Sea water. The characteristic of this variety is its saltness. Its density is about 1·0274, and the average quantity of saline matter which it contains is about 31⁄2 per cent., of which about 27⁄35 are chloride of sodium, and the remainder chiefly chloride of magnesium and sulphate of magnesium.
The average proportion of organic carbon and nitrogen in 23 samples of sea water was ·278 carbon, ·165 nitrogen, as compared with Thames water averages of ·203 parts carbon, ·033 nitrogen, in 100,000 parts of water.
Analysis of sea water (British Channel), by Dr Schweitzer, of Brighton:—
| 1000 gr. contained— | Grains |
| Water | 963·745 |
| Chloride of sodium | 28·059 |
| Chloride of potassium | 0·766 |
| Chloride of magnesium | 3·666 |
| Bromide of magnesium | 0·029 |
| Sulphate of magnesium | 2·296 |
| Sulphate of calcium | 1·406 |
| Carbonate of calcium | 0·033 |
| ———— | |
| 1000· |
Pur. Pure water is perfectly transparent, odourless, and colourless, and evaporates without residue, or even leaving a stain behind. The purest natural water is that obtained by melting snow or frozen rain, that has fallen at some distance from any town. Absolutely pure water can only be obtained by the union of its gaseous constituents; but water sufficiently pure for all purposes may be procured by the careful distillation of common water.
Among the methods adopted for improving the quality of water are:
(a) For reducing the amount of organic and suspended matter.—1. Filtration through or agitation with coarsely powdered, freshly burnt charcoal, either animal or vegetable, but preferably the former. When in good condition a filter of animal charcoal will not only remove suspended matter in water, but will considerably reduce the amount of organic matter, and also the calcareous and gaseous impurities held in solution; but it, however, loses its power of removing lime in a week or two, and of abstracting the organic matter in about three to four months, and then becomes foul, and requires to be recharged. Spongy metallic iron is more energetic in its action than charcoal, and remains serviceable for a twelvemonth. 2. Free exposure to the action of the air, by which the organic matters become oxidised and insoluble, and speedily subside. This may be easily effected by agitating the water in contact with fresh air, or by forcing air through it by means of bellows. 3. The addition of a little sulphuric acid has a like effect; 15 or 20 drops are usually sufficient for a gallon. This addition may be advantageously made to water intended for filtration through charcoal, by which plan at least 2⁄3 of the latter may be saved. (Lowitz.) 4. An ounce of powdered alum (dissolved), well agitated with a hogshead or more of foul water, will purify it in the course of a few hours, when the clear portion may be decanted. When the water is very putrid about 1⁄2 dr. (or even 1 dr. per gall.) may be employed; any alum that may be left in solution may be precipitated by the cautious addition of an equivalent proportion of carbonate of sodium. 5. A solution of ferric sulphate acts in the same way as alum; a few drops are sufficient for a gallon. 6. Agitation with about 1⁄2 to 1 per cent. of finely powdered black oxide of manganese has
similar effect to the last. 7. The addition of a little aqueous chlorine, or chlorine gas, to foul water, cleanses it immediately. This method has the advantage of the water being perfectly freed from any excess of the precipitant by heat.
(b) For reducing amount of inorganic matter.—1. Distillation separates all non-volatile matter, including organised bodies. It is used to obtain a potable water from sea water. The waste heat of the cook’s galley is amply sufficient for this purpose. There are several patent contrivances for the distillation of water on ship board. 2. Hard water may be softened by adding carbonate of soda to the water so long as it turns milky. The precipitation of the hardening ingredients, lime and magnesia, is most rapid when the water is heated. The water cannot be used for drinking purposes, from the unpleasant flavour of the carbonate of soda. When used on a hard water intended for washing, it effects a saving of soap equal to about fifteen times its own cost. Sea water can be made fit for washing by this means. It removes both the “temporary” hardness, due to carbonates of calcium and magnesium, and the “permanent,” due to the sulphates, chlorides, and nitrates of these metals. 3. Hard water may be both aerated and softened by the addition of a few grains of bicarbonate of potassium per gallon, followed by half as much lime juice or tartaric acid as is sufficient to saturate the alkali in the carbonate thus added. 4. The “temporary” hardness may be nearly removed by ebullition, or, as recommended by Professor Clarke, by mixing the hard water with lime water, when the calcium combines with the excess of carbonic acid, which previously rendered the carbonate of calcium soluble, and is precipitated as carbonate (chalk), together with the carbonate originally present. This method removes, at the same time, much of the organic matter, and carries down suspended matter. The water is often made more palatable than before. The directions are:—For every degree of hardness on Clarke’s scale each 1000 gallons of water to be softened requires one ounce of quicklime. Slake the lime and work up to a thin cream with water and pour into the cistern, which already contains at least 50 gallons of water to be softened. Then add the remainder of the 1000 gallons in such a way as to stir up and mix uniformly with the contents of the cistern. In about three hours the milky water is clear enough for washing. After twelve hours’ rest the water is fit to drink. If the exact hardness of the water is not known, water may be added to the milk of lime till, on adding a drop of nitrate of silver to a cupful of the cistern water, the brown tint indicative of an excess of lime is replaced by a very faint yellow. 5. To save boilers from scaling, water intended for steam purposes is sometimes treated with lime to remove
carbonates, and then the sulphate of calcium (which forms a very tenacious scale) is decomposed with baric chloride (Haen’s process). The precipitated mineral matter may also be prevented from forming a scale or fur by adding organic substances, such as potatoes, sound or otherwise, swedes, mangolds, or other vegetable. Oak bark, spent tan, sawdust; and their decoctions are efficacious on account of the tannic acid they contain, but they attack the boiler plates at the same time. Zinc suspended in the water is said to answer well. It has been recommended to polish the inside of the boiler plates with black lead or coat it with linseed oil and dissolved india rubber. Numerous chemical preparations, most of which do more harm than good, are also sold.