Chapter II: Forensic Speeches (16)

The composition of house refuse, which must obviously affect its calorific value, varies considerably in different localities, according to the condition, habits and pursuits of the people. Towns situated in coal-producing districts invariably yield a refuse richer in unconsumed carbon than those remote therefrom. It is also often found that the refuse from different parts of the same town varies considerably--that from the poorest quarters frequently proving of greater calorific value than that from those parts occupied by the rich and middle classes. This has been attributed to the more extravagant habits of the working classes in neglecting to sift the ashes from their fires before disposing of them in the ash-bin. In Bermondsey, for example, the refuse has been found to possess an unusually high calorific value, and this experience is confirmed in other parts of the metropolis. Average refuse consists of breeze (cinder and ashes), coal and coke, fine dust, vegetable and animal matters, straw, shavings, cardboard, bottles, tins, iron, bones, broken crockery and other matters in very variable proportions according to the character of the district from which it is collected. In London the quantity of house refuse amounts approximately to 1¼ million tons per annum, which is equivalent to from 4 cwt. to 5 cwt. per head per annum, or to from 200 to 250 tons per 1000 of the population per annum. Statistics, however, vary widely in different districts. In the vicinity of the metropolis the amount varies from 2.5 cwt. per head per annum at Leyton to 3.5 cwt. at Hornsey, and to as much as 7 cwt. at Ealing. In the north of England the total house refuse collected, exclusive of street sweepings, amounts on the average to 8 cwt. per head per annum. Speaking generally, throughout the country an amount of from 5 cwt. to 10 cwt. per head per annum should be allowed for. A cubic yard of ordinary house refuse weighs from 12¼ to 15 cwt. Shop refuse is lighter, frequently containing a large proportion of paper, straw and other light wastes. It sometimes weighs as little as 7¼ cwt. per cubic yard. A load, by which refuse is often estimated, varies in weight from 15 cwt. to 1½ tons.

Refuse disposal.

The question how a town's refuse shall be disposed of must be considered both from a commercial and a sanitary point of view. Various methods have been practised. Sometimes the household ashes, &c., are mixed with pail excreta, or with sludge from a sewage farm, or with lime, and disposed of for agricultural purposes, and sometimes they are conveyed in carts or by canal to outlying and country districts, where they are shot on waste ground or used to fill up hollows and raise the level of marshland. Such plans are economical when suitable outlets are available. To take the refuse out to sea in hopper barges and sink it in deep water is usually expensive and frequently unsatisfactory. At Bermondsey, for instance, the cost of barging is about 2s. 9d. a ton, while the material may be destroyed by fire at a cost of from 10d. to 1s. a ton, exclusive of interest and sinking fund on the cost of the works. In other cases, as at Chelsea and various dust contractors' yards, the refuse is sorted and its ingredients are sold; the fine dust may be utilized in connexion with manure manufactories, the pots and pans employed in forming the foundations of roads, and the cinders and vegetable refuse burnt to generate steam. In the Arnold system, carried out in Philadelphia and other American towns, the refuse is sterilized by steam under pressure, the grease and fertilizing substances being extracted at the same time; while in other systems, such as those of Weil and Porno, and of Defosse, distillation in closed vessels is practised. But the destructor system, in which the refuse is burned to an innocuous clinker in specially constructed furnaces, is that which must finally be resorted to, especially in districts which have become well built up and thickly populated.

Types of destructors.

Various types of furnaces and apparatus have from time to time been designed, and the subject has been one of much experiment and many failures. The principal towns in England which took the lead in the adoption of the refuse destructor system were Manchester, Birmingham, Leeds, Heckmondwike, Warrington, Blackburn, Bradford, Bury, Bolton, Hull, Nottingham, Salford, Ealing and London. Ordinary furnaces, built mostly by dust contractors, began to come into use in London and in the north of England in the second half of the 19th century, but they were not scientifically adapted to the purpose, and necessitated the admixture of coal or other fuel with the refuse to ensure its cremation. The Manchester corporation erected a furnace of this description about the year 1873, and Messrs Mead & Co. made an unsatisfactory attempt in 1870 to burn house refuse in closed furnaces at Paddington. In 1876 Alfred Fryer erected his destructor at Manchester, and several other towns adopted this furnace shortly afterwards. Other furnaces were from time to time brought before the public, among which may be mentioned those of Pearce and Lupton, Pickard, Healey, Thwaite, Young, Wilkinson, Burton, Hardie, Jacobs and Odgen. In addition to these the "Beehive" and the "Nelson" destructors became well known. The former was introduced by Stafford and Pearson of Burnley, and one was erected in 1884 in the parish yard at Richmond, Surrey, but the results being unsatisfactory, it was closed during the following year. The "Nelson" furnace, patented in 1885 by Messrs Richmond and Birtwistle, was erected at Nelson-in-Marsden, Lancashire, but being very costly in working was abandoned. The principal types of destructors now in use are those of Fryer, Whiley, Horsfall, Warner, Meldrum, Beaman and Deas, Heenan and Froude, and the "Sterling" destructor erected by Messrs Hughes and Stirling.

