rising in the world by his own industry, I would answer that I am not now discussing the relative advantages of large and small farms, but am confining myself to the agricultural labourer in the broad acceptation of the term. Every employer knows, and every man of common sense must feel, that it is as important to the farmer to have his regular men at work at all times, as it is to the manufacturer or tradesman, and that the business of the farm could not be carried on without such regularity. I regard it, then, as a fatal error for the labourer to follow any pursuit that would at all interfere with the claim of his employer upon him; for, be it remembered, that it is upon hired labour that the working man must chiefly depend for his subsistence; and any scheme that has a tendency to interfere with this his chief capital, must very shortly end in disappointment and distress."

The following account of the Silsoe allotments is taken from Mr. Morton's paper in the 'Journal of the Royal Agricultural Society :' They date from the enactment of the new Poor Law, and the early promoters of the scheme were driven to it by the pressure of the poor's rates. The improvement in the condition of the labourer there and elsewhere is, no doubt, partly the effect of the new Poor Law, which has taught him that his first dependence must be on his own exertions; but a share in that improvement around Silsoe must

certainly be allowed to the allotment system as there established. At first the allotment tenantry were allowed a considerable extent of land apiece-two acres or more. As much, indeed, as they declared their ability to manage was allotted to each applicant. But as these have gradually fallen in or failed, they have been subdivided; and from a rood to half an acre is now the ordinary extent allowed. There have been no restrictions placed upon the cultivators of these plots, but such as are also laid upon the farmers of the district. There is no formal provision against Sunday labour or against immorality, nor are there any special legal securities taken for the relapse of the land to the owner in case he should require it. Every security, nevertheless, exists as to a these particulars in the general sense of propriety which prevails, as well as in the knowledge that sufficient power exists in the management to enforce it. On riding round these allotments late in May, 1859, we saw poppies, turnip-seed, onions, peas, and cabbages, in some cases grown to a large extent; but the ordinary crops were wheat and potatoes for home consumption. In a few instances the land is in the hands of market-gardeners; but, as a general rule, the allotments are occupied by agricultural and other labourers; and the following table, extracted from Mr. Trethewy's paper, gives their extent and their number in the several parishes, together with interesting details regarding parochial rates since the period of their establishment :

We conclude with Mr. Trethewy's statement of the superiority of these clustered field-gardens over detached cottage-gardens, and of the advantages of encouraging rivalry by an annual judgment of cultivation and exhibition of produce :

(1) Every man has the advantage of the experience of the whole field, and generally benefits by it; whereas in a garden there are not those opportunities. (2) How frequently does one see a garden overrun with weeds, overgrown with trees, bushes, and fences, absolutely excluding sun and air, and producing next to nothing to the cultivator! In an open field-allotment the sun and air are freely admitted; the land is more easily kept clean, and the state of cultivation patent to all the neighbourhood. (3) I believe example has a strong influence in promoting good and clean cultivation among all classes of occupiers. With a view to encourage it amongst the allotment tenants of the district, a society, called the "Silsoe and Ampthill Labourers' Friend Society," was established about seventeen years ago. It offers several prizes annually for competition, and great interest is excited among the exhibitors. This society is under the patronage of Earl de Grey, and has Lord Wensleydale as president; while the stewards consist entirely of tenant-farmers, who thus evince their sense of its usefulness. The subscribers comprise the clergy and gentry of the neighbourhood, and the exhibition is invariably fully attended. In fact, all classes unite to promote the object it has in view; and the result is, an exhibition of fruits, vegetables, &c., that would surprise any one who had never before witnessed it. I believe this to be a most useful institution; and, where allotments prevail to any extent, I would strongly recommend the establishment of similar associations."

The almost universal testimony of experience on this subject confirms the conclusion to which, after Mr. Trethewy's paper, the discussion before the Central Farmers' Club led-that the system may always be expected to benefit both labourers and their employers, excepting under extravagant misguidance or neglect; that is, excepting (1) where the land set apart for the purpose is altogether unsuitable in character, or (2) too distant from the cottages of the allottees, or (3) where an excessive extent is permitted to the tenantry, or (4) an excessive rent demanded from them, or, lastly (5), where the tenantry are left entirely to themselves, and no effort made to excite their rivalry or pride in good cultivation.

