ON PHYSICS, OR NATURAL PHILOSOPHY.
No. XLIII.

(Continued from page 242.)

SOURCES OF HEAT.

CHEMICAL SOURCES.

bon which is converted directly into carbonic acid, disengages the same quantity of heat as if it were first converted into carbonic oxide, and then the latter into carbonic acid.

The heat produced by a burning body is distributed in two ways; first, by the calorific rays which proceed directly from the body; secondly, by the heat which the particles, after being converted into carbonic acid, carry along with them, when drawn up by a current of air. By the latter way, a very Chemical Combinations.-Chemical combinations are gene- ascertained by any one by means of a very simple experiment, considerable proportion of the heat escapes, as may be easily rally accompanied by a development of heat more or less abund-shown in fig. 229. Thus, we find that we can hold the finger ant according to the nature of the substances. When these combinations operate slowly, as when iron is oxidised in the air, the heat developed is insensible; but when they are produced rapidly, as in the mixture of anhydrous sulphuric acid with water, the disengagement is very intense. In most cases, this disengagement of heat is accompanied with combustion.

Combustion.-Every chemical combination which is accompanied with the development of light and heat, is called combustion. In the combustions presented to us by wood-fires, oil-lamps, and wax-candles, it is the carbon and the hydrogen of the wood, the oil, and the wax, which are combined with the oxygen of the air. But there are combustions in which oxygen plays no part. For example, if into a vessel full of chlorine, we throw some powder of antimony, or pieces of phosphorus, these bodies will combine with the chlorine and produce a powerful development of light and heat. Several combustibles burn with a flame. A flame is, in fact, only a gas or a vapour carried to a high temperature by the effect of combustion. Its illuminating power varies with the products which are formed during combustion. The presence of a solid body in a flame increases its illuminating power. The flames of hydrogen, carbonic oxide, and alcohol, are pale, because they only give out gaseous products. But the flames of waxcandles, oil-lamps, and carburetted hydrogen gas, have a great power of illumination, because they contain an excess of carbon, which, undergoing only an incomplete combustion, become incandescent in the flame. Much greater intensity is given to a flame, by placing in it platinum wire or amianthus. The temperature of a flame has no specific ratio to its illuminating power. The flame of hydrogen, which is the palest, is that which developes the greatest heat.

Heat of Combustion.-Several philosophers, among whom may be mentioned Lavoisier, Rumford, Dulong, MM. Despretz and Hess, have been engaged with researches relating to the quantity of heat developed by different bodies during combustion and combination. In these researches, the calorimeter of Rumford was employed. It consists of a rectangular copper vessel filled with water, in which a worm is placed, passing through the bottom of the vessel and terminating below in an inverted funnel. Under this funnel are placed the burning bodies on which the experiments are made. The products of combustion, by being disengaged in the worm, heat the water in the vessel, and after the elevation of its temperature, the quantity of caloric developed may be determined. Assuming as the unit of heat, the quantity of caloric necessary to raise one kilogramme of water by 1° Centigrade, Dulong found that a kilogramme of the substances in the following table disengaged in their combustion the number of units placed in

a line with their names:

Fig. 229.

or thumb at a small distance from the side of the flame of a lighted candle, without feeling the heat too intense to bear its action; but when we hold the finger above the flame, in the direction of its axis, we are forced, by the greater heat evolved in this direction, to remove it to a much greater distance.

ILLUMINATION.

Modes of Lighting.-As the method of producing an artificial light for the purpose of supplying the want of the light of the sun, is more connected with the principles of flame, combustion, and heat, than with light considered by itself, we shall treat here shortly on this subject. The light of a common fire was naturally the first step in the art of illumination. The property which resinous woods possess of giving out a flame not only continued difficult to extinguish, but soon led to their use in the form of torches. Virgil speaks of them in the 2nd book of the Georgics, and in the 7th book of the Eneid. "Ipsa inter medias flagrantem fervida pinum

Sustinet."

