Chapter C: D E F are the four printing cylinders, named in the order of their (22)

The theory of etherification demonstrates that when strong sulphuric acid is mixed with alcohol, there is formed, on the one hand, a more aqueous sulphuric acid, and, on the other, sulphovinic acid. When this mixture is made to boil, the sulphovinic acid is decomposed, its dihydrate of carbon combines with the alcohol, and constitutes ether; while the proportion of sulphovinic acid progressively diminishes. Mr. Hennell, of the Apothecaries’ Hall, first explained these phenomena, and he was confirmed in his views by the interesting researches of Serullas. The acid left in the retort is usually of a black colour, and may be employed to convert into ether half as much alcohol again; an experiment which may be repeated several times in succession.

The most profitable way of manufacturing ether has been pointed out by Boullay. It consists in letting the alcohol drop in a slender stream into the acid, previously heated to the etherifying temperature. If the acid in this case were concentrated to 1·846, the reaction would be too violent, and the ether would be transformed into bicarburetted hydrogen (dihydrate of carbon.) It is therefore necessary to dilute the acid down to the density of 1·780; but this dilution may be preferably effected with alcohol instead of water, by mixing three parts of the strongest acid with 2 of alcohol, specific gravity 0·830, and distilling off a portion of the ether thereby generated; after which the stream of alcohol is to be introduced into the tubulure of the retort through a small glass tube plunged into the mixture; this tube being the prolongation of a metallic syphon, whose shorter leg dips into a bottle filled with the alcohol. The longer leg is furnished with a stop-cock, for regulating at pleasure the alcoholic streamlet. The distilled vapours should be transmitted through a worm of pure tin surrounded by cold water, and the condensed fluid received in a glass bottle. The quantity of alcohol which can be thus converted into ether by a given weight of sulphuric acid, has not hitherto been accurately determined; but it is at least double. In operating in this way, neither sulphurous acid, nor sweet oil of wine is generated, while the residuary liquid in the retort continues limpid and of a merely brownish yellow colour. No sulphovinic acid is formed, and according to the experiments of Geiger, the proportion of ether approaches to what theory shows to be the maximum amount. In fact 57 parts of alcohol of 0·83 sp. grav. being equivalent to 46·8 parts of anhydrous alcohol, yield according to Geiger, 33-1/2 parts of ether; and by calculation, they should yield 37-1/4.

The ether of the first distillation is never pure, but always contains a certain quantity of alcohol. The density of that product is usually 0·78, and if prepared by the first of the above methods, contains besides alcohol, pretty frequently sulphurous acid, and sweet oil of wine, impurities from which it must be freed. Being agitated with its bulk of milk of lime, both the acid and the alcohol are removed at the same time; and if it be then decanted and agitated, first with its bulk of water, next decanted into a retort containing chloride of calcium in coarse powder and distilled, one third of perfectly pure ether may be drawn over. Gay Lussac recommends to agitate the ether, first with twice its volume of water, to mix it, and leave it in contact with powdered unslaked lime for 12 or 14 hours, and then to distil off one third of pure ether. The remaining two thirds consist of ether containing a little alcohol. If in preparing ether by Boullay’s method, the alcohol be too rapidly introduced, much of this liquid will come over unchanged. If in this state the ether be shaken with water, a notable quantity of it will be absorbed, because weak alcohol dissolves it very copiously. The above product should therefore be re-distilled, and the first half that comes over may be considered as ether, and treated with water and lime. The other half must be exposed afresh to the action of sulphuric acid.

Pure ether possesses the following properties. It is limpid, of spec. grav. 0·713, or 0·715 at 60°; has a peculiar penetrating strong smell; a taste at first acrid, burning, sweetish, and finally cooling. It has neither an acid nor alkaline reaction; is a non-conductor of electricity, and refracts light strongly. It is very volatile, boiling at 96° or 97° F., and produces by its evaporation a great degree of cold. At the temperature of 62·4, the vapour of ether balances a column of mercury 15 inches high, or half the weight of the atmosphere. When ether is cooled to -24° F. it begins to crystallize in brilliant white plates, and at -47° it becomes a white crystalline solid. When vapour of ether is made to traverse a red hot porcelain tube, it deposits within it one half per cent. of charcoal, and there are condensed in the receiver one and two thirds per cent. of a brown oil, partly in crystalline scales, and partly viscid. The crystalline portion is soluble in alcohol, but the viscid only in ether. The remainder of the decomposed ether consists of bi-carburetted hydrogen gas, tetrahydric carburet, carbonic oxide gas, and one per cent. at most of gaseous carbonic acid.

Ether takes fire readily, even at some distance from a flame, and it should not therefore be poured from one vessel to another in the neighbourhood of a lighted candle. It may be likewise set on fire by the electric spark. It burns all away with a bright fuliginous flame. When the vapour of ether is mixed with 10 times its volume of oxygen, it burns with a violent explosion, absorbs 6 times its bulk of oxygen, and produces 4 times its volume of carbonic acid gas.

Ether alters gradually with contact of air; absorbing oxygen, and progressively changing into acetic acid and water. This conversion takes place very rapidly when the ether is boiled in an open vessel, while the acid enters into a new combination forming acetic ether. Ether should be preserved in bottles perfectly full and well corked, and kept in a cool place, otherwise it becomes sour, and is destroyed. It contains in this state 15 per cent. of its bulk of azote, but no oxygen gas, as this has combined with its elements. Ether is composed of oxygen 21·24; hydrogen 13·85; carbon 65·05. This composition may be represented by 1 prime equivalent of water, and 4 primes of bi-carburetted hydrogen gas; in other words, ether contains for 1 prime of water, once as much olefiant gas as alcohol, and its prime equivalent is therefore 468·15 to oxygen 100. By my analysis, as published in the Phil. Trans. for 1822, ether is composed of oxygen 27·10; hydrogen 13·3; and carbon 59·6 in 100 parts. The density of my ether was 0·700. One volume of vapour of ether consists of one volume of aqueous vapour and two volumes of olefiant gas (bi-carburetted hydrogen,) while alcohol consists of two volumes of each.