GARGOYLE, GORGOL, or GURGOYLE, in Gothic architecture, a spout which is carried out from parapets in order to discharge the water from roofs clear of the wall. Mediæval architects, who almost invariably made the subsidiary features of their buildings of an ornamental character, so as to conduce to the general effect, saw at an early period the service which these humble objects might be made to render. Instead of having merely plain projecting pipes for their spouts, they covered the pipe with a block of stone, which they carved in general accordance with the rest of the sculpture; but, regardful of the ignoble purpose to which it was applied, gave it a decidedly grotesque character. Sometimes it is a human figure in a constrained

attitude and with a distorted countenance; sometimes an animal or a monster. Usually the water is made to pass through the open mouth, but sometimes it passes from a pipe concealed below. Occasionally the figures appear to be caricatures of particular persons or bodies of men; occasionally they are gross; but almost always, as we have said, they are grotesque. They appear to have been first used in the Early English style; and they were most prominent in that and the Decorated.

GARLIC, a hardy perennial plant with bulbous roots, found growing wild in the island of Sicily, and in several other parts of the south of Europe. In gardens it is cultivated chiefly on account of its bulbs, which are much used in cookery, and occasionally in medicine. It is the Allium sativum of botanists, and is regularly grown for the market. For this purpose, a light tolerably rich soil is selected in a dry warm situation. The ground should be well dunged for the crop which precedes garlic, and not when the garlic is planted; because, when this is done, the bulbs are very apt to canker, and to be infested with maggots.

It may either be planted in beds or in rows; if in beds, the distance between the plants may be seven or eight inches; if in rows (which is most recommended), they may be one foot apart, and six inches between the plants in the row. In gardens where the soil is light and dry, the best season for planting is late in autumn; but where the soil is wet, the operation should be deferred until spring, that is, to any time in February or March.

The plant is propagated by offsets, which it produces annually in considerable numbers, and which are commonly called cloves. The season of ripeness, which is generally in the end of July or August, is easily known by the leaves changing from green to yellow. At this period the bulbs should be taken up and spread out in the sun to dry, after which they may be tied in bunches and kept in a dry house for winter use, in the same way as onions.

GARLIC, OIL OF. When cloves of garlic [ALLIUM SATIVUM, in NAT. HIST. Div.] are distilled with water in the manner described under ESSENTIAL OILS, 0.2 per cent of an oil is obtained of yellow colour, acrid taste, and strong disagreeable smell. After drying with chloride of calcium, and rectifying over potassium, it is obtained pure and colourless. It then constitutes the sulphide of the radical allyl (CH) [ORGANIC RADICALS] and has the formula (CH,,S). The oxide of allyl, and a compound of allyl still richer in sulphur than the sulphide, appear also to be contained in the crude oil of garlic.

Sulphide of allyl is lighter than water, refracts light strongly, may be distilled without undergoing decomposition, is but slightly soluble in water, but very soluble in alcohol or ether. Sulphuric acid dissolves it without alteration, nitric acid converts it into oxalic and formic acids. On the addition of nitrate of silver to it, sulphide of silver is precipitated, and after a time crystals of double nitrate of silver and allyl are deposited. Sulphide of allyl also precipitates and forms double salts with the salts of gold, mercury, platinum, and palladium.

The mercury compound (C,H,S,2HgS+C ̧H ̧Cl,2HgCl) is decomposed on being distilled with sulphocyanide of potassium, sulphide of allyl being reproduced together with sulphocyanide of allyl (oil of mustard). Other plants besides garlic contain sulphide of allyl; see ESSENTIAL OILS, alliaria, cress, onion, radish, &c.

