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Note: This is a sub-section of 1876 Institution of Mechanical Engineers
Visits to Works (Excursions) - Birmingham area
On Tuesday afternoon, 18th July, the Members visited Nettlefolds' Screw Works at Smethwick, where the process of manufacture of wood screws was shown. The length of wire to form the screws is cut off by machines, which also upset one end by a blow to form the head. These "blanks" then pass to a machine in which the head of each is turned, the blank being held in a revolving chuck, and the tool brought up to it, and the nick is then cut across the head by a small circular saw; the supply of the blanks to the machine is by a self-acting feed, and the chuck holds and releases the blank by self-acting means. After being sorted and examined, the blanks next pass to the screwing or "worming" machine, in which each is gripped by the head end in a revolving jaw; and after the other end has been turned off to a point by one tool, the thread is cut by a traversing tool, taking a succession of cuts of increasing depth. As soon as completed, the jaw is opened to release the screw, and takes hold of a fresh blank by self-acting means. The finished screws are cleaned by washing in revolving riddles with a strong solution of soda, and then dried in shakers, sorted, examined, and packed. The screwing shop covers about 1 acres, and contains upwards of 2000 machines, turning out altogether about half a million screws per hour; the machines being self-acting, one woman can attend to several of them, having only to supply the hoppers with blanks and to change the cutters as they become worn.
All the machines and tools used are made at the works, and special precautions are taken to ensure accuracy and uniformity in shaping the cutters required for so large a number of machines. These are formed out of steel rings, turned exactly to standard dimensions and then divided into segments, each of which is used as a tool after having been hardened and ground : accuracy of angle in the grinding being ensured by fixing the cutter in a slide-rest that traverses across the face of the grindstone at the correct inclination. The small circular saws employed for cutting the nicks in the screw heads last on the average for cutting about 1000 screws each, and consequently a fresh supply of 4000 to 5000 saws per day is required. The saw blanks are stamped by a press out of a strip of steel, and 150 of them are compressed together on a mandril; the whole block is then turned cylindrical, and placed in a vertical slotting machine, having a number of cutters. The saws are then hardened and tempered; and those that have been used up once are softened and re-cut a second and third time.
The works comprise also a wire mill, a bolt and nut mill, and a nail mill, in the last of which are made spikes and staples &c. out of wire bent cold at one operation, at the rate of from 90 to 360 per minute according to the size. The driving power of the works consists of two pairs. of Corliss engines, with 28 in. cylinders and 4 ft. stroke, running at about 58 rev. per miu.; and a pair of horizontal compound engines with 22 in.. and 36 in. cylinders, and 3 ft. 6 in. stroke; and two pairs of horizontal condensing engines with 24 in. cylinders and 3 ft. 6 in. stroke. The Members were entertained at luncheon at the works by Mr. Nettlefold.
Messrs. James Watt and Co.'s Engine Works at Soho were also visited by the Members, where four large pumping engines for the South Staffordshire Water Works were seen in process of construction, and a pair of pumping engines with 27 in. cylinders and 3 ft. stroke for the Equilmalt Graving Dock in British Columbia; also several engines of various sizes for London breweries, and a compound beam engine for the Worthing Water works.
On Wednesday afternoon, 19th July, the Members visited the Small Arms Factory at Small Heath, and the processes of manufacture of the Martini-Henry rifle etc. were shown. The forgings are made in dies under steam stamps, steam hammers being employed for the larger work, such as the steel breeds-bodies of the Martini-Henry rifle; these are first forged solid in a die, and then punched hot from each side, leaving only a small fin as waste in the centre of the hole. The bodies are shaped by a series of revolving cutters, taking both sides at once; and similar cutters or "milling machines" are used for shaping the other portions of the work; several hundreds of these machines are employed, acting upon the copying principle, and by this means details of the most complex shapes are finished almost without being touched by hand, and all the work is made in exact duplicate and interchangeable. The shaping and recessing of the gunstocks is performed in a number of successive operations by a series of copying machines.
In the boring of the barrels, after being bored out near to the gauge, they are finished by long square steel rimers ground very truly with two cutting edges, and packed with a thin wood strip and one or more liners of paper: the rimering being repeated if necessary, with an additional liner of paper interposed between the rimer and the wood packing-strip. The barrels are set by hand, if not perfectly straight after boring; and are then rifled by a series of very fine cuts of a rifling tool, which takes from 5 to 20 cuts for each groove in succession.
