Count Rumford investigated the subject in 1793. His experiments on the uplifting and metal-tearing power of small quantities of powder led him to further inquiries in order to explain how any firearms could resist such force.

He charged muskets with powder made up of a mixture of grains of various sizes, from the finest in use to grain the size of peas, and fired these charges against screens of very thin paper, placed one behind the other, and twelve inches apart. The large grains were blown out like shot and struck the screen, some passing through as many as five screens in succession. The grains were collected unconsumed, though evidently burned outside, and extinguished by their projection into the cold air. In some cases they set fire to the screens as they passed through them.

By dropping a piece of red-hot iron into the barrel of a horsepistol and then upon this one of the large grains, it was projected by its own explosion, and seen burning in the air by the train of light left behind. These and other experiments proved that the rapidity of the explosion must vary inversely with the size of the grains, other conditions being equal.

This principle was not fairly appreciated at the time, but is now systematically applied in practical gunnery. Were it not, the projection of the great masses now thrown from our huge guns would be practically impossible. If all the force of the charge were developed before the great shot had started, the metal of the powder-chamber would be torn, as it was in Rumford's experiments.

I quote one of these as an example. An iron cylinder 24 inches diameter and 2 inches long, with a bore of only inch, leaving 1 inch, or five times its diameter, of solid iron of the best quality all around, was charged with 24 grains of powder, and firmly plugged. The space occupied by the powder was but one-tenth of a cubic inch. On firing this by means of a red-hot ball applied to the closed end of the cylinder, "it burst the barrel asunder, notwithstanding its enormous strength, and with such a loud report as to alarm the whole neighbourhood." He tells us that "it is impossible to describe the surprise of those who were spectators of the phenomenon. They literally turned pale with affright and astonishment, and it was some time before they could recover themselves."

By testing the tenacity of the iron used, and by other experiments in which a loose plug lifted great weights, Rumford concluded that the explosive force exerted was equal to 54,750 atmospheres, or 277 tons to the square inch. The Woolwich experiments with the crushergauge inside the 81-ton gun, charged with 220 lbs. to 250 lbs. of

powder, indicated but one-tenth of this, viz., 27 to 28 tons per square inch. My next Notes may help to explain these great discrepancies.

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MODERN ARTILLERY GUNPOWDER.

FEW years ago, when the 81-ton gun was a novelty, Dr. Abel invited the Fellows of the Chemical Society to witness a general demonstration of the scientific achievements of Woolwich Arsenal. When we assembled by the side of the monster cannon, most of us-though we ought to have known better-anticipated a stunning shock to our ear-drums, and many ears were plugged by fingers.

The explosion was magnificent; it was awful, but not deafening; it was not a bang, but a roar. I have fired many a soap bubbie charged with the mixed gases obtained by voltaic decomposition of water, and have been insensible to other sounds some few minutes afterwards, but nothing of this kind followed the discharge of the great gun. The subsequent gun-cotton experiments made on the same day were far more startling.

The reason of this is not difficult to understand. The great chamber of the great gun is filled with compressed gases, which, by their elastic outstriving, push the ball forwards. It leaves the muzzle, and then comes the outpouring of the gas, which, by its expansion in free air, produces the sound wave. But some time is occupied in the ejection of all this gas, and hence the prolonged roaring character of the explosion, so different from the crack of a pistol, or the still sharper crack of the water gases, dynamite, gun-cotton, or the fulminates.

The achievements of modern artillery are largely due to unacknowledged adoption of the principles established by Rumford, as stated in my last Note. Instead of using ordinary gunpowder in grains, the great 81-ton guns are fired with powder made into solid cubes of 1-inches diameter, or corresponding prisms. These are equivalent to grains about the size of a hen's egg.

A grain of ordinary powder fires at once with a puff, a 11-inch cube with a protracted fizz; and if the size of the cube or prism is properly adjusted to the length of the bore, the duration of this fizz, under the conditions of firing, should correspond to the time. occupied by the projectile in travelling along the bore and clearly out of it. It is thus started with a comparatively moderate force, and its velocity is continuously accelerated by the continuously increasing development of expanding gases. An enormous velocity

is thus attained when it reaches the muzzle, with a minimum strain upon the gun at any one moment.

Here we may discover an explanation of one of the causes of the discrepancy between Rumford's results and those obtained at Woolwich. In the latter, the expansive force of the outstraining gases was acting within an expanding chamber, one of its walls being the moving projectile. In Rumford's, all the walls were rigidly closed, and the powder being heated by means of the red-hot ball applied outside, the temperature of the whole was raised simultaneously until it reached 600°, the explosion point, and then came the sudden instantaneous strain.

PROPAGATION OF GASEOUS EXPLOSIONS.

HE preceding Notes were suggested by a paper recently commu

Chatelier. A little reflection must lead us to the inference that even when a mixture of explosive gases is fired by applying a light to one part of the chamber containing them, the travelling of the explosion throughout must occupy some time.

