and upon this 5 lb. of gun cotton was laid. Wires communicating with a magnetic apparatus were affixed to a detonating tube, which was placed in contact with one of the discs of gun cotton. But surely they won't all detonate, for only their circumferences touch at one point?' Wait and see; back over the heavy furrows a good 150 yards, no one being anxious to stand too near this time. The time of suspense was short, and then the explosion was heard. One mass of wood only was seen to plunge away from the palisade; it was the recumbent trunk upon which the cotton had been laid. The palisades themselves were standing, though a good deal damaged-no practicable breach. But there still remained a long space of palisading yet untouched, and here, instead of 5 lbs., 15 were laid, partly built on each other. The excitement began to increase. It was the old story of the targets and the guns, and now several people might have been found to back the palisades. Fuse and wires were placed. Everybody retired to a safe distance. Man's nervous organization is curiously elaborated, and it is not to be wondered at that there were several exclamations of, ‘Please tell us just when you are going to fire.' Some persons put two good banks between them and the expected explosion, others sought the grateful shelter of a ditch. All were trying to combine the maximum of view with the minimum of danger. At last came the sharp, powerful crash, so unlike the dull roar of gunpowder, and this time there could be no mistake about the effect. Huge logs were seen performing summersaults at greater or less distances from the explosion, while smaller pieces, some about a couple of feet square, bounded like rabbits over the field. Men of science, officers, country gentlemen, and bumpkins were soon spread over the ploughed field, each striving to be first in at the death. On reaching the target the effect appeared to have been tremendous. In some places a treetrunk had been cut in half, almost as with a rough saw, only not so straight; in others the solid wood was mangled, so that it could be pulled to pieces by the hand. Three logs had been cut down or smashed, and it was clear that no stockade or New Zealand pah could withstand such deadly effects for an instant. Exclamations of astonishment showed the mental impressions produced. 'Superbe!' 'Prodigious!' 'Extraordinary!' 'Magnificent!' Mais c'est une maniere de faire les allumettes! And all this had been done by only 15 lbs. of the cotton. Three times the quantity made up into a cylinder could be carried with ease by a man at a run, who might also drag the ends of the two wires as they unwound from a reel kept in a position of safety. Is there no hint here for the colonists? No fire need be seen, for there is no match to light. Surely plenty of volunteers could be found to perform such work at night, and so restore the superiority of civilized man over savages. It had been contemplated to tie a ring of gun cotton round a living tree, and see if it could not be cut down; but there was not time enough. The experiments were over for the day, and the visitors returned to London, satisfied that they had seen a most marvellous phenomenon, and one which is only a first step to a whole array of novelties in the arts of war and of peace.” When the tremendous powers of modern artillery with improved gunpowder, and all the terrible refinements in the management of gun cotton, are considered, it is amusing to compare the latter with the bows and arrows used only three centuries and a half ago. Extract from the "Edinburgh Courant." "I have seen a man who conversed with a man who fought at Flodden Field,' may be said by a venerable octogenarian gentleman, to whom we are indebted for the following most inte resting memorandum :-The writer of this, when an infant, saw Peter Garden, who died at the age of 126. When twelve years old, on a journey to London about the year 1670, in the capacity of page in the family of Garden of Troup, he became acquainted with the venerable Henry Jenkins, and heard him give evidence in a court of justice at York, that he 'perfectly remembered being employed, when a boy, in carrying arrows up the hill at the battle of Flodden.'" NITROGEN AND HYDROGEN, AMMONIA, H,N=17. Many thousand years ago the Egyptians worshipped a god " Ammon,” and it is said that as this compound was first obtained from a substance found near a temple devoted to the worship of this divinity, situated in the Oasis of Ammonium (Siwah), in the Libyan Desert, celebrated for its oracle and visited by Alexander the Great, as the compound was first discovered near this temple, it was called Sal Ammoniac. Quicklime and sal ammoniac, or ammonia hydrochlorate, NH,HCl, when mixed and gently heated, give calcium chloride, ammonia, and water. CaCl2+2NH3+H2O Calcium chloride, ammonia, and water. Calcic oxide and ammonia hydrochlorate Ammonia is also given off when animal matter is heated, such as the horns of animals, and hence it was called "hartshorn." The first ammonia was doubtless obtained by the Arabs near the temple of Jupiter Ammon, by heating camels' dung. Coal is the great source of ammonia, and this is not surprising when it is understood that it contains 2 per cent. of nitrogen. Guano and other manures are applied to the land because they contain free ammonia, or other nitrogenous matter, ready to change into ammonia and to be assimilated by plants. When sal ammoniac and quicklime are heated in a flask provided with a cork and tube, the gas may be collected over mercury. It is colourless, but possesses a very strong odour, affecting greatly the olfactory nerves, and causing a flow of water from the eyes, and hence is used as a refreshing stimulant, and is slowly evolved from mixtures called "smelling salts." Being lighter than air, it may be collected by holding a clean dry bottle over the mouth of a flask containing the mixture of lime and ammoniacal salt; it is better, however, to pass the gas first through a bottle containing quicklime, in order to remove the moisture. Calcic chloride must not be used, as it absorbs ammonia and forms a definite compound with that body. The specific gravity of ammoniacal gas is o'590, air being 1000; and therefore it fills an inverted bottle by displacement. Ammonia cannot be collected over water, as it is so very soluble in that liquid. At the freezing-point water takes up 1,050 times its volume; at 59°, 727 times its volume; at 78°, 586 times its volume. By conducting the ammoniacal gas into a series of Wolfe's bottles provided with safety tubes, the ordinary solution of ammonia may be prepared. C FIG. 483.