In the museum of the factory were shown specimens of the different varieties of rifles and other small arms, with sets of details of the separate parts, and the gauges used in their examination.
On Wednesday evening a number of the Members and their friends dined together at the Royal Hotel.
On Thursday, 20th July, an Excursion was made by the Members by special train to visit the Sandwell Colliery near Birmingham;— Earl Dudley's Lye Cross Colliery;— the Hailstone Quarry of Mr. T. P. Jones near Rowley;— Earl Dudley's Round Oak Iron Works;— and Messrs. Cochrane's Woodside Iron Works, near Dudley.
The Sandwell Colliery is situated on the Great Western Railway, 3 miles from Birmingham, on the eastern boundary of the South Staffordshire coalfield, and underneath the lower new red or permian formation. Until the present company undertook to prove it, no trial sinking had been attempted, though: several borings had been put down during the last half century; none of them however were carried deep enough to prove coal or even coal measures, and great interest attaches consequently to this undertaking, which has succeeded in proving the Thick coal in that locality. One borehole put down forty years ago, half a mile east of the present pits, was carried to a depth of about 220 yards, and then abandoned; but experience has now shown that had it been carried a little deeper the coal measures must have been struck. It was not till 1870 that the Sandwell trial sinking was started, on the proposal of the present engineer of the company, Mr. Henry Johnson, and in 1874 the Thick or Ten-Yard coal was reached, and was found to be 6 yds. 2 ft. 6 in. thick. The second shaft was then commenced, and reached the coal in 1 years. The first or trial shaft had been sunk under many difficulties, sometimes with every prospect of success, and at others with almost every hope gone; but being persevered with through good report and ill report, it resulted in the present success.
The first pit is 10 ft. diameter and 440 yds. depth to the bottom. The Thick coal was reached at 418 yds., and the present inset is at 423 yds. The drivings or explorations made in this pit while the second shaft was being sunk extend about 1,000 yds. to the north, 60 yds. to the south, 300 yds. west towards the old coalfield, and about 200 yds. east towards Birmingham; over this area the coal is found to be about 8 yds. thick, having a dip due east of about 1 in 7. The second pit is 15 ft. diameter, belled out at the bottom to 20 ft. and groined into a brick archway, which is 20 ft. wide and 16 ft. high, for four lines of tramway. This pit will be worked with two steel ropes 11 in. diameter, and double-decked cages, each cage carrying four tubs with 15 cwt. of load in each, making 3 tons of coal raised per trip. The cages will be guided by six wire-rope conductors 12 in. diameter.
The winding engines are a pair of horizontal high-pressure direct-acting engines, made by Messrs. Coupe of Wigan, having 36 in. cylinders with 6 ft. stroke, double-beat equilibrium valves, and 18 ft. drums. There are eight plain cylindrical boilers, 5 ft. 6 in. diameter and 40 ft. length, with hemispherical ends, fitted with feed and steam indicators in duplicate, and fed by a pair of donkey pumps; the stack is 8 ft. square inside throughout and 203 ft. high. A tunnel 5 ft. high, passing from the neighbouring railway cutting underneath the boilers and engine house, contains all the blow-off pipes from the boilers, and serves as a drain. The pit frame or head gear to the 15 ft. pit consists of four uprights 60 ft. high, and two sloping legs 72 ft. long, of pitch pine 16 in. and 14 in. square, well braced together and carrying a pair of 16 ft. pulleys. A high-pressure hauling engine with 18 in. cylinder is fixed to work an endless-chain tramway to a wharf on the Birmingham Canal about 600 yds distant, and the colliery has also communication with the Great Western and North Western Railways.
The water at the colliery is now very little, only about 50 gal]. per min., but in sinking the first shaft it was about 050 gall. per min.; the pumps lifting 230 yds. are in three sets, all bucket lifts, with working barrels 13 in. and 14 in. diameter and 6 ft. stroke; they are worked by a condensing beam engine with 45 in. cylinder and 5 ft. Gin. stroke, supplied with steam by three double-fined Cornish boilers 7 ft. 6 in. diameter and 30 ft. length.
The Lye Cross Colliery is situated nearly in the centre of the basaltic mound constituting the Rowley Hills, to the south-east of 4 Dudley, and forming a continuation of the chain of silurian hills, consisting of Sedgley, Wren's Nest, and Dudley Castle.
