Chapter VII: Preface (7)

The cause of overflowing wells has been ascribed to a variety of circumstances. But, as it is now generally admitted that the numerous springs which issue from the ground proceed from the infiltration of the waters progressively condensed in rain, dew, snow, &c. upon the surface of our globe, the theory of these interior streamlets becomes by no means intricate; being analogous to that of syphons and water jets, as expounded in the treatises of physics. The waters are diffused, after condensation, upon the surface of the soil, and percolate downwards, through the various pores and fissures of the geological strata, to be again united subterraneously in veins, rills, streamlets, or expanded films, of greater or less magnitude, or regularity. The beds traversed by numerous disjunctions will give occasion to numerous interior currents in all directions, which cannot be recovered, and brought to the day; but when the ground is composed of strata of sand, or gravel very permeable to water, separated by other strata nearly impervious to it, reservoirs are formed to our hand, from which an abundant supply of water may be spontaneously raised. In this case, as soon as the upper stratum is perforated, the waters may rise, in consequence of the hydrostatic pressure upon the lower strata, and even overflow the surface in a constant stream, provided the level from which they proceed be proportionally higher.

The sheets of water occur principally at the separation of two contiguous formations; and, if the succession of the geological strata be considered, this distribution of the water will be seen to be its necessary consequence. In fact, the lower beds are frequently composed of compact sandstone or limestone, and the upper beds of clay. In level countries, the formations being almost always in horizontal-beds, the waters which feed the artesian wells must come from districts somewhat remote, where the strata are more elevated, as towards the secondary and transition rocks. The copious streams condensed upon the sides of these colder lands may be therefore regarded as the proper reservoirs of our wells.

_Fig._ 26. represents the manner in which the condensed water of the heavens distributes itself under the surface of our globe. Here we have a geological section, showing the succession of the several formations, and the sheets or laminæ of water that exist at their boundaries, as well as in their sandy beds. The figure shows also very plainly that the height to which the water reascends in the bore of a well depends upon the height of the reservoir which supplies the sheet of water to which the well is perforated. Thus the well A, having gone down to the aqueous expanse A A, whose waters of supply are derived from the percolation M, will afford rising waters, which will come to the surface; whilst in the well B, supplied by the sheet P, the waters will spout above the surface, and in the well C they will remain short of it. The same figure shows that these wells often traverse sheets of water, which rise to different heights. Thus, in the well C there are five columns of ascending waters, which rise to heights proportional to the points whence they take their origin. Several of these will be spouting or overflowing, but some will remain beneath the surface.

The situation of the intended well being determined upon, a circular hole is generally dug in the ground, about 6 or 8 feet deep, and 5 or 6 feet wide. In the centre of this hole the boring is carried on by two workmen below, assisted by a labourer above, as shown in _fig._ 27.

The handle (_fig._ 28.) having a female screw in the bottom of its iron shank, with a wooden bar or rail passing through the socket of the shank, and a ring at top, is the general agent to which all the boring implements are to be attached. A chisel (_fig._ 29.) is first employed, and connected to this handle by its screw at top. If the ground is tolerably soft, the weight of the two workmen bearing upon the cross bar, and occasionally forcing it round, will soon cause the chisel to penetrate; but if the ground is hard or strong, the workmen strike the chisel down with repeated blows, so as to peck their way, often changing their situation by walking round, which breaks the stones, or other hard substances, that may happen to obstruct its progress.

The labour is very considerably reduced, by means of an elastic wooden pole, placed horizontally over the well, from which a chain is brought down, and attached to the ring of the handle. This pole is usually made fast at one end, as a fulcrum, by being set into a heap of heavy loose stones; at the other end the labourer above gives it a slight up and down vibrating motion, corresponding to the beating motion of the workmen below, by which means the elasticity of the pole in rising lifts the handle and pecker, and thereby very considerably diminishes the labour of the workmen. See _fig._ 27.

When the hole has been thus opened by a chisel, as far as its strength would permit, the chisel is withdrawn, and a sort of cylindrical auger (_fig._ 30.) attached to the handle (_fig._ 28.), for the purpose of drawing up the dirt or broken stones which have been disturbed by the chisel. A section of this auger is shown in _fig._ 31., by which the internal valve will be seen. The auger being introduced into the hole, and turned round by the workman, the dirt or broken stones will pass through the aperture at bottom (shown at _fig._ 32.), and fill the cylinder, which is then drawn up, and discharged at the top of the auger, the valve preventing its escape at bottom.