ETHER, ACETIC, is used to flavour silent corn spirits in making imitation brandy. It may be prepared by mixing 20 parts of acetate of lead, 10 parts of alcohol, and 11-1/2 of concentrated sulphuric acid; or 16 of the anhydrous acetate, 5 of the acid, and 4-1/2 of absolute alcohol; distilling the mixture in a glass retort into a very cold receiver, agitating along with weak potash lye the liquor which comes over, decanting the supernatant ether, and rectifying it by re-distillation over magnesia and ground charcoal.

Acetic ether is a colourless liquid of a fragrant smell and pungent taste, of spec. grav. 0·866 at 45° F., boiling at 166° F, burning with a yellowish flame, and disengaging fumes of acetic acid. It is soluble in 8 parts of water.

Acetic ether may be economically made with 3 parts of acetate of potash, 3 of very strong alcohol, and 2 of the strongest sulphuric acid, distilled together. The first product must be re-distilled along with one fifth of its weight of sulphuric acid; as much ether will be obtained as there was alcohol employed.

ETHIOPS, is the absurd name given by the alchemists to certain black metallic preparations. Martial ethiops was the black oxide of iron; mineral ethiops, the black sulphuret of mercury; and ethiops _per se_, the black oxide of mercury.

EVAPORATION, (Eng. and Fr.; _Abdampfen_; _Abdunsten_, Germ.) is the process by which any substance is converted into, and carried off in, vapour. Though ice, camphor, and many other solids evaporate readily in dry air, I shall consider, at present, merely the vaporization of water by heat artificially applied.

The vapour of water is an elastic fluid, whose tension and density depend upon the temperature of the water with which it is in contact. Thus the vapour rising from water heated to 165° F. possesses an elastic force capable of supporting a column of mercury 10·8 high; and its density is such that 80 cubic feet of such vapour contain one pound weight of water; whereas 32-1/2 cubic feet of steam of the density corresponding to a temperature of 212° and a pressure of 30 inches of mercury, weigh one pound. When the temperature of the water is given, the elasticity and specific gravity of the vapour emitted by it, may be found.

Since the vapour rises from the water only in virtue of the elasticity due to its gaseous nature, it is obvious that no more can be produced, unless what is already incumbent upon the liquid have its tension abated, or be withdrawn by some means. Suppose the temperature of the water to be midway between freezing and boiling, viz. 122° Fahr., as also that of the air in contact with it, to be the same but replete with moisture, so that its interstitial spaces are filled with vapour of corresponding elasticity and specific gravity with that given off by the water, it is certain that no fresh formation of vapour can take place in these circumstances. But the moment a portion of vapour is allowed to escape, or is drawn off by condensation to another vessel, an equivalent portion of vapour will be immediately exhaled from the water.

The pressure of the air and of other vapours upon the surface of water in an open vessel, does not prevent evaporation of the liquid; it merely retards its progress. Experience shows that the space filled with an elastic fluid, as air or other gaseous body, is capable of receiving as much aqueous vapour as if it were vacuous, only the repletion of that space with the vapour proceeds more slowly in the former predicament than in the latter, but in both cases it arrives eventually at the same pitch. Dr. Dalton has very ingeniously proved, that the particles of aeriform bodies present no permanent obstacle to the introduction of a gaseous atmosphere of another kind among them, but merely obstruct its diffusion momentarily, as if by a species of friction. Hence, exhalation at atmospheric temperatures is promoted by the mechanical diffusion of the vapours through the air with ventilating fans or chimney draughts; though under brisk ebullition, the force of the steam readily overcomes that mechanical obstruction.

The quantities of water evaporated under different temperatures in like times, are proportional to the elasticities of the steam corresponding to these temperatures. A vessel of boiling water exposing a square foot of surface to the fire, evaporates 725 grains in the minute; the elasticity of the vapour is equivalent to 30 inches of mercury. To find the quantity that would be evaporated from the same surface per minute at a heat of 88° F. At this temperature the steam incumbent upon water is capable of supporting 1·28 inch of mercury; whence the rule of proportion is 30 : 1·28 ∷ 725 : 30·93; showing that about 31 grains of water would be evaporated in the minute. If the air contains already some aqueous vapour, as it commonly does, then the quantity of evaporation will be proportional to the difference between the elastic force of that vapour, and what rises from the water.

Suppose the air to be in the hygrometric state denoted by 0·38 of an inch of mercury, then the above formula will become: 30 : 1·28 - 0·38 ∷ 725 : 21·41; showing that not more than 21-1/2 grains would be evaporated per minute under these circumstances.

The elastic tension of the atmospheric vapour is readily ascertained by the old experiment of Le Roi, which consists in filling a glass cylinder (a narrow tumbler for example) with cool spring water, and noting its temperature at the instant it becomes so warm that dew ceases to be deposited upon it. This temperature is that which corresponds to the elastic tension of the atmospheric vapour. See VAPOUR, Table of.

Whenever the elasticity of the vapour, corresponding to the temperature of the water, is greater than the atmospheric pressure, the evaporation will take place not only from its surface, but from every point in its interior; the liquid particles throughout the mass assuming the gaseous form, as rapidly as they are actuated by the caloric, which subverts the hydrostatic equilibrium among them, to constitute the phenomena of ebullition. This turbulent vaporization takes place at any temperature, even down to the freezing point, provided the pneumatic pressure be removed from the liquid by the air pump, or any other means. Ebullition always accelerates evaporation, as it serves to carry off the aqueous particles not simply from the surface, but from the whole body of the water.

