Laurence Holker Potts

Dr. Laurence Holker Potts (1789–1850), M.D.

From 1844:-

'Formation of Sub-marine and other Foundations by Pneumatic Power.— On Saturday evening se'nnight Dr. Ryan delivered a private lecture in the theatre of the Royal Polytechnic Institution, Regent-street, descriptive of Dr. Potts' discovery of the applicability of pneumatic power to the formation of foundations in bogs, mosses, or sands, in the construction of railways, bridges, docks, breakwaters, &c. He was assisted by Dr. Potts, who exhibited models of his apparatus, and conducted several interesting experiments, in illustration of the working of the system.

'Dr. Ryan commenced his lecture by remarking that Dr. Potts' attention had been first directed to the subject by a careful inspection of the beautiful structures built by the coral insect, and he had endeavoured to imitate nature by carrying out his system in detail. The tedious and laborious nature of the present process of pile-driving by means of the iron weight, technically termed a " monkey," which requires the employment of several men for some minutes to raise it to the falling point, even to obtain the result of a depression of a single inch, is well known; and the importance of the invention, if it can be successfully brought into practice, must be apparent to every one from the following description.

'The invention is mainly directed to the formation of sub-marine foundations, though it is equally applicable to the construction of every kind of erection, which has hitherto called for coffer dams, or required the aid of wooden piles. The main feature consists in the substitution of pneumatic power for manual labour, in the first process of driving the piles. Dr. Potts proposes to use hollow iron tubes as piles. The lower extremity of the pile is open, and it is placed in a vertical position upon the bank or other ground, whether composed of sand, mud, or other substance, miscible with or diffusible in water. To the upper extremity of the tube is affixed an air tight cap, with a flexible tube of jointed metal or elastic hose, termed the "proboscis," extending to a close receiver, from which the air is extracted by an air-pump, or by the condensation of steam or any of the other modes which will produce suction, the object being to remove the pressure of the atmosphere, and form a vacuum. When the air within the receiver, the connecting tube, and the pile, becomes sufficiently attenuated, a mixed body of sand or mud and water flows up through the pile into the receiver, and as often as the latter is filled with the mixed body so raised, the contents are discharged through a valve at the bottom. As the sand or mud is thus raised in the pile, the pressure of the atmosphere being removed from its interior, the pile descends by its own weight, and the external pressure of the atmosphere, the rapidity being necessarily proportioned to the degree of exhausting power applied, and the supply of water from beneath. The pile descends with considerable rapidity in loose materials such as sand and shingle, and provision is made for disturbing and bringing under its operation materials of greater tenacity and bulk, large boulders, for instance, and for supplying the water to serve for their temporary suspension in the current. A succession of tubes may be added to the first by means of screws, internal socket, flange or other joint, and the shape may be cylindrical, angular, or conical, according to the nature of the work, and they may be provided with external edges or wings so as to fit each other, and form a continuous line or wall of piles. In works where an insular or detached erection may be required, as in the commencement of a break-water or lighthouse, it is proposed to use an apparatus termed by the inventor a " syphunculus." Here he has again followed nature, by constructing this caissoon or syphunculus on the principle of that beautiful shell-fish the nautilus pompilius, which, having a variety of internal chambers, by letting the water in or out, can elevate or depress itself at pleasure. This caissoon having been made of the proper size, and the annulus divided into the several air-chambers, as in the nautilus, it can be floated to the proper place, and sunk by the gradual admission of water. The piles once sunk, Dr. Potts proposes to make a mass of concrete in the interior so as to form a firm and solid foundation for whatever kind of structure it is proposed to rear. This mass may be formed by the use of Roman cement, by the composition employed by General Pasley, by Medway mud, burnt up with lime, and by other substances described in the inventor's patent. This being mixed up with chalk, shingle, sand, or whatever other substance may be found convenient, a hydraulic pump is then employed for the purpose of binding them together, and forming one impenetrable mass. Dr. Potts has been several years engaged in investigating into the subject, and he is now naturally very sanguine of success. We understand the subject occupies the attention of the Commissioners for the construction of harbours of refuge round the coast, and the decision will be looked forward to with great interest. The lecture was attended by several scientific gentlemen, who seemed to entertain a good opinion as to the worth and practicability of the invention.'

