Part 20
The sandy Beds of Watercourses in arid countries frequently contain pools of stagnant water; but the places where these pools are to be found are not necessarily those where they have been found in preceding years. The conditions necessary for the existence of a pool are not alone those of the rocky substratum of the river-bed, but more especially, the stratifications of mud and clay left after each flooding. For instance, an extensive bed of sand, enclosed between two layers of clay, would remain moist, and supply well-water during the dry season; but a trivial variation in the force and Amount of the current, in different years, might materially affect the place and the character of the deposition of these clay strata.
In searching the beds of partly dried-up watercourses, the fact must never be forgotten, that it is especially in little tributaries at the point where they fall into the main one, that most water is to be found; and the most insignificant of these should never be overlooked. I presume that the bar, which always accumulates in front of tributaries, and is formed of numerous layers of alluvial deposit, parallel to the bed of the great stream, is very likely to have one, at least, of its layers of an impervious character. If so, the bar would shut in the wet sand of the tributary, like a wall, and prevent it from draining itself dry.
When a river-bed has been long followed by a traveller, and a frequent supply of water found along it, in pools or even in wells, say at every 5 or 10 miles--then, should this river-bed appear to lose itself in a plain that is arid, there is no reason why the traveller should be disheartened; for, on travelling further, the water will be sure to be found again, those plains being always green and grassy where the water in such river-beds entirely disappears.
By Sea-shore.--Fresh water is frequently to be found under the very sands of the sea-shore, whither it has oozed underground from the upper country, and where it overlies the denser salt water; or else abuts against it, if the compactness of the sand resists free percolation. In very many places along the skirt of the great African desert, fresh water is to be found by digging two or three feet.
Fountains.--Fountains in arid lands are as godsends. They are far more numerous and abundant in limestone districts than in any others, owing to the frequent fissures of those rocks: therefore, whenever limestone crops out in the midst of sand deserts, a careful search should be made for water. In granite, and other primary rocks, many, but small springs, are usually seen.
The theory of ordinary fountains is simple enough, and affords help in discovering them. In a few words, it is as follows:--All the water that runs from them has originally Been supplied by rain, dew, or fog-damp, falling on the face of the land and sinking into it. But the subsoil and rocks below, are far from being of a uniform character: they are full of layers of every imaginable degree of sponginess. Strata of clay wholly impenetrable by water, often divide beds of gravel that imbibe it freely. There are also cracks that make continuous channels and dislocations that cause them to end abruptly; and there are rents, filled with various materials, that may either give a free passage or entirely bar the underground course of water. Hence, when water has sunk into the earth, it does not by any means soak through it in an equable degree. It is an easier matter for it to ooze many miles, along a layer of gravel, than to penetrate six inches into a layer of clay that may bound the gravel. Therefore, whenever a porous earth or a fissured rock crops out to the light of day, there is, in ignorance of all other facts, some chance of a spring being discovered in the lowest part of the outcrop. A favourable condition for the existence of a large and permanent fountain, is where a porous stratum spreads over a broad area at a high level, and is prolonged, by a gradually narrowing course, to an outlet at a lower one. The broad upper part of the stratum catches plenty of water during the wet season, which sinks into the depths as into a reservoir, and oozes out in a regular stream at its lower outlet. A fissured rock makes a still easier channel for the water.
[Fig 1 and Fig. 2].
As examples of ordinary cases of fountains, we will take those represented in the following figures. Fig. I is a mountain. Fig. 2 is a model, made to explain more clearly the conditions represented in fig. I. It will be observed that there is a ravine, R, in front; a line of fault, L, M. N, on its left side, Supposed to be filled with water-tight rock; and a valley, V (fig. 1), on the extreme right. The upper part of the mountain is supposed to be much more porous than its base, and the plane which divides the porous from the non-porous rock, to cut the surface of the mountain along the line, A, N, M, B, C, D, E, F. The highest point of the plane is F, and the lowest point A. The effect of rain upon the model fig. 2 would be, to wet its upper half: water would ooze out along the whole of the lines A, N, and M, B, C, D, E, F; and there would be a small fountain at A, and a large one at M. But in the actual mountain, fig. 1, we should not expect to find the same regularity as in the model. The rind of the earth, with its vegetation and weather-impacted surface, forms a comparatively impermeable envelope to the mountain, not likely to be broken through, except at a few places. But ravines, such as r, would be probably denuded of their rind, and there we should find a line of minute fountains at the base of the porous rock. If there be no actual fountains, there would at least be some vegetation that indicated dripping water: thus the appearance is well known and often described, of a ravine utterly bare of verdure above, but clothed with vegetation below a sharply defined line, whence the moisture proceeds that irrigates all beneath. We should also be almost certain of finding a spring breaking forth near m or even near a. But in the valley V we should only see a few signs of former moisture, along e, f; such as bunches of vegetation upon the arid cliff, or an efflorescence of salts. Whenever a traveller remarks these signs, he should observe the inclination of the strata, by which he would learn the position of m, where the probability of finding water is the greatest. In a very arid country, the anatomy of the land is so manifest, from the absence of mould, that geological indications are peculiarly easy to follow.