The vapours, exhaled from a liquid at any temperature, contain more heat than the fluid from which they spring; and they cease to form whenever the supply of heat into the liquid is stopped. Any volume of water requires for its conversion into vapour _five and a half times_ as much heat as is sufficient to heat it from the freezing to the boiling temperature. The heat, in the former case, seems to be absorbed, being inappreciable by the thermometer; for steam is no hotter than the boiling water from which it rises. It has been therefore called _latent heat_; in contradistinction to that perceived by the touch and measured by the thermometer, which is called _sensible heat_. The quantity of heat absorbed by one volume of water in its conversion into steam, is about 1000° Fahr.; it would be adequate to heat 1000 volumes of water, one degree of the same scale; or to raise one volume of boiling water, confined in a non-conducting vessel, to 1180°. Were the vessel charged with water so heated, opened, it would be instantaneously emptied by vaporization, since the whole caloric equivalent to its constitution as steam, is present. When, upon the other hand, steam is condensed by contact with cold substances, so much heat is set free as is capable of heating five and a half times its weight of water, from 32° to 212° F. If the supply of heat to a copper be uniform, five hours and a half will be required to drive off its water in steam, provided one hour was taken in heating the water, from the freezing to the boiling pitch, under the atmospherical pressure.

Equal weights of vapour of any temperature contain equal quantities of heat; for example, the vapour exhaled from one pound of water, at 77° F., absorbs during its formation, and will give out in its condensation, as much heat as the steam produced by one pound of water, at 212° F. The first portion of vapour with a tension = 30 inches, occupies a space of 27·31 cubic feet; the second, with a tension of 0·92 inch, occupies a space of 890 cubic feet.[29] Suppose that these 890 volumes were to be compressed into 27·31 in a cylinder capable of confining the heat, the temperature of the vapour would rise from 77° to 212°, in virtue of the condensation, as air becomes so hot by compression in a syringe, as to ignite _amadou_. The latent heat of steam at 212° F. is 1180° - 180 = 1000; that of vapour, at 77°, is 1180 - 45 = 1135°; so that, in fact, the lower the temperature at which the vapour is exhaled, the greater is its latent heat, as Joseph Black and James Watt long ago proved by experiments upon distillation and the steam engine.

[29] One pound avoirdupois of water contains 27·72 cubic inches; one
cubic inch of water forms 1696 cubic inches of steam at 212° F.:
therefore one pound of water will form 27·31 cubic feet of such steam:
and 0·92 : 30 ∷ 27·31 : 890 cubic feet.

From the preceding researches it follows, that evaporation may be effected upon two different plans:--

1. Under the ordinary pressure of the atmosphere; and that either,

A, by external application of heat to boilers, with _a_, an open fire; _b_, steam; _c_, hot liquid _media_.

B, by evaporation with air; _a_, at the ordinary temperature of the atmosphere; _b_, by currents of warm air.

2. Under progressively lower degrees of pressure than the atmospheric, down to evaporation in as perfect a vacuum as can be made.

It is generally affirmed, that a thick metallic boiler obstructs the passage of the heat through it so much more than a thin one, as to make a considerable difference in their relative powers of evaporating liquids. Many years ago, I made a series of experiments upon this subject. Two cylindrical copper pans, of equal dimensions, were provided; but the metal of the one was twelve times thicker than that of the other. Each being charged with an equal volume of water, and placed either upon the same hot plate of iron, or immersed, to a certain depth, in a hot solution of muriate of lime, I found that the ebullition was greatly more vigorous in the thick than in the thin vessel, which I ascribed to the conducting substance up the sides, above the contact of the source of heat, being 12 times greater in the former case than in the latter.

If the bottom of a pan, and the portions of the sides, immersed in a hot fluid medium, solution of caustic potash or muriate of lime, for example, be corrugated, so as to contain a double expanse of metallic surface, that pan will evaporate exactly double the quantity of water, in a given time, which a like pan, with smooth bottom and sides, will do immersed equally deep in the same bath. If the corrugations contain three times the quantity of metallic surface, the evaporation will be threefold in the above circumstances. But if the pan, with the same corrugated bottom and sides, be set over a fire, or in an oblong flue, so that the current of flame may sweep along the corrugations, it will evaporate no more water from its interior than a smooth pan of like shape and dimensions placed alongside in the same flue, or over the same fire. This curious fact I have verified upon models constructed with many modifications. Among others, I caused a cylindrical pan, 10 inches diameter, and 6 inches deep, to be made of tin-plate, with a vertical plate soldered across its diameter; dividing it into two equal semi-cylindrical compartments. One of these was smooth at the bottom, the other corrugated; the former afforded as rapid an evaporation over the naked fire as the latter, but it was far outstripped by its neighbour when plunged into the heated liquid medium.

If a shallow pan of extensive surface be heated by a subjacent fire, by a liquid medium, or a series of steam pipes upon its bottom; it will give off less vapour in the same time when it is left open, than when partially covered. In the former case, the cool incumbent air precipitates by condensation a portion of the steam, and also opposes considerable mechanical resistance to the diffusion of the vaporous particles. In the latter case, as the steam issues with concentrated force and velocity from the contracted orifice, the air must offer less proportional resistance, upon the known hydrostatic principle of the pressure being as the areas of the respective bases, in communicating vessels.

In evaporating by surfaces heated with ordinary steam, it must be borne in mind that a surface of 10 square feet will evaporate fully one pound of water per minute, or 725 × 10 = 7250 gr., the same as over a naked fire; consequently the condensing surface must be equally extensive. Suppose that the vessel is to receive of water 2500 libs, which corresponds to a boiler 5 feet long, 4 broad, and 2 deep, being 40 cubic feet by measure, and let there be laid over the bottom of this vessel 8 connected tubes, each 5 inches in diameter and 5 feet long, possessing therefore a surface of 5 feet square. If charged with steam, they will cause the evaporation of half a pound of water per minute. The boiler to supply the steam for this purpose must expose a surface of 5 square feet to the fire. It has been proved experimentally that 10 square feet surface of thin copper can condense 3 libs of steam per minute, with a difference of temperature of 90 degrees Fahr. In the above example, 10 square feet evaporate 1 lib. of water per minute; the temperature of the evaporating fluid being 212° F., consequently 3 : 1 ∷ 90 : 90/3. During this evaporation the difference of the temperature is therefore = 30°. Consequently the heat of the steam placed in connection with the interior of the boiler, to produce the calculated evaporation should be, 212 + 30 = 242°, corresponding to an elastic force of 53·6 inches of mercury. Were the temperature of the steam only 224, the same boiler in the same time would produce a diminished quantity of steam, in the proportion of 12 to 30; or to produce the same quantity the boiler or tubular surface should be enlarged in the proportion of 30 to 12. In general, however, steam boilers employed for this mode of evaporation are of such capacity as to give an unfailing supply of steam.

