A solution of the gas in water reddens blue litmus-paper, which is again restored to its original colour by boiling the paper in water, because the carbonic acid gas is driven off by the heat.

It is partly the carbonic dioxide dissolved by the rain which gradually filters through the strata, and dissolves the calcium carbonate and other matters found in spring-water. Carbonic dioxide is also produced in water by the oxidation of the organic matter by the oxygen of the air. Oxygen and organic matter in solution in water react upon one another, and carbonic dioxide is produced, whilst the oxygen originally dissolved in the water is reduced in quantity.

Various ingenious propositions have been made to enable persons to go with impunity into an atmosphere containing corbonic dioxide or other dangerous gases, or to attend on large voltaic batteries where nitrous fumes are evolved. The most practical and thoroughly useful contrivance is that of M. Galibert, and called by him the "Patent Respiratory Apparatus," being a most important

and valuable invention for the protection of life and property against danger arising from fire, also of persons exposed to danger from exhalations of gas, foul air in mines, sewers, &c., &c. It is simple, cheap, and effective.

This invention has been successfully introduced throughout the French empire, and the inventor has obtained many prizes and medals in acknowledgement of its merits.

A reservoir, of the capacity of five cubic feet, made of stout canvas, and

fireproof, is filled with air by means of a small bellows belonging to the apparatus, and placed on the back of the operator, as shown in the drawing, being suspended from braces passed over his shoulders, and further held in position by a belt round the body. There are india-rubber tubes, the two ends of which are inserted into the reservoir, the operator holding the other end in his mouth by means of a mouthpiece of horn to which they are attached, thus enabling him to breathe freely from the supply of air drawn through the tubes from the reservoir, without any inconvenience from dense smoke or poisonous gases.

The eyes of the operator are covered with goggles, so fitted as to effectually protect them from any gas or smoke, and the nostrils are closed by a small and simple instrument for that purpose.

The fire department of Paris has provided all its stations with the respiratory apparatus of M. Galibert. The city of Paris has adopted them, after experiments, for disinfecting sewers, &c.; the gas companies of Paris, and of all the large towns; the Transatlantic Steamship Company, many railway companies, the principal mining companies, and a great number of towns, for use in the fire departments, having adopted them after making decisive experiments.

These experiments have been described by the Counseil d'Hygiène et de Salubrité de Paris, by the Annales des Mines, et des Ponts et Chaussées, the "Moniteur," "Constitutionnel," "Presse," "Mondes," and all the journals of the cities and towns in which experiments with this invention have been made. It has already been the means of saving nearly one hundred lives, and the inventor has received acknowledgments of its merits by numerous prizes and medals from public institutions. It is perfectly simple in its use, and the price is so low as to place one or more within the reach of all persons having property to protect.

The "Times," speaking of the invention, says,

"A very interesting and successful experiment was tried in Portsmouth Dockyard by M. Galibert, a Frenchman, the inventor of an apparatus to enable the wearer to breathe freely in the midst of the most dense smoke arising from a fire. Rear-Admiral Wellesley, Admiral Superintendent of the yard, the Hon. Captain Egerton, Captain W. Chamberlain, and the principal officers of the dockyard were present in the foundry, the drying-room of which was appropriated for the trial, and in which a quantity of straw, shavings, oakum, &c., had been placed, and which at three o'clock was ignited, the only aperture (the door) being then closed, so that the place was soon filled with a dense volume of smoke. M. Galibert then produced the apparatus, which consisted of a canvas bag, fireproof, which he inflated with air by a small pair of bellows; two gutta-percha tubes were affixed, at the end of which was a mouthpiece, which fitted to the teeth, the nostrils being at the same time closed by a small spring. The bag was then slung on his back. Being thus prepared, he entered the room, the door closed upon him, and there he remained eight minutes and fifty seconds, at the expiration of which time the door was opened, and he came out apparently without the slightest exhaustion; after which one of the police constables, John Lacy, No. 157, volunteered to try the experiment, which the admiral permitted, and being fully equipped and instructed by the inventor, he entered the room, where he remained three minutes-sufficiently long to test the utility of the apparatus. One of the labourers followed, and remained six minutes, and both men stated that they found no inconvenience

while in-they could breathe as freely as in the open air, and could have remained any length of time. Subsequently a ladle was heated, in which a quantity of sulphur was put, thus rendering the smoke still more dense; but M. Galibert, after being in six minutes, returned again without the slightest inconvenience. The thermometer was at 91°."

CARBONIC OXIDE.

Carbonic Oxide (symbol, CO; atomic weight, 28).-When carbonic dioxide is passed through red-hot charcoal, it parts with one atom of oxygen, which unites with another of carbon to form carbonic oxide.

This gas is even more poisonous and insidious than carbonic acid, and is produced in considerable quantities during the burning of bricks, where the conditions are favourable for the passage of carbonic acid gas through red-hot charcoal (the cinders called "breeze") with which the bricks are burnt.