Wells.--Digging Wells.--In default of spades, water is to be dug for with a sharp-pointed stick. Take it in both hands, and, holding it upright like a dagger, stab and dig it in the ground, as in fig. 1; then clear out the loose earth with the hand, as in fig. 2. Continue thus working with the stick and hand alternately, and a hole as deep as the arm is easily made. In digging a large hole or well, the earth Must be loosened in precisely the same manner, handed up to the surface and carried off by means of a bucket or bag, in default of a shovel and wheelbarrow.
[Fig. 1. And Fig. 2.--sketches of digging as described above].
After digging deeply, the sand will often be found just moist, no water actually lying in the well; but do not, therefore, be disheartened; wait a while, and the water will collect. After it has once begun to ooze through the sides of the well, it will continue to do so much more freely. Therefore, on arriving at night, with thirsty cattle, at a well of doubtful character, deepen it at once, by torch-light, that the water may have time to collect; then the cattle may be watered in the early morning, and sent to feed before the sun is hot.
It often happens when digging wells in sandy watercourses, that a little water is found, and that below it is a stratum of clay. Now if the digging be continued deeper, in hopes of more water, the result is often most unfortunate; for the clay stratum may prove extremely thin, in which case the digging will pierce it: then the water that had been seen will drain rapidly and wholly away, to the utter discomfiture of the traveller.
Kerkari.--I am indebted to correspondents for an account of a method employed in the plains of the Sikhim Himalaya, and in Assam, where it is called a "Kerkari," also in lower Bengal, for digging deep holes. The natives take a freshly cut bamboo, say three inches in diameter: they cut it just above one of the knots, and then split the wood as far as to the next joint, in about a dozen places, and point the pieces somewhat. The other end of the instrument should be cut slantingly, to thrust into the earth, and its other end is afterwards worked vertically with both hands.
[Unlabelled figure of kerkari].
The soft soil is thus forced into the hollow of the bamboo, and spreads out its blades, as is intended to be shown in the figure. The bamboo is next withdrawn and the plug of earth is shaken out: it is then reintroduced and worked up and down as before. It is usual to drive a stake in the ground to act as a toothed comb, to comb out the plug of earth. Mr. Peal writes from Assam:--"I have just had 4 holes dug in the course of ordinary work, in hard earth. Two men dug the holes in 1 1/2 hour; they were 3 feet 6 inches deep and 6 inches in diameter. I weighed the clay raised at each stroke. In 4 consecutive strokes the weights were 1 1/4 lbs., 1 3/4 lbs., 1 3/4 lbs., 2 lbs. Another trial gave 7 lbs. lifted, after 5 or 6 strokes." According to the above data, an Assamese workman makes a hole, 1 foot deep and 6 inches in diameter in 6 minutes. Holes 10 feet deep and 6 inches wide can be made, as I am informed, by this contrivance.
Protecting Wells.--The following extract from Bishop Heber, though hardly within the scope of the 'Art of Travel,' is very suggestive. "The wells of this country (Bhurtpoor, India), some of which are very deep, are made in a singular manner. They build a tower of masonry of the diameter required, and 20 or 30 feet high from the surface of the ground. This they allow to stand a year or more, till its masonry is rendered firm and compact by time; then they gradually undermine it, and promote its sinking into the sandy soil, which it does without difficulty, and altogether. When level with the surface, they raise its walls higher; and so go on, throwing out the sand and raising the wall, till they have reached the water. If they adopted our method, the soil is so light that it would fall on them before they could possibly raise the wall from the bottom; nor, without the wall, could they sink to any considerable depth." A stout square frame of wood scantling, boarded like a sentry-box, and of about the same size and shape, but without top or bottom, is used in making wells in America. The sides of a well in sandy soil are so liable to fall in, that travellers often sink a cask or some equivalent into the water, when they are encamped for any length of time in its vicinity.