I shall now illustrate by some peculiar forms of apparatus, different systems of evaporation. _Fig._ 381. explains the principles of evaporating in vacuo. A B represents a pan or kettle charged with the liquor to be evaporated. The somewhat wide orifice _c_, secured with a screw-plug, serves to admit the hand for the purpose of cleaning it thoroughly out when the operation is finished; _h_ is the pipe of communication with the steam boiler; _b_ is a tube prolonged and then bent down with its end plunged into the liquor to be evaporated, contained in the charging back, (not shown in the figure). H is a glass tube communicating with the vacuum pan at the top and bottom, to shew by the height of the column the quantity of liquid within. The eduction evaporating pipe C is provided with a stop-cock to cut off the communication when required. _i_ is a tube for the discharge of the air and the water from the steam-case or jacket; the refrigerator E is best formed of thin copper tubes about 1 inch in diameter, arranged zig-zag or spirally like the worm of a still in a cylinder. The small air-tight condenser F, connected with the efflux pipe _f_ of the refrigerator, is furnished below with a discharge cock _g_, and surrounded by a cooling case, for the collection of the water condensed by the refrigerator. In its upper part there is a tube _k_, also furnished with a cock, which communicates with the steam boiler, and through which the pan A B is heated.

The operation of this apparatus is as follows: after opening the cocks C, _f_, _g_, and before admitting the cold water into the condenser E, the cock of the pipe _k_ is opened, in order that by injecting steam it may expel the included air; after which the cocks _k_ and _g_ are to be shut. The water must now be introduced into the condenser, and the cock _b_ opened, whereon the liquid to be evaporated rises from the charging back, through the tube _b_, and replenishes the vacuum pan to the proper height, as shown by the register glass tube H. Whenever the desired evaporation or concentration is effected, the cock C must be closed, the pipe _k_ opened, so as to fill the pan with steam, and then the efflux cock _a_ is opened to discharge the residuary liquor. By shutting the cocks _a_ and _k_, and opening the cock _b_, the pan will charge itself afresh with liquor, and the operation will be begun anew, after _b_ has been shut and C opened.

The contents of the close water cistern F, may be drawn off during each operation. For this purpose, the cock _f_ must first be shut, the cold water is to be then run out of the condenser G, and _k_ and _g_ are to be opened. The steam entering by _k_ makes the water flow, but whenever the steam itself issues from the cock _g_, this orifice must be immediately shut, the cock _f_ opened, and the cold water again introduced, whereupon the condensed water that had meanwhile collected in the under part of the refrigerator, flows off into the condenser vessel F. Since some air always enters with the liquor sucked into the pan, it must be removed at the time of drawing off the water from the two condensers, by driving steam through the apparatus. This necessity will be less urgent if the liquor be made to boil before being introduced into the vacuum pan.

Such an apparatus may be modified in size and arrangement to suit the peculiar object in view, when it will be perfectly adapted for the concentration of extracts of every kind, as well as saline solutions containing vegetable acids or alkalis. The interior vessel of A B should be made of tinned or plated copper. For an account of Howard’s vacuum pan, made upon the same principle, see SUGAR.

When a boiler is set over a fire, its bottom should not be placed too near the grate, lest it refrigerate the flame, and prevent that vivid combustion of the fuel essential to the maximum production of heat by its means. The evil influence of leaving too little room between the grate and the copper may be illustrated by a very simple experiment. If a small copper or porcelain capsule containing water be held over the flame of a candle a little way above its apex, the flame will suffer no abatement of brightness or size, but will continue to keep the water briskly boiling. If the capsule be now lowered into the middle of the flame, this will immediately lose its brightness, becoming dull and smoky covering the bottom of the capsule with soot; and, owing to the imperfect combustion, though the water is now surrounded by the flame, its ebullition will cease.

_Fig._ 382. is a section of two evaporating coppers _en suite_, so mounted as to favour the full combustion of the fuel. A is the hearth, in which wood or coal may be burned. For coal, the grate should be set higher and be somewhat smaller, _a_ is the door for feeding the fire; _d_, an arch of fire-bricks over the hearth; _c_, a grate through which the ashes fall into the pit beneath, capable of being closed in front to any extent by a sliding door _b_. B and C are two coppers encased in brickwork; _f_ the flue. At the end of the hearth near _m_, where the fire plays first upon the copper, the sole is made somewhat lower and wider, to promote the spreading of the flame under the vessel. The second copper, C, receives the benefit of the waste heat; it may be placed upon a higher level, so as to discharge its concentrated liquor by a stop-cock or syphon into the first. When coals are burned for heating such boilers, the grate should be constructed as shown in the figure of the brewing copper, page 116.

_Fig._ 383. represents a pan for evaporating liquids, which are apt, during concentration, to let fall crystals or other sediment. These would be injured either by the fire playing upon the bottom of the pan, or, by adhesion to it, they would allow the metal to get red hot, and in that state run every risk of being burnt or rent on the sudden intrusion of a little liquor through the incrustation. When large coppers have their bottoms planted in loam, so that the flame circulates in flues round their sides, they are said to be _cold-set_.

