is dissolved, while much is only held in suspension, as to render it highly offensive at some seasons, though previously to entering London it is a water of excellent quality. A general view of the composition of rivers shows carbonate of lime to be their principal mineral constituent, generally amounting to one half of the entire solid residue of the water, and sometimes forming of it; and this we find to be the very substance which is continually withdrawn from sea water for the production of the shells of mollusks and crustaceans, and the structures of the coral animals. It has been estimated that the quantity of this salt annually carried into the sea by the Rhine is sufficient for the formation of the shells of 332,539 millions of oysters. Next to carbonate of lime, its sulphate, or gypsum, occurs most abundantly in river waters. Being much more soluble than the carbonate, it would be found in much larger proportion, were it not that rocks containing it bear an exceedingly small proportion to limestone rocks; but wherever they exist, the rivers passing over them become impregnated. Thus the Arve, which, taking its rise in the valley of Chamouni, comes in contact with the great masses of gypsum of the western side of Mont Blanc, contains 6.5 parts of sulphate of lime and 6.2 parts of sulphate of magnesia to 8.3 parts of carbonate of lime (analysis 55); and the Red river, after traversing the plains of the Llano Estacado, much of the surface of which is covered with thick beds of gypsum, holds in solution .00185 of its weight of sulphate of lime, sulphate of magnesia, and chloride of sodium in nearly equal proportions, without any carbonate of lime. The chlorides but rarely form a considerable part of the constituents of rivers, unless near their mouths, where some mixture with sea water has taken place, as in the analyses of the Thames and Exe (Nos. 48 and 49). If the case were the reverse, a continual and rapid accumulation of salt, &c., would take place in the ocean, since the chlorides are not largely removed by marine animals and plants, as is the case with the carbonate and sulphate of lime. The organic matters carried into the sea by rivers are by no means insignificant in quantity; and they probably cooperate with those produced by the death of marine animals and plants, in decomposing the excess of sulphates, and restoring the equilibrium of composition in sea water. The water of lakes, agreeing generally with that of the principal rivers which feed them, can but seldom present any prominent peculiarity of composition (see analyses Nos. 43 and 44). The water of Lough Neagh in Ireland, which has the property of petrifying wood, or rather of causing its impregnation with iron, contains part only of soluble constituents, part of this being peroxide of iron, and about of it suspended matters, chiefly oxide of iron. Spring waters, in their passage through various rocks, come in contact with so great a variety of substances,

500

that all the alkalies and alkaline earths, alumina, the oxides of iron, manganese, zinc, copper, and many other metals, carbonic, sulphuric, sulphurous, nitric, phosphoric, boracic, silicic, and hydrosulphuric acids, chlorine, bromine, iodine, fluorine, sulphur, hydrogen, carburetted hydrogen, oxygen, and nitrogen, as well as various organic substances, are to be found in one or the other of them. The longer the water remains in contact with the rocks, the greater is generally the quantity dissolved; but chloride of sodium and sulphate of lime, received while passing through beds of salt or gypsum (see SALT), are the only substances with which it becomes saturated. In limestone regions, the continued percolation of the water suffices to remove considerable portions of the rocks, forming great caverns; as in the case of the Mammoth cave of Kentucky, and of many of those in the German mountains; while in some instances the surface of the ground is from such cause eventually made to fall in. Bischof has calculated that the springs and rivers of the Teutoburger forest and the Haarstrang remove annually more than 1,000,000 cubic feet of limestone; and that the Pader springs alone could remove in 67 days a cone of limestone 150 feet in diameter at the base and 25 feet high. Though, save in some mineral waters, usually present in very small quantity, common salt is still, with the exception of carbonate of lime, the most invariably present constituent of spring waters. Its quantity is however usually only such as to aid in imparting palatableness to the water, without giving an appreciable taste. Springs near the sea in many instances receive a suffi cient influx of uncorrected sea water to be rendered brackish; while on the other hand there are numerous instances of springs of perfectly fresh water rising at greater or less distances from shore in the midst of the waters of the ocean; of these, some remarkable and long celebrated examples occur in the gulf of Mexico.-The applications and uses of water are so multifarious, that any difficulty in the case must be rather in the way of finding any operations, either of nature or of art, in which it is not present, and does not play an important part. If the air were deprived of moisture, it would be harsh and irritating when breathed; without the presence of water in soils, that ultimate comminution, or perhaps solution, of their materials, requisite to their entrance into the rootlets of plants, would be impossible; and finally water becomes the indispensable solvent and vehicle by presence of which only can the materials of nutrition be introduced within the vessels of either vegetable or animal bodies, or can there undergo the requisite changes, be conveyed to the tissues to be nourished, and, when in the animal system finally broken down and rendered effete, be again absorbed, conveyed to the organs of excretion, and cast without the domain of life. Thus, water is in every way indispensable to the very continuance of vegetable and animal ex