Scanty wells in hot climates should be brushed over, when not in actual use, to check their evaporation.
Snow-water.--It is impossible for men to sustain life by eating snow or ice, instead of drinking water. They only aggravate the raging torments of thirst, instead of assuaging them, and hasten death. Among dogs, the Esquimaux is the only breed that can subsist on snow, as an equivalent for water. The Arctic animals, generally, have the same power. But, as regards mankind, some means of melting snow into water, for the purposes of drinking, is an essential condition of life in the Arctic regions. Without the ingenious Esquimaux lamp (p. 205), which consists of a circle of moss wicks, fed by train-oil, and chiefly used for melting snow, the Esquimaux could not exist throughout the year, in the countries which they now inhabit.
That eating large quantities of snow should seriously disturb the animal system is credible enough, when we consider the very large amount of heat that must be abstracted from the stomach, in order to melt it. A mouthful of snow at 32 degrees Fahr., that is to say, no colder than is necessary for it to be snow at all, robs as much heat from the stomach, as if the mouthful had been of water 143 degrees colder than ice-cold water, if such a fluid may, for the moment, be imagined to exist. For the "latent heat" of water is 143 degrees Fahr. In other words, it takes the same quantity of heat to convert a mass of snow of 32 degrees into water of 32º, as it does to raise the same mass of water from 32 degrees to 141º + 32 degrees = 175 degrees Fahr. It takes in practice about as long to melt snow of a low temperature into water, as it does to cause that same water to boil. Thus to raise snow of 5 degrees below zero Fahr. To 32 degrees, takes 37 degrees of heat, and it requires 143 degrees more, or 180 degrees altogether, to melt it into water. Also it requires 180 degrees to convert water of 32 degrees into water of 212 degrees, in other words, into boiling water.
Distilled Water.--It will take six or seven times as long to convert a kettle full of boiling-water into steam, as it did to make that kettle boil. For the "latent heat" of steam is 967 degrees Fahr.; therefore, if the water that was put into the kettle was 60 degrees, it would require to be raised through (212 degrees--60º degrees =) 152º degrees of temperature in order to make it begin to boil; and it would require a further quantity of heat, to the extent of 967 degrees (= about 6 1/2 times 152 degrees), to boil it all away. Hence, it is of no use to attempt to distil, until you have provided abundance of good firewood of a fit size to burn quickly, and have built an efficient fireplace on which to set the kettle. Unfortunately, fuel is commonly deficient in those places where there is a lack of fresh water.
Rate of Distillation.--A drop per second is fully equivalent To an imperial pint of water in three hours, or be an imperial gallon in an entire day and night.
The simplest way to distil, but a very imperfect one, is to light a fire among stones, near a hollow in a rock, that is filled, or can be filled with salt-water. When the stones are red-hot, drop them one by one into it: the water will hiss and give out clouds of vapour, some of which may be collected in a cloth, and wrung or sucked out of it. In the same way a pot on the fire may have a cloth stretched over it to catch the steam.
[Sketch of still as described below].
Still made with a Kettle and Gun-barrel.--There is an account of the crew of the 'Levant' packet, which was wrecked near the cosmoledo Islands, who supplied themselves with fresh water by means of distillation alone, and whose Still was contrived with an iron pot and a gun-barrel, found on the spot where they were wrecked. They procured, On the average, sixty bottles, or ten gallons, of distilled water in each twenty-four hours. "The iron pot was converted into a boiler to contain salt water; a lid was fitted to it out of the root of a tree, leaving a hole of sufficient size to receive the muzzle of the gun-barrel, which was to set as a steampipe; the barrel was run through the stump of a tree, hollowed out in the middle, and kept full of cold water for the purpose of condensation; and the water so distilled escaped at the nipple of the gun-barrel, and was conducted into a bottle placed to receive it." The accompanying sketch is taken from a model which I made, with a soldier's mess-tin for a boiler, and a tin tube in the place of a gun barrel. The knob represents the breech; and the projection, through which the water is dropping, the nipple. I may remark that there is nothing in the arrangement which would hurt the most highly-finished gun barrel; and that the trough which holds the condensing water may be made with canvas, or even dispensed with altogether.
Condensing Pipe.--In default of other tubes, a reed may be used: one of the long bones of an animal, or of a wading bird, will be an indifferent substitute for a condensing pipe.
Still, made with Earthen Pots and a Metal Basin.--A very simple distilling apparatus is used in Bhootan; the sketch will show the principle on which it is constructed.
[Sketch of apparatus].