This mode of lighting is still used in some countries to this day, as in Corsica and in China; but on account of the smoke it can only be employed in the open air. The inflammability of oily bodies, and especially of animal fat, must have been tions in the remotest times. The substitution of the pure discovered in the practice of the most simple culinary prepararesinous matter for the branches which contain it, the extraction of animal fat and vegetable oil, were grand steps in the progress of the art of illumination. Resinous matter, solid grease and wax fixed round a wick composed of fibrous matter, gave rise successively to the torch, the candle, and the wax light. Oil, extracted either from animal or vegetable matter, was burned in lamps, which were at first small vessels furnished with a hollow beak or spout, in which the wick was placed. In all these cases, whether lamp, candle, or torch, the combustible matter melted by the heat, rose in the wick in consequence of capillary action, as formerly explained. Small resinous torches, manufactured from the products of the pinus maritima, on a large scale in the moors of Gascony, are still, in many parts of France, the only mode of lighting employed during the long nights of winter. The gaseous products of the combustion are carried off by the chimney, under the mantelpiece of which the torches are placed. The unhealthy candle, compared with this imperfect light, was a vast improvement. But the candle is beginning to disappear in our towns, in order to give place to the stearic wax-lights, which are only half the price of the real wax-lights, and have an equally pure smell. The modern lamp, successively modified by Argand, Carcel, and others, has only a very distant resemblance to the lamps of antiquity. Whatever be the substance used in the production of the light, the flame, which is the illuminating cause, is the result of the combustion of a gas more or less charged with solid particles. This will be explained by fig. 230, in which AA is a vertical section of a candle through the BB, is the cotton wick which is set on fire. The 121

The experiments of Dulong, M. Despretz, and M. Hess, establish the principle that a body which burns produces always the same quantity of heat in order to arrive at the same degree of oxidation, whether this degree be reached immediately or by degrees. For example, a quantity of car-middle.

VOL. V.

width of the cylindric roll of tallow has been calculated in such The small transverse or horizontal marks, represent the a proportion to that of the wick, that its edges do not melt, place occupied by the particles of oxygen; the round points but form a wall which hinders the melted matter from gutter-on the nearly vertical lines, represent the place occupied by ing. Thus the melted grease is confined as it were in a small cup, represented at c c, and forms a bath of a sufficient depth

Fig. 230.

0
FL B LE

A

the particles of hydrogen. It is quite evident that the most active combination takes place in the exterior part, where the particles of both gases are in immediate contact; and that it goes on diminishing from the border to the centre of the flame, where there is none. What the candle, the wax-light, and the lamp realise on the small scale, and simultaneously with the process of combustion, has been effected on the great scale, and previously to combustion itself; in other words, we extract the carburetted hydrogen gas from the bodies which contain it, and we burn it by means of gas-burners properly supplied with it. This invention is entirely a modern one. Notwithstanding the ultimate resemblance which exists in all these various modes of illumination, there are particulars belonging to each worthy of notice.

Candle Lights. In the manufacture of candles, a mixture of beef and matton tallow is preferred. The former alone is too soft and too easily melted; while the latter gives less light, as being too diffient to melt. The raw tallow, separated as much as possible from Dreign matter, such as blood, etc., is first chopped small, and then meteli in east-iron or copper vessels. It is then passed through a strainer in orter to purify it, sometimes more than once, if necessary, The wicks are made of cotton; they must be free from knots, slightly twisted, and perfectly dry. The proper lengths went by the hand. There are different processes for fixing the smile round the wick. The oldest a1 simplest monsters in dryping the wick, for some irstants, in the punte t tort, stretching it and rolling it in the hands or on a table. The wicks tis prepared, are suspended round a eroular fi ime, o ile red by a counter-weight, by means of a valley fixen to the celling. By pressing slightly on the tram, the wilks dre dipped in the melted tallow at as low a temperature as ssible. When they are covered with a layer of sufficient a kness, the frame is permitted to ascend by the action of the unter-weight, and the candles, or rather partially conted wisas, tre showed all round the wick BB, of which the fibres are similar in effect to cool in the air, until they are ready for a new dip in D to a series of small tubes. The hot liquid is imbibed by the melted tallow, by which they are covered with a new coat as wiek and rises in it in consequence of capillary action. But before; this process is continued until they have acquired the as it rises, the heat increases, it is then reduced to vapour, is necessary thickness. Thus are the ordinary d'p-con decomposed, and is finally converted into carburetted hydro- Mould-candles are made in the following manner-In gen. The extremity of every thread of cotton, therefore, are composed of a mixture of 1 part of tin and 2 becomes a small gas-burner, or rather a collection of small | lead, well polished in the inside, and formed in t gas-burners. The flame of a wax-light, or a candle, is always of a candle. These moulds having been fixed in a verneal composed of three distinct parts. The first oo, the interior, is position, the wick is passed through them, stretelek, vaļ that where the gas is disengaged before there is any combus- centrally fixed in that position. The taliow is then poursi tion. It is quite dark. In the second LL, surrounding the into them at a very gentle heat; for if too hot they would stick former, the combination of the hydrogen gas proceeding from to the moulds. As candles grow old, they whiten and seconce the candle, and the oxygen gas proceeding from the air, com- of a better quality. Prolonged exposure to the air or to the mences. In the third, the exterior part, FF, is shown the dew hastens the whitening process. zone in which this combination is completed. In fig. 231, is roughly represented a more distinct account of this process.