Fryer's.

The general arrangement of the destructor patented[1] by Alfred Fryer
in 1876 is illustrated in fig. 1. An installation upon this principle
consists of a number of furnaces or cells, usually arranged in pairs
back to back, and enclosed in a rectangular block of brickwork having
a flat top, upon which the house refuse is tipped from the carts.

A large main flue, which also forms the dust chamber, is placed
underneath the furnace hearths. The Fryer furnace ordinarily burns
from 4 to 6 tons of refuse per cell per 24 hours. It will be observed
that the outlets for the products of combustion are placed at the
back near the refuse feed opening, an arrangement which is imperfect
in design, inasmuch as while a charge of refuse is burning upon the
furnace bars the charge which is to follow lies on the dead hearth
near the outlet flue. Here it undergoes drying and partial
decomposition, giving off offensive empyreumatic vapours which pass
into the flue without being exposed to sufficient heat to render them
entirely inoffensive. The serious nuisances thus produced in some
instances led to the introduction of a second furnace, or "cremator,"
patented by C. Jones of Ealing in 1885, which was placed in the main
flue leading to the chimney-shaft, for the purpose of resolving the
organic matters present in the vapour, but the greatly increased cost
of burning due to this device led to its abandonment in many cases.
This type of cell was largely used during the early period of the
history of destructors, but has to a considerable extent given place
to furnaces of more modern design.

Whiley's.

A furnace[2] patented in 1891 by Mr Henry Whiley, superintendent of
the scavenging department of the Manchester corporation, is automatic
in its action and was designed primarily with a view to saving
labour--the cells being fed, stoked and clinkered automatically.
There is no drying hearth, and the refuse carts tip direct into a
shoot or hopper at the back which conducts the material directly on
to movable eccentric grate bars. These automatically traverse the
material forward into the furnace, and finally push it against a
flap-door which opens and allows it to fall out. This apparatus is
adapted for dealing with screened rather than unscreened refuse,
since it suffers from the objection that the motion of the bars tends
to allow fine particles to drop through unburnt. Some difficulty has
been experienced from the refuse sticking in the hopper, and
exception may also be taken to the continual flapping of the door
when the clinker passes out, as cold air is thereby admitted into the
furnace. As in the Fryer cell, the outlet for the products of
combustion into the main flue is close to the point where the crude
refuse is fed into the furnace, and the escape of unburnt vapours is
thus facilitated. Forced draught is applied by means of a Roots
blower. The Manchester corporation has 28 cells of this type in use,
and the approximate amount of refuse burnt per cell per 24 hours is
from 6 to 8 tons at a cost per ton for labour of 3.47 pence.

Horsfall's.

Horsfall's destructor[3] (fig. 2) is a high-temperature furnace of
modern type which has been adopted largely in Great Britain and on
the continent of Europe. In it some of the general features of the
Fryer cell are retained, but the details differ considerably from
those of the furnaces already described. Important points in the
design are the arrangement of the flues and flue outlets for the
products of combustion, and the introduction of a blast duct through
which air is forced into a closed ash-pit. The feeding-hole is
situated at the back of and above the furnace, while the flue opening
for the emission of the gaseous products is placed at the front of
the furnace over the dead plate; thus the gases distilled from the
raw refuse are caused to pass on their way to the main flue over the
hottest part of the furnace and through the flue opening in the
red-hot reverberatory arch. The steam jet, which plays an important
part in the Horsfall furnace, forces air into the closed ash-pit at a
pressure of about ¾ to 1 in. of water, and in this way a temperature
varying from 1500° to 2000° F., as tested by a thermo-electric
pyrometer, is maintained in the main flue. In a battery of cells the
gases from each are delivered into one main flue, so that a uniform
temperature is maintained therein sufficiently high to prevent
noxious vapours from reaching the chimney. The cells being charged
and clinkered in rotation, when the fire in one is green, in the
others it is at its hottest, and the products of combustion do not
reach the boiler surfaces until after they have been mixed in the
main flue. The cast iron boxes which are provided at the sides of the
furnaces, and through which the blast air is conveyed on its way to
the grate, prevent the adhesion of clinker to the side walls of the
cells, and very materially preserve the brickwork, which otherwise
becomes damaged by the tools used to remove the clinker. The wide
clinkering doors are suspended by counterbalance weights and open
vertically. The rate of working of these cells varies from 8 tons per
cell per 24 hours at Oldham to 10 tons per cell at Bradford, where
the furnaces are of a later type. The cost of labour in stoking and
clinkering is about 6d. per ton of the refuse treated at Bradford,
and 9d. per ton at Oldham, where the rate of wages is higher.
Well-constructed and properly-worked plants of this type should give
rise to no nuisance, and may be located in populous neighbourhoods
without danger to the public health or comfort. Installations were
put down at Fulham (1901), Hammerton Street, Bradford (1900), West
Hartlepool (1904), and other places, and the surplus power generated
is employed in the production of electric energy.