From 1847:-

'NEW BEACON ON THE GOODWIN SANDS.
The honourable corporation of Trinity House have recently erected a new beacon on the southern extremity of the Goodwin Sands, and its stability is rendered a matter of demonstrative certainty. Our readers may recollect that few years ago an attempt was made in a most favourable situation upon the sand, to erect a landmark and lighthouse, be called the "Light of all Nations," and the difficulty as well as the failure, of that undertaking, may give some idea of the value of any plan which securely drives a foundation series of solid piles through the shifting sands or any loose shingle. The unsuccessful plan of Mr. Bush was based upon the expectation of allowing caissons " to descend by their own weight; in this way, a depth of 28 feet was reached, but they would not descend any further. Those for general purposes were intended to be constructed 30 feet in diameter, diminishing 1 foot in 6, and 42 feet high. Now, that such a contrivance will sink a certain depth, there can be no doubt; it will descend through the sand and water a certain way by its own gravity. But the failure of this principle depends upon this, that there is a natural limit to the extent of the descending power, the caissons being dependent for descent upon their "own weight;" at least, such is the conclusion or understanding to which we come, after a careful perusal of the not very intelligible development of the plan given in that gentleman's evidence before the parliamentary commission in 1845, on the subject of harbour refuge. In advance upon the proved inefficient contrivance of caissons so constructed, we have to describe the pneumatic process for sinking piles, patented by Dr. Potts. We cannot adduce a fact which proves the perfect success of the doctor's principle more striking than this - that for the foundation of the new beacon, cast iron columns have been made to penetrate the sand to 32 feet, the central column is 2 feet 6 inches in diameter, the others narrower, and all well secured together means of wrought iron rods and clips, every square foot of the sand being susceptible of being covered the same way till nothing is presented but a forest of closely-packed, tightly-wedged piles, that may driven by this process downwards any required depth. Dr. Potts has for many years devoted his mind to the subject, but there are some peculiarities in driving piles of wedges through wet or shifting sand that require or admit a peculiarity of adaptation. If a bar of iron three inches diameter he driven into the Goodwin Sands 13 feet, as was done by Captain Bullock, it would require 46 blows of a ram of 1 cwt. at 10 feet fall to drive it only a single inch further. Now the principle of the doctor is very simple and ingenious.— If a hollow cylinder, open at the lower end, inverted in water over the sand in which it is intended to be sunk, and if attached at the upper surface be a tube, connected with an exhausting air-pump, it will be found that as the cylinder becomes exhausted, it will progressively descend, its lower rim will cut its way through the sand, gravel, or shingle, and the space in the tube previously occupied by air, will be filled by the gradual ascent of the displaced materials, and this will go on till the tube has not another cubical inch of air to be exchanged for sand from below. Obviously, as the sand rises in the tube, the tube itself must sink. This an exposition of the principle. The tubes being driven, they are readily emptied of their sand, and may be easily filled with concrete, into which iron rods or masts may be inserted, or in fact, a series of iron square hollow pillars, with hearts of stone, may be laid accurately in juxtaposition to form a foundation of mingled stone and iron. The advantage of having large masses deeply driven into the sand, or into any loose foundation, is, that no transverse screws at the foot of the pile are necessary, as seems to have been deemed so in the construction of several lighthouses of modern date raised upon piles. The rapidity with which the piles may be sunk is very surprising—more may be done an hour by the air pump and hollow tube, whether circular or square, whether of metal or of wood, than can be performed week in the most favourable situation by the old method of driving a heavy wooden iron-shod and pointed pile, by means of monkey or a ram; we believe in some districts the thing is called a “ tup," essentially nothing more than a hoisted mass of iron allowed to fall upon the upper end of the pile. Of course, this ingenious adaptation of a great natural law is applicable to other instances than driving foundation into shoals of sand at sea. Foundations for railways and bridges, for large buildings, such as our Custom House, near the Thames, which lately required a new and permanent foundation, may be rapidly constructed this process. The Lords of the Admiralty, the Board of Ordnance, the Trinity Board, and other branches of government, have verified the truth of this novel principle, and are adopting upon various parts of the English coast. The Trinity Board directed a pile of 2½ feet diameter to be driven on the pneumatic principle, and the state of the weather required it to be done at three intervals. Saturday, July 19, 1845, the pile, in three hours, descended 22 feet; the following Monday, in one hour, it descended 10 feet further; on Saturday, the 26th, in an hour and a half, the application of the air pump caused the tube to descend another 19 inches ; thus making an aggregate descent 33 feet 7 inches, in five hours and half, not as the result of brute force, which very probably, exerted its most tremendous extent, could not have accomplished, but as the triumph of ingenuity and science over the untaught exertion of human muscles, the quiet subjection of inert passive matter to the dominion of philosophic mind. Franklin, harmlessly beguiling the destructive lightning by means of a kite and string, or an iron wire, ensuring results the most astonishing, by a simplicity apparatus that gave into his hand power over the elements, was but his day the exponent of a principle seized by Dr. Potts—an intelligent familiarity with the laws of the material universe, with the principles that govern the displacement physical masses and the relations they respectively bear, has enabled him to make the yielding air his servant in driving into the earth the heaviest bodies. The adoption of the system must be universal, and though engineers and contractors cannot but be already familiar with the process, there is in the doctor's invention so much of the history of human progress, that we doubt not our notice of it will be acceptable to the general reader,— Canterbury Journal'