Fig. 231.

Wax-lights.-In the same manner as cinlles are moulded, so are wax-lights, only they are more apt to adhere to the sides of the mould, which renders the operation more diffie alt. The mode of their manufacture differs very little from that of candles. By means of a spoon or ladle, the melted wax is poured successively over the top of the wick, along which it cools and solidifies. When they have enched the proper thickness, they are lifted and rolled on a table to give them the proper regularity of form; a process which is tiled by the use of a polished board instead of the hands. candles have long been in great demand on account at transparency and whiteness. They are moulde 1, and in theor manufacture a solid substance called spermadi, express.d from the brain of the whale, and purified, is employed. bat is mixed with about 3 per cent. of very white wix. times a small quantity of colouring matter is intro Viccx i ta wax-lights, but this has no influence on the brightness of the colour of the light.

r

of holding 440 gallons, lined with lead, and heated by steam, the periodical action of the compression, the proper level of which is conveyed directly into the vat by means of a circular the oil is constantly restored. An apparatus, long known tube pierced with holes; when the tallow is melted, about 132 under the name of Mariotte's vessel, at last furnished the gallons of a solution of lime, containing about 120 lbs. of means of keeping the level of a running liquid at a constant quicklime, is added, and the mixture is continually stirred. After six or seven hours, the saponification is terminated, and Fig. 333. the soap of lime has formed a consistent mass, which becomes very hard on cooling. It is next reduced to a very fine powder, and decomposed by sulphuric acid, diluted with water, in vats similar to the first, and heated by steam; when the fatty acids being set free, form an oily stratum on the surface of the acid liquids. The melted fat is decanted, and washed several times, while hot, with water charged with sulphuric acid, and then with fresh water; it is finally run into tin moulds forming cakes of 6 or 8 lbs. in weight. This mass, which is still a mixture of stearic, margaric, and oleic acids, is first powerfully compressed when cold by the hydraulic press, in order to express the greater part of the oleic acid, and then compressed, when at a temperature of 90° or 100°, in order to drive out the remainder. The oleic acid thus expressed is of a deep brown colour, and contains nearly all the margaric acid, with a certain quantity of the stearic acid. The cakes remaining after this compression are again melted, in contact with a dilute solution of sulphuric acid, which removes the last traces of lime from the fatty substance; after which it is freed from the adhering acid by washing it in boiling water. It is then poured into moulds, where it becomes solid, and it is thus brought into commerce, as refined stearic acid, used for the manufacture of stearic lights. In the first process of making stearic lights, the wicks, twisted like those of the common wax-lights, became charred in the same manner as the wick of a candle, and required to be snuffed every minute. M. Jules Cambacérès substituted plaited wicks for twisted ones, and this fortunate invention was completely successful. In consequence of the plaiting, the wick in proportion as the light burned was turned and slightly bent downwards, so that the extremity was made to consume itself in the flame.