A is a pear-shaped pan, charged with the liquid to be evaporated; it is furnished with a dome cover, in which there is an opening with a flange _f_, for attaching a tube, to conduct the steam wherever it may be required. _a_ is the fire-place; _b_, the ash-pit. The conical part terminates below in the tube _g_, furnished with a stop-cock at its nozzle _h_. Through the tube _c d c´_, furnished above and below with the stop-cocks _c_ and _c´_, the liquid is run from the charging back or reservoir. During the operation, the upper cock _c_ is kept partially open, to replace the fluid as it evaporates; but the under cock _c´_ is shut. The flame from the fire-place plays round the kettle in the space _e_, and the smoke escapes downwards through the flue _i_ into the chimney. The lower cylindrical part _g_, remains thus comparatively cool, and collects the crystalline or other solid matter. After some time, the under stop-cock _c´_, upon the supply-pipe, is to be opened to admit some of the cold liquor into the cylindrical neck. That cock being again shut, the sediment settled, and the large stop-cock (a horizontal slide-valve would be preferable) _h_ opened, the crystals are suffered to descend into the subjacent receiver; after which the stop-cock _h_ is shut, and the operation is continued. A construction upon this principle is well adapted for heating dyeing coppers, in which the sediment should not be disturbed, or exposed to the action of the fire. The fire-place should be built as for the brewing copper.

_Fig._ 384. represents an oblong evaporating pan, in which the flame, after beating along its bottom, turns up at its further end, plays back along its surface, and passes off into the chimney. A is a rectangular vessel, from 10 to 15 feet long, 4 to 6 feet broad, and 1 or 1-1/2 feet deep. The fire-bricks, upon which the pan rests, are so arranged as to distribute the flame equably along its bottom.

EUDIOMETER, is the name of any apparatus subservient to the chemical examination of the atmospheric air. It means a _measure of purity_, but it is employed merely to determine the proportion of oxygen which it may contain. The explosive eudiometer, in which about two measures of hydrogen are introduced into a graduated glass tube, containing five measures of atmospheric air, and an electric spark is passed across the mixture, is the best of all eudiometers; and of these the syphon form, proposed by me in a paper published by the Royal Society of Edinburgh in 1819, is probably the surest and most convenient. Volta’s explosive eudiometer as made in Paris, costs 3 guineas; mine may be had nicely graduated for 6 or 8 shillings.

EXPANSION (Eng. and Fr.; _Ausdehnung_, Germ.), is the increase of bulk experienced by all bodies when heated, unless a change of chemical texture takes place, as in the case of clays in the potter’s kiln. Table I. exhibits the linear expansion of several solids by an increase of temperature from 32° to 212° Fahr.; Table II. exhibits the expansion in bulk of certain liquids.

TABLE I.--_Linear Dilatation of Solids by Heat._

Dimensions which a bar takes at 212°, whose length at 32° is 1·000000.

+--------------------+-----------------------+-----------+----------+
| | |Dilatation |Dilatation|
| Substances. | Authority. | in | in Vulgar|
| | |Decimals. |Fractions.|
+--------------------+-----------------------+-----------+----------+
|Glass tube, |Smeaton, |1·00083333 | |
| do. |Roy, |1·00077615 | |
| do. |Deluc’s mean, |1·00082800 | 1/1116 |
| do. |Dulong and Petit, |1·00086130 | 1/1148 |
| do. |Lavoisier and Laplace, |1·00081166 | 1/1122 |
|Plate glass, | do. do. |1·000890890| 1/1142 |
| do. crown glass,| do. do. |1·00087572 | 1/1114 |
| do. do. | do. do. |1·00089760 | 1/1090 |
| do. do. | do. do. |1·00091751 | |
| do. rod, |Roy, |1·00080787 | |
|Deal, |Roy, as glass, | -- | |
|Platina, |Borda, |1·00085655 | |
| do. |Dulong and Petit, |1·00088420 | 1/1131 |
| do. |Troughton, |1·00099180 | |
| do. and glass, |Berthoud, |1·00110000 | |
|Palladium, |Wollaston, |1·00100000 | |
|Antimony, |Smeaton, |1·00108300 | |
|Cast-iron prism, |Roy, |1·00110940 | |
|Cast-iron, |Lavoisier, by Dr Young |1·00111111 | |
|Steel, |Troughton, |1·00118990 | |
|Steel rod, |Roy, |1·00114470 | |
|Blistered Steel, |Phil. Trans. 1795, 428,|1·00112500 | |
| do. |Smeaton, |1·00115000 | |
|Steel not tempered, |Lavoisier and Laplace, |1·00107875 | 1/927 |
| do. do. do. | do. do. |1·00107956 | 1/926 |
| do. tempered yel- | | | |
| low,| do. do. |1·00136900 | |
| do. do. do. | do. do. |1·00138600 | |
| do. do. do. | | | |
| at a higher heat,| do. do. |1·00123956 | 1/807 |
|Steel, |Troughton, |1·00118980 | |
|Hard Steel, |Smeaton, |1·00122500 | |
|Annealed steel, |Muschenbroek, |1·00122000 | |
|Tempered steel, | do. |1·00137000 | |
|Iron, |Borda, |1·00115600 | |
| do. |Smeaton, |1·00125800 | |
|Soft iron, forged, |Lavoisier and Laplace, |1·00122045 | |
|Round iron, wire | | | |
| drawn,| do. do. |1·00123504 | |
|Iron wire, |Troughton, |1·00144010 | |
|Iron, |Dulong and Petit, |1·00118203 | 1/846 |
|Bismuth, |Smeaton, |1·00139200 | |
|Annealed gold, |Muschenbroek, |1·00146000 | |
|Gold, |Ellicot, by comparison,|1·00150000 | |
| do. procured by | | | |
| parting, |Lavoisier and Laplace, |1·00146606 | 1/682 |
| do. Paris stan-| | | |
| dard, unannealed,| do. do. |1·00155155 | 1/645 |
| do. do. | | | |
| annealed,| do. do. |1·00151361 | 1/661 |
|Copper, |Muschenbroek, |1·0019100 | |
| do. |Lavoisier and Laplace, |1·00172244 | 1/581 |
| do. | do. do. |1·00171222 | 1/584 |
| do. |Troughton, |1·00191880 | |
| do. |Dulong and Petit, |1·00171821 | 1/582 |
|Brass, |Borda, |1·00178300 | |
| do. |Lavoisier and Laplace, |1·00186671 | |
| do. | do. do. |1·00188971 | |
|Brass scale, sup- | | | |
| posed from Hamburg,|Roy, |1·00185540 | |
|Cast brass, |Smeaton, |1·00187500 | |
|English plate-brass,| | | |
| in rod,|Roy, |1·00189280 | |
| do. do. in a | | | |
| trough form,| do. |1·00189490 | |
|Brass, |Troughton, |1·00191880 | |
|Brass wire, |Smeaton, |1·00193000 | |
|Brass, |Muschenbroek, |1·00216000 | |
|Copper 8, tin 1, |Smeaton, |1·00181700 | |
|Silver, |Herbert, |1·00189000 | |
| do. |Ellicot, by comparison,|1·0021000 | |
| do. |Muschenbroek, |1·00212000 | |
| do. of cupel, |Lavoisier and Laplace, |1·00190974 | 1/524 |
| do. Paris stan- | | | |
| dard,| do. do. |1·00190868 | 1/524 |
|Silver, |Troughton, |1·0020826 | |
|Brass 16, tin 1, |Smeaton, |1·00190800 | |
|Speculum metal, | do. |1·00193300 | |
|Spelter solder; | | | |
| brass 2, zinc 1,| do. |1·00205800 | |
|Malacca tin, |Lavoisier and Laplace, |1·00193765 | 1/516 |
|Tin from Falmouth, | do. do. |1·00217298 | 1/462 |
|Fine pewter, |Smeaton, |1·00228300 | |
|Grain tin, |do. |1·00248300 | |
|Tin, |Muschenbroek, |1·00284000 | |
|Soft solder; lead 2,| | | |
| tin 1,|Smeaton, |1·00250800 | |
|Zinc 8, tin 1, a | | | |
| little hammered,| do. |1·00269200 | |
|Lead. |Lavoisier and Laplace, |1·00284836 | 1/351 |
| do. |Smeaton, |1·00286700 | |
|Zinc, | do. |1·00294200 | |
|Zinc, hammered out | | | |
| 1/2 inch per foot,| do. |1·00301100 | |
|Glass, from 32°, to | | | |
| 212°,|Dulong and Petit, |1·00086130 | 1/1161 |
| do. from 212°, to | | | |
| 392°,| do. do. |1·00091827 | 1/1089 |
| do. from 392°, to | | | |
| 572°,| do. do. |1·00101114 | 1/987 |
+--------------------+-----------------------+-----------+----------+

