in Egypt; it is now eliminated, by chemical means, in large quantities from the liquor, or water, in which it is deposited from the gas. Another impurity is carbonic acid gas, the same gas which passes from our lungs at every exhalation, and vitiates the atmosphere of our dwelling-rooms. These and other noxious gases have to be eliminated from the coal-gas.

To accomplish this, the gas, when it leaves the coal, is passed through long ascending pipes, the ends of which curl downwards and dip beneath the surface of water in a horizontal tube, called the "hydraulic main.” The gas is here cooled to about 120 or 130 degrees Fahrenheit, and a portion of the watery vapour and tar is deposited. From this main it passes through a series of upright pipes stuffed with bricks and coke, and cooled by a descending shower of water; this causes the ammonia and the remainder of the watery vapour and the tar to fall into the trough beneath. To rid the gas of the sulphuretted hydrogen and the carbonic acid gas, it is next passed into a vessel called a purifier, which contains slaked lime, or oxide of iron and sawdust, which rapidly absorb these compounds.

The purified gas rises into one of those large iron domes which you have seen at gasworks. This dome is called a "gas-holder," because it is the reservoir which holds the gas in store for supplying the pipes that lead through our streets to feed the street-lamps, factories, houses, &c. The gasholder is, in principle, like a large tumbler turned upside downwards, the rim being deeply immersed in a large tank of water. As the gas is very light, it cannot sink into the water; therefore, as its quantity increases, it pushes the

dome higher and higher, but is never allowed to force the holder so far as to take the rim out of the water, or all the gas would escape.

Experienced chemists are appointed to test the gas, under order of Parliament, every day, to prove whether the gas is of sufficient illuminating power, and also free from impurity. By exposing a sheet of acetate-of-lead paper to the gas they discover whether there is much sulphuretted hydrogen in it, as that kind of impurity soon stains the paper. A sheet of turmeric paper (paper dyed with turmeric, prepared from an East Indian root of that name) similarly used, proves the presence of ammonia. There are other methods of testing the existence of impurities, but these sufficiently show the plan of operation.

Gas has been made from oil, wood, peat, and suchlike substances; but none of these have succeeded so well as coal. All kinds of coal do not yield an equal amount of gas; the Scotch cannel gives off the most, the English cannel comes next, while the common gascoal is supplied largely from Newcastle, North Durham, part of the Midland counties, and some places in Scotland. The bright cannel coal, so much used by blacksmiths to give a great heat, is too dear for general use in gas-making; but when the London fogs necessitate gas being burned all day the gas companies are obliged to use cannel coal, because it yields more swiftly, as well as in larger quantities. The companies cannot store more gas than will supply London for a single day, so that a sudden fog, or a strike of the workmen, would cause the Metropolis to be in a state of almost total darkness within twenty

four hours, unless some unusual steps were taken to produce the requisite quantity with greater rapidity than is commonly done.

Most of the larger gasworks are now under the control of Parliament with reference to the quality of the gas supplied, on account of the companies having a monopoly in the laying down of pipes and the supply of gas. If various manufacturers had the right to oppose each other, all would aim to produce the best article, so as to get the greatest number of customers; but it would be so inconvenient to have the pipes of different companies threading their way under our streets, that only one company is allowed this privilege in each district. As they might be tempted to supply common material, they are compelled to produce gas of a particular illuminating power, and of a certain standard of purity.

I'-so-lat-ed, standing alone, away from

others.

Me'-ter, an instrument for measuring
and registering the quantity of
gas consumed.
El-e-men'-ta-ry, first, simplest, rudi-
mentary.
Sul-phur-et'-ted hy-dro-gen, a gas com-

posed of sulphur and hydrogen, having the smell of rotten eggs. A'-ce-tate of Lead, a white salt composed oflead and acetic acid or vinegar.

E-lim'-in-at-ed, taken out, extracted.
De-pos'-it-ed, thrown down.
Car-bon'-ic a-cid, a gas formed when
carbon is burnt in the open
air.
Hy-draul'-ic main, a principal pipe con-
taining water.
Can'-nel coal, a black coal sufficiently
hard to be made into trinkets,
and to receive a polish. It burns
with a bright, smokeless flame.
Mon-o'-pol-y, sole power to produce and
sell.

DICTATION EXERCISE.

Among the many peculiar constructions of nature, there is not one which appears to me more singular than that of the snake. To see a creature without legs able to glide swiftly along, to climb trees, and, though possessing jaws of but slight power, yet able to crush by its embrace creatures of considerable strength, is really a wonderful sight.

THE sea-eagle is a large and powerful bird. It is common in the north and west of Scotland, and especially in the Hebrides, and is here called the "erne" or "bog-eagle." It lives principally on fish, which it obtains in no honest manner.

The following account of a rencontre between a seaeagle and an osprey or fish-hawk, admirably illustrates the habits of both these tyrants of the air :

"Elevated on the high dead limb of some gigantic

tree, that commands a wide view of the neighbouring sea and ocean, the sea-eagle seems calmly to contemplate the motions of the various feathered tribes that pursue their avocations below: the snow-white gulls slowly winnowing the air, the busy sandpipers coursing along the sands, trains of ducks streaming over the surface, silent and watchful cranes intent on wading, clamorous crows, and all the winged multitudes that subsist by the bounty of this vast magazine of nature.

"High over all these hovers one whose action instantly arrests his whole attention. By his wide curvature of wing and sudden suspension in the air, he knows him to be the fish-hawk settling over some devoted victim in the deep. His eye kindles at the sight, and balancing himself with half-opened wings on the branch, he watches the result. Down, rapid as an arrow from heaven, descends the distant object of his attention, the roar of his wing reaching the ear as it disappears in the deep, making the surges foam around. At this moment the eager looks of the eagle are all ardour, and levelling his neck for flight, he sees the fish-hawk emerge, struggling with his prey, and mounting in the air with wild screams of exultation.

"These are the signals for our hero, who, launching forth, instantly gives chase, and soon gains on the fish-hawk, while each exerts his utmost to mount above the other, displaying in these rencontres the most elegant and sublime aërial evolutions.

"The unencumbered eagle rapidly advances, and is just on the point of reaching his opponent, when with a sudden scream of despair and honest execration, the latter drops his fish. The eagle, poising himself for a moment, as if to take a more certain aim, descends like