1850 Death Notice: 'At his house in Buckingham Street, Strand, London, on the 23d ult, Dr Potts, the inventor of the hydraulic pile-driving process, and other mechanical inventions. He belonged originally to the medical profession but by inclination, even from school-boy days, and while a class-fellow with the present Premier and the Duke of Bedford, he appears to have devoted himself to mechanical and engineering pursuits. His name, however, will be most closely associated for the future with the ingenious process for driving piles.'

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Biography

POTTS, LAURENCE HOLKER (1789–1850), physician and inventor, son of Cuthbert Potts, surgeon, and Ethelinda Margaret Thorpe, daughter of John Thorpe, M.D., F.S.A. [see Thorpe, John], was born in Pall Mall, London, on 18 April 1789.

He was educated at Westminster School and at a school in Northamptonshire, and in 1805 he was apprenticed to Mr. Birch, surgeon, of Warwick. In 1810 he was entered at St. George's Hospital and became a house-pupil of Sir Benjamin Brodie; William Frederick Chambers [q. v.] and (Sir) Charles Locock [q. v.] were house-pupils at the same time. He passed the College of Surgeons in 1812, and graduated M.D. at Aberdeen in 1825. In 1812 he was appointed surgeon to the Royal Devon and Cornwall miners militia, then quartered in Ireland. The regiment returned to Truro in 1814, and was subsequently disbanded, Potts starting in practice in the town.

He had always taken much interest in scientific pursuits, and in 1818 took an active part in founding the Royal Institution of Cornwall. He gave several courses of lectures there, and was in the habit of making gratuitous analyses of minerals for the miners.

In 1828 he became superintendent and physician of the Cornwall county lunatic asylum at Bodmin. This appointment he resigned in 1837, removing in the following year to Vanbrugh Castle, Blackheath, where he established an institution for the treatment of spinal diseases. Here he established a workshop for the manufacture of the various appliances and apparatus, of which he devised many new forms. He had at the same time a town house in Buckingham Street, Strand, to which a workshop was attached. His increasing interest in his inventions diverted his attention from his patients, and Vanbrugh Castle was eventually given up.

In 1843 he took out a patent (No. 9642) for conveying letters on a railway formed by suspending wires or light rods from distant points, making use of church towers, or any other lofty structures available. The patent also includes a velocipede and a boat propelled by paddles worked by hand. He was also the author of many minor inventions.

But the invention with which his name is closely connected is for a method of sinking foundations, for which he obtained a patent in 1843 (No. 9975). It consists in the sinking of hollow piles of iron, open at the lower end and closed at the top by a cap. A partial vacuum being then formed within the tube by means of a pump, the shingle, sand, &c., are caused to flow up through the pile by the pressure of the atmosphere, the rush of water from below breaking up the soil and undermining the lower edges of the pile. The pile descends by its own gravity, assisted by the pressure of the air on its closed end, and when it is filled, the contents are discharged by a pump. As the tube descends the cap is removed and a fresh length attached. The tubes may be of large size, when they practically become coffer-dams. The invention was well received, and at first it promised to be a great success.