Warner's.

Warner's destructor,[4] known as the "Perfectus," is, in general
arrangement, similar to Fryer's, but differs in being provided with
special charging hoppers, dampers in flues, dust-catching
arrangements, rocking grate bars and other improvements. The refuse
is tipped into feeding-hoppers, consisting of rectangular cast iron
boxes over which plates are placed to prevent the escape of smoke and
fumes. At the lower portion of the feeding-hopper is a flap-door
working on an axis and controlled by an iron lever from the tipping
platform. When refuse is to be fed into the furnace the lever is
thrown over, the contents of the hopper drop on to the sloping
firebrick hearth beneath, and the door is at once closed again. The
door should be kept open as short a time as possible in order to
prevent the admission of cold air into the furnace at the back end,
since this leads to the lowering of the temperature of the cells and
main flue, and also to paper and other light refuse being carried
into the flues and chimney. The flues of each furnace are provided
with dampers, which are closed during the process of clinkering in
order to keep up the heat. The cells are each 5 ft. wide and 11 ft.
deep, the rearmost portion consisting of a firebrick drying hearth,
and the front of rocking grate bars upon which the combustion takes
place. The crown of each cell is formed of a reverberatory firebrick
arch having openings for the emission of the products of combustion.
The flap dampers which are fitted to these openings are operated by
horizontal spindles passing through the brickwork to the front of the
cell, where they are provided with levers or handles; thus each cell
can be worked independently of the others. With the view of
increasing the steam-raising capabilities of the furnace, forced
draught is sometimes applied and a tubular boiler is placed close to
the cells. The amount of refuse consumed varies from 5 tons to 8 tons
per cell per 24 hours. At Hornsey, where 12 cells of this type are in
use, the cost of labour for burning the refuse is 9½d. per ton.

Meldrum's

The Meldurm "Simplex" destructor (fig. 3), a type of furnace which
yields good steam-raising results, is in successful operation at
Rochdale, Hereford, Darwen, Nelson, Plumstead and Woolwich, at each
of which towns the production of steam is an important consideration.
Cells have also been laid down at Burton, Hunstanton, Blackburn and
Shipley, and more recently at Burnley, Cleckheaton, Lancaster,
Nelson, Sheerness and Weymouth. In general arrangement the destructor
differs considerably from those previously described. The grates are
placed side by side without separation except by dead plates, but, in
order to localize the forced draught, the ash-pit is divided into
parts corresponding with the different grate areas. Each ash-pit is
closed air-tight by a cast iron plate, and is provided with an
air-tight door for removing the fine ash. Two patent Meldrum
steam-jet blowers are provided for each furnace, supplying any
required pressure of blast up to 6 in. water column, though that
usually employed does not exceed 1½ in. The furnaces are designed for
hand-feeding from the front, but hopper-feeding can be applied if
desirable. The products of combustion either pass away from the back
of each fire-grate into a common flue leading to boilers and the
chimney-shaft, or are conveyed sideways over the various grates and a
common fire-bridge to the boilers or chimney. The heat in the gases,
after passing the boilers, is still further utilized to heat the air
supplied to the furnaces, the gases being passed through an air
heater or continuous regenerator consisting of a number of cast iron
pipes from which the air is delivered through the Meldrum "blowers"
at a temperature of about 300° F. That a high percentage (15 to
18%) of CO_2 is obtained in the furnaces proves a small excess of
free oxygen, and no doubt explains the high fuel efficiency obtained
by this type of destructor. High-pressure boilers of ample capacity
are provided for the accumulation during periods of light load of a
reserve of steam, the storage being obtained by utilizing the
difference between the highest and lowest water-levels and the
difference between the maximum and working steam-pressure. Patent
locking fire-bars, to prevent lifting when clinkering, are used in
the furnace and have a good life. At Rochdale the Meldrum furnaces
consume from 53 lb. to 66 lb. of refuse per square foot of grate
area per hour, as compared with 22.4 lb. per square foot in a
low-temperature destructor burning 6 tons per cell per 24 hours with
a grate area of 25 sq. ft. The evaporative efficiency of the Rochdale
furnaces varies from 1.39 lb. to 1.87 lb. of water (actual) per 1
lb. of refuse burned, and an average steam-pressure of about 114
lb. per square inch is maintained. The cost of labour and
supervision amounts to 10d. per ton of refuse dealt with. A
Lancashire boiler (22 ft. by 6 ft. 6 in.) at the Sewage Outfall
Works, Hereford, evaporates with refuse fuel 2980 lb. of water per
hour, equal to 149 indicated horse-power. About 54 lb. of refuse are
burnt per square foot of grate area per hour with an evaporation of
1.82 lb. of water per pound of refuse.