GARNISHEE. [ATTACHMENT.] GARTER, ORDER OF THE, one of the most ancient and illustrious of the military orders of knighthood in Europe, was founded by King Edward III. The precise year of its institution has been disputed, though all authorities agree that it was established at Windsor after the celebration of a tournament. Froissart says, Edward established the order on resolving to rebuild Windsor Castle, "which King Arthur had founded in time past," and fixed the first celebration of the order on "St. George's day next ensuing," that is April 23, 1344. Walsingham and Fabyan agree with this as the date of its foundation. Stow, who, according to Ashmole, is corroborated by the statutes of the Order, says 1350. Camden says it was founded after the battle of Crecy, at which Edward displayed his garter as a signal for the attack. | The precise cause of the origin or formation of the Order is likewise not distinctly known. The common story respecting the fall of the Countess of Salisbury's garter at a ball, which was picked up by the king, and his retort to those who smiled at the action, Honi soit qui mal y pense, which afterwards became the motto of the order, is not entirely given up as fable. A tradition certainly obtained as far back as the time of Henry VI. that this Order received its origin from the fair sex. Ashmole's opinion was, that the Garter was selected at once as a symbol of union and a compliment to the ladies. This Order was founded in honour of the Holy Trinity, the Virgin Mary, St. George, and St. Edward the Confessor. St. George, who had become the tutelary saint of England, was considered as its especial patron and protector. It was originally composed of twenty-five knights, and the sovereign (who nominates the other knights), twentysix in all. This number received no alteration till the reign of George III., when it was directed that princes of the royal family and illustrious foreigners on whom the honour might be conferred should not be included. The number of these extra-knights was fifteen in 1860. The military knights of Windsor are also considered as an adjunct of the Order of the Garter.

The officers of the Order are a prelate, who is always the Bishop of Winchester; a chancellor, who till 1837 was the Bishop of Salisbury, but is now the Bishop of Oxford, in consequence of Berkshire, and of course Windsor, being transferred to that diocese; a registrar, who is the Dean of Windsor; garter principal king-at-arms of the Order; and a gentleman usher of the black rod. The chapter ought to meet every year on St. George's day, in St. George's chapel, Windsor, where the installations of the Order are held, and in which the banners of the several knights are suspended.

The original dress of the Knights of the Garter was a mantle, tunic, and capuchin or hood, of the fashion of the time, all of blue cloth; those of the knights companions differing only from the sovereign's by the tunic being lined with miniver instead of ermine. All the three garments were embroidered with garters of blue and gold, the mantle having one larger than all the rest on the left shoulder. The dress underwent various changes. Henry VIII. remodelled both it and the statutes of the Order, and gave the knights the collar, and the greater and lesser George, as at present worn. The last alteration in the dress took place in the reign of Charles II.: the principal parts of it consist of a mantle of dark blue velvet lined with white taffeta, and a surcoat of crimson velvet lined with white taffeta; a hood of crimson velvet; a cap or hat of black velvet lined with white taffeta, with an ostrich and heron plume; the stockings are of white silk, and the garter, which is of dark blue velvet, having the motto embroidered in gold letters, is worn under the left knee. The collar is of gold, of twentysix pieces, each in the form of a garter, enamelled azure, appended to which is "the greater George," a figure of St. George encountering the dragon. The badge is a gold medallion representing St. George and the dragon, which is worn suspended over the left shoulder by a blue ribbon; hence it is a form of speech to say, when an individual has been appointed a knight of the garter, that he has received the blue ribbon. There is also a star of eight points argent, St. George's cross in the centre gules, encircled with the garter, worn on the left breast. The fashion of wearing the blue ribbon suspended from the left shoulder was adopted in the latter part of the reign of Charles II. It is not generally known that, from the first institution of the Order of the Garter to at least as late as the reign of Edward IV., ladies were admitted to a participation in the honours of the fraternity. The queen, some of the knights-companions' wives, and other great ladies, had robes and hoods of the gift of the sovereign, the former garnished with little embroidered garters. The ensign of the garter was also delivered to them, and they were expressly termed Dames de la fraternité de St. George. The splendid appearance of Queen Philippa at the first grand feast of the Order is noticed by Froissart. Two monuments also are still existing which bear figures of ladies wearing the garter the Duchess of Suffolk's, at Ewelme, in Oxfordshire, of the time of Henry VI., represents her wearing it on the wrist, in the manner of a bracelet; Lady Harcourt, at Stanton Harcourt, in Oxfordshire, of the time of Edward IV., wears the garter on her left arm above the elbow.

