Life of Richard Trevithick by F. Trevithick: Volume 1: Chapter 1
Chapter 1: Early Cornish Engines
During many centuries the wants of the mining interests of Cornwall led to improvements in pumping machinery
The ancient tin streamer in the Cornish valleys used the fall of the running stream to separate the grains of tin from the mass of sand and gravel.
The tin sand of the valleys having all been washed, the miner followed the mineral vein in its downward course, and successive miners, working a lower strata, were obliged to use pumps or other means for removing water from their excavations. Adits were driven from lowest convenient surface level, to assist in draining the workings. Every day added to the depth, and call for improved machinery.
The open launder of the tin streamer had been converted into a chase launder or pipe, haying a square leather bag, attached to a long wooden handle, serving as a bucket in the primitive hand-pump, but increased depths overtaxed the strength of the square-sided pump, and cylindrical wooden pumps were made, bound by iron hands. The rag and chain pump then came into use, being a revolving or endless chain, moving upwards through the pump, having at every two or three feet of its length a piston made of a ball of rags bound together, or of Wood edged with cloth or leather, for up to this time valves had not been used.
The observed fact that water would rise to a certain height in a pump, following a well-constructed piston, suggested the use of a bottom or stop valve, preventing the descent of the water, and also the use of a valve in the piston or bucket. In 1663 the Marquis of Worcester applied steam to force water up a pipe; other inventive men varied the methods and even constructed model steam-engines, but failed to help the working miner.
The ever-increasing depth and size of the pumps required the power of water-wheels and horse-whims until about the year 1702 Savery is said to have erected the first steam pumping-engine in Cornwall, of which he wrote thus in the Miner's Friend:— " I have known in Cornwall a work with three lifts of about 18 feet each, lift and carry a 3.5 inch bore; that cost forty-two shillings a day. I dare undertake that my engine shall raise you as much water for eight-pence as will cost you a Shilling to raise the like with your old engines in coal pits."
Savery's boiler was of cast iron. A vacuum was formed in a receiver by admitting steam to drive out air, and then condensing this steam by pouring cold water on the outer surface of the receiver, caused the water in the shaft to rise by the weight of the atmosphere into the void in the receiver; a valve prevented its return, while another valve opened it passage to the upcast pipe from the receiver toward, the surface of the mine; a supply of steam again passed from the boiler to the receiver, forcing the contained water upwards through the pipes. The only moving parts of the machine were the vales.
This engine illustrated three leading principles of the modern steam-engine,-the use of steam to expel the atmosphere, its condensation by cold forming a vacuum, and the more direct use of steam as a strongly expansive manageable agent.
Savery's engine, requiring to be fixed near the bottom of the shaft, or within 30 feet of the level of the water to be raised, never came into general use, and absence of moving parts made it unsuitable for any other purpose than the raising of water, and even for that there are not many traces of its practical application.
In 1705 Newcomen, from Devonshire, combining the ideas of others with his own great mechanical genius, constructed, or it may fairly be said, invented the means of giving motion to a beam by using a cylinder and piston. The steam pressure in the boiler was 1 or 2 lbs. on the square inch above the pressure of the atmosphere, sufficient to drive the air out of the cylinder and prepare it for the vacuum. This was known as the “Atmospheric Engine," its power being measured by the weight of the atmosphere on a piston, whose underside was in a vacuum
In 1712 such an engine was erected at Griff in Warwickshire which raised a load equal to 10 or 11 lbs on each square inch of the piston. Others followed, and many improvements were made. The first steam-cylinder was about 23 inches in diameter.
In 1720 Newcomen erected at Ludgvan-lez, in Cornwall, a pumping engine with a cylinder of 47 inches in diameter, working at the rate of fifteen strokes a minute.
