Soon after the middle of the last century Dr. Watson made many experiments on coal gas, which he details in his 'Chemical Essays:' he distilled the coal, passed the gas through water, conveyed it through pipes from one place to another, and did so much that we are only surprised he did not introduce it into general use.

But although the properties of coal gas were known to so many persons, no one thought of applying it to a useful object until the year 1792, when Mr. Murdoch, an engineer, residing at Redruth in Cornwall, erected a little gasometer and apparatus, which produced gas enough to light his own house and offices. Mr. Murdoch appears to have had no imitators, but he was not discouraged, and in 1797 he erected a similar apparatus in Ayrshire, where he then resided. In the following year he was engaged to put up a gas-work at the manufactory of Boulton and Watt, at Soho. This was the first application of gas in the large way; but, excepting in manufactories or among scientific men, it excited little attention until the year1802, when the front of the great Soho manufactory was brilliantly illuminated with it on the occasion of the public rejoicings at the peace. Accustomed as we are to the common use of gas, we cannot even now but be struck with such a display on a large scale: but the superiority of the new light over the dingy oil lamps used at that day, when thus brought into public view, produced an astonishing effect. All Birmingham poured forth to view the spectacle, and strangers carried to every part of the country an account of what they had seen. It was spread about everywhere by the newspapers, easy modes of making gas were described, and coal was distilled in tobacco-pipes at the fire-side all over the kingdom. Soon after this several manufacturers, whose works required light and heat, adopted the use of gas: a button manufactory at Birmingham used it largely for soldering; Halifax, Manchester, and other towns followed. A single cotton-mill in Manchester used above 900 burners, and had several miles of pipe laid down to supply them; the quantity made averaged 1250 cubic feet per hour, producing a light equal to that of 2500 candles. Mr. Murdoch, who erected the apparatus used in this mill, sent a detailed account of his operations to the Royal Society in 1808, for which he received their gold medal.

But although the use of gas was thus spreading in the manufacturing towns, it made little progress in London. This may be accounted for, in some measure, by the circumstance that no means had as yet been found out for purifying it. It was dirty, it had a disagreeable smell, and it caused headache when used in close rooms, besides spoiling delicate furniture. This was of little consequence in a manufactory, where there is generally ventilation enough to carry off unpleasant vapours, and rarely very delicate organs or fine furniture to suffer from their influence. But these defects were fatal to its general introduction in London, and until they could be removed there was small hope of success; though attempts were made, lectures delivered, and a number of interesting experiments made by a German named Winsor, whose perseverance and sanguine temper were very efficient in making the matter known to the public. But Winsor was deficient in chemical knowledge and mechanical skill, while he largely overrated the powers of the new instrument which he was zealously endeavouring to introduce. He took out a patent in 1804; and issued a flaming prospectus of a National Light and Heat Company, promising to subscribers of 51. a fortune of at least 5707. per annum, with a prospect of ten times as much. A subscription was soon raised, it is said, of 50,000l. which was all expended in experiments without profit to the subscribers. Winsor however gained experience, and is said, we know not how truly, to have introduced the important measure of purifying gas by lime. In 1807 he lighted up Pall Mall, which continued for some years to be the only street in London in which gas was used. In 1809 the National Light and Heat Company applied to Parliament for a charter, but they were opposed by Mr. Murdoch on the score of prior discovery, and the charter was refused. It was however granted on a subsequent application, and

The great success which attended gas-light in London has extended itself throughout Great Britain. Every large town has long had gas; the smaller towns have followed, and there is now scarcely a place in the kingdom without it. The continental nations have slowly followed our example; Paris for some years, and more recently the towns of Lyon, Marseille, Bordeaux, Nantes, Caen, Boulogne, Amiens, and several others, have adopted it. It is in use in many parts of Germany and Belgium, and St. Petersburg has a small establishment, which is rapidly increasing under the superintendence of a gentleman from one of the London works. The larger towns in the United States also burn gas; and even in the remote colony of New South Wales, the town of Sydney has introduced this valuable invention, which we have no doubt will be found there, as it has been in London, as useful in preventing nocturnal outrage as an army of watchmen.

It will not be necessary to say much about oil gas: the light it produces is, it is true, much greater than that given out by an equal quantity of coal gas; but although it was introduced with success in some places where coal was dear, it has always yielded to coal wherever the two came into competition. The process of manufacture is exceedingly simple, and the machinery is much cheaper. But the cost of the oil itself is the great objection, and we fear it wil be found insuperable. Oil gas was for some time rendered portable; it was forced into strong vessels with a power equal to 450 lbs. upon the square inch, and, thus confined, could be carried about and placed upon a table. As each vessel contained about thirty times as much compressed gas as it would hold in its natural state, one of the capacity of a quarter of a foot would give light for several hours. But even such a size as this was very clumsy, and the process seems to be declining.