When Queen Anne attended the thanksgiving at St. Paul's in 1702, and again in 1704, she wore the garter set with diamonds, as sovereign of the Order, tied round her left arm.

GAS, a term originally employed by chemists as synonymous with air. It was first used in a very general sense by Van Helmont; but in consequence of the great number of permanently-elastic fluids discovered by Priestley, so different in their properties from common air, and in order to avoid any confusion from the use of the same word to express both, Macquer employed the term gas, which has been universally adopted to distinguish from mere vapours all such elastic fluids as had not been rendered liquid or solid by reducing their temperature.

The experiments of Professor Faraday have however shown that elastic fluids which may be liquefied by reducing the temperature and increasing the pressure, are included in this definition. [GASES, LIQUEFACTION OF.] Still however there exists this difference between bodies in the elastic state :--vapours generated by the agency of artificial heat are reduced to solids or liquids when the heat is withdrawn; while gases preserve their aëriform state at common temperatures. It must however be admitted that the difference is one of degree only, and though not an essential one, it is usefully retained. The number of gaseous bodies is great, and they possess in many respects such different properties, that it would be impossible to give a general description of them. The qualities therefore peculiar to each gas will be stated under its proper head; thus it will appear that some gases are elementary or simple in their nature, while by far the greater number are compound bodies; few of them exist in nature, but are mostly the products of chemical agency. Gases differ as to colour, odour, taste, specific gravity, and solubility in water; they vary also in their effects upon the animal economy, and in their relations to heat: most of them are either combustible or supporters of combustion, but one important gas at least belongs to neither class. Their powers of chemical combination are also extremely different; two gases only possess alkaline properties, whilst there are several gaseous acids. One most important circumstance relative to gaseous bodies has been much discussed, and very opposite conclusions have been arrived at respecting it by philosophers of eminence; it is this, whether all gases, under the same volume and pressure, have the same specific heat. That this is the case, has been maintained by Haycraft, and Marcet and Delarive, and some others; while Dalton, Delaroche and Berard, Dulong and Dr. Apjohn, &c., are of opinion that equal volumes of different gases have not the same specific heat under similar circumstances.

It would be useless to detail the processes or to describe the apparatus by which chemists and physicists have arrived at such discordant results. The experiments of Delaroche and Berard, which are in general most relied upon, though complicated, were made with great care; they transmitted known quantities of gas, heated to 212° in a uniform current, through a calorimeter, the serpentine of which was surrounded with water, the temperature of which, as well as of the gas at its exit, being ascertained during the course of the process by very delicate thermometers. These chemists operated with a considerable quantity of gas, and used other precautions to avoid the errors into which other experimentalists had fallen.

The following is a statement of the results obtained by Delaroche and Berard, Dulong, and Apjohn, of the specific heats of equal volumes of the gases mentioned, under equal pressures:—

Dr. Apjohn observes that the numbers which he has arrived at correspond tolerably well with those of Delaroche and Berard, except in the case of hydrogen; and he admits that he does not speak with much confidence of the numbers attached to nitrogen and oxygen.

There are some other properties which gases possess in common though they vary in degree. There is however one circumstance in which they all agree, whether they are elementary or compound, and whatever may be the difference of their specific gravity: they are subject to suffer the same increase of volume, when subjected to the same increase of temperature.

According to Dalton, when 100 volumes of air are heated from 32° to 212", they become 132.5 volumes; by Gay-Lussac's experiments they increase to 137.5 volumes; by Crichton's to 137-48: the expansion therefore of each volume, according to Dalton is, to GayLussac, and to Crichton for one degree of Fahrenheit's thermometer.