istence. The dews deposited from and rain falling through the atmosphere bring to the earth many of the substances needful to enable plants to form originally the organic materials on which animal life is subsequently maintained, the most important of these being in fact carbonic acid, the water itself, and ammonia, the presence and value of the last of these having been first shown in Liebig's discovery that it furnishes a chief source of the nitrogen entering into the albuminous vegetable compounds. In countries in which rain is rare or unknown,. vegetation can be supported only by laborious artificial irrigation, as is true in parts of Egypt, India, &c.; and a country destitute of springs and rivers becomes comparatively uninhabitable, as in case of the desert of Sahara; its oases, however, when within them the supply of water is even limited, becoming centres of population. The solvent power of water lies at the foundation of a great proportion of the processes employed in the arts and manufactures, and in analytical chemistry. Without rivers and oceans but little of the commerce of the world could be carried on; and, indeed, without water, our most rapid and efficient means of land transportation, the railroad worked by steam power, would be unavailable. Water is also, through its weight and momentum, one of the most important sources of mechanical power; the estimates of M. Daubrée showing that the motive force of the streams of Europe is equal to that of from 273,508,970 to 364,678,620 horses working incessantly during the entire year. The agency of water in a geological point of view, as in washing away cliffs, excavating valleys, and otherwise modifying the earth's surface, has produced in past ages effects of almost incredible magnitude; it has in fact removed entire groups of strata, over districts of hundreds of square miles, so completely that their former existence is only known by means of a few small fragments which have escaped the denuding action. The most conspicuous instance of this action in recent geological times is the excavation of the gorge of the Niagara, cut to an average depth of 200 to 300 feet for a distance of 7 miles. The energetic action of the waves upon cliffs bordering the sea may be judged of by the fact that the average of the observed force of the waves at the Skerryvore lighthouse on the British coast was in summer 611 lbs. on a square foot, and in winter 2,026 lbs.; while the greatest force observed amounted to 6,087 lbs., or nearly 3 tons. On the E. coast of England this action has proceeded so far that some towns, which at the time of the Norman conquest were several miles inland, are now upon the sea shore; and the site of at least one important seaport of the 12th century is now several miles at sea. The quantity of water upon the globe is in due proportion to its importance, the waters of the oceans, lakes, and rivers covering 2 times as much of the earth's VOL. XVI.-18

surface as is occupied by dry land; the exact proportion, so far as hitherto known, is 276 to 100 for the entire globe, 154 to 100 for the northern and 628 to 100 for the southern hemisphere.-The provision of an ample supply of good water, both for drinking and bathing purposes, has always been considered an object of the first importance; and some of the finest examples we still possess of the engineering and architectural skill of the Romans are their aqueducts and baths, which have seldom been equalled, and never surpassed, in modern times. Until 40 or 50 years ago, most modern European cities were not nearly so well supplied with this necessary of life as many ancient, or even as some modern oriental ones; but a great change has since taken place; the importance of a copious supply for the preservation of the health of large cities is fully recognized; and the Croton water works of New York, the Fairmount water works of Philadelphia, with those of Boston and Brooklyn, are among the improvements for this purpose in the United States. In countries in which water is scarce, immense tanks are constructed to preserve all the rain water that can be colÏected, and some of these in Hindostan cover very large spaces of ground. Very extensive engineering works in the forms of canals and aqueducts have also been undertaken in various countries, as in Tuscany and India, to obtain water for irrigation; and some of the aqueducts or "flumes" constructed in California to bring water to gold diggings, rank in extent at least among the first of their kind. The labors, on the other hand, undertaken to keep out the waters of the sea, or restrain rivers within their proper limits, have been even more gigantic; examples are seen in the dikes of Holland and of some parts of England, the levees extending for hundreds of miles along the Mississippi, and those of the Po; the last named of which requires to be continually raised, so that the river now runs along the top of an embankment far above the level of the surrounding country. The quality of water supplied to towns is of equal importance with the quantity; and sufficient attention has not always been paid to this point, nor to the manner in which it is distributed for use. The dangers arising from the use of lead pipes, and the precautions which should be taken against them, are described under LEAD. In the table of analyses will be found the composition of the water supplied to many of the principal cities both of Europe and America. The chief requisites are, that the water shall not contain too much mineral matter, which renders it "hard" and unfit for washing and cooking, nor too much organic matter, which by its decomposition renders it flat and disagreeable in taste, and very unwholesome. The hardness of most waters is diminished by boiling, so that some of them in this way become suitable for washing; and waters impregnated with organic impurities are in the same way often made far