The best working engine in Cornwall in 1746 was at the Pool Mine, interestingly described by Borlase [1]: -
The most powerful as well as constant engine hitherto invented is the fire-engine. This engine is now well known to the learned; but as their books do not reach everywhere, and this machine is especially serviceable for the working of deep mines, and of great advantage to the public revenue, a general explanation of its principal parts, its powers, and profit to the Government, may not be improper. The principal members of this engine are exhibited in the engraving annexed; the cistern or boiler T, the cylinder P, and the bob 0I, turning on an axis which rests in the middle of the wall Y. The following is the process of its several operations: The cistern T, full of boiling water, supplies steam (by means of an upright tube and valve which shuts and opens) to fill the hollow cylinder P, and expel the air through a horizontal tube S, placed at its bottom. As the steam rises, the piston, which plays up and down in the cylinder, rises, and when it is got near the top opens a clack, by which cold water is injected, and condenses the vapour into nearly the twelve thousandth space which it before occupied, and the cylinder being then nearly empty the piston of iron edged with tow and covered with water (to prevent any air from above getting into the cylinder), is driven down by the pressure of the atmosphere (with the force of about 17 lbs. on every square superficial inch) nearly to the bottom of the cylinder; at this instant it opens the valve which lets in the steam from the boiler T, and then the piston ascends till it opens the condensing clack above, which brings it down again to open the under clack and admit the steam, and thus continues ascending and descending as long as the managers think proper; this process is quick or otherwise, as the steam is by increase or subtraction of fire made more or less violent, to drive the engine faster or slower. To this piston the end of the bob 0 is fastened by an iron chain, and as the piston descends in the cylinder P this end of the bob is drawn downwards, and vice versa. As the end 0 is drawn down, the other end of the bob I ascends, and by a chain I K draws up with it, from an iron or brass cylindrical tube, called a pit-barrel, through a tyre of wooden pumps, a column of water out of the mine equal in diameter to the bore of that tube, and in height to each stroke or motion of the piston in the cylinder P, and the sweep of the bob I K. Many improvements have lately been added to this excellent piece of mechanism, among which I cannot but mention one in particular, which is, that as this engine stood formerly, if the firemen chanced to nod, the violence of the motion increasing with the fire, the weighty bob 0 I beat, shocked, and endangered the whole machine, and the fabric it is enclosed in; but now, when the fire is at the extreme height, and the bob begins to beat and strike the springs, it lets fall a trigger into a notch and stops the injection-cock, and the whole movement is stopped till the injection of the cold water into the cylinder is restored; so that this engine is now brought to such perfection that in a great measure it tends, regulates, frees, and checks itself. Several subordinate members, wires, clacks, and valves are all moved, opened, and shut by the force of the steam and the motion of the piston; inasmuch as that by enlarging the cylinder and other parts in proportion, few Cornish mines are subject to more water than this engine will master. Its power is in proportion to the diameter of the cylinder principally, the strength of the steam, and the depth it draws. This is the fire-engine which in the year 1746 belonged to the Pool Mine and the cylinder's diameter from the outer edge was but 3 feet; but they make them much larger now, and it is imagined that if they were still to increase the diameter of the cylinder and make it also shorter than they do now, the force would be augmented, and though the column of water exhausted would be shorter, yet might this be well remedied by increasing the number of tubes, which the greater pressure on the piston would easily manage. A cylinder of 47 inches bore at Lugvanlez-work, in the parish of Ludgvan, making about fifteen strokes in a minute, usually drew through pit-barrels of 15 inches diameter, from a pump 30 fathoms deep. The cylinder at Herland (or Drednack) Mine, in the parish of Gwinear, is 70 inches in diameter, and will draw a greater stream of water at any equal depth, in proportion to the square of its diameter.
The only objections to this engine are the great expenses in erecting and vast consumption of coals in working it. To obviate these expenses several methods have been suggested of increasing the elasticity of the steam and reducing the size of the boiler, which can be decided only by experience, and to that we must refer them.
The cylinder, 36 inches in diameter, rested on a large slab of stone, which seems to have served as the top of the steam-boiler. A hole cut in the stone, having a valve in it, was the steam-pipe. The piston was packed with tow; a layer of water on its top prevented leakage of air or steam. A piston-rod and chain connected the piston with the arched head of the wood beam. The steam pressure was 1 or 2 lbs. on the square inch above the pressure of the atmosphere, and the valves were self-acting, enabling the engine to make fifteen strokes a minute. If the engineman fell asleep and the steam becoming stronger made the engine work too rapidly, the self-acting gear, by shutting off the injection, caused the engine to cease working.