The last two measurements by an air thermometer.

TABLE II.

_Expansion of certain Liquids by being Heated from 32° to 212°._

+----------------------------+-----------------+----------+----------+
| | |Expansion |Expansion |
| Substances. | Authority. | in |in Vulgar |
| | |Decimals. |Fractions.|
+----------------------------+-----------------+----------+----------+
|Mercury, |Dulong and Petit.|0·01801800| 1/55·5 |
|do. in glass, | do. do. |0·01543200| 1/65 |
|Water, from its maximum | | | |
|density, |Kirwan. |0·04332 | 1/23 |
|Muriatic acid (sp. gr. | | | |
|1·137), |Dalton. |0·0600 | 1/17 |
|Nitric acid (sp. gr. 1·40), | do. |0·1100 | 1/9 |
|Sulphuric acid (sp. gr. | | | |
|1·85), | do. |0·0600 | 1/17 |
|Alcohol (to its boiling | | | |
|point)? | do. |0·1100 | 1/9 |
|Water, | do. |0·0460 | 1/22 |
|Water, saturated with common| | | |
|salt, | do. |0·0500 | 1/20 |
|Sulphuric ether (to its | | | |
|boiling point)? | do. |0·0700 | 1/14 |
|Fixed oils, | do. |0·0800 | 1/12·5 |
|Oil of turpentine, | do. |0·0700 | 1/14 |
+----------------------------+-----------------+----------+----------+

If the density of water at 39° be called 1·00000,
at 212° it becomes 0·9548,
and its volume has increased to 1·04734;
at 77° it becomes 0·9973587,
and its volume has increased to only 1·00265,
which, though one fourth of the whole range of temperature,
is only 1/18 of the total expansion.
Water at 60° F. has a specific gravity of 0·9991953,
and has increased in volume from 39° to 1·00008,
which is only about 1/58 of the total expansion to 212°, with 1/64 of
the total range of temperature.

All gases expand the same quantity by the same increase of temperature, which from 32° to 212° Fahr. = 180°/480 = 3/8, or 100 volumes become 137·5. For each degree of Fahr. the expansion is 1/480.

When dry air is saturated with moisture, its bulk increases, and its specific gravity diminishes, because aqueous vapour is less dense than air, at like temperatures.

The following Table gives the multipliers to be employed for converting one volume of moist gas at the several temperatures, into a volume of dry gas.

+------------+-----------+
|Temperature.|Multiplier.|
+------------+-----------+
| 53° F. | 0·9870 |
| 54 | 0·9864 |
| 55 | 0·9858 |
| 56 | 0·9852 |
| 57 | 0·9846 |
| 58 | 0·9839 |
| 59 | 0·9833 |
| 60 | 0·9827 |
| 61 | 0·9820 |
| 62 | 0·9813 |
| 63 | 0·9806 |
| 64 | 0·9799 |
| 65 | 0·9793 |
| 66 | 0·9786 |
| 67 | 0·9779 |
| 68 | 0·9772 |
| 69 | 0·9765 |
| 70 | 0·9758 |
| 71 | 0·9751 |
| 72 | 0·9743 |
| 73 | 0·9735 |
+------------+-----------+

EXTRACTS. (_Extraits_, Fr.; _Extracten_, Germ.) The older apothecaries used this term to designate the product of the evaporation of any vegetable juice, infusion, or decoction; whether the latter two were made with water, alcohol, or ether; whence arose the distinction of aqueous, alcoholic, and ethereous extracts.