Some other substances have been proposed for gasmaking, such as rosin, wood, and peat. Rosin has been tried at more than one establishment, but it has not been found to produce a gas much better than coal gas, while the cost is much greater. An American, some years ago, took out a patent for making gas from cotton seeds, which are, it appears, of very little value in America; but whether or not he has reaped any advantage from the suggestion, we are not informed. The superior cheapness of coal, in those places where it can be procured, will probably always put it above any other material that could be proposed for the manufacture of gas.

Manufacture.-Although in the large way there are many practical difficulties to be surmounted in the manufacture of coal gas, the operation is easily understood; it is merely a process of distillation. A quantity of coal is put into a retort, which is well closed, and placed upon the fire; the temperature is raised to redness, which decomposes the coal, and drives the gas resulting from the decomposition. through a pipe leading from the retort to the receptacle prepared for it. A mass of coke remains, of greater bulk, though less weight, than the coal first put in. This coke must be taken

out, and replaced by a fresh supply of coal, and the process is to be repeated as often as may be requisite. Such is the theory of gas-making; the manner of putting it to practice remains to be described. The first part of the apparatus is the retort, which is made of cast-iron; the shape of this vessel has been somewhat altered from that which it first

a

had. The original form is shown in this figure; it held about 15 lbs., and was placed in an upright position for the convenience of throwing in the coals; it was found to answer perfectly well; and so far as making gas is concerned, it could not be much improved. But the removal of the coke after the gas was made was found to be troublesome. Different means were devised to remedy the defect, one of which was to have an aperture near the bottom of the retort, at which the coke might be raked out, in addition to the one at the top where the coal was put in, as in this figure. This remedied the defect; but the trouble of stopping the retort, which is a work of some time, was thus doubled, and the probability of an escape of gas was much increased: the plan was consequently abandoned. Afterwards much larger retort was adopted, shaped as the first, but holding about fifteen hundred-weight of eoal, which would of course require feeding but rarely, and was emptied by a sort of grated iron or basket, called a grappler, suspended by chains. The grappler was put into the retort when empty, and was drawn out by a crane when the distillation was over. It was found however that the heat of the fire would not readily penetrate to the interior of such a large mass of coal; the outer portion formed a cake of nonconducting matter which protected the remaining coal, and caused the expenditure of much fuel. The gas was injured in its illuminating power by being formed so slowly, being deprived of its bituminous admixture by the continued heat. It was consequently found expedient to revert after all to the smaller-sized retort, and to lessen the inconvenience of taking out the coke it was placed in an horizontal position; the difficulty of filling a retort in this position was obviated by the use of a scoop or semicylindrical shovel long enough to reach to the end of it. This form of retort, which is still in common use, differs in different establishments only as one is a little larger or smaller than another, or more or less flattened, so as to expose a larger surface to the fire

than would be the case with a true cylinder. The retorts are placed in ovens, in groups of three,five, seven, or more, according to the size of the establishments; and their mouths, where the coal is put in, stand out in front of the ovens. Just behind the mouth of the retort a pipe a leads from it perpendicularly upwards several feet; then taking a sudden turn, b, it descends again about a yard, and enters a much larger pipec, technically called the hydraulic main, which runs through the whole building, and receives the gas produced from all the retorts. This great main is generally about half full of the tar and water which leave the coal with the heated gas, and rise with it in the state of vapour, but are condensed by the coldness of the main. Into this mixture the end of the pipe dips, and is thus closed against a return of gas, which would take place if the supply should slacken. A section of the ascending pipe and hydraulic main half full of liquid is shown in the figure.

The gas is now made; but it is very impure, being mixed with water, tar, sulphuretted hydrogen gas, and other impurities. The tar and water are easily got rid of, little more being required for this purpose than to cool the gas and to allow the deposit to run off. This is effected by forcing it through a tube which is bent, as in the figure,

m

and which is kept cool by being immersed in cold water; or still better, as lately adopted in the principal establish' ment in London, by allowing cold water to drop upon it this last method has been found to lower the temperature from 20 to 25 degrees more than the old way.