The boiler is not particularly described, but the drawing represents a large caldron or pot of metal with a hollowed bottom, under which the fire was placed and circulated through mason-work flues around the sides. The top of the boiler, being nearly flat, was its weakest part, and was strengthened by a stone cover, or possibly this stone cover, in the earlier engines, formed the boiler-top.
In 1756, several were at work; about a dozen are specified; one of them at the Herland Mine having a cylinder of 70 inches in diameter.
The only objection to the engine is the cost of the coal. To lessen this, several methods had been suggested for increasing the elasticity of the steam, and reducing the size of the boiler.
Such were the Newcomen atmospheric open-top cylinder steam-engines, among which Trevithick, sen., lived, depending mainly on the vacuum and weight of the atmosphere for their power, but yet having caused the discovery that an increased pressure of steam in the boiler added to the speed and power of the engine, they only needed an inventor who should design a smaller and stronger boiler, to give steam of greater elastic force.
This Pool Mine, now called North Wheal Crofty, adjoined Dolcoath Mine, and was within half a mile of the house in which Richard Trevithick, sen., lived, then a boy eleven years of age. It is more than likely that in early manhood he exercised an authority over it, for shortly after that period, in 1765, he was the manager of Dolcoath, and resided just midway between the two mines, both of which were worked under the Dedunstanville interest for which Trevithick was the agent. In 1746 the Cornish pumping engine worked fifteen strokes a minute, and was so under control from its well-contrived gear and valve work, that the engine regulated its own movements, and its power was only limited by the diameter of the cylinder and the strength of the steam. In 1758 Borlase wrote:- “Several methods have been suggested for increasing the elasticity of the steam, and reducing the size the boiler, which can be decided only by experience, and to that we must refer them." And we shall find that shortly after that period Richard Trevithick, sen., took the first step in overcoming the difficulty.
In 1830 the writer saw at the Weith in Camborne a floor about 12 feet square of blocks of granite, known as the old Moor-stone boiler, and conversed with several old men, who, when boys, played in it, when it had sides or walls three or four feet high of blocks of granite.
Captain Joseph Vivian recollected hearing, when a boy, his uncles Simon and John Vivian talk of having taken a contract to break up this boiler, and cut out the copper pipes in the inside.
Mr. C. E. Edwards, a smith at Perran, near Marazion, has the screw-plate and taps used in constructing a granite boiler for Gwallon Mine, near the present Wheal Prosper.
His great-grandfather, Edwards, was a smith in Ludgvan-lez when Newcomen put his great engine there, about 1720. His grandfather was married in 1764, and set up the smith's shop C. E. Edwards still works in, bringing as a marriage present those old taps and screw-plate, said to be the first used in Cornwall. When a boy he often heard his grandfather talk of the old smiths who failed to clamp together by lambs’ tails (bands of iron tightened by cutters in lieu of bolts) the blocks of granite forming the boiler at the Gwallon Mine; and one of these smiths said, go over to Edwards at Ludgvan-lez, he can make screws that will draw them up beautiful.
Gwallon Mine was less than a mile from Newcomen's early engine at Ludgvan-lez. James Banfield, for many years the principal smith in the engineering works of Harvey and Co, at Hayle, says:—
In 1813 I was rivet-boy at the making of Captain Trevithick's high-pressure boilers at Mellinear Mine. The largest boiler-plates then to be had in Cornwall were 3 feet by 1 foot. My father served his apprenticeship in 1784 with uncle Jan Hosking, a famous smith, on Long-stone Downs in Lelant parish. Father has often told me how the work used to be made when he was a young man. The only wrought iron they could get was Spanish bar, 2 inches square, hammered thin in the middle that it might be bent for the convenience of carriage. It was red-short iron difficult to work; and Swedish or Danish bar, said to come from Siberia, 3.25 inches wide, and 5/8ths of an inch thick. Whatever was wanted in the mine had to be made with such bars.
In 1746, the only wrought iron of commerce in Cornwall being small bars, to make a wrought-iron boiler was a difficult and almost hopeless undertaking.
Small boiler-plates and boilers were made in Staffordshire or Shropshire; but the Cornish roads did not admit of the easy conveyance of heavy weights. For fifty years after the erection of these early engines, the coal and mineral from the ports and mines were conveyed on mules, the roads being unsuitable for wheel carriages.