Beaman and Deas.

The Beaman and Deas destructor[5] (fig. 4) has attracted much
attention from public authorities, and successful installations are
in operation at Warrington, Dewsbury, Leyton, Canterbury, Llandudno,
Colne, Streatham, Rotherhithe, Wimbledon, Bolton and elsewhere. Its
essential features include a level-fire grate with ordinary type
bars, a high-temperature combustion chamber at the back of the cells,
a closed ash-pit with forced draught, provision for the admission of
a secondary air-supply at the fire-bridge, and a firebrick hearth
sloping at an angle of about 52°. From the refuse storage platform
the material is fed into a hopper mouth about 18 in. square, and
slides down the firebrick hearth, supported by T-irons, to the grate
bars, over which it is raked and spread with the assistance of long
rods manipulated through clinkering doors placed at the sides of the
cells. A secondary door in the rear of the cell facilitates the
operation. The fire-bars, spaced only 3/32 in. apart, are of the
ordinary stationary type. Vertically, under the fire-bridge, is an
air-conduit, from the top of which lead air blast pipes 12 in. in
diameter discharging into a hermetically closed ash-pit under the
grate area. The air is supplied from fans (Schiele's patent) at a
pressure of from 1½ to 2 in. of water, and is controlled by means of
baffle valves worked by handles on either side of the furnace,
conveniently placed for the attendant. The forced draught tends to
keep the bars cool and lessen wear and tear. The fumes from the
charge drying on the hearth pass through the fire and over the
red-hot fire-bridge, which is perforated longitudinally with
air-passages connected with a small flue leading from a grated
opening on the face of the brickwork outside; in this way an
auxiliary supply of heated oxygen is fed into the combustion chamber.
This chamber, in which a temperature approaching 2000° F. is
attained, is fitted with large iron doors, sliding with balance
weights, which allow the introduction of infected articles, bad meat,
&c., and also give access for the periodical removal of fine ash from
the flues. The high temperatures attained are utilized by installing
one boiler, preferably of the Babcock & Wilcox water-tube type, for
each pair of cells, so that the gases, on their way from the
combustion chamber to the main flue, pass three times between the
boiler tubes. A secondary furnace is provided under the boiler for
raising steam by coal, if required, when the cells are out of use.
The grate area of each cell is 25 sq. ft., and the consumption varies
from 16 up to 20 tons of refuse per cell per 24 hours. In a 24-hours'
test made by the superintendent of the cleansing department, Leeds,
at the Warrington installation, the quantity of water evaporated per
pound of refuse was 1.14 lb., the average temperature in the
combustion chamber 2000° F. by copper-wire test, and the average air
pressure with forced draught 2½ in. (water-gauge). At Leyton, which
has a population of over 100,000, an 8-cell plant of this type is
successfully dealing with house refuse and filter press cakes of
sewage sludge from the sewage disposal works adjoining, and even with
material of this low calorific value the total steam-power produced
is considerable. Each cell burns about 16 tons of the mixture in 24
hours and develops about 35 indicated horse-power continuously, at an
average steam-pressure in the boilers of 105 lb. The cost of labour
at Leyton for burning the mixed refuse is about 1s. 7d. per ton; at
Llandudno, where four cells were laid down in connexion with the
electric-light station in 1898, it is 1s. 3¼d., and at Warrington
9½d. per ton of refuse consumed. Combustion is complete, and the
destructor may be installed in populous districts without nuisance to
the inhabitants. Further patents (Wilkie's improvements) have been
obtained by Meldrum Brothers (Manchester) in connexion with this
destructor.

