Report on mining and the mechanical preparation of ores

Front matter

MTED BY

UNITED STATES OF AMERICA

C CUCC CC

Chapter I. Boeing Shafts Of Large Section, And Artesian-well Boring

Introduction—Boring large mining shafts in the department of Moselle—Surface prepa¬ rations—Tools and methods of boring—Tubbing—Concreting—Tools used at the second shaft—Lining the shafts—Operation of lowering the sections of tubbing—The moss-box—General observations on boring apparatus—Kind’s new trepan—Sinking and baring artesian wells—Boring tools of D ego usee and Laurent—Trepan with free fall—Trepan of Dm Brothers.—pp. 7-31.

Chapter II. Drilling Engines And Coal-cutting Machines

Machines for boring and drilling by percussion—Trouillet’s excavator—Drilling ma¬ chines actuated by steam or compressed air—Sommeilier’s drilling engine—Doring’s drill—Bergstroem’s drill—Haupt’s drill—Beaumont and Locock’s drilling engine— Drilling by rotation of the tools—Lisbet and Jacquet’s borer—Leschot’s drill—De La Rocbe-Tollay and Perret’s boring apparatus—Machines for cutting out coal.—pp 32-52.

TRANSPORTATION, HOISTING, AND PUMPING.

Chapter III. Underground Tramming; Hoisting And Pumping Engines

Introductory — Transportation underground ; tramming — Evrar’s lubricating axleboxes—Examples of underground transportation—Hoisting engines—Steam brakes— Diameter of winding drums—Iron derricks—Pumping and draining machinery— Cornish engines—Ordinary pumping engines—Raising water by guided kibbles— Chain pump—Russian pump.—pp. 53-63.

Chapter IV. Man-engines And Parachutes

Descent of miners by means of fixed ladders—Lowering men by means of cables—Con¬ struction of the man-engine—The rods—Landing places or stages—Support of the ro( l, s —Hydraulic regulators—Movement of the man-engine—Parachutes for the pre¬ vention of accidents to cages.—pp. 64-81.

CONTENTS.

MECHANICAL PREPARATION OF ORES.

Chapter V. Ore-crushing, And Ore-dressing Machinery And Processes

Introductory notice of the condition of the art—Substitution of iron for wood in ore-dressing machines—Ore-breaking and crushing machines—Blake’s rock-breaker, its construction and operation—Crushing by rollers—Stamp-mills—Rittinger’s improved stamp-mill—Iron-stem stamps—Ore-dressing machinery and processes—Machines for classifying or sizing crushed ores—Treatment of stamp stuff—Washing by sieves and jigs—Separation of ores by falling through a column of water—Slime separa¬ tors—Shaking tables and circular buddies—Chain elevators—Conclusion.—pp. 82-104.

LIST OF PLATES.

Plate I. —Tools fok boring large shafts.

Plate II. —Boring and Drilling Machines.

Plate III. —Drilling and Coal-cutting Machines.

L—BORING, DRILLING, AND EXCA¬ VATING.

Chapter I. Boring Shafts Of Large Section, And Arte¬ Sian-well Boring

Introduction—Boring large mining shafts in the department of Moselle- Surface PREPARATIONS—TOOLS AND METHODS OF BORING—TUBBING—CONCRET¬ ING—Tools used at the second shaft—Lining the shafts—Operation of low¬ ering THE SECTIONS OF. TUBBING—TlIE MOSS-BOX—GENERAL OBSERVATIONS ON BORING APPARATUS—KIND’S NEW TREPAN—SINKING AND BORING ARTESIAN WELLS—

Tools of Degous^e and Laurent—Trepan with drop—Trepan of Messrs. Dru Brothers.

Introduction

Until within a few years tools and apparatus for boring into the earth to great depths were used almost exclusively for obtaining water, or to explore for beds of coal or for mineral deposits. Fifty years ago the art of boring was in a primitive condition, as practiced by the well-borers of Artois and Italy; but now, thanks to the French societies of art, agricul¬ ture, and industry, it has received a new impulse, and scientific engineers have been called to project and direct extensive operations of this nature. Under their influence the art which was so long neglected has been rapidly developed, and the boring rod has passed from the hands ot workmen simply into those of skillful engineers. The humble boring rod of Bernard Palissy has now been converted into an engine which is applied in many ways, and which accomplishes results at the depth of several hundreds of metres as complicated and difficult as any which may lie attained at or near the surface.

