Зображення сторінки
PDF
ePub

colour blue, though it occurs also white and grey; some specimens are entirely blue, others are only spotted, striped, or flamed with it. Externally and internally its lustre is shining aud splendent, and completely pearly. It occurs in wedge-shaped concretions, which are often very promis. cuous, and then pass into large and coarse grained distinct concretions. It feels greasy; is easily frangible, and the specific gravity is from 3.5 to 3.6. It is infusible before the blow-pipe, and is found to consist of

[merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

It is peculiar to the primitive mountains, where it occurs imbedded in talc slate, and mica slate, accompanied with grenatite. It is found in many parts of Europe. It is reckoned the link which connects talc with actynolite and trenolite.

KYLLINGIA, in botany, a genus of the Triandria Monogynia class and order. Natural order of Gramina. Cyperoideæ, Jussieu. Essential character: ament ovate or oblong, imbricate; flowers with a bivalve calyx and corolla. There are seven species, natives of the East and West Indies.

L Ör 1, the eleventh letter and eighth 4 consonant of our alphabet. It is a semi-vowel, formed in the voice by intercepting the breath between the tip of the tongue and the fore-part of the palate, with the mouth open.

There is something of aspiration in its sound, and therefore the Welsh usually double it, or add an h to it; as in llan, or than, a temple.

In English words of one syllable, it is usually doubled at the end; as in all, wall, mill, &c. but in words of more syllables than one, it is only single at the end; as in fortel, proportional, &c. It may be placed after most of the consonants, as in blue, clear, flame, &c. but before none of them. As a numeral letter, L denotes 50; and with a dash over it, thus, L, 50,000.

LA, in music, the syllable by which Guido denotes the last sound of each hexachord if it begins in C, it answers to our A; if in G, to E; and if in F, to D.

LABDANUM, or LADANUM, is a resin obtained from the surface of the crystus creticus, a shrub which grows in Syria and the Grecian islands. It is collected while

L.

moist, by drawing over it a kind of rake, with thongs fixed to it, from which it is afterwards scraped. When it is very good it is black, soft, and has a fragrant odour and a bitterish taste. Water dissolves about. a twelfth part of it, and the matter taken up possesses gummy properties. When distilled with water, a small quantity of vola. tile oil arises. Alcohol may also be impreg nated with a taste and odour of labdanum.

LABATIA, in botany, a genus of the Tetrandria Monogynia class and order. Natural order of Guajacana, Jussieu. Essential character: calyx four-leaved, inferior; corolla subcampanulate, four-cleft, with two minute segments in the division of the corolla; capsule four-celled; seeds solitary. There are two species, viz. L. sessiliflora, which is a native of Hispaniola ; and L. guianensis is a tree exceeding forty feet in height, and three in diameter; the bark is of a russet colour; the wood is hard and white; the largest leaves are eight inches in length, and three in width; flowers axillary, or on the branches in pairs or threes, each on its pedicel; corolla greenish. It is called by the natives of Guiana, pourama pouteri,

LABEL, in heraldry, a fillet usually placed in the middle along the chief of the coat, without touching its extremities. Its breadth ought to be a ninth part of the chief. It is adorned with pendants; and when there are above three of these, the number must be specified in blazoning. This is a kind of addition to the arms of a second brother, to distinguish him from the first, and is esteemed the most honourable of all differences.

LABEL, in law, a narrow slip of parch. ment hanging from a deed, writ, or other writing, in order to hold the appending seal.

LABEL of a circumferentor, a long thin brass ruler, with a sight at one end, and a centre hole at the other; chiefly used with a tangent line, to take altitudes.

LABIAL letters, those pronounced chiefly by means of the lips. See LETTER.

LABIATED flowers, monopetalous flowers, consisting of a narrow tube, with a wide mouth, divided into two or more lips. See BOTANY.

LABORATORY. A laboratory properly fitted up with apparatus, is essentially necessary to a chemist whose objects lead him to make researches, experiments, and processes, upon all the different scales of operation. That great interest which the important science of chemistry has excited in all ranks of men, within the last thirty years, has rendered it easy to procure very complete sets of apparatus ; which at least in the metropolis may be collected in a short time, by those who like Boyle, Cavendish, Lavoisier, and other great men, are in possession of ample means. But on the other hand, it is proper to remark, that many of our greatest discoverers, such as Scheele, Priestley, Berthollet, Wollaston, Dalton, Crawford, and a numerous set of eminent men, have from choice, or from motives of prudence, made use of very simple, cheap, and small sized apparatus. It is undoubtedly true that many operations can only be performed upon a scale of considerable magnitude, and that many facts of great value display themselves upon the extensive theatre of nature or in large manufactories, which are either not seen, or require uncommon discernment to perceive them in the contracted space, and during the short time employed in the performance of a philosophical experiment. But it is no less true that experiments upon a small scale do likewise possess their exclusive advantages. During the fusion and