In order to penetrate deeper into the ground, an iron rod, as _a_, _fig._ 33., is now to be attached to the chisel, _fig._ 29., by screwing on to its upper end, and the rod is also fastened to the handle, _fig._ 28., by screwing into its socket. The chisel having thus become lengthened, by the addition of the rod, it is again introduced into the hole; and the operation of pecking or forcing it down, is carried on by the workmen as before. When the ground has been thus perforated, as far as the chisel and its rod will reach, they must be withdrawn, in order again to introduce the auger, _fig._ 30., to collect and bring up the rubbish; which is done by attaching it to the iron rod, in place of the chisel. Thus as the hole becomes deepened, other lengths of iron rods are added, by connecting them together, as _a b_ are in _fig._ 34. The necessity of frequently withdrawing the rods from the holes, in order to collect the mud, stones, or rubbish, and the great friction produced by the rubbing of the tools against its sides, as well as the lengths of rods augmenting in the progress of the operation, sometimes to the extent of several hundred feet, render it extremely inconvenient, if not impossible, to raise them by hand. A tripedal standard is, therefore, generally constructed by three scaffolding poles tied together, over the hole, as shown _fig._ 27., from the centre of which a wheel and axle, or a pair of pully blocks is suspended, for the purpose of hauling up the rods, and from which hangs the fork, _fig._ 35. This fork is to be brought down under the shoulder, near the top of each rod, and made fast to it by passing a pin through two little holes in the claws. The rods are thus drawn up, about seven feet at a time, which is the usual distance between each joint, and at every haul a fork, _fig._ 36., is laid horizontally over the hole, with the shoulders of the lower rod resting between its claws, by which means the rods are prevented from sinking down into the hole again, while the upper length is unscrewed and removed. In attaching and detaching these lengths of rod, a wrench, _fig._ 37., is employed, by which they are turned round, and the screws forced up to their firm bearing.

The boring is sometimes performed for the first sixty or a hundred feet, by a chisel of 2-1/2 inches wide, and cleared out by a gouge of 2-1/4 diameter, and then the hole is widened by a tool, such as is shown at _fig._ 38. This is merely a chisel, as _fig._ 29., four inches wide, but with a guide, _a_, put on at its lower part, for the purpose of keeping it in a perpendicular direction; the lower part is not intended to peck, but to pass down the hole previously made, while the sides of the chisel operate in enlarging the hole to four inches. The process, however, is generally performed at one operation, by a chisel of four inches wide, as _fig._ 29., and a gouge of three inches and three quarters, as _fig._ 30.

It is obvious, that placing and displacing the lengths of rod, which is done every time that the auger is required to be introduced or withdrawn, must, of itself, be extremely troublesome, independent of the labour of boring, but yet the operation proceeds, when no unpropitious circumstances attend it, with a facility almost incredible. Sometimes, however, rocks intercept the way, which require great labour to penetrate; but this is always effected by pecking, which slowly pulverises the stone. The most unpleasant circumstance attendant upon this business is the occasional breaking of a rod into the hole, which sometimes creates a delay of many days, and an incalculable labour in drawing up the lower portion.

When the water is obtained in such quantities and of such quality as may be required, the hole is dressed or finished by passing down it a diamond chisel, funnel mouthed, with a triangular bit in its centre; this makes the sides smooth previous to putting in the pipe. This chisel is attached to rods, and to the handle, as before described; and, in its descent, the workmen continually walk round, by which the hole is made smooth and cylindrical. In the progress of the boring, frequent veins of water are passed through; but, as these are small streams, and perhaps impregnated with mineral substances, the operation is carried on until an aperture is made into a main spring, which will flow up to the surface of the earth. This must, of course, depend upon the level of its source, which, if in a neighbouring hill, will frequently cause the water to rise up, and produce a continued fountain. But if the altitude of the distant spring happens to be below the level of the surface of the ground where the boring is effected, it sometimes happens that a well of considerable capacity is obliged to be dug down to that level, in order to form a reservoir, into which the water may flow, and whence it must be raised by a pump; while, in the former instance, a perpetual fountain may be obtained. Hence, it will always be a matter of doubt, in level countries, whether water can be procured, which would flow near to or over the surface; if this cannot be effected, the process of boring will be of little or no advantage, except as an experiment to ascertain the fact.