more pure, though by loss of their gases left even more flat and unpalatable than before. It is said that marsh waters may be in many instances so far improved as to fit them for drinking and culinary use, by previously steeping in them certain herbs, or by rubbing the inside of the kettles they are to be boiled in with bitter seeds or herbs. For this purpose the tea plant is employed by natives of China and Japan, the strychnos potatorum in parts of India, and the bitter almond on the banks of the Nile. So, where no better method presents itself, bad waters may often be rendered much more safely drinkable by first filtering them through fresh clean sand and clay, or sand and charcoal, or even by pouring them for some time from one vessel to another in the sun. Rain water collected in towns or in their immediate vicinity, since it passes through an atmosphere unusually loaded with soot and other foreign matters, requires in the way of fitting it for use more than the ordinary care. Thus, before being used it should be boiled and strained; or what is still better, it should be effectually filtered before admission to the cistern-the filtering materials, as in case of all highly impure waters, requiring frequent purification or renewal. The attempt is made to free the water of the Thames supplied to London, at least in certain parts, of the great amount of suspended matters, by filtering it through thick beds of sand and gravel. Rain water collected upon leaden or soldered metallic roofs will be certain to dissolve and hold in solution the dangerous salts of lead. In rare instances, the water supply of towns becomes deteriorated by the growth in it of immense numbers of microscopic animals and plants. Some years since the Cochituate water, supplied to Boston, suddenly acquired a very disagreeable fishy smell and taste; and this was found to arise from the presence in it of great numbers of animalcules, the decomposition of which set free an oil imparting the offensive qualities. The water supplied to the city of Amsterdam was found, in 1856, to assume a similar fish-like smell, and on standing to give a reddish deposit; but in this case the cause was determined to be the presence and decomposition of masses of algae, confervæ, and other water plants. Mr. Medlock found that by allowing such waters to remain for some hours in contact with a considerable surface of iron, its organic impurities could be either destroyed or rendered insoluble; and Dr. Muspratt regards this means, combined with subsequent filtration, as the best yet discovered for purifying waters of the character referred to. In many manufacturing processes involving chemical principles, as for example those of dyeing and brewing, the quality of the water employed becomes of great importance. The celebrated Burton ale has never been successfully produced except in the original locality, Burtonon-Trent, England; and the fact is found to be due to the quality of the water there employed,

among the constituents of which are calcareous salts in considerable amount.-The securing of an abundant supply of fresh water at sea is an object of great importance, but at the same time one very difficult of attainment. Fresh water stored in casks or tanks in the hold of a ship soon becomes very offensive; though the organic matters usually complete their decomposition within a month or two, and the water is subsequently of tolerably good quality. The water of the ocean so abounds in saline matters, that the drinking of it only increases instead of relieving thirst, and that it is wholly unfit for dietetic purposes. The importance of having at command means of obtaining fresh water from that of the sea has long been appreciated, and considerable progress is already made in this direction. Thus, a drinkable water is obtained from that of the ocean, either by subjecting it to great pressure and afterward filtering; or better by freezing, separating the ice carefully from the remaining saline liquor, and then thawing; or by any of the contrivances for boiling it and condensing the steam, in a word, for the distillation of it. Many British government ships are now supplied with the apparatus devised by Mr. Grant, in the use of which the cooking of food and the purifying of water for drinking go on at the same time-a portion of the heat being applied to vessels containing sea water, and distilling it. Other arrangements for distilling sea water are also in use; and so far as quantity is concerned, any of these give very satisfactory results. But usually the distilled water, even though afterward impregnated with air, has a disagreeable taste and odor. These Dr. Normandy has traced to the presence of organic matter, which becomes charred during distillation, certain of its products passing over with the water. By filtration through charcoal, he removed the offensive qualities; and he further improved the water for drinking by subsequently impregnating it, not with air, but with the gases which it had contained before distillation. For these and certain economical reasons, his apparatus has proved very valuable, and it is employed upon many vessels intended for long voyages. For certain chemical modes of softening hard waters, or purifying them from matters in suspension, see FILTER; and further in reference to the use of water for culinary purposes, see ALIMENT.Water fulfils an important part in the ceremonial observances of most religions. In almost all, it is employed as a means of purification before the offering of sacrifices, or entering upon any solemn act of religious service. The Moslem is required by his religion to wash 7 times a day. Among Christian sects, water forms, in the rite of baptism, the medium of initiation into the church; in the Roman Catholic church especially it is, after being blessed, employed under the name of "holy water" in many ceremonies.-In medicine, water is, apart from incidental uses, itself a remedy of great importance. (See BATH, and HYDROPATHY.) Taken internal