The diameters of artesian wells formerly did not exceed 0 ra .30, (11.81 inches,) but they have been increased regularly, until at Passy, near Paris, an artesian well was commenced at more than one metre in dia¬ meter, and was completed with a diameter of 0 m .70 at the bottom. It is now known to be possible to sink shafts, either for wells or for mining purposes, with diameters as great as 4 m .10, or over thirteen feet, and through strata of great hardness.

Apparatus for these purposes, shown in the Exposition by Messrs. Kind and Chaudron, Degousee. Charles Laurent, and by Dru Brothers, mark the new era in the art of sinking shafts and wells, and make it evi¬ dent that the new methods and engines are destined to have a great influ-

PARIS UNIVERSAL EXPOSITION.

ence upon the development of coal-fields, especially such as underlie per¬ meable strata heavily charged with water, and alternating with imperme¬ able beds of solid rock, as in the coal basins of Mons and La Moselle, in France.

I.—BOEING LARGE MINING SHAFTS.

These new methods of boring shafts avoid the necessity of pumping out the water during the operations of sinking, as must always be done when the work is performed by hand labor. This method of working in a shaft full of-water is called in France a niveau plein , in distinction to the other and old methods of working with the shaft drained, called a niveau plat.

The importance of this mode of sinking will be evident from the fol¬ lowing brief notice of the coal basin of Saarbruck. This basin extends beyond the limits of the Rhine provinces, in the department of La Moselle. The coal occurs under barren strata, composed of the (gres des Vosges ) sandstone formation of the Vosges, and the new red sandstone formation, (gres rouge.) The formations are at first very silicious and full of fissures, giving free passage to water. They then become argillaceous, and finally, near the junction with the coal measures, are impermeable to water.

Eleven mining concessions have been made in this department since 1820, and in 1858 it was estimated that twenty-one millions of francs had been expended, and chiefly in prospecting.

Boring and tubbing (lining the shaft) from the surface was completely successful for the first time, from 1854 to 1850, at St. Vaast, and later at Bessaix, in Belgium, in 1802 and 1803 5 but in these two first attempts the water-bearing strata were scarcely 0 m .70 thick, and the pits were of small dimensions.

I 11 order to explain the apparatus and these methods of sinking in detail, we give a description of the work of sinking shafts of large dimen¬ sions in the department of the Moselle.

SHAFTS IN THE DEPARTMENT OF MOSELLE.

The works about to be described were executed at L’Hopital (Moselle) for the St. Avoid company, represented by Messrs. Pereire and Morny, upon the method called the niveau plein of Messrs. Kind and Chaudron, under the direction of Mr. Levy, the company’s engineer. The work was under the superintendence of Mr. Chatelain, engineer, formerly a pupil of the Eeole Centrale des Arts et Manufactures of Paris. Two pits were sunk; one for an air-shaft (No. 1 ) with a diameter of l m .80 within the tubbing, and 2 m .56 in its greatest diameter; the other (or No. 2 ) for a winding or hoisting shaft was bored with a diameter of 4 m . 10 , and was 3 m .40 when finished. The operations, according to this method, suc¬ ceed iu the following order:

1. Construction upon the surface—buildings and derricks.

2. Boring the pits.

MINING-BORING LARGE SHAFTS.

3. Lowering the tubbing.

4. Puddling or packing.

5. Packing at tlie base of the tubbing.

BORING SHAFT No. 1.

Surface preparations. —The preliminary operations consisted in the construction of the necessary buildings for the engines and tools, and the erection of a derrick over the site of the pit. All these were of tem¬ porary construction, intended to be used merely during the progress of the work.

The derrick was made of four supports strongly framed together, and sustaining a platform about thirty feet above the surface of the ground. Upon this a railway or tramroad was laid for the trucks, which carried the boring tools and rods.

The engines for sinking comprised the capstan , the jumper , and the donkey-engine. The capstan was used for lowering and hoisting the boring tools in the pits, and for lowering the tubbing or lining of the shaft. The engines used at L’Hdpital had a nominal force of 25 horse power. The diameter of the cylinder was 0 m .56, and the length of stroke 0 m .70. The respective diameters of the gearing were l m .70 and 0 m .35. Admit¬ ting an effective pressure of three atmospheres, the iidtial force upon the driving shaft was 48,513 kilogrammes. These machines worked regularly; nevertheless we think it would be well to increase the size of the engine, inasmuch as the tendency is constantly to an increase of the size and weight of tools in use.