Heenan.

The Heenan furnaces are in operation at Farnworth, Gloucester,
Barrow-in-Furness, Northampton, Mansfield, Wakefield, Blackburn,
Levenshulme, Kings Norton, Worthing, Birmingham and other places, and
are now dealing with over 1200 tons of refuse per day. The general
arrangement of this destructor somewhat resembles that of the Meldrum
type. The cells intercommunicate, and the mechanical mixture of the
gases arising from the furnace grates of the various cells is sought
by the introduction of a special design of reverberatory arch
overlying the grates. The standard arrangement of this destructor
embodies all modern arrangements for high-temperature refuse
destruction and steam-power generation.

Sterling.

Destructors of the "Sterling" type, combined with electric-power
generating stations, are installed at Hackney (1901), Bermondsey
(1902) and Frederiksberg (1903)--the first-named plant being probably
the most powerful combined destructor and electricity station yet
erected. In these modern stations the recognized requirements of an
up-to-date refuse-destruction plant have been well considered and
good calorific results are also obtained.

In addition to the above-described destructors, other forms have been
introduced from time to time, but adopted to a less degree; amongst
these may be mentioned Baker's destructor, Willshear's, Hanson's
Utilizer, Mason's Gasifier, the Bennett-Phythian, Cracknell's
(Melbourne, Victoria), Coltman's (Loughborough), Willoughby's, and
Healey's improved destructors. On the continent of Europe systems for
the treatment of refuse have also been devised. Among these may be
mentioned those of M. Defosse and M. Helouis. The former has
endeavoured to burn the refuse in large quantities by using a forced
draught and only washing the smoke.[6] Helouis has extended the
operation by using the heat from the combustion of the refuse for
drying and distilling the material which is brought gradually on to
the grate.

Destructor accessories.

Boulnois and Brodie's improved charging tank is a labour-saving
apparatus consisting of a wrought iron truck, 5 ft. wide by 3 ft.
deep, and of sufficient length to hold not less than 12 hours supply
for the two cells which it serves. The truck, which moves along a
pair of rails across the top of the destructor, may be worked by one
man. It is divided into compartments holding a charge of refuse in
each, and is provided with a pair of doors in the bottom, opening
downwards, which are supported by a series of small wheels running on
a central rail. A special feeding opening in the reverberatory arch
of the cell of the width of the truck, situated over the drying
hearth, is formed by a firebrick arch fitted into a frame capable of
being moved backwards and forwards by means of a lever. The charging
truck, when empty, is brought under the tipping platform, and the
carts tip directly into it. When one of the cells has to be fed, the
truck is moved along, so that one of the divisions is immediately
over the feeding opening, and the wheel holding up the bottom doors
rests upon the central rail, which is continued over the movable
covering arch. Then the movable arch is rolled back, the doors are
released, and the contents are discharged into the cell, so that no
handling of the refuse is required from tipping to feeding. This
apparatus is in operation at Liverpool, Shoreditch, Cambridge and
elsewhere.

Various forms of patent movable fire-bars have been employed in
destructor furnaces. Among these may be mentioned Settle's,[7]
Vicar's,[8] Riddle's rocking bars,[9] Horsfall's self-feeding
apparatus,[10] and Healey's movable bars;[11] but complicated movable
arrangements are not to be recommended, and experience greatly
favours the use of a simple stationary type of fire-bar.

A dust-catching apparatus has been designed and erected at Edinburgh,
by the Horsfall Furnace Syndicate, in order to overcome difficulties
in regard to the escape of flue dust, &c., from the destructor
chimney. Externally, it appears a large circular block of brickwork,
18 ft. in diameter and 13 ft. 7 in. high, connected with the main
flue, and situated between the destructor cells and the boiler.
Internally it consists of a spiral flue traversing the entire
circumference and winding upwards to the top of the chamber. There is
an interior well or chamber 6 ft. diameter by 12 ft. high, having a
domed top, and communicating with the outer spiral flue by four ports
at the top of the chamber. Dust traps, baffle walls and cleaning
doors are also provided for the retention and subsequent weekly
removal of the flue dust. The apparatus forms a large reservoir of
heat maintained at a steady temperature of from 1500º to 1800° F.,
and is useful in keeping up steam in the boiler at an equable
pressure for a long period. It requires no attention, and has proved
successful for its purpose.