In order to keep the strata pure, and uncontaminated with mineral springs, the hole is cased, for a considerable depth, with a metallic pipe, about a quarter of an inch smaller than the bore. This is generally made of tin (though sometimes of copper or lead) in convenient lengths; and, as each length is let down, it is held by a shoulder resting in a fork, while another length is soldered to it; by which means a continuous pipe is carried through the bore, as far as may be found necessary, to exclude land springs, and to prevent loose earth or sand from falling in, and choking the aperture.

Mr. John Good, of Tottenham, who had been extensively employed in boring the earth for water, obtained a patent, in Aug. 1823, for certain improved implements contrived by him to facilitate his useful labours; a description of which cannot fail to be interesting.

The figures annexed exhibit these ingenious tools; _fig._ 39. is an auger, to be connected by the screw-head to the length of rods by which the boring is carried on. This auger is for boring in soft clay or sand; it is cylindrical, and has a slit or opening from end to end, and a bit, or cutting-piece at bottom. When the earth is loose or wet, an auger of the same form is to be employed, but the slit or opening reduced in width, or even without a slit or opening. A similar auger is used for cutting through chalk; but the point or bit at bottom should then project lower, and, for that purpose, some of these cylindrical augers are made with moveable bits, to be attached by screws, which is extremely desirable in grinding them to cutting edges. _Fig._ 40. is a hollow conical auger, for boring loose sandy soils; it has a spiral cutting edge coiled round it, which, as it turns, causes the loose soil to ascend up the inclined plane, and deposit itself in the hollow within. _Fig._ 41. is a hollow cylinder or tube, shown in section, with a foot-valve, and a bucket to be raised by a rod and cord attached at the top; this is a pumping tool, for the purpose of getting up water and sand that would not rise by the auger. When this cylinder is lowered to the bottom of the bore, the bucket is lifted up by the rod and cord, and descends again by its own gravity, having a valve in the bucket, opening upwards, like other lift pumps; which, at every stroke, raises a quantity of water and sand in the cylinder equal to the stroke; the ascent and descent of the bucket being limited by a guide-piece at the top of the cylinder, and two small knobs upon the rod, which stop against the cross-guide. _Fig._ 42. is a tool for getting up broken rods. It consists of a small cylindrical piece at bottom, which the broken rod slips through when it is lowered, and a small catch with a knife-edge, acted upon by a back-spring. In rising, the tool takes hold of the broken rod, and thereby enables the workmen at top to draw it up. Another tool for the same purpose, is shown at _fig._ 43., which is like a pair of tongs; it is intended to be slidden down the bore, and for the broken rod to pass between the two catches, which, pressed by back-springs, will, when drawn up, take fast hold of the broken rod.

_Fig._ 44. is a tool for widening the hole, to be connected, like all the others, to the end of the length of rods passed down the bore; this tool has two cutting-pieces extending on the sides at bottom, by which, as the tool is turned round in the bore, the earth is peeled away. _Fig._ 45. is a chisel, or punch, with a projecting piece to be used for penetrating through stone; this chisel is, by rising and falling, made to peck the stone, and pulverize it; the small middle part breaking it away first, and afterwards the broad part coming into action. _Fig._ 46. is another chisel, or punching tool, twisted on its cutting edge, which breaks away a greater portion of the stone as it beats against it.

The manner of forcing down lengths of cast-iron pipe, after the bore is formed, is shown at _fig._ 47.; the pipe is seen below in the socket, at the end of which a block is inserted; and from this block a rod extends upwards, upon which a weight at top slides. To this weight cords are shown to be attached, reaching to the top of the bore; where the workmen alternately raise the weight and let it fall, which, by striking upon the block in its middle, beats down the pipe by a succession of strokes; and when one length of pipe has, by these means, been forced down, another length is introduced into the socket of the former. Another tool for the same purpose is shown at _fig._ 48., which is formed like an acorn; the raised part of the acorn strikes against the edge of the pipe, and by that means, it is forced down the bore. When it happens that an auger breaks in the hole, a tool similar to that shown at _fig._ 49. is introduced; on one side of this tool a curved piece is attached, for the purpose of a guide, to conduct it past the cylindrical auger; and at the end of the other side is a hook, which, taking hold of the bottom edge of the auger, enables it to be drawn up.