Oil-lights.-Among the ancients, lamps were varied in form and matter. They were made of terra-cotta, bronze, silver, and even of gold. They had one or more wicks; and Suidas gave to a lamp the name of icosymica, because that it had twenty wicks. Still they were all constructed on the same plan. They were vessels in the form generally of an oblong cup, furnished with a gutter or spout, over the lip of which projected the extremity of a round wick placed in the vessel and lying soaked in the oil. These lamps were smoky and spread a disagreeable smell around them. It was by the light of such a lamp that Demosthenes composed those sublime orations which his enemies said smelt of the oil. The wick was regularly charred after a certain time, and it was necessary to trim it, because the level of the oil in the vessel was continually lowered by the combustion. Fig. 232 represents a Fig. 232.

height. The chemist Proust appears to have been the first who, towards the end of the last century, applied the idea of Mariotte's vessel to the reservoir of a lamp with a constant level. Fig. 234 represents one of the forms which has been Fig. 234.

given to this reservoir. The stop-cock at the bottom being then the cork is replaced. When the lamp is to be lighted, shut, the cork at the top is removed and the reservoir filled; the stop-cock below is opened, the oil rises in the shorter branch to the left, and supplies the wick; but it does not rise in this branch above the lower level of the open tube immersed in the reservoir. In proportion as the oil is consumed, the level sinks in the reservoir, and the vacuum thus formed is filled with the air which enters at the bottom of the open tube, and rises in bubbles through the liquid, but the level in the shorter branch remains constantly the same.

The lamp furnished with the side reservoir furnished with a flat wick, where the combustion operated in a much better manner than in the thick irregular wicks of the ancient lamps, was a very great improvement, especially when the wick was surrounded with a glass chimney. By means of the lattel addition, a current of air was established which continually kept up the flame and guarded it from the wavering motions produced by the exterior air. Thus surrounded, the flame gave out a much more vivid light, and was prevented from smoking. It was reserved, however, for Argand to carry this arrangement to the highest degree of perfection, by inventing a burner with a cylindrical wick and a double current of air. The new current of air is produced in the centre or axis of the wick, and rises from the bottom of the wick-case. The invention of this burner, called the Argand burner, was first announced in February, 1784. It is the union of the constant level of Proust with the burner of Argand which forms the wall lamps manufactured on the great scale by Quinquet, and known by the name of the manufacturer. For hall lamps, or suspensory lamps in general, the lateral reservoir was unsightly and inconvenient by reason of the shadow which it projected. To remedy this inconvenience, shadowless lamps were invented, having the reservoir in a circular form round the burner, and carrying an unpolished lamp-glass of a globular shape, which, by its effect, completely neutralised the shadow of the reservoir and conduits. If we substitute, for Towards the end of the last century, the pump or spring- the unpolished lamp-glass, a metal reflector, we shall have the lamp, in common use, was a great improvement on the ancient astral lamp of Bordier-Marcet. In the astral and shadowless lamp; see fig. 233. The upper part of this lamp is moveable, lamps the constancy of the level is not perfect, and the intenand can be made to descend into the reservoir by compressing sity of the light always decreases in proportion as the level of a spring; it is sufficient to exert this compression to make the the oil is lowered. Lamps also have been invented having oil rise in the reservoir from above and soak the wick. By the reservoir situated above the burner. and furnishing a

specimen of an antique lamp. The ancients found that this mode of lighting was susceptible of improvement, and they invented a variety of ingenious arrangements, of which the description has been transmitted to us in the writings of the celebrated Hero, of Alexandria, who flourished at the end of the second century B.C. Cardan, who died in 1575, gives a description of a mechanical lamp analogous to that of Hero. It appears that these various kinds of lamps were very little in use, since the authors referred to only speak of them as objects of curiosity.

256

THE POPULAR EDUCATOR.

superabundance of oil to the wick until it was completely exhausted. This has been accomplished on different principles by MM. Carcel, Girard, and Thilorier, and by many other succeeding inventors.