The starting of this colliery was the first attempt to sink through the basalt, to win the coal known to be lying beneath (although at two neighbouring collieries workings had been previously carried under the basalt), and was an undertaking of considerable magnitude, as it was not known what thickness of basalt covered the coal measures. The sinking has proved thoroughly successful, the thickness of basalt being considerably less than was supposed, only 68 yards of basalt having to be sunk through before the rock forming the upper portion of the coal measures was reached; and 92 yards further down (or 168 yards from the surface) the Two-foot and Brooch coal seams were struck, and 50 yards lower the Thick or Ten-Yard scam, and below that the other seams in regular succession, as in other parts of this coalfield. The basalt was followed by 10 inches of natural soil of a dark colour, and under this was the ordinary red brick-clay usually found in the district as the surface clay.
The Rowley hills owe their origin to an outburst of basaltic lava (whose funnel, or point of emergence from below, has however not yet been discovered) having spread over that portion of the coalfield, and protected it from the denudation which elsewhere removed some of the upper portion of the carboniferous strata. Dykes and sheets of intruded igneous rock occur between the coal seams in some places, similar to the basalt, except that there has been more or less mutual reaction between the molten basalt and the coal measures, whereby the former has become "green rock" and "white rock," according to the nature and extent of the change it underwent whilst cooling, and the coal has become charred for several inches distance from the basalt.
The coal measures of the Staffordshire coalfield were deposited on a floor of silurian rocks, peaks of which are seen protruding through the coal measures at Sedgley, Wren's Nest, and Dudley Castle, and are quarried for the silurian limestone of which they consist. The actual extent of the Staffordshire coalfield is not definitely proved; and, as sinkings to the east of the formerly supposed boundary of the coalfield have proved that it extends further and further eastwards, under the permian rocks, there seem some grounds for supposing that it will ultimately prove to be continuous with the Warwickshire coalfield.
The sinking of the Lye Cross shafts was commenced in August 1872 and completed in July 1874. The downcast shaft is 12 ft. 6 in. diam. in the clear, and the upcast 8 ft.; they are sunk through the coal to a depth of 13 yds. below the coal before forming the "insets," which are at the right level to meet the coal (which forms a saddle, dipping in both directions from the shaft) at sufficient distance to support the shaft firmly, namely 100 yds. from bottom of shaft. The insets are 13 ft. high and 25 ft. width, with four lines of rails, for some distance from the shaft. Gate roads have been driven in different directions to the extent of 3 miles. The upcast shaft is sunk to the same level as the downcast, but the air drift follows the rise of the coal; • the shaft has a brick continuation about 40 ft. high above ground. Wire-rope guides are used, with screw adjustments at top and bottom.
The thickness of the various strata passed through in sinking the shaft was as follows:-
The first 3 yds. of the Rowley Rag was partially decomposed, and the rest was in the form of very large boulders, the outside crust of which was in many cases much decomposed. When this bed was nearly passed through, a large quantity of water was met with, which suspended sinking operations for about three weeks. As the coffering for keeping back the water seas required to extend to a depth of 75 yds., and there was no sufficient foundation for it, 4 ft. headings were then driven into the sides of the shaft, and six large oak timbers inserted to form a seating for the curb to rest upon, and the coffering made with hydraulic lime effectually kept back the water; this lime was a mixture of black and white lime, coke-dust, and clinkers (without ash), ground in a mortar mill, mixed with water, and applied hot. The brickwork of the shaft is 2 ft. to 3 ft, thick iu some portions. The water from behind the coffering is carried down into the pit by a pipe under sufficient pressure for feeding the underground boiler; it also supplies two drinking fountains for the men. The water is remarkably pure and fresh for drinking; when first drawn it contains a large quantity of minute air bubbles, giving a milky appearance to the water, which gradually escape.
The roads in the pit are very wide and high, and heavily timbered with oak 16 x 14 in. Underground is a manager's office where the men are paid, a dining room for the colliers, and stables for the pit horses.
The winding engine is horizontal, with a pair of cylinders, 26 in. diam. and 6 ft. stroke, working to about 240 H.P. The winding drum is 14 ft. diam. parallel, and is fitted with a powerful differential steam break, which is worked by the ordinary foot treadle, and dispenses entirely with the ordinary break. Round wire rope is used 1 in. diameter. The pit frames are 45 ft. high, with pulleys 14 ft. diam. The boilers are three in number, plain cylindrical, with hemispherical ends, 5 ft. 6 in. diam. x 39 ft. long, and working at a pressure of 40 to 50 lb. per sq. in. An underground engine is used for hauling coal up an incline of 17 in. per yd. or nearly 1 in 2 from the lower workings to the bottom of the shaft; horizontal engine, with 15 in. cylinder, 3 ft. stroke, winding on a 6 ft. drum with a round wire rope. Steam is supplied by an underground boiler, plain cylindrical with hemispherical ends, 4 ft. 6 in. diam. x 32 ft. long, working at 50 lb. per sq. in. The flue of this boiler passes into the upcast shaft, thus forming the furnace for the ventilation of the mine; but an auxiliary furnace is provided, which can be used to assist the ventilation if required.