The separation of the sulphuretted hydrogen gas is a much more troublesome process: it cannot be got away by any washing or cooling, but passes through these processes without change. Worse than the other impurities mentioned, which are only offensive from dirt, this gas is a poison; in any considerable quantity it proves fatal, and is always very unwholesome. It can only be separated by some substance for which it has a chemical attraction, but which has no influence on coal gas. Such a substance is lime. Lime was suggested as a purifier by Dr. Henry, of Manchester, as early as the year 1808, though it was not used on a large scale until some years later; while a variety of inefficacious plans, such as passing the gas through hot iron tubes, and washing it with water, were often tried. The lime is used by being mixed up with water into a thin pasty mass, which the workmen call cream. The cream is placed in a cylindrical vessel, and is constantly stirred by an instrument called an agitator, which is an upright shaft with large flat pieces of wood or metal standing out perpendicularly from it, not unlike a chocolate-mill: the agitator is kept constantly revolving on its shaft, while the flat leaves pass through the whole mass of cream, keeping it well mixed. The gas as it comes from the condenser passes into the lime, and comes from it partially purified; it then enters another purifier, made and furnished precisely in a similar way; after that another; and often a fourth in large works. When it leaves the last vessel it may be considered pure. The accompanying figure will give an idea of the

B

b

A

manner of arranging the purifiers. They are not all upon the same level; but the one marked C is higher than the middle one, marked B, and the lowest is A. This arrangement is made in order that the filling of the vessels may be accomplished with as little labour as practicable. The lime is mixed with water in a vessel placed above C, into which it descends by a pipe not in the figure; from C it is taken to B, and from B to A. The gas goes in the opposite direction: it enters the vessel A by the tube a, and is conveyed under the partition d, through which it passes by little holes into the upper division; it then passes through b into B, and then to C, from whence it comes out pure. The agitator is marked e. It will be understood that by this arrangement the fresh-made gas first meets a mixture which is deteriorated by having already purified a portion of gas in the higher vessels; it goes from that vessel into one filled with a more active agent; and then, almost pure, it goes into a mixture fresh from the reservoir, if there are but three purifiers in the set; but if there are four, it passes into a third before arriving at that one which contains the fresh mixture. In order to know whether or not the gas be pure, it is tested by a solution of acetate of lead, which is a colourless liquid. It is a property of sulphuretted hydrogen gas to produce a brown precipitate with any salt of lead; if therefore any of this gas be mixed with the coal gas which is placed in contact with the colourless solution, it will show itself by turning the liquid brown. The most usual way of testing is to open a stop-cock fixed for that purpose in some part of the pipe which leads the gas into

the last purifying vessel, and to put a card dipped in the solution in front of the small stream of gas which then issues out. If 1-20,000th part only of the bulk of gas should be sulphuretted hydrogen, it will produce a brown spot on the card; and as the whole of the gas, after undergoing this scrutiny, passes through the last purifier, it may now be considered quite pure. When the card shows any impurity, the fresh cream is admitted more freely, and the spoiled lime drawn away from the lowest vessel. This stuff, which has a nauseous smell, used to be allowed to run to waste, to the great annoyance of the public; but it is now usually dried, and employed as cement to lute the covers to the retorts.

In the manufacture of oil gas all the processes of filling and emptying retorts, condensing, and purifying, are avoided. It is only necessary to project a small stream of oil into a red-hot retort, in which pieces of brick or coke are inclosed; the gas immediately passes off through another pipe, and may be at once received into the gasometer. The only purification necessary, if it can be called so, is to allow the gas to pass through some cool vessel, which may receive any undecomposed oil that may have been carried off, to prevent its being wasted in the gasometer.

a

с

The gasometer a is a very large cylindrical vessel from 30 to 60 feet in diameter, closed at the top and open at bottom; it is suspended by a rope and weight e in a tank filled with water, in which it rises and falls freely, being kept in its place by the guide-wheels ff. Two tubes cc pass under and through the water, reaching above its surface into the hollow of the gasometer; one of them comes from the purifiers to admit the gas into the gasometer, the other carries it off when wanted for use. The action of this part of the apparatus is simple; in the figure the gasometer is near the top of the water, and full of gas, which has no communication with the air, because the edge of the gasometer is under water. If now it be pressed downwards, which is effected by lessening the weight e, the gas will be forced through the pipe which is to convey the gas out, and which must be left open for the purpose. When the gasometer reaches the bottom it will be full of water, and ready to receive gas again, which is admitted through the other tube; the gasometer then rises to the top as the gas goes in, and may be pressed down again. In this way it is alternately filled and emptied. In most establishments there are many gasometers, some filling, and others emptying. As it is a most unwieldy part of the apparatus, and takes up an enormous deal of room, many attempts have been made to lessen its bulk. The only contrivance which has succeeded in diminishing the inconvenience is termed the telescope gasometer, which has recently been adopted in several of the metropolitan establishments. In this plan, two gasometers, one inside the other, are placed in a single tank; they are shown in the figure as when drawn up and full of gas, but without any of the necessary appendages. When the gas is let in, the smaller gasometer rises first, and when it reaches the top of the water, its lower rim, which is turned up, and full of water, catches the upper rim of the larger gasometer, which is turned down over it; the two then become one, and the water which runs round the rim prevents the gas from getting out between them. This gasometer is not in reality less bulky than the old one, but as the increased space it takes up is in height, and not breadth, nearly one half of the area is saved; and there seems to be no reason

why three or more cylinders should not be placed in one tank in a similar way.