The discovery of this law has supplied chemists with a simple rule for determining what the known bulk of a gas at any temperature will be at any other temperature. Suppose, for example, it is desired to know what the bulk of 100 cubic inches of air at 32° will be at 60°:

portions of nitrogen and sulphur. On exposure to the heat of the retorts, the hydrogen escapes partly in a free state and partly combined with the other elements, carbon, oxygen, nitrogen, and sulphur; the oxygen combines partly with hydrogen, forming aqueous vapour, and partly with carbon, producing carbonic oxide and carbonic acid gases; the nitrogen is evolved chiefly as ammonia, but partly also as cyanogen; the sulphur chiefly as sulphuretted hydrogen, but likewise as bisulphide of carbon; whilst a considerable proportion of the most fixed element, the carbon, remains in the retort as coke. Several of the gaseous or volatile compounds thus formed unite with each other to form secondary compounds. Thus, portions of the carbonic acid, sulphuretted hydrogen, and cyanogen, unite with ammonia to form respectively, carbonate of ammonia, sulphide of ammonium, and cyanide of ammonium. After leaving the retorts, these volatile and gaseous matters are cooled down nearly to atmospheric temperature, when nearly all the vaporous matters condense, forming a liquid consisting of two layers, a lower one called tar [COAL TAR], and an upper one containing chiefly the ammoniacal compounds above mentioned dissolved in water. [GAS LIQUOR.] The permanently gaseous product of the operation is called crude or impure gas, and generally contains the whole of the following ingredients:

The total quantity of these constituents, as well as the relative proportions in which several of them are generated, depends greatly upon the temperature at which the distillation is conducted. As a general rule, the lower the temperature the less gas is produced, but the greater is its illuminating effect when burnt. On the other hand, when a higher temperature is employed, a large volume of gas, but of inferior quality, is obtained. Abstracting the impurities in the above list, it will be seen that gas contains two classes of constituents: namely-luminiferous constituents, or gases yielding light on combustion; and diluents, or nonluminiferous constituents, gases which practically yield no light on combustion. To the first class alone is the illuminating power of gas due; but one, at least, of the non-luminiferous gases is also necessary in order to enable the first class of constituents to burn without smoke and consequent loss of light. The members of the first class are all decomposed slowly at a red, and rapidly at a white, heat, depositing a large amount of carbon in the solid form, and being resolved into nonluminous gases. It is therefore obvious that, in the process of gasmaking, more or less of these valuable constituents must be thus decomposed; the amount depending, on the one hand, upon the length of time during which they are exposed to a high temperature, and on the other, upon the number of the particles of such constituents which come into contact with the heated walls of the retort. Two methods for the prevention of this decomposition present themselves. The first consists in the rapid removal of the gases from the retort, and the second in the dilution of the luminiferous gases, whilst still in the retort, by the admixture or injection of non-luminous constituents. The first of these remedies has been extensively applied in the form of exhausters, which greatly facilitate the escape of the gases from the retorts, whilst both remedial measures have been secured in White's process of gas manufacture, in which a current of non-luminous gases is made to sweep through the retort, and thus rapidly remove the decomposable luminiferous constituents. This latter process, however, though undoubtedly based upon sound philosophical principles, has not come into extensive use, owing to certain mechanical difficulties in carrying it out.

The objects to be kept in view in the generation of gas for illuminating purposes are the following :—

1. The formation of a due proportion of illuminating and nonilluminating constituents; so that, on the one hand, the combustion of the gas shall be perfect, and without the production of smoke or unpleasant odour; and, on the other, the volume of gas required to produce a certain amount of light shall not be too great. For the production of an amount of light equal to that of twenty sperm candles of six to the pound, a consumption of gas greater than five cubic feet per hour ought not to be required.

2. The extraction of the largest possible amount of gaseous illuminating compounds from a given weight of materials.

3. The presence of the largest possible proportion of hydrogen amongst the non-illuminating constituents, to the exclusion of light carburetted hydrogen and carbonic oxide, so as to produce the least amount of heat and atmospheric deterioration in the apartments where the gas is consumed.