Fourcroy made many researches upon these preparations, and supposed that they had all a common basis, which he called the _extractive_ principle. But Chevreul and other chemists have since proved that this pretended principle is a heterogeneous and very variable compound. By the term _extract_ therefore is now meant merely the whole of the soluble matters obtained from vegetables, reduced by careful evaporation to either a pasty or solid consistence. The watery extracts, which are those most commonly made, are as various as the vegetables which yield them; some containing chiefly sugar or gum in great abundance, and are therefore innocent or inert; while others contain very energetic impregnations. The conduct of the evaporating heat is the capital point in the preparation of extracts. They should be always prepared if possible from the juice of the fresh plant, by subjecting its leaves or other succulent part, to the action of a powerful screw or hydraulic press; and the evaporation should be effected by the warmth of a water bath, heated not beyond 100° or 120° F. Steam heat may perhaps be applied advantageously in some cases, where it is not likely to decompose any of the principles of the plant. But by far the best process for making extracts is in vacuo, upon the principles explained in the article EVAPORATION. It is much easier to fit up a proper apparatus of this kind, than most practical men imagine. The vacuum may either be made through the agency of steam, as there pointed out, or by means of an air-pump. One powerful air-pump may form and maintain a good vacuum under several receivers, placed upon the flat-ground flanges of so many basins, each provided with a stop-cock at its side for exhaustion. The air-less basin containing the juice being set on the shelf of a water-bath, and exposed to a proper temperature, will furnish in a short time, a large quantity of medicinal extract, possessing the properties of the plant unimpaired.

For exceedingly delicate purposes, the concentration may be performed in the cold, by placing saucers filled with the expressed juice over a basin containing sulphuric acid, putting a glass receiver over them, and exhausting its air.

F.

FAHLERZ. Gray copper-ore, called also Panabase, from the many oxides it contains.

FAINTS, is the name of the impure spirit, which comes over first and last in the distillation of whiskey; the former being called the _strong_, and the latter, which is much more abundant, the _weak_ faints. This crude spirit is much impregnated with fetid essential oil, is therefore very unwholesome, and must be purified by rectification.

FAN (_Eventail_, Fr.; _Fächer_, Germ.); is usually a semi-circular piece of silk or paper, pasted double, enclosing slender slips of wood, ivory, tortoise-shell, whale-bone, &c., arranged like the tail of a peacock in a radiating form, and susceptible of being folded together, and expanded at pleasure. This well-known hand ornament is used by ladies to cool their faces by agitating the air. Fans made of feathers, like the wing of a bird, have been employed from time immemorial by the natives of tropical countries.

_Fan_ is also the name of the apparatus for winnowing corn. For an account of the powerful blowing and ventilating fan machine, see FOUNDRY and VENTILATOR.

FARINA (_Farine_, Fr.; _Mehl_, Germ.); is the flour of any species of corn, or starchy root, such as potato, arrow root, &c. See BREAD and STARCH.

FATS, (_Graisses_, Fr.; _Fette_, Germ.) occur in a great number of the animal tissues, being abundant under the skin in what is called the cellular membrane, round the kidneys, in the folds of the omentum, at the base of the heart, in the mediastinum, the mesenteric web, as well as upon the surface of the intestines, and among many of the muscles. They vary in consistence, colour, and smell, according to the animals from which they are obtained; thus, they are generally fluid in the cetaceous tribes, soft and rank-flavoured in the carnivorous, solid and nearly scentless in the ruminants, usually white and copious in well-fed young animals; yellowish and more scanty in the old. Their consistence varies also according to the organ of their production; being firmer under the skin, and in the neighbourhood of the kidneys, than among the movable viscera. Fat forms about one twentieth of the weight of a healthy animal. But as taken out by the butcher it is not pure, for being of a vesicular structure it is always enclosed in membranes, mixed with blood, blood-vessels, lymphatics, &c. These foreign matters must first be separated in some measure mechanically, after the fat is minced small, and then more completely by melting it along with hot water, passing it through a sieve, and letting the whole cool very slowly. By this means a cake of cleansed fat will be obtained. Many plans of purifying fats have been proposed; one of the best is to mix two per cent. of strong sulphuric acid with a quantity of water, in which the tallow is heated for some time with much stirring; to allow the materials to cool, to take off the supernatant fat, and re-melt it with abundance of hot water. More tallow will thus be obtained, and that considerably whiter and harder than is usually procured by the melters.

I have found that chlorine, and chloride of lime do not improve, but rather deteriorate the appearance of oils and other fatty bodies. According to Appert, minced suet subjected to the action of high-pressure steam in a digester, at 250° or 260° F., becomes so hard as to be sonorous when struck, whiter, and capable when made into candles, of giving a superior light. A convenient mode of _rendering_ minced tallow, or melting it, is to put it in a tub, and drive steam through it from numerous orifices in ramifying pipes placed near the bottom. Mr. Watt assures me that his plan of purifying fats, patented in March 1836, has been quite successful. He employs dilute sulphuric acid, to which he adds a little nitric acid, with a very small quantity of bichromate of potash, “to supply oxygen;” and some oxalic acid. These are mixed with the fat in the steaming tub. When the lumps of it are nearly dissolved, he takes for every ton of fat, one pound of strong nitric acid, diluted with one quart of water; to which he adds two ounces of alcohol, naphta, sulphuric ether, or spirits of turpentine; and after introducing this mixture, he continues the boiling for half an hour. The fat is finally washed.--As I do not comprehend the _modus operandi_ of these ingredients, I shall abstain from any comment upon the recipe.