Many other contrivances are used before the gas is carried to its destination: a meter, to measure it; a governor, to equalize the flow; a pressure-gauge, to indicate the resistance offered to its passage; a tell-tale, to show the quantity manufactured during every hour: but the description of these would exceed our limits.

The tubes which convey the gas are of course larger or smaller according to the number of burners which they supply. The largest in use are about eighteen inches in diameter, the smallest about a quarter of an inch. A pipe of one inch in diameter is large enough to supply gas produc ing a light equal to that of 100 mould candles, each consuming 175 grains of tallow per hour; and the quantity supplied by larger tubes is more than proportionably larger, a four-inch pipe equalling 2000 candles, instead of 1600. This augmentation arises from the diminished friction in large tubes. In laying the pipes care is taken to place them sufficiently deep under the surface of the ground to be safe from injury by carriages rolling over, and they are disposed in straight lines so far as is practicable. They are also laid in slightly inclined planes, and a vessel is placed at the bottom of each descent to receive and carry off any deposition which would otherwise clog the pipes. They are cast with a socket at one end, in which the smaller end of the adjoining pipe is inserted, and the two are joined by running lead between the joints, which is driven in hard by a punch.

The burners are of many different forms, and each has its technical name. The argand burner is like the lamp of that name. The fan is a spreading semicircle of small jets. The cock-spur, a head with three jets only. The batswing is a thin sheet of gas produced by its passing through a fine saw-cut in a hollow globe. The argand and the batswing are said to give the best light with a given quantity of gas, but this seems to be very uncertain.

The gas is turned off from the burners by a stop cock, and some curious inventions have been produced to make the stop-cock close of itself by the cooling of the burner when the light is from any cause extinguished. A patent has recently been taken out for a stop-cock which appears less likely to get out of order than those commonly used. In this invention the gas is stopped off by a piece of leather which is pressed against a portion of the tube where the gas passes, by means of a brass screw working in a hole at the side of the tube. The gas does not come in contact with the brass-work, so that no corrosion takes place, and a frequent cause of escape is thereby obviated.

Experiment has shown that every burner should have its full supply of gas, as a greater light will thus be obtained without a proportionate increase of consumption. The experiment was tried with an argand burner of three-quarters of an inch in diameter; a sufficient quantity of gas was turned on to give a light equal to that of a mould candle; the consumption in this case was a foot and a half per hour. The light was then increased until it equalled four candles, but notwithstanding the light was quadrupled, the consumption of gas was not even doubled; it was only two feet per hour, or half a foot per candle; while in the first trial, the light of one candle consumed a foot and a half, or three times as much. The following statement shows the result of the whole experiment, which was continued as long as the burner consumed all the gas that was admitted; when that

It is evident from this experiment that it is more economical to diminish the number of burners than the supply of gas; and we are of opinion that a plan might be devised by which one or more of the little holes with which a burner is perforated might be stopped off when the light is to be diminished, instead of effecting the same object by lowering the gas.

GASCOIGNE, SIR WILLIAM. [HENRY V.]
GASCONY. [GUIENNE.]

GASHOLDER and GASOMETER. These are vessels employed in the preparation, preserving, and using such gases as are insoluble in water, and employed in chemical investigations.

Many varieties of these have been invented. That which is most useful is Pepys's improved gasometer, of which the annexed cut is a representation. It consists of a copper

cylinder A, on the top of which is supported, by the legs hh, the pan or cistern b. The hollow cylinder A is plain on the inside, except a small projection at the bottom of d. It has the following six openings into it :-From the top proceed the pipes ƒ and g, each of which also communicates separately with the pan b; f, as shown by the dotted lines, extends nearly to the bottom of A. The short tube e also opens directly into the upper part of the cylinder; d is a pretty large opening formed by a short pipe which enters the cylinder at an angle of about 45°, and passes down for an inch or two in the same direction. At this angle the water will not run out through it from the cylinder A, provided all the tubes that would admit the pressure of the air are closed by turning off the cocks. This opening d has a stopper which may be screwed on when wanted. Besides these four openings, which are essential to the apparatus, there are two others, kk, one at top and the other at bottom, which communicate only with the graduated glass tube i, soldered into kk, which is of brass: the use of this is to show the level of the water within the cylinder; and the quantity of gas is also read off on the scale.