Au electric signal is used from the pit bottom to the engine room at the surface, and from the underground winding engine to the bottom of the incline, worked by a Leclanche battery. In any case of a tub getting off the rails on the incline, the two electric wires are arranged to make contact and give a signal for stopping the hauling engine, so as to prevent damage to the road.
The colliery is worked on the pillar and stall system, with pillars 10 yds. square, and stalls 8 to 9 yds. wide. A stall about 80 yds. long by 8 yds. high was shown specially illuminated, presenting a striking scene.
The Members were entertained at luncheon at the colliery by Mr. E. Fisher Smith.
At the Hailstone Quarry, situated on the slope of the Rowley Hills, basalt or "Rowley Rag" stone is worked on an extensive scale, with a face of about 75 ft. height extending t mile length. The basalt is of a very compact character in this quarry, and does not show a columnar structure. The blasting is done with gunpowder in preference to dynamite, the latter having been found to shatter the stone to a greater extent, and cause a larger proportion of slack. The stone is broken by heavy hammers into squared blocks of various sizes for use as pitching and kerbstones &c., and the slack is broken up for road metalling.
At the Round Oak Iron Works, three of the Casson-Dormoy puddling furnaces fired with coal were seen in use, and another fired with gas. The rabbles are worked by mechanical means; and air heated by passing through a wrought-iron casing surrounding the furnace stack is forced in through the grate by a blower, and in the gas furnace a further supply is passed through passages in the crown and bridge wall, and delivered at a high temperature to meet the gas on entering the puddling chamber, producing an intense flame, the quality of which is regulated by adjusting the supply of air. The gas is generated in a producer at one end of the furnace, to which screened slack is supplied from a hopper by a fluted feed- roller. The pig iron has a preliminary heating between the puddling chamber and the stack; and the waste gases are utilised by passing through a horizontal boiler fixed above the furnace for generating steam.
The forge boilers are fired by Henderson's mechanical stokers, supplied with the smallest refuse slack direct from the pits. The slack is discharged from trucks into the hoppers of the stokers, from which it is delivered by a feeding roller on to a pair of rapidly revolving horizontal discs, having projecting blades that distribute the slack over the fire in a finely divided and uniform shower.
At the Woodside Iron Works, a quantity of bridge work, roofing and railway iron work, was seen in progress, and in the pipe foundry the casting of some large mains of 36 in. and 40 in. diam. for the Manchester Water Works. At the blast furnaces a pair of Cowper's regenerative hot-blast stoves were seen in progress of construction, being the first erected in South Staffordshire; they are 21 ft. diam. and 57 ft. high, and the firebrick regenerators about 45 ft. high. The wrought-iron casings of the stoves are erected without scaffolding, by means of a circular platform inside, suspended from the shell itself by several Weston's pulleys: the pulleys being shifted up one by one when a new ring of plates has been added all round, the platform is then hauled up after them. A circular projecting rail runs all round the top of each stove, from which is suspended a light travelling platform, for convenience of examination if required. The blast furnace to which this pair of stoves is to be applied is closed at the top with a bell and self-closing gear, and the materials are raised by a pneumatic hoist worked by the pressure of the blast.
On Friday, 21st July, an Excursion was made by the Members by special train to visit the Dudley Port Limestone Pit of Messrs. Dixon and Borne;— Messrs. James Russell and Sons' Crown Tube Works at Wednesbury;— and the Needle Works at Redditch of Messrs. Henry Milward and Sons and Messrs. Samuel Thomas and Sons.