Wrought iron, copper, tin, and lead pipes, are occasionally used for lining the bore; and as these are subject to bends and bruises, it is necessary to introduce tools for the purpose of straightening their sides. One of these tools is shown at _fig._ 50., which is a bow, and is to be passed down the inside of the pipe, in order to press out any dents. Another tool, for the same purpose, is shown at _fig._ 51., which is a double bow, and may be turned round in the pipe for the purpose of straightening it all the way down; at _fig._ 52., is a pair of clams, for turning the pipe round in the hole while driving.

When loose stones lie at the bottom of the hole, which are too large to be brought up by the cylindrical auger, and cannot be conveniently broken, then it is proposed to introduce a triangular claw, as _fig._ 53., the internal notches of which take hold of the stone, and as the tool rises, bring it up. For raising broken rods, a tool like _fig._ 54. is sometimes employed, which has an angular claw that slips under the shoulder of the rod, and holds it fast while drawing up.

In raising pipes, it is necessary to introduce a tool into the inside of the pipe, by which it will be held fast. _Fig._ 55. is a pine-apple tool for this purpose; its surface is cut like a rasp, which passes easily down into the pipe, but catches as it is drawn up; and by that means brings the pipe with it. _Fig._ 56. is a spear for the same purpose, which easily enters the pipe by springing; at the ends of its prongs there are forks which stick into the metal as it is drawn up, and thereby raise it.

These are the new implements, for which the patent was granted. In the process of boring, there does not appear to be any thing new proposed; but that these several tools are to be employed for boring, packing, and otherwise penetrating, raising the earth, and extracting broken or injured tools. There are also suggestions for employing long buckets, with valves opening upward in their bottoms, for the purpose of drawing water from these wells when the water will not flow over the surface; also lift pumps, with a succession of buckets for the same purpose. But as these suggestions possess little if any novelty, it cannot be intended to claim them as parts of the patent.

ASPHALTUM. Native bitumen, so called from the lake Asphaltites.

ASSAY and ASSAYING. (_Coupellation_, Fr.; _Abtreiben auf der capelle_, Germ.) This is the process by which the quality of gold and silver bullion, coin, plate, or trinkets is ascertained with precision, or by which the quantity of either or both these precious metals is determined in any given alloy. It is, therefore, a case of chemical analysis, in which peculiar methods are employed to attain the object in view with accuracy and dispatch. Assaying has been also extended of late years, to determine the quantity of palladium and platina in certain bullion and gold dust brought from Brazil.

The art of assaying gold and silver _by the cupel_, is founded upon the feeble affinity which these metals have for oxygen, in comparison with copper, tin, and the other cheaper metals; and on the tendency which the latter metals have to oxidize rapidly in contact with lead at a high temperature, and sink with it into any porous earthy vessel in a thin glassy or vitriform state. The porous vessel may be made either of wood-ashes, freed from their soluble matter by washing with water; or, preferably, of burned bones reduced to a fine powder.

The lead added to the silver or gold to be assayed, serves chiefly to dissolve the oxidized copper, whence it appears that the quantity of lead requisite for silver assays, ought to be directly proportional to the quantity which the silver and copper would separately require. It has been found by experiment, that 16 parts of lead are quite sufficient to pass 1 of copper through the cupel; and that 3/10 of lead presents the most suitable proportion for passing one of silver. From these principles, however, if we should always regard the dose of lead to be employed for any alloy as being equal to (16 × C) + (3/30 × S) we should certainly commit an error. The phenomena of cupellation is of a more complex nature. Long practice and delicate trials alone can guide to the proper quantity of lead to be employed for every various state of the alloy. The following Table contains the results of M. D’Arcet’s elaborate experiments upon this subject:--

+---------------+--------+-------------+
| Alloy. |Lead for|Ratio of the |
+-------+-------+ 1 of |Copper to the|
|Silver.|Copper.| Alloy. | Lead. |
+-------+-------+--------+-------------+
| 1000 | 0 | 3/10| 0 |
| 950 | 50 | 3 | 1 : 60 |
| 900 | 100 | 7 | 1 : 70 |
| 800 | 200 | 10 | 1 : 50 |
| 700 | 300 | 12 | 1 : 40 |
| 600 | 400 | 14 | 1 : 35 |
| 500 | 500 |16 or 17| 1 : 32 |
| 400 | 600 |16 -- 17| 1 : 26·7 |
| 300 | 700 |16 -- 17| 1 : 22·9 |
| 200 | 800 |16 -- 17| 1 : 20 |
| 100 | 900 |16 -- 17| 1 : 17·8 |
| 0 | 1000 |16 -- 17| 1 : 16 |
+-------+-------+--------+-------------+

Bismuth may be used as a substitute for lead in cupellation; two parts of it being nearly equivalent to three of lead. But its higher prices will prevent its general introduction among assay masters.