II. Purification of Gas.-A reference to the list of substances contained in crude or impure gas, given above, shows that there are five distinct compounds, all of which must be regarded as impurities. Of these, however, two-namely, bisulphide of carbon and aqueous vapour -may be left out of consideration, since the first, although highly objectionable in gas, as the cause of the sulphurous odour always perceived when gas is burnt in unventilated apartments, cannot be removed by any practicable process; whilst the second, which does little harm except diminish to some extent the illuminating power of the gas, cannot readily be abstracted, owing to the hydraulic nature of the apparatus used for the storage and measurement of gas. The processes used for the purification of gas are therefore restricted to the removal of sulphuretted hydrogen, carbonic acid, and ammonia. One hundred volumes of crude gas contain on an average the following quantities of these impurities :—

The two chie ingredients used for their removal, with more or less success, are hydrate of lime and hydrated peroxide of iron.

The first was formerly used suspended in water as milk of lime, through which the gas was made to bubble; but it is now almost universally employed in the solid pulverulent form. By direct chemical affinity, the hydrate of lime removes only sulphuretted hydrogen and carbonic acid from the impure gas; but the water which it contains enables it also to remove the greater part, at least, of the ammonia. The sulphuretted hydrogen forms, with hydrate of lime, water and a non-volatile sulphide of calcium, according to the following equation:CaOHO+HS CaS+ 2HO.

Carbonic acid is rapidly absorbed by hydrate of lime, forming a basic carbonate, thus:2(CaO HO) + CO,

= CaO CO, + CaO HỌ + HỌ. Basic carbonate of lime.

The

In both these reactions water is set at liberty, which assists in absorbing and retaining ammonia as mentioned above. When hydrated peroxide of iron is used for the purification of gas, the carbonic acid is totally unacted upon, but the ammonia is perhaps more completely absorbed than by the lime process. carbonic acid is either subsequently absorbed by slaked lime or, as is more frequently the case, it is suffered to remain in the gas, occasioning a considerable loss of light, but no additional nuisance to the consumer. The action of hydrate and peroxide of iron in removing sulphuretted hydrogen consists in the formation of sulphide of iron, water and free sulphur, thus:

Fe 0, 3HO+3HS 2FeS+S+6HO.

The cost of hydrated peroxide of iron would effectually prevent its use, if, like lime, it were only once available for the purpose; but the peculiarity and value of this oxide as a purifying agent consist in its capability of revivification; that is, restoration to its original condition, or nearly so. This is effected by simple exposure to atmospheric air, the oxygen of which is so rapidly absorbed by the sulphide of iron as to occasion considerable risk of ignition unless the supply of air be moderate. Hydrated oxide of iron is regenerated, and the sulphur previously combined with the iron is set at liberty in the following manner:

2FeS +30 + 3HO = Fe2O3, 3HO + 28.

This alternate absorption of sulphuretted hydrogen and revivification might probably be carried on for an infinite number of times, were it not that the free sulphur ultimately accumulates to such an extent as to greatly reduce the efficiency of the mixture, and the sulphur therefore requires occasional removal either by distillation or roasting.

As it reaches the consumer, gas is very rarely contaminated with even a trace of sulphuretted hydrogen, but it frequently contains carbonic acid and invariably bisulphide of carbon, to which latter substance, giving as it does sulphurous acid on combustion, nearly all the annoyance experienced from the use of gas in dwelling-houses is due. In conclusion, sulphuretted hydrogen may be readily detected in gas by allowing a jet of the latter to blow upon a piece of white paper moistened with a solution of acetate of lead; the slightest discoloration of the paper shows the presence of sulphuretted hydrogen. Carbonic acid is best detected by allowing the gas to bubble through clear and transparent lime-water which will become turbid if the acid gas be present. Ammonia is recognised by allowing a jet of the gas to blow against paper tinted yellow with infusion of turmeric; ammonia changes the yellow of this paper to reddish brown. Bisulphide of carbon is detected by condensing the aqueous vapour formed by a gas flame: if the condensed product redden litmus paper this impurity is present.