The Dudley Port Limestone Pit has great interest attached to it, as being one of the several places where the Dudley or Wenlock limestone has been extensively worked below the coal measures of the South Staffordshire district. Previous to the first opening of this bed of limestone at Dudley Port, the only means of supplying the blast furnaces with limestone for smelting purposes was confined to the outcrop of the Wenlock beds at Dudley Castle, Wren's Nest, and in the neighbourhood of Walsall. Since the sinking to this bed by Jeavons about the year 1825, there have been several successful deep sinkings in different parts of the coalfield. The Wenlock limestone is described by Jukes as forming " two bands of solid concretionary and flaggy limestone, with many calcareous nodules, concretions, and small flaggy beds, both between, above, and below them. It contains innumerable characteristic fossils; indeed the quarries of Dudley are the most famous in the world for upper silurian organisms; shells, corals, encrinites of very numerous genera and species, and trilobites, are all in a state of perfection, such as no other locality in Britain exhibits."
At Messrs. Dixon and Burne's pit, Dudley Port, the depth from the surface to the bottom of the Thick coal is 123 yds., and at a depth of 186 yds. below the surface the coal measures rest slightly unconformably upon the Wenlock shale (locally called "bavin "). This shale or bavin, intermixed with inferior limestone, is 34 yds. thick, making a total depth of 220 yds. from the surface to the top of the grey or thin limestone; thus the bavin forms the roof of the limestone workings. This grey or thin bed, which is used principally for smelting purposes, is the same as that exposed in the escarpment round the Dudley Castle and Wren's Nest hills. About 33 yds. below this bed lies the blue or thick limestone, which is from 10 to 12 yds. thick, and is used for making lime for building and agricultural purposes. This latter bed is not usually worked, the Earl of Dudley being the only producer of it in this district, and that only upon a small scale.
The grey or thin limestone, in which the workings visited are situated, is from 8 to 12 yds. thick, and for the most part excessively hard and crystalline, containing in places fine specimens of crystallised spar. The bed is worked on the " pillar and stall " system, with pillars 14 yds. square generally, but considerably less in some places, and stalls 14 yds. wide, the full thickness of the bed being worked in one face by blasting off successive portions from the bottom upwards, ladders being used to reach the upper parts. The thickness of the seam varies suddenly in some places : the seam being apparently folded back on itself at one part, thus changing the thickness suddenly from 8 to 12 yds. Springs of fresh water, pleasant to drink, occur in places in the workings; and water is now filling the lower workings and rising slowly, so that pumping is expected to be required before long.
The shaft is about 240 ft. depth, and partly lined with brickwork; winding engine, an old tappet-motion beam engine; flat hemp rope, with iron cage containing a single iron skip for limestone. A second shaft is used for raising water by an iron bucket, having a self-acting valve at bottom, which discharges the water into an iron launder run across the pit mouth.
The limestone is nearly level throughout these workings, instead of the high inclination, fully 45°, of the limestone at Wren's Nest, which has consequently to be worked in galleries at different levels below one another. The excavations of this pit have occupied the last 25 years, and extend over an area of 15 acres, presenting a remarkable effect when ilhuninated, from the large dimensions and great extent of the excavations.
The workings were shown specially illuminated on the occasion of the visit, and several blasting shots were fired.
At Messrs. James Russell and Sons' Crown Tube Works, Wednesbury, the Members were shown the manufacture of wrought- iron tubes butt-welded and lap-welded. The tubes are made from flat strips of plate, or "skelps," first bent up hot into a rough tubular form by a squeezing machine, one portion at a time, or by drawing through a die which bends up the whole length of the skelp at one operation; the rough tubes are then heated for welding.
The butt-welded tubes are drawn out of the furnace at a welding heat through the jaws of a pair of draw-tongs with a circular opening, by which the weld is closed, half the length of the tube being welded at one heat, and the other half at a second heat; the tubes are straightened by rolling upon a table under the pressure of a heavy reciprocating plate. Small tubes are made by this process up to 12 ft. length; and for the manufacture of heating or refrigerating coils and still-worms successive lengths are welded together end to end. Coils are made of as much as 450 ft. length, the tubes being tested by hydraulic pressure both before and after coiling, as the coiling puts a severe strain upon the weld.
In making lap-welded tubes, which are made of larger diameters up to as much as 16 in. diameter, the skelps are bevelled at the edges, and welded by drawing out of the furnace through a pair of rolls with semicircular grooves, forming a circle of the required diameter for the tube, in the centre of which is the head of a long mandril, and the welding is rapidly effected by the compression between the mandril head and the rolls. The mandril is of slightly smaller diameter than its head, which is loose upon it; and when the welding is completed, the head falls off, and the mandril is then readily withdrawn from the tube. In the smaller sizes of lap-welded tubes the skelps are drawn through a die, which bends them into shape and effects the welding in one operation. Steel tubes are also made in the same way as the iron tubes, extra care and skill being applied to secure good welds. The furnaces throughout the works are all fired by gas supplied from a set of Siemens gas producers.