The first rope used at the air-shaft had a section of 54 square centime¬ tres, capable of sustaining a strain of 5,400 kilogrammes. It was made of good hemp $ but after working for one year, it broke in lifting a trepan weighing 3,858 kilogrammes. The tool fell from a height of 86 metres, taking with it 17 metres of the rope. This accident occasioned a stop¬ page of nine days. The cable was replaced by another having a section of 85 square centimetres, and after using it for fourteen months the work was suspended for three days in order to make a new splice.

The second machine—the jumper—was made of an engine cylinder, open at the bottom and closed at the top. The piston-rod was connected directly with the wooden beam, carrying the tool for cutting and boring at its other end. By the alternate lifting and falling of this tool with the attached beam, the rock was cut away. The diameter of the piston of the jumper was 0 m .60, and the greatest length of stroke was one metre. The jumper did'not require any repairs during the whole opera¬ tion of sinking the shaft.

The third machine—the donkey-engine—was used to work a pump for hot and for cold water. It is indispensable for the supply of the boiler, as the capstan and the jumper work irregularly. Experience has shown that the feed-pumps should be in duplicate, so as to avoid the necessity of stopping for repairs.

PARIS UNIVERSAL EXPOSITION.

The preparations for sinking the air-shaft were commenced in October, 1802, and were finished in the following month of April. The expense was as follows :

Machines and tools. 37,320.91

Boring the pits. —Before commencing the sinking with the special tools, a preparatory pit was sunk to a depth of 21 m .40, and was lined with masonry to a diameter of 2 m .80 up to within five metres of the surface, where the diameter was increased to four metres. This shoulder in the stone lining afforded a foundation for a platform.

The sinking was accomplished by two different operations. First, a central pit of l m .37 was sunk and then enlarged to 2 m .20. The debris of this enlargement fell into the first pit. The tubbing was inserted in the enlarged pit.

The boring tools employed in these operations will now be described: the scraper, the scrape-hook, and the different apparatus used indiscrim¬ inately in the two pits will be afterward noticed.

The little trepan first employed is represented by Fig. 1 , Plate I. It weighs 2,085 kilogrammes, and is formed of two principal parts—the fork and the blade. The blade is l m .26 long, and is provided with teeth of cast-steel, or of iron faced with steel, intended to cut the rock. These teeth increase the diameter of the trepan to l m .37. The blade is joined by means of keys to two strong iron arms, which are united above with a central shaft, which was connected by a slide with the suspension apparatus.

This trepan worked easily through the sandstone of the Vosges —gres des Vosges. The fall given was 0 m .30. The progress per day was at first 0 m .79, and it diminished to 0 m .52, and then to 0 m .28 at a depth of 121 metres 5 but at 135 metres in depth, in a stratum of strongly aggregated silicious red sandstone, the progress was only 0 m .15 and 0 m .ll. It was soon found that this trepan was too light to stand the shocks of the blows, and three successive ruptures of the stem made it necessary to procure a stronger trepan, shown by Fig. 2, Plate I, weighing 3,858 kilogrammes, divided among the various parts as follows:

Kilos.

Body of trepan. 2, 700

Guide. 340

Blade .. 230

Four teeth of the head. 148

Four intermediate teeth. 88

Plates and keys. 352

Total weight... 3, 858

MINING—BORING LARGE SHAFTS.

The teeth are fixed upon this mass of iron by means of keys. The sockets for the reception of the tenons are conical, and are 0 m .10 in diame¬ ter at the base and 0 m .09 at the top. The progress in the work made by this trepan, from the commencement, was from 0 m .28 to 0 m .32, and even as high as 0 m .83, giving a mean of 0 m .39, being three times as much as made by the first trepan. This shows clearly that the heavy trepans are best for the hard strata.

The trepan which was first used for the enlargement of the pit to the diameter of 2 ra .56 had a blade 2 m .46 in length; it was formed like the little trepan first used, and had a blade fixed upon a fork, and weighed in all 3,980 kilogrammes, divided as follows:

Kilos.