III. The combustion of gas.-The production of artificial light depends upon the fact, that at certain high temperatures all matter becomes luminous. The higher the temperature the greater is the

intensity of the light emitted. The heat required to render matter luminous in its three states of aggregation differs greatly. Thus, solids are sometimes luminous at comparatively low temperatures, as phosphorous and phosphoric acids. Usually, however, solids require a temperature of 600° or 700° Fahr., to render them luminous in the dark; and must be heated to 1000° Fahr. before their luminosity becomes visible in daylight. Liquids require about the same temperature. But to render gases luminous, they must be exposed to an immensely higher temperature; even the intense heat generated by the oxhydrogen blowpipe scarcely suffices to render the aqueous vapour produced visibly luminous, although solids, such as lime, emit light of the most dazzling splendour when they are heated in this flame. Hence, those gases and vapours only can illuminate, which produce or deposit solid or liquid matter during their combustion. This dependence of light upon the production of solid matter is strikingly seen in the case of phosphorus, which when burnt in chlorine produces a light scarcely visible; but, when consumed in the air or oxygen, emits light of intense brilliancy; in the former case, the vapour of chloride of phosphorus is produced, in the latter solid phosphoric acid. Several gases and vapours possess this property of depositing solid matter during combustion, but a few of the combinations of carbon and hydrogen are the only ones capable of practical application: these latter compounds evolve during combustion, only the same products as those generated in the respiratory process of animals, namely, carbonic acid and water. The solid particles of carbon which they deposit in the interior of the flame, and which are the source of light, are entirely consumed on arriving at its outer boundary; their use as sources of artificial light, under proper regulations, is therefore quite compatible

with the most stringent sanatory rules.

The light emitted during the combustion of coal gas is due entirely to the illuminating class of its constituents, which yield an amount of light proportional to the quantity of carbon contained in a given volume; thus, propylene and butylene yield respectively 50 and 100 per cent. more light than olefiant gas, because they contain respectively 50 and 100 per cent. more carbon in a given volume.

It would not be desirable to employ a gas containing only lumini. ferous ingredients, even if it were possible to manufacture such a gas, because it is exceedingly difficult to consume these constituents without the production of smoke attendant on imperfect combustion. An inflammable diluting material is therefore necessary to give the flame a sufficient volume, so as to separate the particles of carbon farther asunder, and thus diminish the risk of their imperfect combustion. All the three diluents above mentioned perform this office equally well; but if we study their behaviour during combustion we shall find that in a sanatory point of view hydrogen is greatly to be preferred. The two objections most frequently urged against the use of gas in apartments are, first, the heat which it communicates to the atmosphere; and, second, the deterioration of the air by the production of carbonic acid. Now, in their action upon the atmosphere in which they are consumed, the above three diluents present striking differences in these two respects.

One cubic foot of light carburetted hydrogen, at 60° Fahr., and 30 inches barometrical pressure, consumes two cubic feet of oxygen during its combustion, and generates one cubic foot of carbonic acid, yielding a quantity of heat capable of heating 5 lbs. 14 oz. of water from 32 to 212°; or causing a rise of temperature from 60° to 80-8° in a room containing 2500 cubic feet of air.

One cubic foot of carbonic oxide at the same temperature and pressure, consumes during combustion half a cubic foot of oxygen, generates one cubic foot of carbonic acid, and affords heat capable of raising the temperature of 1 lb. 14 oz. of water from 32° to 212°; or that of 2500 cubic feet of air from 60° to 66.6°.

One cubic foot of hydrogen at the same temperature and pressure, consumes half a cubic foot of oxygen, generates no carbonic acid, and yields heat capable of raising the temperature of 1 lb. 13 oz. of water from 32° to 212°; or that of 2500 cubic feet of air from 60° to 66.4°.

