n-:u. 



TKR. 



tote <rf itun over red-hot iron, it jnrU with its oxygon to the 

 mrtal. and iU hydrogen ii evolved u gas. Submitted to the action of 

 the electric force, iU two coiutituenU are respectively evolved, and 

 may be cotttcted in quantity, from the two terminal* of the battery; 

 that from the negative pole, hydrogen, occupying twice the bulk 

 of that from the positive pole, oxygen. A given bulk of hydrogen 

 being only one-sixteenth the weight of an equal bulk of oxygen, it 

 follow* from the fact just mentioned that) the respective proportion* 

 ,i,-ht of hydrogen and oxygen in water are one of the former to 

 eight of the latter. Many other experiment* might be described 

 demonstrating both synthetically and analytically that water is the 

 protoxide of hydrogen ; that it contain* one equivalent of hydrogen 

 ill 1 1 and one equivalent of oxygen (O = 8). 



Water act* upon other bodiea with four different degree* of intensity. 

 Chemically, it unite* to form, first, hydratn; in these the water is 

 most intimately combined, and can only be separated in many oases 

 by a temperature approaching redness : slaked lime is *uch a hydrate. 

 Secondly, water combines with crystalline bodies, ns seen in sulphate 

 of magnesia, which contain* six equivalents (HgO, SO,, HO + ttAq.), 

 carbonate of soda, which has ten (Nat), CO, + 10 Aq.), Ac. This water 

 is generally termed voter of cryttaUitatim, to distinguish it from the 

 former, or voter of hydratiun. Thirdly, water, acting chemico-mecha- 

 nically, is a more or leas powerful solvent for most bodies. On its 

 uses in thin respect it is scarcely necessary to enlarge. Us capacity 

 for dissolving oxygen and carbonic acid enables it to support the life 

 of fiahe* and sub-aquatic plants, and without which it would be 

 unpleasant and mawkish as a beverage. Chlorine, sulphurous acid, 

 and sulphuretted hydrogen gases are re-agents whose chemical value 

 would be much restricted if they could not be obtained in the state 

 of solution in water. It* property of dissolving solids enables it to 

 be used as a vehicle for the conveyance of organic and inorganic 

 matter to the tissues of animal* and plants, and as an indispensable 

 medium in nearly all arts and manufactures. When water has 

 taken up as much of a body as it can dissolve, it is said to be satu- 

 rated ; and if at this point some of it be removed by spontaneous or 

 artificial evaporation, the dissolved solid is again deposited, either in an 

 amorphous state or in beautiful geometrical forms called cryilali. The 

 fourth action of water is purely mechanical ; it is seen in the gradual 

 wearing away of solid insoluble matter, and is largely concerned in the 

 formation of the channels of streams, Ac. 