-Retort fitted to a series of Wolfe's Bottles, All provided with safety tubes. Whilst the ammonia is being dissolved the water becomes very hot, and if kept at 60° by the application of a current of cold water, it will dissolve onethird of its weight of the gas, and, becoming specifically lighter, is then found to have increased in bulk by one-half. The specific gravity of the strongest solution of ammonia at 57° is o‘884, water being 1'000. Various safety tubes are made when gases are passed into water or other solutions: one of the most elegant is that shown in the annexed cut. The object of a safety tube is to prevent the flask being crushed or the liquid returning into the materials by any sudden condensation and formation of a vacuum. Blotting-paper coloured yellow with turmeric, called turmeric-paper, is instantly changed to a reddish brown when brought in contact with ammonia. Other alkalies affect the turmeric in the same manner; but the effect of ammonia is soon distinguished from others, because, on the application of heat to the paper, the ammonia is driven off, and the yellow colour of the turmeric is restored. At a pressure of seven atmospheres, at 60°, ammonia (the gas) condenses into a liquid, and is used in M. Carré's freezing apparatus, which was exhibited on a grand scale at the Great French Exhibition of 1867. Ammonia is formed by the union of three volumes of hydrogen with one of nitrogen, and its symbol is therefore H,N. There are two other compounds of nitrogen and hydrogen, which have not vet been obtained in an isolated form, viz., Amidogen, H,N=16. FIG. 484. THE HALOGENS CHLORINE, IODINE, BROMINE, AND FLUORINE. A Group of Monads. CHLORINE. Symbol, Cl. Atomic weight, 35'5. The fact that sea-salt is the chief source of Chlorine is sufficient to demonstrate its plentifulness; and its presence in soils, plants, animals, natural waters, sea-water, sea-salt, and rock-salt, all confirm the statement. This gas, discovered by Scheele in the year 1774, is called chlorine from the Greek XAwpoo, green, in allusion to its peculiar yellowish-green colour. The gas is easily procured by boiling hydrochloric acid with black oxide of manganese. To obtain chlorine from salt, the latter is first mixed with the black oxide of manganese, and the sulphuric acid, diluted with water, is then added. The proportions are 4 parts by weight of salt, 3 of black oxide of manganese, 10 sulphuric acid previously diluted with 7 of water. When these materials are carefully heated, the following change occurs: The gas must be carefully collected, and even the first portions mixed with air should be passed into a spare jar. If by accident the chlorine is inhaled, it causes the most violent irritation of the air-passages, and this occurs frequently when the chlorine is largely diluted with air, so that no inexperienced manipulators (boys, for instance) should be allowed to make it without a proper person to assist them. When very largely diluted with air, the odour is not disagreeable, reminding one of the smell of the sea. Chlorine is much heavier than air; 100 cubic inches weigh 775 grains at 60° F., 30 in. bar. The density of this gas being 2 times greater than air, it may be collected by displacement like carbonic acid, and, as recommended in the collection of ammonia, it is better to deprive the chlorine of moisture by passing it through a Wolfe's bottle containing a small quantity of sulphuric acid or calcic chloride. The operator who employs this method must be very careful, and probably, to prevent accident, it is better to put warm water in the pneumatic trough, and use that in preference to the displacement method, because water at 60° dissolves quite twice its volume of chlorine, and thus all danger may be avoided by being able to watch the collection of the gas. A lighted taper placed in chlorine gas burns with a reddish flame, an abundance of smoke being produced, in consequence of the chlorine combining with the hydrogen, whilst the carbon is deposited in part. The great affinity (or desire to combine) between hydrogen and chlorine is shown in a very striking manner when equal volumes of the two gases are placed in a thin bulb of glass. If this bulb be held in a red light produced by passing the electric light through red glass, no change occurs; but directly the violet rays, obtained in excess by passing the light through violet glass, are allowed to fall upon the mixed gases, they explode, and hydric chloride is produced. FIG. 485.-Preparation and collection of Chlorine by displacement. If the eyes are protected by a screen of wire gauze held before the bulb, no harm can occur from the bits of very thin glass. Hydrogen is now regarded as a metal, and analogy indicates more "presumptive evidence" that this is the case, because other metals, though they do not explode with chlorine, are quite ready to burn, and do, in fact, take fire when sprinkled in fine powder into this gas, viz., finely-powdered antimony, copper, and gold in leaf, also arsenic, likewise phosphorus. Chlorine has very powerful bleaching properties, and is in effect an oxidizing agent. It is always ready to unite with the hydrogen of water: the latter undergoing decomposition, oxygen is eliminated; and this in the nascent, condensed state, like ozone, destroys many vegetable colours. A little solution of sulphate of indigo is rapidly bleached when shaken with some chlorine gas. Chlorine gas unites with oxygen in various proportion, 1. Hypochlorous anhydride, Cl2O=87. 2. Chlorous anhydride, Cl,O,=119. 3. Chloric peroxide, CIO,=67'5. From the two first, by union with hydrogen, are the following: 1. Producing hypochlorous acid, HCIO=52'5. 3. chlorous acid, HC10,=68'5. no known acid yet obtained. 4. (No corresponding oxide of chlorine yet discovered); producing chloric acid, HCIO,=84'5. 5. (No corresponding oxide of chlorine yet discovered); producing perchloric acid, HC10,=100 ̊5. THE COMPOUNDS OF CHLORINE WITH HYDROGEN. HYDRIC CHLORIDE (Spirit of Salt), HYDROCHLORIC ACID (Muriatic Acid), HCl=36'5.-As already stated, equal volumes of chlorine and hy |