combination of substances, in the whole no larger than a pepper-corn before the blowpipe, the effects take place with rapidity, and many of them, such as the escape of gas by effervescence, the changes of colour, and transparency by differences in the heat applied, the manner of acquiring the solid state, &c. which cannot be seen in the furnace, are in the course of a few seconds remarked and ascertained. The saving of time is also an object of leading importance. The same considerations are likewise applicable to processes of fusion, or other applications of heat in a small vessel, such as a tobacco-pipe, placed in a common fire, urged by the bellows if necessary. Humid operations may also be very advantageously conducted by single drops of liquid, and small particles of solid bodies laid upon a glass plate, or in the metallic spoon, and the lamp for distillations, and other works even upon a scale of some magnitude, has long been a favourite instrument with chemists. These will come under our notice as we proceed.

Under our article CHEMISTRY we have given a concise sketch or enumeration of the practical treatment of bodies, which leads us to point out the instruments in this place.

For the mechanical division of bodies it is requisite the chemist should have the usual instruments for cutting, breaking, rasping, filing, or shaving. One or more mortars for pounding; the best are made of hard pottery. A stone and muller for a levigating. A pair of rollers for laminating metals. A forge for many, or most of the purposes in which the blast heat of a small fire is required; and various other tools and implements, not peculiar to chemistry.

Messrs. Aikin, in their Chemical Dictionary, give the following list of implements and materials; which, upon deliberate examination, we highly approve :

A gazometer, with the connecting tubes, blow pipe, &c.

A bladder, or silk bag, with stop cock, fitting the above.

A pneumatic water trough.

A copper still with worm tub, the still fitting into the top of the Black's furnace. A blow-pipe, with spoon, &c.

Lamps-an Argand, and others of common construction, for oil and alcohol. An apparatus for drying precipitates by steam.

Scales and weights.

Large and small iron stands for retorts, &c.

[ocr errors]

Mortars one of hard steel, one of bellmetal, and one or two of Wedgwood

ware.

A silver crucible and spatula.
A platina crucible and spatula.
A jointed iron tube for conveying gases.

The following articles in glass: Retorts of different sizes, plain and stoppered, and long necked for gases.

Receivers to fit the above, plain and stoppered, with or without an adopter.

Plain jars for gases, different sizes.
Lipped jars for mixtures, precipitates, &c.
A graduated eudiometer jar.

Bell receivers, two or three sizes.
Proof bottles.

Capsules, or small evaporating caps. Water glasses (such as are used at table)which are very convenient for gentle evaporations.

Florence flasks.

Matrasses-two

or three very small, and others of common size, round and flat bottomed.

Funnels-ribbed, and one plain with a very long neck for charging retorts.

Wine glasses-common or lipped. Watch glasses, for evaporating minute quantities at a very gentle heat. Common decanters.

A bottle for specific gravity of fluids. Phials of all sizes, plain,and with ground stoppers.

Plain glass tube of various thickness and bore, out of which may easily be made, Syphon tubes,

Bent tubes for gases,

Capillary tubes, for dropping liquids, and various other useful articles.

[blocks in formation]

A tube of safety, separate.

A barometer.

Ditto rods, for stirring corrosive fluids. Several stone-ware jars, with tin covers, for holding salts, &c.

Also the following sundries: Wire- different sizes and kinds, viz. iron, copper, brass, silver, and platina. Gold, silver, and brass leaf-tinfoil. Wooden tripod stands for receivers, &c. Fire tongs-various shapes. Steel spatula and pallet knives. Iron ladles.

Diamond for scratching glass.

Files-flat, three-cornered, and fat-tailed.
Hammers.

A vice and anvil.
Pincers.

Shears and scissars.
A magnet.
Sieves.

Filtering paper.

Corks.

Bladders-spirit varnish-sponge-tow -linen-flannel.

Windsor and common bricks-tiles-sand Lutes of various kinds.

For more extensive and delicate researches it is also necessary to have

A mercurial pneumatic trough.

A mercurial gazometer.

A burning lens of considerable power.
An electrical apparatus.

A Galvanic apparatus.
A detonating jar.

A glass or silver alembic.

The fuel to be employed has been already mentioned under that article, and a supply should be kept near at hand, broken down ready for use.

With regard to the different substances or re-agents to be kept, the chemist will, of course, wish to have a specimen of all the simple or individual substances, such as the acids, earths, metals, &c. but the sim

Thermometers-common, and with the ple and compound substances which are of

bulb naked, to dip into liquors.

The following in earthen-ware. Crucibles-Hessian, common, and black lead, of different sizes and shapes, with stands and covers.

[blocks in formation]

general use, ought also to stand on the shelves.