Salt water is placed in a pot, set over the fire. Another vessel, but without top or bottom, which, for the convenience of illustration, I have indicated in the sketch by nothing more than a dotted line, is made to stand upon the pot. It serves as a support for a metal basin, S, which is filled with salt water, and acts as a condenser. When the pot boils, the steam ascends and condenses itself on the under surface of the basin S, whence it drops down and is Collected in a cup, C, that is supported by a rude tripod of sticks, T, standing in the inside of the iron pot.
Occasional Means of Quenching Thirst.--A Shower of Rain will yield a good supply. The clothes may be stripped off and spread out, and the rain-water sucked from them. Or, when a storm is approaching a cloth or blanket may be made fast by its four corners, and a quantity of bullets thrown in the middle of it; they will cause the water that it receives, to drain to one point and trickle through the cloth, into a cup or bucket set below. A reversed umbrella will catch water; but the first drippings from it, or from clothes that have been long unwashed, as from a macintosh cloak, are intolerably nauseous and very unwholesome. It must be remembered, that thirst is greatly relieved by the skin being wetted, and therefore it is well for a man suffering from thirst, to strip to the rain. Rain-water is lodged for some days in the huge pitcher-like corollas of many tropical flowers.
Sea-water.--Lives of sailors have more than once been saved when turned adrift in a boat, by bathing frequently and keeping their clothes damp with salt-water. However, after some days, the nauseous taste of the salt-water is very perceptible in the saliva, and at last becomes unbearable; such, at least was the experience of the surgeon of the wrecked 'Pandora.'
Dew-water is abundant near the sea-shore, and may be collected in the same way as rain-water. The storehouse at Angra Pequeña, in S. W. Africa, in 1850, was entirely supplied by the dew-water deposited on its roof. The Australians who live near the sea, go among the wet bushes with a great piece of bark, and brush into it the dew-drops from the leaves with a wisp of grass; collecting in this way large quantities of water. Eyre used a sponge for the same purpose, and appears to have saved his life by its use.
Animal Fluids are resorted to in emergencies; such as the contents of the paunch of an animal that has been shot; its taste is like sweet-wort. Mr. Darwin writes of people who, catching turtles, drank the water that was found in their Pericardia; it was pure and sweet. Blood will stand in the stead of solid food, but it is of no avail in the stead of water, on account of its saline qualities.
Vegetable Fluids.--Many roots exist, from which both natives and animals obtain a sufficiency of sap and pulp, to take the place of water. The traveller should inquire of the natives, and otherwise acquaint himself with those peculiar to the country that he visits; such as the roots which the eland eats, the bitter water-melon, etc.
To purify water that is muddy or putrid.--With muddy water, the remedy is to filter, and to use alum, if you have it. With putrid, to boil, to mix with charcoal, or expose to the sun and air; or what is best, to use all three methods at the same time. When the water is salt or brackish, nothing avails but distillation. (See Distilled Water," p. 218.)
To filter Muddy Water.--When, at the watering-place, there is little else but a mess of mud and filth, take a good handful of grass or rushes, and tie it roughly together in the form of a cone, 6 or 8 inches long; then dipping the broad end into the puddle, and turning it up, a streamlet of fluid will trickle down through the small end. This excellent plan is used by the Northern Bushmen--at their wells quantities of these bundles are found lying about. (Anderson.) Otherwise suck water through your handkerchief by putting it over the mouth of your mug, or by throwing it on the gritty mess as it lies in the puddle. For obtaining a copious supply, the most perfect plan, if you have means, is to bore a cask full of auger holes, and put another small one, that has had the bottom knocked out, inside it; and then to fill the space between the two, with grass, moss, etc. Sink the whole in the midst of the pond; the water will run through the auger-holes, filter through the moss, and rise in the inner cask clear of weeds and sand. If you have only a single cask, holes may be bored in the lower part of its sides, and alternate layers of sand and grass thrown in, till they cover the holes; through these layers, the water will strain. Or any coarse bag, kept open with hoops made on the spot, may be moored in the mud, by placing a heavy stone inside; it will act on The same principle, but less efficiently than the casks. Sand, charcoal, sponge, and wood, are the substances most commonly used in properly constructed filters: peat charcoal is excellent. Charcoal acts not only as a mechanical filter for solid impurities, but it has the further advantage of absorbing putrid gases. (See below, "Putrid Water.") Snow is also used as a filter in the Arctic regions. Dr. Rae used to lay it on the water, until it was considerably higher than its level, and then to suck the water through the snow.