From what has been said regarding the solvent powers of water, both 

 upon gaseous and solid matter, it is obvious that pure water is never 

 met with in nature. If we trace water from the moment when it 

 assumes the liquid condition to the time when it finally makes its way 

 to the ocean, we find it gradually accumulating impurities of various 

 kinds. At the moment of condensation it exerts its solvent power and 

 absorbs gases from the air. When it falls to the earth it percolates 

 through strata more or less soluble and more or less pervious to water, 

 and dissolves, according to circumstances, various quantities of the 

 solid matters which it there meets with. If the surface of the earth 

 where it falls be very hard and insoluble, the water becomes only very 

 slightly contaminated with solid matter. Loch Katrine, for instance, 

 contains only 24 grains of solid matter in a gallon of the water ; the 

 Dee. at Aberdeen, contain* 4 grains ; and the Tay, at Perth, contains 

 5 grains. Frequently, also, when the strata through which the water 

 percolates are pervious, supposing they are at the same time compara- 

 tively insoluble, very little solid matter gets into solution. Such is 



the case with the green sand formation, where the water i* very free 

 from mineral matter* of a solid kind. < :.-u.T.dly, however, water 

 with more constituenta<than those just indicated, and the quantity 

 varies from 5 to 50 grains per gallon. When the latter quantity U 

 exceeded, the water frequently acquires a taut*-, and may be rty 

 as abnormal water. The water of tie ocean U in this condition 

 rivers which flow into the sea carry with them matters dissolved, and 

 leave them there, for the solid matters are not carried back by evapo- 

 ration. Therefore, the sea contains a larger proportion of these sub- 

 stances than is contained in the water of riven ; and we get this effect 



on a still more exaggerated scale when, in hot climate*, river* 

 themselves into lakes which have no outlet. This is the case with thu 

 Dead Sea. The river Jordan, which i* constantly (lowing into it, 

 contains 76 grains of solid matter in the gallon ; and none of this matter 

 is returned again into the atmosphere, or no practical amount 

 fore, there is a constant accumulation of the saline matters going on 

 there, and in this Dead Sea we have no less than 2600 grains of solid 

 constituents to the gallon of water. The same effect takes place in a 

 lake in the north of Australia, discovered a few mouths ago. It U 

 highly charged with saline matters, and is known to possess no 

 There is a similar instance in the celebrated Elton Lake in Russia, 

 which is II miles long, 8 miles broad, and on an average only !.'. 

 inches deep. In summer it appears to be covered with snow, in 

 consequence of the evaporation of the water forming a crust of saline 

 matter. No less than 200,000 tons of salt are yearly extracted from 

 this lake. 



In addition to these mineral and saline constituents, water also dis- 

 solves certain organic substances, so that we may classify the impuri- 

 ties contained in water as ncchaniral, or those that are merely suspended 

 in the water mechanically, and not dissolved, inline impurities, and 

 organic impurities. We will consider these separately. 



First, as regards mtchcmical impurities. They consist, in the first 

 place, of mineral substances which are usually innocuous, and have no 

 effect upon the drinker. Next we have vegetable or animal matters, 

 which are generally of an exceedingly noxious character ; and then wu 

 have living organisms, which perhaps attract the attention of the 

 water-drinker more than the other substances contained in the water. 

 These organisms consist of auimalcula and animals of a larger size. 

 We have in the New Hiver water twenty-six species of these animals, 

 in the Thames water twenty-nine species; twenty-four species have 

 been detected in the West Middlesex water, and so on, varying in 

 number in different waters. It has been stated that some of these 

 little animals are very deleterious to health, but this has not been at 

 all clearly made out. Looked at from a chemical point of view, they 

 are exceedingly useful in the water, especially if it In; at all impure. 

 Each little animal is a small furnace, which occupies itself in consuming 

 the organic matter, and converting it into its ultimate inorganic com- 

 pounds carbonic acid, water, and ammonia, or nitric acid. They feed 

 upon the dead organic matter in the water, and remove it far more 

 readily than it would be removed by the oxidising property of the 

 air. It is, of course, desirable to remove them before the water is 

 used as a beverage, and this can be done by nitration. The animals 

 themselves cannot pass through the filter, but the ova can. This fact 

 has an important bearing upon the storing up of water, and will be 

 alluded to again presently. 



We come now to the lalinc impurities. The nature of these will be 

 readily seen by an inspection of the following diagram. 



SOLID COXSTITOIXT* CONTAINED IK OXK GALLON OF VARIOUS WATKKS srrruKD TO Tows*. 



The Karnham water is from the green sand : it ha* been suggested 

 as a supply f..r Ix-udon. That from Loch Katrine is perhaps purer 

 than the water supplied to any town in the United Kingdom. The 

 Manchester water can always bo drawn from the pipes, the supply 

 being continuous, instead of intermittent, and this is now the case in 

 nearly all large towns except Ixindmi. 



hese constituents are termed tvrthy talii, and some of them 

 are a/l-a/iit tat-'i. Carbonate of lime, sulphate of lime, and nitrate of 

 lime, carbonate of magnesia, and, occasionally, chloride of calcium and 



chloride of magnesium, are salts of the alkaline earths; others are 

 alkaline salts. 



The property of " hardness " in water is due to the first of these 

 classes of constituents to the alkaline earths the lime and magnesia 

 salts present in the water. Hard water may be defined as a water 

 capable of decomposing a considerable quantity of soap, and forming 

 with the soap an in<>liiMc prvripitate. These salts of lime coml.ine 

 with the stearic acid, and form an insoluble stearate of lime, the curdy 

 nutter which i* produced by washing in such waters. This stearate 