Potts gave evidence on 10 June 1844 before the royal commission on harbours of refuge (cf. Report, p. 119), when Mr. James Walker, president of the Institution of Civil Engineers, and a member of the commission, spoke very highly of the new method. The matter was taken up by the Trinity Board, and on 16 July 1845 an experimental tube, two feet six inches diameter, was driven to a depth of twenty-two feet into the Goodwin Sands in two or three hours. This was intended to form the foundation of a beacon, which, however, does not seem to have been completed until 26 Aug. 1847, when it was announced to mariners (Mechanics' Magazine, 9 Aug. 1845, p. 96; Civil Engineers' and Architects' Journal, December 1847, p. 388). Several small beacons were erected on sands lying near the mouth of the Thames in 1845–6 (cf. Findlay's paper in Transactions of the Society of Arts, 15 Dec. 1847, lvi. 269).

In 1845 Potts became acquainted with Charles Fox of the firm of Fox & Henderson [see Fox, Sir Charles], who spent a considerable sum of money upon the invention, and used it wherever they had an opportunity (Proceedings of the Institution of Civil Engineers, xxvii. 301). The first large work upon which it was employed was the viaduct which carries the Chester and Holyhead railway across Maeldreath Bay in the Isle of Anglesey. Nineteen tubes, one foot diameter and sixteen feet long, were successfully sunk in the sand during the summer of 1846. A full account of this undertaking, with engravings, is given in the ‘Civil Engineers' and Architects' Journal,’ (December 1847, p. 388).

It was also employed successfully for sinking the piers for a railway bridge over the Ouse at Huntingdon, but it failed at the bridge over the Nen at Peterborough, in consequence of the presence of boulders in the clay forming the river-bed. The foundations for the South-Western railway bridge over the Thames, between Datchet and Windsor, were laid by Potts's method; but on 12 Aug. 1849, when the line was ready to be opened, one of the tubes suddenly sank, causing a fracture in the girder resting upon it (Times, 14 Aug. 1849, p. 3).

G. W. Hemans tried it with cylinders ten feet diameter in 1850, during the construction of a bridge over the Shannon at Athlone, on the Midland Great Western railway of Ireland, but the expense of pumping out the air was very considerable, and much trouble was caused by boulders, which the trial borings had failed to indicate (cf. Proceedings of the Institution of Civil Engineers, xxi. 265, xxvii. 301, 305, xxviii. 349, 353, l. 131; Humber, Bridges, 3rd edit. pp. 180, 247; Civil Engineers' and Architects' Journal, December 1850, p. 392; Burnell's Supplement to Weale's Theory of Bridges, 1850, p. 100).

Potts read a paper on his method before the Society of Arts on 10 May 1848, for which he received the Isis gold medal (Transactions, lvi. 441). He devoted the last years of his life almost exclusively to the perfecting of his invention, upon which he expended a very considerable fortune. Unhappily, it was not a financial success; and experience has proved that its application is very limited. It is rarely used now (cf. Newman, Cylinder Bridge Piers, 1893, p. 41). It had, however, one very important result, as it incidentally gave rise to the system of sinking foundations by compressed air, an invention of great importance.

It was intended to employ Potts's method to sink the piers of Rochester Bridge (commenced about 1849), but it was found that the river-bed was encumbered with the remains of a very ancient bridge, and that the cylinders could not be forced through the obstructions. It then occurred to Mr. J. Hughes, the engineer in charge of the work, to reverse the process, and to pump air into the cylinders to force the water out, so that the men could work at the bottom of the cylinders, as in a diving-bell. As the material was excavated from the space covered by the cylinders they sank by their own weight. An ‘air-lock’ provided the means of ingress and egress to the cylinders. An account of the work was read by Hughes before the Institution of Civil Engineers in 1851 (cf. Proceedings, x. 353, also published separately). It was afterwards pointed out that the same method had been previously used in France, though on a very small scale.

Potts died on 23 March 1850. He married, in 1820, Miss Anne Wright, of Lambessow, Cornwall. Four daughters and two sons, John Thorpe and Benjamin L. F., both of whom were trained as engineers at the London Works, Smethwick, near Birmingham, under Fox & Henderson, survived him.

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