For many purposes the ordinary degree of purity in which these substances are obtained by the common processes are sufficient; so, for example, the small quantity of potash in common sulphuric acid, and of iron in common muriatic acid, seldom interferes with any of the uses to which those re-agents are applied; but it is also necessary frequently to have them in the utmost purity when employed as tests for delicate purposes. The chemist will therefore find it of advantage to reserve a

separate set of a few of the most necessary re-agents in their utmost purity, and if only employed when absolutely required, a very moderate quantity will suffice. In the subjoined list we have distinguished by the word pure those substances which require particular pains to be obtained absolutely pure. Mixtures of each of the stronger acids and water in two or three different and known proportions should also be kept. N. B. The letter D implies that the dry substance should be kept, and S, that it should be in solution.

[blocks in formation]
[merged small][ocr errors]
[blocks in formation]

gen gas.

Sulphate of Iron. D. and S.

Strontian. S.

Barytes. S.

gas.

saturated with nitrous

Lime. D. and S.

Alumina. S.

Oxymuriate of Potash. D.

Phosphate of Soda. D. and S.

Ammonia. D.

Acetite of Barytes. S.

Alumina. S.

[blocks in formation]
[blocks in formation]

Gold-leaf.

[blocks in formation]
[ocr errors]

Catechu. Isinglass.

Olive oil.

Linseed-oil, drying.
Oil of Turpentine.
Black flux.

Distilled water, in great plenty.

The most convenient arrangement for a laboratory where space is not wanted, seems to be that of two rooms, and a shed or apartment which can be thrown open to communicate with the air. The first may contain the books of register, of practical reference, together with the more delicate philosophical aud chemical instruments, products, and preparations. The second may be provided with the work-bench, hammers, anvil, vice, and other tools, and the different furnaces; and the shed may be devoted to experiments of danger, such as arise from explosions, noxious vapours, and the breaking of vessels. It will be most convenient that these should be upon the ground floor, to secure the advantage of a ready supply of water or fuel, and other articles of heavy consumption. The first of which articles may be largely wanted, in case of accidental combustion, as well as on common occasions. But it is likewise necessary that the place should be dry, in order that labels may be preserved, and other inconveniences avoided. This is the principal general argument, in favour of a laboratory above the ground floor.

It would carry as too far beyond the limits of our work if we were to give draw ings and descriptions of the great variety of vessels, furnaces, and apparatus, which have been contrived for general and particular purposes of chemistry; and many of the culinary and domestic vessels may also be applied in experimental chemistry. We shall therefore confine ourselves to a few of the most simple and useful.

In Plate Laboratory, fig. 1, represents a retort, a, and receiver, b. These vessels are used for distillation; The subject is put into the belly of the retort, a, and exposed to heat, and the volatile products pass over into the receiver, b, which may be kept cool by the application of wet cloths, or by immersion in cold water, or otherwise, if needful. The place of junction is secured either by fitting the necks together by grinding, or by means of a lute, which see farther on. At c, in the receiver, is a neck closed by a stopper. Receivers or retorts, with this additional neck, are said to be tubulated. Fig. 2, is an alembic, of which a is the body, b the head, and c the

neck. Generally speaking, this is not a very useful instrument. In large distillations an alembic or still is used, but the condensation is effected by a spiral pipe, called the worm, which passes through a tub of cold water. In the use of the alembic, fig. 2, the beak is inserted into a receiver. When the volatile product of a body exposed to be dried, or to undergo evaporation by heat, is not required to be preserved, the process is performed in an

open vessel.

The application of heat to vessels is made either by naked fire, or by the intervention of some heated substance, which is then called a bath, Chemical baths are made of sand, or of melted lead, or the fusible metal, or of brine, and very frequently of water. The evaporable liquids form a bath which cannot be heated beyond their respective boiling points; and the other baths, the most common of which is that of sand, are chiefly valuable for giving a regular heat without sudden changes,

This last purpose is effected likewise with glass vessels, by coating them with a lute,

A very great number of furnaces have been constructed for chemical and manufacturing purposes, for which we must necessarily refer to the extensive works appropriated to these objects, The operative chemist may have occasion for them of dif ferent sizes and figures. A great deal may be done with the common German stove, and with small furnaces made out of blacklead pots, But, in general, the philosophical chemist will be well accommodated with one good furnace, convertible to dif ferent uses; and out of many such we select that of Dr, Black, for its simplicity and efficacy, as described in his lectures.

Plate-iron is by far the best material for the outside of an experimental furnace: but, as its metal communicates heat very fast, this must be cut off by a proper lute lining. The Doctor so far succeeded in this respect, that his furnace, though only two inches thick in the middle, will not scorch paper applied to its outside, when it is melting iron within. He adopted the simplest rectilineal shapes, because workmen find great difficulty in executing curved and uncom mon forms; and not one of a score of them will do it with accuracy. Indeed, those highly praised forms seemed to him of very little importance in most cases.

The body, or fire-place, is the only part of this furnace that requires description; the ash pit, with its door and registers and

« НазадПродовжити »