Blade. 906

Six teeth of the head. 102

Three intermediate teeth. 48

Two plates. 430

Total weight. 3,980

In order to avoid the frequent breaking out of the teeth, this trepan was lifted only 0 m .20. The progress made with it daily was from l m .10 to 0 m .18 at the last, when a stratum of hard sandstone was encountered and the weight of the trepan was found to be insufficient. Two blades, one above the other, were then united to the fork by rings and bolts, as shown in Fig. 3, Plate I. Each of these blades carried the teeth so as to cut the strata in two steps. This new tool weighed about 5,000 kilo¬ grammes. It worked four months, and required frequent repairs. The rate of progress per day was only 0 m .ll. It was then decided to replace this trepan by a more massive one, weighing 8,000 kilogrammes, and 2 m .50 in diameter, constructed as shown in Fig. 4, Plate I. With this the progress was increased to 0 m .34 a day, thus showing a second time that in hard rock heavy trepans are required.

The diameter of the pit at the beginning was 2 m .5G; at 134 ra depth it was reduced to 2 m .45; at 155 m depth it was reduced to 2 m .40; from 155 m .00 to 155 m .50 depth it was reduced to 2 m .33; from 155 m .50 to 158 m .00 depth it was reduced to 2 m .25. At this depth the little pit was continued for a depth of seven metres, and a circular curb of 0 m .40 was fixed to receive the base of the tubbing.

The work of sinking this air-shaft lasted about twenty-eight months and a half. The central pit required 392 days, including 46 days during which work was stopped, so that only 346 of actual work were necessary. The enlarging operations to a diameter of 2 m .56 occupied 469 days, including 148J days of no work. The depth of the central pit being 143">.7<), (equal to 471.46 feet,) the mean progress for each working day was 4™.15, (13 feet,) and the enlarging to 2 m .40 gave a daily mean of 4 m .25 for a depth of 136 m .60.

PARIS UNIVERSAL EXPOSITION.

The expenses of boring were as follows:

Salaries and wages.

Fuel.

Oil and grease.

Ropes.

Iron, steel, and repairs to tools Cartage and sundries.

Francs.

93,013. 39

Tubbing.— Before entering upon a description of the operation of tubbing the air-shaft, it will be best to explain the system adopted by Messrs. Kind and Cliaudron.

The tubbing of the pits is accomplished by lowering into them a metallic cylinder, which finally rests upon a proper seat or foundation, carefully cut for it at the bottom. This cylinder is made smaller than the bore of the pits, and the space between the cylinder and the walls is afterward puddled or filled in with concrete, so as to make a solid con¬ tinuous lining. The metallic cylinder or tubbing is formed in sections of a cylinder, made of cast iron, and provided with flanges projecting inward, by which they are securely bolted together. (See Figs. 5, 6, 7, and 8, Plate 1.) One section or length is added after another to the top as the whole descends in the pit, so that at the completion of the work the whole pit is lined with iron from the top to the bottom. The outer surface of all these sections of the cylinder is quite smooth; but in the inside, besides the flanges for the bolts, there are horizontal ribs or webs cast with each segment, and intended to strengthen them.

The thickness of the tubbing will evidently vary with the diameter of the pits and that of the different segments, according to their position in the pit. Messrs. Kind and Cliaudron determine the thickness by the following formula:

E represents the thickness of the tub, 11 the radius, and P the pressure expressed in kilogrammes upon the square. The flanges for bolting the rings together should be carefully faced in a lathe, and exactly at right angles with the perpendicular of the shaft. The joints are made tight by a packing of lead, in the form of a ring, 0 m .003 thick, covering all the surface of the flange, so that after the bolts are tightened there will be a surplus of lead along the points suitable for calking. The first attempts to secure a tight packing for the joint at the bottom of the shaft to prevent the entrance of water at the lower part of the tubbing were unsuccess¬ ful, but the difficulty was finally overcome by the use of what is now known as the a moss-box.” This consists of an attachment to the lower end of the tubbing of an inner tub, or cylinder, provided with a flange at the bottom projecting outward. The bottom of the tubbing is also

MINING—BORING LARGE SHAFTS.

provided with a flange projecting outward toward the sides of the pit. The space between these two flanges is filled with a packing or wrapping of moss.—(See Fig. 5, Plate I.) This moss is securely held in its place by a web or net drawn tightly around it. The whole, including the inner cylinder, is suspended by iron tie-rods, which prevent its falling out from the bottom of the tubbing, but which do not interfere with the descent of the tubbing upon the moss when the lower flange reaches and rests in the seat or shoulder cut in the rock at the bottom of the pit. At this time the whole weight of the tubbing being allowed to press upon the moss by means of the upper flange, it is compressed and extended outward forci¬ bly against the side of the pit, and thus forms a complete and perfectly water-tight joint. Its office and operation is similar to that of the “ seedbag” used by the borers of petroleum wells in Pennsylvania. The out¬ ward movement of the moss is facilitated by thin segments of sheet iron, 0 m .005 thick, so placed at the upper and lower parts of the moss box, at an angle of fifty or fifty-five degrees, that they present a sloping surface, upon which the moss slides outward when the pressure commences.