The traditions relating to granite boilers may not absolutely lead to the conclusion of their use; but the many difficulties in procuring a good boiler are evident. Borlase's drawing shows a close intimacy of boiler and stonework; the steam-pipe leading from the top of the boiler into the bottom of the cylinder being merely a hole in the large stone resting on the top of the boiler, on which the cylinder was supported.
The drawing, coupled with tradition, implies, almost to a certainty, the use of granite in the construction or early steam-engine boilers; and the cutting out of copper pipes from a boiler during the childhood of a person still living, seems to prove that even in those early days we had tubular boilers; for in the granite boiler it is impossible to imagine any other way of getting up steam than by some internal fire-place, as suggested by those tubes. Such is the history of the steam pumping engine in Cornwall up to 1758, enabling the miner to follow to a greater depth the glittering tin, sparkling in its bed of hard rock, from which its minute pin-point particles were separated by stamping the lode-stone into sand, and washing it in a gentle stream, on the higher portion of which the heavier tin settled, while the lighter refuse went with the stream, except in the chance eddies and hollows where again the greater gravity of the particles of tin settled them at the bottom, while the waste earth still floated away, on and on to the sea.
If the ore be very full of clammy slime, it is turned from the area C into a pit near by, called a buddle, L I, to make it stamp the freer without choking the grates, and brought hack to C. If the ore is not slimy, it is shovelled forward from C into a sloping channel of timber E, called the pass, from whence it slides by its own weight and the assistance of a small rill of water, D, into the box at Y; then by the lifters a b c. falling on it after being raised by the axletree d, which is turned round by the water-wheel B, it is pounded or stamped small; to make the lifters more lasting, and fall upon the ore with the greater force, they are armed at the bottom with large masses of iron of 140 lbs. weight each, called stamp-heads; and to assist the attrition, the rill of water D keeps the ore perpetually wet, the stamp-heads cool, till the ore in the box is pulverized, and small enough to pass through the holes of an iron grate it V. The grate is a thin plate of iron, no more than one tenth of an inch thick, one foot square, full of small holes punched in it the bigness of a moderate pin, not always of the same diameter, but as the different size of the tin granules requires; for the larger the crystals enclosing the metals are, the larger must be the holes, and vice versa, so that in suiting the grate to nature of the tin, the skill of the dresser appears. From this grate the tin is carried by a smaller gutter e, into the fore pit F, where it makes its first and purest settlement, the lighter parts running forwards with the water through holes made in the partition f, into the middle pit (much of the same shape and size as the fore pit), and thence into the third pit H: what settles in A and H is called the slimes, and what runs off from them is good for nothing. The fore pit F, as soon as full is emptied, and the contents carried to the buddle I, a pit 7 feet long, 3 wide, and 2 deep; the dresser standing in the buddle at I, spreads the pulverized ore at K, called the head of the buddle, in small ridges parallel to the run of the water which enters the huddle at L, and falling equally over the cross-bar M, washes the slime from the ridges (which are moved to and fro with a shovel) till the water, permeating every part, washes down the whole into the buddle I: whilst the dresser's hands are employed in stirring the ridges at K, he keeps his foot going always, and moves the ore to and fro so as the water may have full power to wash and cleanse it from its impurities; the buddle fills, and the tin is sorted into three divisions; that next the head, at y, is the purest; the middle, at h, is next in degree; that at i most impure of the three; and each of these divisions goes through a different process. The fore part at A is taken out first, and carried to a large tub N, called the keeve; there immersed in water, it is moved round with a shovel for a quarter of an hour, by which means the impurities rise from the ore, and become suspended in the water; the tin ore is then sifted in a sieve purposely constructed, and if it needs, must be sent to be buddled again, then returned to the keeve and worked as before with a shovel, which they call tozing the tin; the keeve is then packed, that is, beat with a hammer or mallet on the sides, that the ore within may shift and shake off the waste, and settle the purer to the bottom. The foul water then on the top of the keeve is poured off, and the sordes which settles above the tin is skimmed off, and what remains is pure enough to be sent to the melting house, and is then called black tin.