These gentlemen have worked upon the difficult experimental problem of measuring that time, or the velocity of explosive transmission. They admit their inability to do this accurately, but claim to approximate within ten per cent.

With mixtures of hydrogen and oxygen, they obtained a maximum velocity of 59 feet per second; with hydrogen and air, 14 feet per second; with coal gas and air, 33 feet per second. This maximum was obtained when the proportion of hydrogen was about ten per cent. in excess of the theoretical quantity demanded for combination with the oxygen; while an excess of oxygen lowered considerably the velocity of explosion. This they attribute to the superior conductivity of hydrogen for heat.

When the gaseous mixtures are heated, the velocity of propagation is increased. Within certain limits, the velocity is not affected by the diameter of the tube in which the experiments are made; but if the tube is very narrow, the friction of its sides has a sensible retarding influence. If the tube is very small, the flame is extinguished. A mixture of coal gas and air in their most explosive proportions is extinguished in a tube of one-eighth of an inch diameter, but a mixture of pure hydrogen and pure oxygen is not extinguished until the tube is reduced to one-thirtieth of an inch diameter,

IN

THE BURSTING OF WATER-PIPES.

Na country like England, where the obstinate natives persist in the practice of burning their fuel in a hole made in the wall, with a shaft rising perpendicularly above it, in order that the greatest possible quantity of the heat of combustion shall be devoted to warming the clouds, and the smallest possible amount shall be radiated from only one side of the fire into the apartment, anything like a severe frost becomes a national calamity.

Last winter, though far less severe than an average winter in Germany or the United States, is made miserably memorable by the domestic calamities connected with the bursting of water pipes, and is recorded in the household accounts of expenditure for mending the same, and repairing the damage done by the general house- and furniture-soaking.

If English houses were equally warmed throughout, as they are in other countries where domestic civilisation has made some progress, the freezing of any water-pipe inside would be impossible in any weather, and all outside water-conveyance can be made underground. But as the domestic fetish of the Englishman and Englishwoman, the hole-in-the-wall" cheerful "fireplace, must be worshipped; as the fire-worshippers must continue to scorch their noses while their backs are matriculating for lumbago; as the cheerfulness of the fetish must be maintained, and its devotees must demonstrate that cheerfulness by staring vacantly at the glowing coals which roast everything and everybody at one side of the room, while the rest of the house is at the mercy of the outside fluctuations of temperature; as all this must go on for a generation or so longer, in spite of Kyrle societies and smoke-abatement exhibitions-some adaptation of water-pipes to our existing domestic barbarism is very desirable.

A very little geometry is required for understanding that if a pipe of circular section be flattened in any degree, its internal capacity must be proportionately lessened; and conversely, that a pipe thus flattened, or made of elliptical section, may have its internal capacity enlarged by simply squeezing it out towards the circular shape. Lead being flexible, a leaden pipe made of elliptical section and filled with freezing water will swell out towards circular shape, and thus allow room for the expanded ice without bursting.

It is proposed that such pipes be made and used, and I think the idea an excellent one, though plumbers are not likely to favour it; but their disapproval should be a strong recommendation to the

householder who has to pay for mending ordinary pipes. I am told that a patent has been secured, but do not know by whom, and as I am going to suggest an infringement, he is entitled to any advertisement this Note may afford.

I recommend all householders to save their existing pipes by simply flattening them with a mallet, taking care to place behind the part which is struck a flat piece of wood, where the pipe rests upon rough brick work. The freezing will simply reverse the work of the mallet, and lead of good quality will bear this double bending.

If freezing water were a rigid solid, the transverse expansion of the cylinder of ice within the tube would be proportionate to its diameter, and thus the elliptical form would be maintained; but freezing water is not a solid, it exerts an equal expansive pressure in all directions; and the walls of the pipe being equally pressed, will give way in the direction of least resistance.

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SLOW COMBUSTION OF FIRE-DAMP.

NEW method of dealing with fire-damp in mines has been devised by Herr Guido Körnet, of Saxony. An oil lamp has its wick, or wicks, covered with caps made of asbestos, the fibres of which are plated with a coating of platinum and palladium. These are raised to a red heat, while they prevent the flame from effective communication with any combustible gas that may surround them.

In this condition they are placed in the mine containing gas in a state of explosive mixture. According to the published accounts, these glowing caps effect a slow combustion of the gas as it comes in contact with them, and this goes on quietly without risk of explosion.

The quantity thus slowly burned is considerable, and experiments are in progress by which the practical efficacy of this method of getting rid of one of the miner's enemies will be tested.

The action of these platinized fibres is analogous to what occurs in the old experiment of " the lamp without flame." Such lamps are still to be bought of chemical-instrument makers. A piece of spongy or finely divided platinum stands over the wick of a spirit-lamp. The lamp is lighted and the platinum made red-hot, then the flame is extinguished, and the platinum continues glowing, its heat being supplied by the slow combustion of the vapour given off by the wick.

If a coil of platinum wire is made red-hot, and suspended above