The operation of lowering the tubbing into its place in the pit is easily performed by means of the arrangements about to be described. Upon the lower edge of the last section but one of the cylinder a hemispherical¬ shaped bottom is attached, which closes the lower end of the column. The attachment to the tubbing is securely made by means of a flange bolted to an annular plate.—(Sec Fig. (>, Plate I.) This hemispherical bottom plate has a central opening into a cast-iron column rising within the tubbing. This column is called the equilibrium column, and at dis¬ tances of from seven to eight metres it is pierced with holes 0 m .01 in diameter, for the purpose of admitting water to the inside of the tubbing as fast as the latter is sunk in the pit. These holes are closed by screws, and as the tubbing is lowered into the pit the water rises around it and within the open column in the center, until the weight of the water displaced is equal to the weight of the tubbing, thus causing the whole to float in the pit. By removing some of the screws closing the holes, water is admitted to the interior, and the cylinder is made to sink. It is found in practice that it is best to allow sufficient water to enter to give a weight of from twenty-five to thirty tons to the tubbing, or, in other words, to permit so much of its weight to be suspended from the surface as to secure its vertical position and its descent in a proper manner.

The apparatus for suspension consists of four upright posts, sustaining a platform through which the six suspending iron rods pass, and are terminated in long screws. This platform must be strong enough to sus¬ tain a weight of thirty tons. Its height above the ground must be equal to that of the four lowest sections of the cylinder, including the moss-box. All these, together with the first sections of the equilibrium column, are first united before being lowered into the pit. Each suspension rod is made in three parts: First, the lower rod, the lower end of which is cut

PARIS UNIVERSAL EXPOSITION.

with a screw-thread, for the reception of a stop-nut after it has been passed through the eye of a flange; second, an adjusting screw, (the minimum length of which is four metres,) placed at the upper part of the rod, upon which a nut works by means of gearing and a crank on the platform, as shown in Fig. 7, Plate 1. The third part of the rods con¬ sists of the intermediate lengths, each four metres long, and coupled to¬ gether like the boring rods. These are added as the tubbing descends.

The connecting flange at the bottom of the tubbing, through which these suspending rods pass, is composed of six segments, bolted together and to the collar of the third section of the tubbing. Its form is shown by Fig. 8. It has six eyes to receive the suspending rods.

After this connecting flange lias been bolted to the tubbing and the moss-box, the hemispherical bottom and the four lowest sections are placed under the platform, and directly over the mouth of the pit; the adjusting screws are united to the connecting flange by intermediate rods, and the whole apparatus is brought into suspension by means of the nuts on the top of the scaffolding. Two workmen are placed at each screw, and by turning the nuts this first portion of the tubbing descends into the pit. After it has been lowered four metres, (the length of the screw on the rods,) the tubbing is suspended to beams resting across the mouth of the pit by means of liolding-hooks catching upon the shoulders of the suspending rods, as in the case of boring apparatus. The screws are then detached and are raised by means of the nuts, so as to leave a distance of four metres between their lower ends and the rods below. A new set of intermediate rods is then added, the suspending hooks are removed, the tubbing again rests upon the screws above, and the lowering is proceeded with as before. This operation is repeated until the tubbing floats in the water of the pit. It is then made fast as before, by the suspension rods, to the beams at the mouth of the pit. The screws are raised to a height of four metres, and then the next section to be added is brought forward and placed on beams over the pit. Fresh intermediate rods are then added through this new section to the rods below, and the suspending hooks are removed. The new section is then raised a little by means of the capstan, so as to permit the removal of the beams upon which it rested. It is then lowered by means of the capstan into the pit, until it rests upon the top of the tubbing below. The joint is then made, and the adjusting screws are worked to effect a further descent of the whole tubbing.