This comparison shows the great advantage which hydrogen possesses over the other diluents, especially over light carburetted hydrogen, which is evidently a very objectionable constituent, and shows that a normal gas for illuminating purposes should consist of illuminating hydrocarbons diluted with pure hydrogen. As an illuminating agent gas is superior to all others in an economical point of view, as seen from the following table, showing the comparative cost of light from various sources equal to 20 sperm candles, each burning for 10 hours at the rate of 120 grains per hour:

Notwithstanding the great economy and convenience attending the use of gas, and in a sanatory point of view, the high position which, as an illuminating agent, coal gas of proper composition occupies, its use in dwelling-houses is still extensively objected to. The objections are partly well founded and partly groundless. As is evident from the foregoing table, even the worst London gases produce, for a given amount of light, less carbonic acid and heat than either lamps or candles; but then, where gas is used, the consumer is never satisfied with a light equal in brilliancy only to that of lamps or candles, and consequently, when three or four times the amount of light is produced from a gas of bad composition, the heat and atmospheric deterioration greatly exceed the corresponding effects produced by the other means of illumination: but by using a gas of high illuminating power, like those of Liverpool or Manchester, it is evident that two or three times the light may be employed with the production of no greater heat or atmospheric deterioration than that caused by wax candles, or the best constructed oil lamps. But there is nevertheless a real objection to the employment of gas

light in apartments, founded upon the production of sulphurous acid during its combustion; this sulphurous acid is derived from bisulphide of carbon, which has already been referred to as incapable of removal from the gas by the present methods of purification.

This impurity, which is more or less encountered in all coal-gas now used, is the principal, if not the only, source of the unpleasant symptoms experienced by many sensitive persons in rooms lighted with It is also owing to the sulphurous acid generated during the combustion of this impurity, that the use of gas is found to injure

gas.

the binding of books, and impair or destroy the delicate colours of tapestry; therefore the production of gas free from this noxious sulphur compound is at the present moment a problem of the highest importance to the gas manufacturer, and one which demands his

earnest attention.

This appa

As it is impossible for the consumer to procure gas free from this objectionable compound, the only method of obviating its unpleasant and noxious effects, is to remove entirely the products of combustion from the apartments in which the gas is consumed, and thus prevent them from mingling with the circumambient air. This suggestion was first made by Faraday, who accomplished this object by his very beautiful and effective ventilating burner. ratus, which is used at Buckingham Palace, Windsor Castle, the House of Peers, and in many public buildings, may be truly said to have brought gas illumination to perfection; for not only are all the products of combustion conveyed at once into the open air, but nearly the whole of the heat is in like manner prevented from communicating itself to the atmosphere of the room. The only obstacles to the universal adoption of this description of burner are its expense, and the difficulty of conveying the ventilating tube safely into the nearest flue without injuring the architectural appearance of the room. The public at large will therefore still await the removal of the objectionable compound in question, by the gas manufacturer, before they will uniFor the method of analysing gas, and for the chemical mode of deterversally adopt this otherwise delightful means of artificial illumination. mining its illuminating power, see GASOMETRIC ANALYSIS, Analysis of

Coal Gas.

GAS LIQUOR. In the manufacture of gas for illuminating purposes, by the destructive distillation of coal, certain liquid products vapour, they condense by the mere cooling of the gas, and then separate are always obtained. Evolved from the heated coal in the state of coal-tar [COAL-TAR]; the other being water containing some matters in into two portions, the one having an oily character and constituting solution, and known as gas-liquor, or the ammoniacal liquor of the gas-works. The substances contained in this solution are ammoniacal gas, and the following compounds of ammonia with volatile acids :—

Carbonate of ammonia, Sulphate of ammonia, Sulphide of ammonium, Chloride of ammonium, Ferrocyanide of ammonium.

On account of the immense demand for ammoniacal salts by metallurgists, calico-printers, colour-makers, artificial manure manufacturers, and others, gas-liquor, although a secondary product in gas-manufacture, is of considerable commercial value. The various methods that a knowledge of chemistry would suggest for the extraction and working of the ammonia contained in gas-liquor have consequently formed the