By boiling crystals of oxalic acid with strong sulphuric acid, the former is decomposed into carbonic acid and carbonic oxide (CO, and CO), the elements (H2O) which form water being removed by the sulphuric acid.

Carbonic oxide burns with a lambent blue flame, and is converted into carbonic acid. The former is lighter than the latter, and has a specific gravity of o'967.

COMPOUNDS OF CARBON WITH HYDROGEN.

To the department of organic chemistry belongs the most numerous portion of the hydro-carbons. There are, however, two compounds of carbon and hydrogen which deserve special notice here:

Light carburetted hydrogen (CH); Heavy carburetted hydrogen (C2H1). Marsh gas-firedamp-light carburetted hydrogen, methyl hydride (CH,) --so dangerous in coal-mines because the gas does not possess any odour to warn the miner of its presence-has no colour or taste, and is evolved from stagnant pools and ditches where dead leaves accumulate and decompose.

Soda and sodium acetate heated together yield sodium carbonate and light carburetted hydrogen gas.

Olefiant gas--heavy carburetted hydrogen, ethylene (C,H.)-is an important constituent of coal-gas, to which it imparts its chief illuminating powers. Methyl hydride burns with a bluish-yellow flame, whilst olefiant gas burns with a luminous and somewhat smoky flame, betraying the excess of carbon it contains; in fact, this gas contains twice as much carbon as marsh gas united with the same molecule of hydrogen. It is prepared by carefully heating one part of alcohol with five of sulphuric acid: the elements of water are removed by the latter, and olefiant gas (C,H,) evolved. It is called olefiant from the Latin oleum, oil, and fio, to make; because the associated Dutch chemists, Brandt, Dieman, Troostwick, and Laurenberg, in the year 1796, found that when it was mixed with chlorine gas, a peculiar liquid resembling a heavy oil was produced.

Both of these hydro-carbon gases are contained in coal-gas, with other compounds of carbon, and various impurities which it is the duty of the "gasworks" to remove before the gas is supplied to the consumer. But the consideration of such an important theme as coal-gas would demand more space than the limits of this work will permit.

BORON.

Symbol, B. Atomic weight, 109.

Sir Humphrey Davy proved this to be an element, and the base of boracic acid, in the year 1807. Boracic acid is obtained from borax, so called from the Arabic buruk, which signifies brilliant.

Wohler and Deville give the following directions for the preparation of amorphous, dull, olive-green boron in the state of powder: 150 grammes of fused boracic anhydride (boracic acid, B.Os), are coarsely powdered and mixed rapidly with 90 grammes of sodium cut into small pieces. The mixture is then introduced into a cast iron crucible previously heated to bright redness; 70 or 80 grammes of solid and previ

ously fused sodium chloride are placed upon the top of the mixture, and the crucible is covered. As soon as the reaction is over, the still liquid mass is thoroughly stirred with an iron rod, and poured whilst red hot in a slender stream into a large and deep vessel containing water acidulated with hydrochloric acid. The pulverulent boron is then collected on a filter, and washed with acidulated water till the boracic acid is got rid of; after which the washing may be continued with pure water until the boron begins to run through the filter. It is finally dried upon a porous slab without the application of heat.

Crystallized Boron. - In order to convert the amorphous into the crystallized form, the same chemists adopt the following method:

"A small Hessian crucible is lined with the powder or amorphous boron, made into a paste with water, the boron being pressed in strongly, as in

FIG. 490.

with charcoal. In the central cavity a

piece of aluminium, weighing from 6 to 9 grammes, is placed; the cover is luted on, and the crucible enclosed in a second, the interval between the two being lined with recently ignited charcoal. The outer crucible is next closed with a luted cover, and the whole exposed for a couple of hours to a heat sufficient to melt nickel; the temperature is then allowed to fall, and when cold the contents of the inner crucible are digested in diluted hydrochloric acid, which dissolves out the aluminium; beautiful crystals of boron are left, generally transparent, but of a dark brown colour.

A quantity of scales of the so-called graphitoid boron-an alloy of boron with aluminium (B,Al)-are formed at the same time in pale copper-coloured opaque plates.

Boron, like carbon and silica, exists in three conditions, viz., amorphous, crystalline, and graphitoidal. Crystallized boron has a specific gravity of 2.68, and Deville exhibited crystals of the octohedral form hard enough to scratch the ruby. In the remarks on silicon reference will be made to the manufacture of artificial precious stones.

The most important compound of boron and oxygen is boracic trioxide, (boracic acid, BO.) It is obtained from the volcanic districts of Tuscany, which puff out jets of steam and gas: they contain small quantities of boracic acid, and are condensed and dissolved in the small lakes and lagoons surrounding the mouth of the jets. The very weak solution thus naturally formed would involve great expense for coal or other fuel if evaporated in the ordinary way; but Nature gives with the weak solution of boracic acid natural steam-jets, and these are used to evaporate the water of the