The straightening of the larger sizes of tubes is done between three rolls revolving together and rather longer than the length of the tube, which is laid longitudinally between the rolls, and straightened by gradually screwing down the top roll to press upon it as it rotates. Short curved elbow pipes of small size are bent in dies under a stamp, and larger sizes in a screw press; plain and flanged sockets for screwing or welding upon the ends of the tubes are also shaped under stamps. The testing of the tubes is done by 70 lb. steam for the gas tubes, and for the steam tubes by hydraulic pressure to a minimum of 500 lb. per inch.
The Members were entertained at luncheon at the works by Mr. Joseph Smith.
At the Redditch Needle Works the series of processes in the manufacture of needles was shown. The steel wire is supplied in coils from 1200 to 3000 yds. length each, according to thickness of wire, varying from 1/22 in. to 1/100 in. for sewing needles; and the following are the successive processes.
The manufacture of needles for the world is carried on mainly at Redditch in England and Aix-la-Chapelle in Germany.
The Members were entertained at luncheon by Messrs. Milward.
Birmingham Sewage Works
On Saturday, 22nd July, the Birmingham Corporation Sewage Works at Saltley were visited. These works were constructed and carried out from the designs and under the superintendence of Messrs. T. and C. Hawksley; the sewage farm in connection with them occupies an area of 266 acres of land in the Tame Valley. The sewage delivered by the two main sewers is treated with a mixture of lime and water to the extent of from 12 to 14 tons of lime per day, the mixture being made in two large circular tanks with revolving stirrers driven by an engine; the water used is pumped up from the main sewer. After this lime-water is poured in, the sewage flows on 1-3rd mile further through the sewers to their outlet, and during the passage the lime becomes thoroughly blended with the sewage, and produces a flocculent condition of its solid contents, causing the heavier portion to sink rapidly to the bottom of the large settling tanks, of which there are two, worked alternately, each 330 ft. long, 90 ft. wide, and 5 ft. 6 in. deep.
The large settling tanks are divided across into sections. In the first sections the grosser solid matters settle at once to the bottom, and in the lower sections the sewage loses a further part of the less dense matters, and then flows over the edge in the condition of water, holding in suspension the finer matter, which however is in quantity very considerable. It is then conducted into a series of 16 secondary tanks, each 150 ft. long, 50 ft. wide, and 5 ft. 6 in. deep, where a further settling is effected; and the effluent water from these tanks is discharged, devoid of smell and nearly colourless, into the river Tame.
A small portion of the effluent water is further purified by intermittent downward filtration through land irrigated by it, and the water flowing from the deep drain pipes of this land is clear and tasteless. In the channel between the roughing and finishing tanks it was Messrs. Hawksley's intention to introduce a small quantity of the crude acid-sulphate of alumina, for the purpose of fixing the remaining ammonia, of mordanting itself with any residual colouring matter, and of producing a further precipitate in addition to the deposition of the finer matters which have escaped from the roughing tanks. It has been ascertained that by this addition a pellucid effluent may be obtained; but it has not as yet seemed necessary to have recourse to this refinement, inasmuch as the existing effluent is in a better condition than is the water of the river Tame, into which it is discharged.
The bulk of the sewage sludge deposited in at tanks, amounting to from 350 to 400 tons per day, is disposed of by double-digging into the land, the extent of land thus treated being such that it takes three years to dig over the whole. A small amount however is dealt with by Genes-al Scott's process for producing Roman cement. A portion of the sludge from the tanks is also being experimentally dealt with by concentrating it in Fryer and Alliott's mechanical subsider, which separates the solid matter by centrifugal force, causing it to accumulate round the sides of a rapidly revolving vessel, while the liquid portion drains off; the sludge consists originally of about 90 per cent. of water with only about 10 per cent. of solid matter, and by this treatment it is sought to remove 70 or 80 per cent. of the water, so as leave the solid matter in a condition resembling plastic clay, in which state it can be sold as manure. Mechanical works for pumping and otherwise dealing with the sludge are about to be erected.
The rye grass grown on the farm averages 13 to 14 tons per acre at each cutting, and several cuttings are obtained each year. After each cutting, the land is immediately irrigated thoroughly with sewage; and in about three weeks the next crop is generally ready for cutting.
A number of Works in the neighbourhood were also opened to the visit of the Members.