We begin this assay process by weighing, in a delicate balance, a certain weight of the metallic alloy; a gramme (= 15·444 gr.) is usually taken in France, and 12 grains in this country. This weight is wrapped up in a slip of lead foil or paper, should it consist of several fragments. This small parcel, thus enveloped, is then laid in a watch glass or a capsule of copper, and there is added to it the proportion of lead suited to the quality of alloy to be assayed; there being less lead, the finer the silver is presumed to be. Those who are much in the habit of cupellation can make good guesses in this way; though it is still guess work, and often leads to considerable error, for if too much lead be used for the proportion of baser metal present, a portion of the silver is wasted; but if too little, then the whole of the copper, &c. is not carried off, and the button of fine silver remains more or less impure. The most expert and experienced assayer by the cupel, produces merely a series of approximate conjectural results, which fall short of chemical demonstration and certainty in every instance. The lead must be, in all cases, entirely free from silver, being such as has been revived from pure litharge; otherwise errors of the most serious kind would be occasioned in the assays.

The best cupels weigh 12-1/2 grammes, or 193 grains. The cupels allow the fused oxides to flow through them as through a fine sieve, but are impermeable to the particles of metals; and thus the former pass readily down into their substance while the latter remain upon their surface; a phenomenon owing to the circumstance of the glassy oxides moistening, as it were, the bone-ash powder, whereas the metals can contract no adherence with it. Hence also the liquid metals preserve a hemispherical shape in the cupels, as quicksilver does in a cup of glass, while the fused oxide spreads over, and penetrates their substance, like water. A cupel may be regarded, in some measure, as a filter permeable only to certain liquids.

If we put into a cupel, therefore, two metals, of which the one is unalterable in the air, the other susceptible of oxidizement, and of producing a very fusible oxide, it is obvious that, by exposing both to a proper degree of heat, we shall succeed in separating them. We should also succeed, though the oxide were infusible, by placing it in contact with another one, which may render it fusible. In both cases, however, the metal from which we wish to part the oxides must not be volatile; it should also melt, and form a button at the heat of cupellation; for otherwise it would continue disseminated, attached to the portion of oxide spread over the cupel, and incapable of being collected.

The furnace and implements used for assaying in the Royal Mint and the Goldsmiths’ Hall, in the city of London, are the following:--

A A A A, _fig._ 58., is a front elevation of an assay furnace; _a a_, a view of one of the two iron rollers on which the furnace rests, and by means of which it is moved forward or backward; _b_, the ash-pit; _c c_ are the ash-pit dampers, which are moved in a horizontal direction towards each other for regulating the draught of the furnace; _d_, the door, or opening, by which the cupels and assays are introduced into the muffle; _e_, a moveable funnel or chimney by which the draught of the furnace is increased. B B B B, _fig._ 59., is a perpendicular section of _fig._ 58.; _a a_, end view of the rollers; _b_ the ash-pit; _c_ one of the ash-pit dampers; _d_ the grate, over which is the plate upon which the muffle rests, and which is covered with loam nearly one inch thick; _f_ the muffle in section representing the situation of the cupels; _g_ the mouth-plate, and upon it are laid pieces of charcoal, which during the process are ignited, and heat the air that is allowed to pass over the cupels, as will be more fully explained in the sequel; _h_ the interior of the furnace, exhibiting the fuel.

The total height of the furnace is 2 feet 6-1/2 inches; from the bottom to the grate, 6 inches; the grate, muffle, plate, and bed of loam, with which it is covered, 3 inches; from the upper surface of the grate to the commencement of the funnel _e_, _fig._ 58., 21-1/2 inches; the funnel _e_, 6 inches. The square of the furnace which receives the muffle and fuel is 11-3/4 inches by 15 inches. The external sides of the furnace are made of plates of wrought iron, and are lined with a 2-inch fire-brick.