When in this manner all the sections have been united, and the me¬ tallic lining is upon the point of reaching the bottom of the pit, the rim of rock or seat upon which the flange of the moss-box is to rest requires to be cleaned. This operation is effected by lowering through the equi¬ librium column a tool represented by Fig. 9, which scrapes the bottom of the pit and throws into the central pit any fragments of rock or accu¬ mulations of earth which rest upon the foundation. The lowering is then continued until the lower flange of the moss-box rests gently upon the

MINING-BORING LARGE SHAFTS.

Tim of rock. The weight of the tubbing increases slowly as the water enters through the holes of the equilibrium column; the moss-box is shortened, the moss is expanded and compressed against the sides of the pit and becomes perfectly tight when the weight of the tubbing rests upon it. At this moment the tubbing must not be abandoned to itself, or it may incline to one side. It is therefore secured carefully at the top by three or four beams fixed upon the last section. The puddling or con¬ creting can then be proceeded with, and the suspension rods can be removed.

Tubbing pit ISA 1.—The following are the details of the operation of lining the air-shaft, or No. 1: The tubbing was composed of seventy sec¬ tions, each two metres high, and I m .80 in diameter inside of the flanges. The thickness of the cylindrical part was as follows: Q m .040 (lj inch) for the sections of the lower part; 0 m .043 for the ten succeeding, and then successively 0 m .040, 0 m .037, 0 m .034, 0 m .031, and 0 m .028u

Each of the sections was provided with two internal flanges 0 m .07 broad and 0 m .03 thick. There were in addition two little ribs 0 m .04 thick and 0 m .025 deep. These were cast at equal distances between the flanges. The flanges had twenty-eight holes for bolts, each 0 m .03 in diameter and 0 U1 .21 apart. The entire tubbing weighed 258 tons, in¬ cluding the bolts. It was furnished by the Fourchambault works.

The moss-box cylinder was cast without any flange at its lower part, and an oak ring was fitted to it to form the base. The width of this box was 0 m .175, its height l m .60, representing a capacity of 1,824 cubic centi¬ metres. The pressure of the tubbing upon the moss reduced it to onesixth of its former volume.

The lowering of the tubbing was effected without the least difficulty the twelve first sections took about fifteen days, but the operation was afterward accelerated and two sections were added daily. Before the addition of the thirtieth section the tubbing was heavier than the water displaced; it was afterward necessary to introduce water to the interior by the equilibrium column. When the moss-box reached the rocky foun¬ dation the compression of the moss commenced, and the equilibrium column maintained its upright position. The tubbing was then allowed to fill with water for two days, in order to gradually obtain the maximum compression of the moss.

The descent of this tubbing lasted forty days, and the expense attend¬ ing the operation was as follows :

Francs.

Cost of sections._... 00, 420. 04

PARIS UNIVERSAL EXPOSITION.

. Francs.

Fuel burned. 1,375. 23

Concreting pit No. 1 .—It lias been shown that the metallic column which forms tlie tubbing can be maintained perfectly tight throughout its entire height, provided the joints are carefully made. At the bottom the moss-box, resting on impermeable soil r is intended to cutoff all communi¬ cation between the upper water-level and the pit to be sunk below. Not¬ withstanding all these precautions, it is indispensable, in order to insure a permanent impermeability of all the joints, to make a complete concreting around the entire height of the tubbing, within the annular space left be¬ tween the soil and the tubbing itself. The expense of concreting pit No. 1 was relatively of small amount. The work lasted twenty-five days. Three sets of workmen were employed, working three spoons of a mean capacity of till *ee hectolitres. Each set was composed of six men—two for work¬ ing the windlass, to which the spoon was attached by a rope; two for working the windlass for the piston-rope; and, lastly, two on the work¬ ing stage to fill the three spoons as they were raised from the pit. The mortar was brought, in a case, upon the working stage by the capstan.

The spoon for concreting (Fig. 10) was made of two sheets of iron united on two wooden uprights. It is provided at its upper part with a piston, which forms part of a movable bottom placed at its lower part. By pushing the piston the bottom is expelled and the mortar filling the case falls out. The concrete used had the following composition: Vassy or Rappe cement, (Haute Saone,) one-fourth; hydraulic lime, one-fourth; sand, one-fourth; and powdered trass, one-fourtli.

The space to be filled around the tubbing was about 236 cubic metres, neglecting the fissures of the soil; 284 cubic metres of materials were employed. The concrete was allowed to harden for one month. Lastly, the water was pumped out, and the false bottom of the tubbing and the equilibrium column were taken apart and removed. The moss box was found to be in good order and perfectly water-tight.