Others have proposed to use vegetable or animal charcoal first, especially for rancid oils, then to heat them with a solution of sulphate of copper and common salt, which is supposed to precipitate the fetid albuminous matter. Milk of lime has been also prescribed; but it is I believe always detrimental.

Davidson treats whale oil with infusion of tan, in order to separate the gelatine and albumine in flocks; next with water and chloride of lime, to destroy the smell; and lastly, with dilute sulphuric acid, to precipitate all the lime in the state of a sulphate. This is certainly one of the cheapest and most effective methods of purifying that substance.

Braconnot and Raspail have shown that solid animal fats are composed of very small, microscopic, partly polygonal, partly reniform particles, which are connected together by very thin membranes. These may be ruptured by mechanical means, then separated by triturating the fresh fats with cold water, and passing the unctuous matter through a sieve. The particles float in the water, but eventually collect in a white granular crystalline appearance, like starch. Each of them consists of a vesicular integument, of the nature of stearine, and an interior fluid like elaine, which afterwards exudes. The granules float in the water, but subside in spirits of wine. When digested in strong alcohol, the liquid part dissolves, but the solid remains. These particles differ in shape and size, as obtained from different animals; those of the calf, ox, sheep, are polygonal, from 1/50 to 1/350 of an inch in diameter; those of the sow are kidney-shaped, and from 1/50 to 1/100; those of man are polygonal, and from 1/50 to 1/600; those of insects are spherical, and at most 1/500 of an inch.

Fats all melt at a temperature much under 212° F. When strongly heated with contact of air, they diffuse white pungent fumes, then blacken, and take fire. When subjected to distillation, they afford a changed fluid oil, carburetted hydrogen, and the other products of oily bodies. Exposed for a certain time to the atmosphere, they become rancid, and generate the same fat acids as they do by saponification. In their fresh state they are all composed principally of stearine, margarine, and oleine, with a little colouring and odorous matter; and, in some species, hircine, from the goat; phocenine, from the dolphin; and butyrine, from butter. By subjecting them to a great degree of cold, and compressing them between folds of blotting paper, a residuum is obtained, consisting chiefly of stearine and margarine; the latter of which may be dissolved out by oil of turpentine.

_Beef and Mutton Suet._--When fresh, this is an insipid, nearly inodorous fat, of a firm consistence, almost insoluble in alcohol, entirely so if taken from the kidneys and mesenteric web of the ox, the sheep, the goat, and the stag. It varies in its whiteness, consistence, and combustibility, with the species and health of the animals. That of the sheep is very white, and very solid. They may all be purified in the manner above described. Strong sulphuric acid develops readily the acid fats by stirring it through melted suet. Alkalis, by saponification, give rise at once to the three acids,--the stearic, margaric, and oleic. Beef suet consists of stearine, margarine, and oleine; mutton and goat suet contain a little hircine. The specific gravity of the tallow, of which common candles are made is, by my experiments, 0·936. The melting point of suet is from 98° to 104° F. The proportion of solid and fluid fat in it is somewhat variable, but the former is in much larger proportion. Mutton suet is soluble in 44 parts of boiling alcohol, of 0·820; beef suet in 44 parts. Marrow fat consists of 76 of stearine, and 24 of oleine; it melts at 115° F.

_Hog’s-lard_ is soft, fusible at 81° F., convertible, by an alkaline solution, into a stearate, margarate, oleate, and glycerine. Its sp. grav. is 0·938, at 50° F; It consists of 62 of oleine, and 38 of stearine, in 100 parts.

_Goose-fat_, consists of 68 oleine and 32 stearine.

_Butter_, in summer, consists of 60 of oleine and 40 of stearine; in winter, of 35 of oleine, and 65 of stearine; the former substance being yellow and the latter white. It differs, however, as produced from the milk of different cows, and also according to their pasture.

The ultimate constituents of stearine, according to Chevreul are, 79 carbon; 11·7 hydrogen; and 9·3 oxygen, in 100 parts.

1,294,009 cwts. of the tallow imported in 1837, were retained for internal consumption. See MARGARINE, OLEINE, SOAP, STEARINE.

FAULTS (_Failles_, Fr.); in mining, are disturbances of the strata which interrupt the miner’s operations, and put him at _fault_, to discover where the vein of ore or bed of coal has been thrown by the convulsions of nature. Many examples of faults are exhibited under PITCOAL.

FEATHERS (_Plumes_, Fr.; _Federn_, Germ.), constitute the subject of the manufacture of the _Plumassier_, a name given by the French (and also the English) to the artisan who prepares the feathers of certain birds for ornaments to the toilette of ladies and for military men, and to him also who combines the feathers in various forms. We shall content ourselves with describing the method of preparing ostrich feathers, as most others are prepared in the same way.

Several qualities are distinguished in the feathers of the ostrich; those of the male, in particular, are whiter and more beautiful. Those upon the back and above the wings are preferred; next, those of the wings, and lastly, of the tail. The down is merely the feathers of the other parts of the body, which vary in length from 4 to 14 inches. This down is black in the males, and gray in the females. The finest white feathers of the female have always their ends a little grayish, which lessens their lustre, and lowers their price. These feathers are imported from Algiers, Tunis, Alexandria, Madagascar, and Senegal; this being the order of their value.

The _scouring process_ is thus performed:--4 ounces of white soap, cut small, are dissolved in 4 pounds of water, moderately hot, in a large basin; and the solution is made into a lather by beating with rods. Two bundles of the feathers, tied with packthread, are then introduced, and are rubbed well with the hands for five or six minutes. After this soaping they are washed in clear water, as hot as the hand can bear.

The whitening or bleaching is performed by three successive operations.

1. They are immersed in hot water mixed with Spanish white, and well agitated in it; after which they are washed in three waters in succession.

2. The feathers are azured in cold water containing a little indigo tied up in a fine cloth. They should be passed quickly through this bath.

3. They are sulphured in the same way as straw hats are (see SULPHURING); they are then dried by hanging upon cords, when they must be well shaken from time to time to open the fibres.