Travelling cranes for transporting refuse and feeding cells are
sometimes employed at destructor stations, as, for example, at
Hamburg. Here the transportation of the refuse is effected by means
of specially constructed water-tight iron wagons, containing
detachable boxes provided with two double-flap doors at the top for
loading, and one flap-door at the back for unloading. There are
thirty-six furnaces of the Horsfall type placed in two ranks, each
arranged in three blocks of six in the large furnace hall. An
electric crane running above each rank lifts the boxes off the wagons
and carries them to the feeding-hole of each well. Here the box is
tipped up by an electric pulley and emptied on to the furnace
platform. When the travelling crane is used, the carts (four-wheeled)
bringing the refuse may be constructed so that the body of the
carriage can be taken off the wheels, lifted up and tipped direct
over the furnace as required, and returned again to its frame. The
adoption of the travelling crane admits of the reduction in size of
the main building, as less platform space for unloading refuse carts
is required; the inclined roadway may also be dispensed with. Where a
destructor site will not admit of an inclined roadway and platform,
the refuse may be discharged from the collecting carts into a lift;
and thence elevated into the feeding-bins.

Other accessory plant in use at most modern destructor stations
includes machinery for the removal, crushing and various means of
utilization of the residual clinker, stoking tools, air heaters or
regenerators for the production of hot-air blast to the furnaces,
superheaters and thermal storage arrangements for equalizing the
output of power from the station during the 24-hours' day.

Working of destructors.

The general arrangement of a battery of refuse cells at a destructor station is illustrated by fig. 5. The cells are arranged either side by side, with a common main flue in the rear, or back to back with the main flue placed in the centre and leading to a tall chimney-shaft. The heated gases on leaving the cells pass through the combustion chamber into the main flue, and thence go forward to the boilers, where their heat is absorbed and utilized. Forced draught, or in many cases, hot blast, is supplied from fans through a conduit commanding the whole of the cells. An inclined roadway, of as easy gradient as circumstances will admit, is provided for the conveyance of the refuse to the tipping platform, from which it is fed through feed-holes into the furnaces. In the installation of a destructor, the choice of suitable plant and the general design of the works must be largely dependent upon local requirements, and should be entrusted to an engineer experienced in these matters. The following primary considerations, however, may be enumerated as materially affecting the design of such works:--

(a) The plant must be simple, easily worked without stoppages, and
without mechanical complications upon which stokers may lay the blame
for bad results. (b) It must be strong, must withstand variations of
temperature, must not be liable to get out of order, and should admit
of being readily repaired. (c) It must be such as can be easily
understood by stokers or firemen of average intelligence, so that the
continuous working of the plant may not be disorganized by change of
workmen. (d) A sufficiently high temperature must be attained in the
cells to reduce the refuse to an entirely innocuous clinker, and all
fumes or gases should pass either through an adjoining red-hot cell
or through a chamber whose temperature is maintained by the ordinary
working of the destructor itself at a degree sufficient to exclude
the possibility of the escape of any unconsumed gases, vapours or
particles. The temperature may vary between 1500° and 2000°. (e) The
plant must be so worked that while some of the cells are being
recharged, others are at a glowing red heat, in order that a high
temperature may be uniformly maintained. (f) The design of the
furnaces must admit of clinkering and recharging being easily and
quickly performed, the furnace doors being open for a minimum of time
so as to obviate the inrush of cold air to lower the temperature ...

(_Continued in volume 8, slice 3, page 109._)

FOOTNOTES:

[1] Patent No. 3125 (1876).

[2] Patent No. 8271 (1891).

[3] Patents No. 8999 (1887); No. 14,709 (1888); No. 22,531 (1891).

[4] Patent No. 18,719 (1888).

[5] Patents No. 15,598 (1893) and 23,712 (1893); also Beaman and
Deas Sludge Furnace, Patent No. 13,029 (1894).

[6] _Compte Rendu des Travaux de la Société des Ingénieurs Civils de
France_, folio 775 (June 1897).

[7] Patent No. 15,482 (1885).

[8] Patents No. 1955 (1867) and No. 378 (1879).

[9] Patent No. 4896 (1891).

[10] Patent No. 20,207 (1892).

[11] Patents No. 18,398 (1892) and No. 12,990 (1892).