecessary, but that it should be probibited
y law.
“T have suffered greatly by this system, and I
shall be glad if my experi e ¢
rte & Riko y experience be turned to the ad-
a A
I have disconnected the sewer. All my drains
and water-pipes discharge themselves over the
mouth of a water-trap outside my house. ‘Lhere is
a space between the pipes and the trap; thus the
sewer gas cannot force its way into the house. In
my case the trap has placed immediately over it the
rain-water pipe, so that ifany gas should pass the
trap it would immediately rise above the house.
“T have had this system in operation for two years,
and it answers admirably.”
And Mr. B. W. Gibsone, M.A., of Eaton-
square, says :—
‘1. What substances, may I ask, do we use on a
large scale as antiseptics and disinfectants? Sul-
phurous acid, carbon, and carbolic acid. That these
three are the very ingredients present in a most
transportable form in coal-smoke is too evident to
every eye and nose above ground. To the sewers.
then, let us consign the offender, there it would be
‘the right thing in the right place, for miasma ‘a
perfect cure.’
“2. What simpler ventilation for sewers than that
each house should contribute its now wasted hot-air
in creating a draught down into them and out at a
distant exit, rather than up from them into, possibly,
some exhausted sleeper’s lungs? ‘Tons of force are
now expended every winter day by our house fires
in sucking up into the rooms through the sinks and
closets (all other entrances for air being carefully
closed) the mephitis of the cesspool.
“ Let me hope, then, sir, that both your great ob-
jects, ventilation of the sewers and smoke drainage,
may at no very distant time simultaneously be
effected by one and the same comprehensive sub-
ordination of our efforts as above indicated. Mean-
while, as instalments of the future perfected good,
we might gradually—
“1. Adopt grates, in some measure at least, smoke-
consunnneg,
“2, Erect on rising grounds, tentatively, lofty
furnace-chimneys, exhausting our cloace ; the heat
would be utilised for public washhouses.
“3. Connect the house flues with the sewers, and
trap the openings to the latter.”
We have quoted from this letter, not because
there is anything at all practicable in the
mode of ventilation proposed, for we shall see
by-and-by that the idea of ventilating sewers
and drains by ‘lofty furnace chimneys” is
impracticable, but because the mention of
sulphurous acid and carbon shows that the
writer has a germ of the true idea of ventila-
tion, which is to dilute the gases with
atmospheric air to the utmost possible extent,
and when the atmosphere contains sulphurous
acid and carbon, as it always does in towns,
so much the better, for these sewer gases are
then not only diluted but destroyed by their
action.
——_oa>—_—_
NOTES ON BRICKWORK.—VIUII.
OR small arches and inverts it is necessary
to have bricks moulded purposely to the
different radii, because in using the common
building bricks the back of the joint is too
thick for sound work. Culverts and sewers
especially require the sides of the bricks to
coincide with the radius of the circle of which
the arch or invert forms a part, so that the
joints may be as nearly as possible of the same
thickness at the back as at the front, other-
wise the unequal extent to which the mortar
joints would be compressed would distort the
work; and besides that the use of square
‘bricks is wasteful of mortar. Arches and inverts are generally turned in half-brick rings, all the bricks being laid as stretchers, and in using square bricks, in arches of greater radius, that system makes better work than if the bricks were laid as headers, because the back of the joint would then be double the thickness; but with radiated bricks there does not seem to be the same reason for this system of half-brick rinys, for it would seem to be as easy to mould the bricks with the thin edge at the end as at the side, and it would also seem that that method would make sounder work. It is usual to retain nearly the same bulk in radiated bricks as in the common square bricks, about Yin. long, 44in. wide, and a mean thickness of 23in. ; but for sewers, where it has been judged that a single half-brick ring was not sufficient and that two made the work unnecessarily thick, bricks have been moulded for the occasion of the dimensions of 9in. long, Gin. wide, and 2#in. mean thick- ness. ‘These were not found to be incon- venient in the handling.
When sewers or culverts are laid in
trenches in the solid ground they need no
footings, as is shown in Fig. 17 and 18, for
the ground can be got out to the shape of
the invert in most cases ; but when culverts
are laid to carry streams under embank-
ments a footing of brickwork is necessary,
as shown in Fig. 19, which represents a cul-
vert 4 feet diameter. For large culverts the
form shown in Fig. 20 is preferable.
It has been considered best to make sewers
egg-shaped, as shown in Fig. 18, with the
object of increasing as much as possible the
hydraulic mean depth when the flow of sew-
age is small in comparison with the whole
capacity of the sewer, by concentrating the
flow instead of allowing it to spread over a
greater width and attain a less depth.
The best proportions of height and width
of an egg-shaped sewer are—height 3, width
2;radius of sides 3, of arch 2, and of in-
vert 1.
FiIc.I3
FICG.A7
eee
Fig. 21 isa bridge of 12 feet span, with
semicircular arches. All arches should be
backed up at the haunches, but semicircular
arches especially so, for that is their weak
point.
Fig. 22 is a bridge with segmental arches,
in which case the abutments require to be
thicker than with semicircular arches ; either,
that is to say, thicker bodily, or to be
strengthened with counterforts, the spaces
between which may be arched oyer. The
rise of the arch in this example is one-fifth
of the span. In all the examples hitherto
mentioned the arches are struck from one
centre.
In Fig. 23, which is a section of a bridge
which carries a road over a railway, the arch
is struck from three centres.
The proper names of the parts of bridges
are as follow. The foundations are those
parts of the abutments and piers below
the plinth, the plinth being formed by a set-
off just above the ground level. The abut-
ment is the mass of masonry—brickwork is
included in the generic name of masonry—
which is placed so as to oppose its resistance
to the horizontal thrust of the arch, the di-
mension of which mass horizontally is re-