The cylinder is filled with water by pouring it into the pan b;d and e being closed, and ƒ and g remaining open, the water runs down into the cylinder, principally at f, and the air is expelled from it by the tube g, at an opening in the bottom of the pan. When the cylinder A is quite full of water, which is known by inspecting the glass-tube, stop the cocks at ƒ and g, and open d, and the water, as already mentioned, will not flow out. Then introduce the beak of the retort, or the tube from which gas is to issue, so deep P. C., No. 669

As the gas

rises into A it displaces an equal bulk of water, which now escapes through d by the side of the retort beak, or tube which conveys the gas. When the gasometer is so full that the level of the water falls to the bottom of the glass tube, take out the retort, and shut the tube d by means of the stopper or screw. The gasometer, now filled with gas, may be safely conveyed anywhere without loss or admixture with the air of the atmosphere.

This apparatus answers various purposes. First, if a bottle or deflagrating jar is to be filled with oxygen or other gas, fill the bottle with water and invert it in the pan b, also containing water, and place it over the opening g; then open the cocks at ƒ and g, and the water will sink into the cylinder at f, and an equal quantity of gas will rise at g and displace the water from the bottle. When this is filled, again shut the cocks at ƒ and g. If it be required to fill a bladder with gas, screw it on the cock at e, open the cock at and let the water sink into the cylinder, and the gas will rise as it did before, but will escape at e into the bladder. The opening at e is also used for supplying a blow-pipe with gas; this is screwed on and connected with a flexible tube.

This instrument is rather a gasometer than a mere gasholder-the latter is a simpler instrument, upon the same principle; but though it may be used for filling a bladder with gas, it cannot be used for filling bottles nor for sup plying a blow-pipe.

GASSENDI, PIERRE (properly Gassend), one of the most distinguished of the naturalists, mathematicians, and philosophers of France, was born 22nd January, 1592, at Chantersier, a village near Digne, in the department of the Lower Alps, of poor parents. Richer in virtue than in worldly goods, they were content to sacrifice their own enjoyments to the education of their child, who, before he reached his fifth year, had already given many premature indications of extraordinary powers. At a very early period he evinced a taste for astronomy, which became so strong, that he is said to have often deprived himself of sleep in order to enjoy the contemplation of the heavens; and the following anecdote betokens the precocious development of that talent of observation and deduction for which he was in after-life so eminently distinguished. A dispute having arisen one evening between some children of his own age whether the moon or clouds were moving, and his companions maintaining that the apparent motion was that of the moon, but that the clouds were stationary, Gassendi proceeded to undeceive them by ocular proof: placing his playfellows beneath a tree, he bade them notice that while the moon was steadily visible between the same branches, different clouds were constantly appearing in succession.

Gassendi was sent to school at Digne, where he made rapid progress in the Latin language, and soon acquired a decided pre-eminence over his schoolfellows. Upon completing the usual course, he returned to Chantersier in order to prosecute his studies in retirement; but he had not been there long when he was invited, at the early age of sixteen, to teach rhetoric at Digne. This office he shortly relinquished, and proceeded to Aix to study divinity. In 1614 he was appointed professor of theology at Digne, and two years afterwards he was invited to Aix to fill the chairs of divinity and philosophy, vacant by the death of Fesac, his master and teacher.

The careful perusal of the works of Vives, Ramus, and Patricius, had thoroughly convinced Gassendi of the faults and defects of the philosophy of the schoolmen, or the socalled followers of Aristotle, but it required no ordinary boldness to call it in question. Animated however by the spirit of truth and free inquiry, Gassendi did not hesitate to submit the principles of the schoolmen to a rigorous and searching criticism, and considered it his duty, as a professor of philosophy, to expose the errors of the prevailing theory. This he did indirectly in a work entitled Exercitationes paradoxicæ adversus Aristoteleos.' The appearance of the first volume, which was published at Grenoble in 1624, gained for its author a well-established and wide-spread reputation; and if on the one hand it gave great offence to the blind partisans of established doctrines, it was on the other highly esteemed by several learned and distinguished individuals, and particularly by Nicholas Peiresc, president of the university of Aix, by whose interest and influence, assisted by Joseph Walter, prior of Valette, Gassendi was promoted to a canonry in VOL. XI.-N