Carcel, a watchmaker, in his invention, placed at the lower part of a cylindro-conic lamp, a spring mechanism, by means of which a small forcing-pump constantly caused the oil to rise to the upper part of the wick. But in order that the rise should be regular, two pumps were necessary, or at least one pump with double action, or a reservoir of compressed air acting against a spring. MM. Gotten, Gagneau, Careau, etc., have successively modified, by improvements and simplifications, the original invention of Carcel, Girard's lamp is conThe structed on the principle of Hero's fountain, described in p. 318, vol. iv.; but it has not come into general use. hydrostatic lamp of Thilorier is represented in fig. 235. It is Fig. 235.

On account of this diminution of pressure, however, and the
precautions required in its management, Thilorier's lamp has
latter can be had at very low prices.
been almost laid aside for mechanical lamps; especially as the
Some years ago, under the name of the Solar lamp, an inge-
The
nious apparatus for illumination was invented, in which, with-
out mechanism of any description, and even with inferior oils
or grease, a flame of perfect whiteness was obtained.
reservoir of oil in this lamp widens towards the top, and
carries in the middle, at its upper part, a burner, into which
the wick is immersed nearly to the level of the liquid; and
though the burner has a double current of air, the combustion
would not be long in becoming very imperfect, in consequence
the chimney support being arranged as shown in fig. 236, the
of the lowering of the level of the oil in the reservoir. But
Fig. 236.

flame undergoes, a little above the wick, a contraction in which it is necessarily mixed with air, in the same way as in smoke-consuming apparatus. Thus it is elongated, and then rising considerably above the level of the oil, gives out an extremely vivid light. By this artifice, the carbonaceous parts not completely burnt, and which give to the flame a reddish tint, are entirely consumed, and the light is rendered perfectly clear.

Lights of various kinds.-The oils of turpentine, naphtha, and petroleum, the essential oils extracted from schists, tar, gases, and resins, being composed, like common oil, of carbon and hydrogen, although in different proportions, it was natural to endeavour to employ them in illumination; but it was impossible to burn them in the apparatus adapted for oillights, because the excess of carbon they contain rendered them too smoky to be borne. In order to obtain a proper light, different means must be employed; thus, highly carburetted oils must be mixed with other liquids which are but slightly carburetted, in order to compensate the excess of carbon in the one by the want of it in the other; next, to supply the flame which they produce with a sufficient quantity of air, so that the excess of carbon may not escape combustion, and form lamp-black; but, on the contrary, may burn in the flame, by combination with the oxygen of the air, when the air is abundantly supplied. The vaporization of the burning liquid powerfully assists these two methods of rendering the above-mentioned fluids available.

constructed on this principle, that if two communicating
vessels are filled with liquids of different densities, and these
liquids be in equilibrium, the heights of the liquids will be to
In 1832, a system of lighting, conducted on these principles,
each other in the inverse ratio of their densities. A solution
of sulphate of zinc, properly prepared, having a considerably
greater density than that of oil, not acting on the metal which was introduced into France. The matter employed was known
contains it, exerting no chemical action on the oil, and sup- under the name of liquid gas, liquid hydrogen, or gazogen. As
porting the variations of temperature without sensible altera- a liquid slightly carburetted for the preceding mixture, alcohol,
tion, was finally employed by M. Thilorier in the construction methylic alcohol (spirit of wood), or ether, has been employed;
of his lamp with complete success, after many others had and the name alcoholate has been proposed for the mixture
failed in the same attempt. In the above engraving, the place itself. Recently, however, unmixed essential oils have been
of the sulphate of zinc is indicated by the deeper shading, and employed for illumination, and by means of very ingenious
that of the oil by the lighter shading; the latter being pressed arrangements, very perfect combustion has been obtained, and
by a denser liquid, rises up to the burner at a higher level a flame almost without smoke. M. Gaudin has invented an
than that of the reservoir. In proportion as the level in the artificial light by directing a current of air upon a jet of some
latter is lowered, the pressure on the ascending column dimi- essential oil, and producing a powerful action at its extremity,
nishes; but the air entering below the sulphate of zinc, as in by throwing it on a ball of quicklime prepared in a particular
Mariotte's vessel, partly replaces the effect of this pressure. I manner. He has thus produced the combustion of the oil of

Residue: Coke, consisting of carbon and earthy matter.