The waste skimmed off is carefully laid by to undergo another washing: whilst the fore part of the buddle I is thus manufacturing at the keeve, another hand is moving forth that part of the buddle h in the same manner as g was before; and in its turn that, and the settlement at i, is promoted to the keeve, and thus what is deposited in the fore pit F, is brought about, as the tinners term it, that is, undergoes all the necessary lotions.
What runs off from F into G and H must be dealt with in another manner. The contents of these pits consist of the small and lighter parts of the ore, and are intimately mixed with a greater quantity of earth and stone bruised to dust by the mill. These are called the slimes, and are carried to the trunk O to be again reworked.[2]
The same principles remain in operation even to the present day, but the work of the man's foot is performed by the more effective movements from the steam-engine, and the plane surface of the old buddle has generally given place to a circular buddle, the tin stuff taking the form of a flat conical mound, the heavy particles of tin remaining near the centre, while the lighter particles are carried by a film of running water toward the circumference of the mound; revolving arms having bits of rag or brushes attached slightly disturb the surface of the tin stuff, inducing by the running water the constant change of position of the particles, the lighter or refuse portions being washed farthest from the centre of the mound.
Not only does Borlase give explicit detail on the mine mechanism of his day, but also indirectly shows when Cornish streams were first poisoned by mineral water.
About fifty years since there were plenty of fine trout in the river Conar in Gwythian". [3]
This would be about 1708; it now sweeps to the sea yearly many thousands of tons of sand from the tin stamps, and from its colour is called the red river; no fish swim in it, though about 1820 the writer caught trout in a tributary stream, from Roseworthy. The destruction of fish one hundred and sixty years ago in the Collar, or valley from the Great Dolcoath mining district, was from tin streaming or shallow mining; but when in after years the steam-engine drained the mines and copper ore was worked, the rivers became still more poisonous.
At Crowliss, a village of Ludgvan, in the year 1739, a flock of geese belonging to James George, tailor, went into the river as usual, and drinking heartily of the water (a very strong mundic), upon their return to the bank nine of them lay down immediately and died. [4]
The water fatal to the thirsty geese came from Ludgvan-lez copper mine; it is now a red stream from tin mines where geese may safely seek for grains of tin, readily taking a taste when passing a heap of craze, or tin ore and sand, to allay the cravings of the gizzard. The writer believes but three geese recovered from the Crowliss flock. Cattle are apt to prefer this mine water, but it gives a rough coat and sometimes causes death. Large quantities of arsenic are taken from the flues of tin-calcining furnaces: in 1868 a field of apparently well-grown oats ripe for the sickle was valueless, from the absence of grain in the pods, caused by arsenical smoke from Stray Park Mine, while the straw was unfit even for bedding for cattle, because they might eat it; cabbages in an adjoining field were uninjured, the numerous little flakes of white arsenic resting on them could be washed off; a grass field near by was utterly untrustworthy, but potatoes thrived well and were said to be comparatively free from disease. The smoking chimney in Cook’s Kitchen[5] is attached to one of these calciners: on going into the flues when the workman was shovelling the arsenic from their sides and bottom into a barrow, the writer breathed a palpable atmosphere of arsenic; on coming out the man took a pasty from a bench, having a suspiciously thick layer of arsenic on it; brushing of with his hand the superfluous poison, he dined heartily. A heap of arsenic of several tons lay by the furnace at the road-side, to be prepared for commercial wants.
Foot Notes
- Notes to drawing of Newcomen Atmospheric Engine, Pool Mine, 1746
- A, south front of fire-engine house
- B, triangle for tending the engine-pumps
- C, arch for main bob to play in
- D, coal-house and fire-place
- E, capstan and cable fur the triangle
- F, balance-bob to assist the draught
- G, the bell.
- H, section from the west
- I, south end of the main bob
- K, main chain, to draw up the water from the bottom
- L, end of balance-bob, marked F in Fig. 1;
- M, a small chain, drawing from the adit to a cistern
- N, force-pump to supply the cistern for the boiler T, etc.
- O, north end of the main bob
- P, the cylinder
- R, the eastern door
- S, pipes to let out the air and steam from the cylinder
- T, the boiler which supplies the steam
- U, the damper to moderate the fire
- W, the fire-place
- X, the ash-pit
- Y, the axis of the main bob