The Poor Man's Filter Made With A Flower-Pot

Plug the hole at the bottom, but not too tightly, with a new piece of sponge, lay over it powdered charcoal two inches thick; cover this with a layer of two inches of clean sand; put on that a layer of clean coarsish gravel three inches deep.

Carbonic acid can be forced into water by pressure to a considerable extent; and effervescing draughts are made upon this principle. The carbonic acid contained in the drink is imprisoned by the cork and thus forced into the liquid by pressure, and absorbed in it. But when the cork is removed the carbonic acid flies off in bubbles or effervescence. Soda water contains eight times its bulk of carbonic acid gas which has been forced into it by pressure; of course when it is uncorked the escape of the imprisoned carbonic acid is somewhat vehement. Ginger beer pops from the same cause when opened, because carbonic acid has been forced into it by the cork. All vinous fermentation produces carbonic acid. The presence of carbonic acid also gives a pleasant acid taste to soda water, ginger beer, champagne, and cider.

Carbonic acid dissolves so readily in water, that water will take up in solution a volume of this gas equal to itself.

It is expelled by boiling, therefore boiled water always tastes flat and insipid.

Water in its ordinary state contains a considerable quantity of atmospheric air dissolved in it. It contains more oxygen than we find in the air itself; and this property of dissolving a large proportion of oxygen renders water fit to be the dwelling place of fish and other creatures which depend on it for the oxygen they breathe.

Water contains much latent heat. This can be proved by pouring cold concentrated sulphuric acid into cold water, when chemical action evolves the latent heat of the water, and the mixture becomes extremely hot; or cold water poured on lime unites with the lime, and becoming solid gives off its latent heat - which is, in fact, required to keep it in a fluid state. In water as much as 11400 of heat may remain latent. Water, therefore, requires a large amount of heat to raise its temperature, the greater proportion of the heat applied to it entering into combination with it as latent heat; and it is this property that renders water capable of cooling us to a great extent. No other liquid when drank cools in the same manner, though some few are better for cold applications.

Water boils at a temperature of 2120 F. under ordinary conditions - i.e., when the pressure of the air is fifteen pounds upon every square inch.

But when the pressure is reduced by ascending mountains, where of course the column of air above is not so high, water will boil at 1840 F. It is therefore possible to determine elevations, by the temperature of the boiling-point of water. (See the adjoining cut of the apparatus used for the purpose).

"The pressure of the air is represented by the height at which a column of mercury is supported: when the mercury is 16.6 inches high, water boils at 1840 F.; if the pressure is doubled, and the column of mercury stands at 32.3 inches, water boils at 216° F. The difference between 16.6 inches and 32.3 inches is very great, and it might be thought that such a fall in the barometer could only be demonstrated by artificial means, and by the creation of a partial vacuum with an air-pump. But it must be remembered that there are certain spots on the surface of the globe where the adventurous traveller may ascend nearly three miles above the level of the sea.

Apparatus for determining Elevations by the Temperature of the Boiling-point of Water.

"The famous De Saussure ascended to the summit of Mont Blanc, which is 15,650 feet above the level of the sea, and where water boils at a temperature of 185.8° F., and the barometer stands at about seventeen inches. The boiling-point of water is lowered about one degree for every 590 ft. De Saussure's observations were verified by Tyndall in August, 1859, when the temperature of boiling water at the summit of Mont Blanc was found to be 184.95° F.

"It is by the careful observation of the temperature at which water boils that the height of any hill or mountain may be determined. Since Dr. Wollaston constructed his instrument for measuring heights by the observation of the boiling-point, improvements have been made, as shown in figure annexed".

Water simmers before it boils. This is caused by its being heated by convection. The water nearest to the fire becomes hot first, and being heated rises, while its place is supplied by the colder portion above. This is in its turn heated and rises up till the whole body of water boils; the ascending current of hot water rises through the centre of the mass, the cold currents descend by the metal sides of the kettle.

It is necessary, as heated water thus always ascends to the surface, that heat should be applied to the bottom, not the top of a kettle or boiler; for if it were applied to the top of a kettle the water below the surface would never boil. If it is desired to cool a liquid, cold must be applied to the top of the vessel; for cold portions always descend and will allow the under warm portions to ascend and be cooled in their turn. The ascending and descending currents of boiling water produce the agitation called "simmering." The bubbles collapse beneath the surface, and the steam is condensed to water again. When it boils the heated bubbles rise to the surface, and steam is thrown off. The entangled air escaping from the water produces the sound called " singing," which ceases when all the water boils.

Water expands, as we have said, with heat, consequently if a kettle be quite filled with cold water it must run over when the water is expanded by heat. Even when not quite filled this occasionally happens from rapid boiling. Steam escaping from the lid and spout are proofs that a kettle boils. Any good conductor placed in it, as an iron spoon, will delay the boiling of water, by carrying off a portion of the heat to itself. Water that boils is not rendered warmer by continued boiling after it has reached the boiling-point 2120, it only escapes in steam - or, as the housewife says, "boils away." Steam ascends as vapour into the higher regions of the air. It is really invisible, but condensed by the coldness of the air becomes a mist. This can be seen by any one observing the spout of a kettle - an empty space will be observed between the spout and the little column of steam. Steam is really there also, but is invisible because the air has not yet chilled it. It is not possible to boil a pot of water by immersing it in boiling water, though gravy, etc., may be wanned thus; - the heat is never sufficient, but brine, which boils at a higher temperature will boil the water in another vessel immersed in it.