Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 13

=LAC'TOSE.= See SUGAR OF MILK.

=LAC'TUCA.= (B. P.) _Syn._ LETTUCE. The leaves and flowering tops of the wild indigenous plant _Lactuca virosa_. They are sedative, narcotic, and powerfully diuretic; also mildly laxative and diaph.o.r.etic. Given in dropsy and visceral obstructions. See LETTUCE, EXTRACT OF.

=LACTUCA"RIUM.= _Syn._ LETTUCE OPIUM. THRIDACE; LACTUCARIUM (Ph. E. & D.). The insp.i.s.sated milky juice of the _Lactuca sativa_ (common garden lettuce), or the _Lactuca virosa_ (strong-scented wild lettuce), obtained, by incision, from the flowering stems, and dried in the air. The latter species yields by far the greatest quant.i.ty. M. Arnaud, of Nancy, adopts the following method of procuring this substance, which appears to be the most productive and simple of any yet published:--Before the development of the lateral branches, the stems of twelve plants are cut, one after another, a little below the commencement of these branches; returning to the first one, a milky exudation is found on the cut portion, and on that which remains fixed in the earth; this milky exudation is adroitly collected with the end of the finger (or with a bone knife), which is afterwards sc.r.a.ped on the edge of a small gla.s.s; the same operation is performed on twelve other heads, and so on; on the third day it is repeated on every portion of the plant remaining in the ground, a thin slice being first cut off the top; this is done every day until the root is reached. As soon as the lactucarium is collected it coagulates; the harvest of each day is divided into small pieces, which are placed on plates, very near each other, but without touching, and allowed to dry for two days, after which they are set aside in a bottle. In this way 15 or 20 times the ordinary product is obtained.

_Prop., &c._ Lactucarium is anodyne, hypnotic, antispasmodic, and sedative, allaying pain and diminishing the force of the circulation. It has been recommended in cases in which opium is inadmissible, and has been administered with advantage in chronic rheumatism, colic, diarrha, asthma, and troublesome cough of phthisis, the irritability and watchfulness in febrile disorders, &c.--_Dose_, 2 to 5 gr.; made into pills, lozenges, or tincture.

=LACTU'CIN.= _Syn._ LACTUCINUM, L. This is the active principle of lactucarium, and is found in the juice of several species of lettuce.

_Prep._ Exhaust lactucarium with hot rectified spirit, agitate the tincture with a little animal charcoal, filter, add a little milk of lime, and evaporate to dryness; digest the residuum in hot rectified spirit; filter, and evaporate by a gentle heat, so that crystals may form.

_Prop., &c._ A nearly colourless, odourless, fusible, neutral, bitter substance; sparingly soluble in cold water and in ether, but freely soluble in alcohol. It possesses feeble basic properties. Good lactucarium contains fully 20% of this substance.

=LAD'ANUM.= See LABDANUM.

=LAENNEC'S CONTRA-STIMULANT.= See DRAUGHT.

=LAKE=. _Syn._ LACCA, L. Animal or vegetable colouring matter, precipitated in combination with oxide of tin or alumina; usually the latter. The term was formerly restricted to red preparations of this kind, but is now indiscriminately applied to all compounds of alumina and colouring matter. The term 'LAKE,' when unqualified by an adjective, is, however, understood to apply exclusively to that prepared from cochineal.

_Prep._ Lakes are made--1. By adding a solution of alum, either alone or partly saturated with carbonate of pota.s.sa, to a filtered infusion or decoction of the colouring substance, and after agitation precipitating the mixture with a solution of carbonate of potash.--2. By precipitating a decoction or infusion of the colouring substance made with a weak alkaline lye, by adding a solution of alum.--3. By agitating recently precipitated alumina with a solution of the colouring matter, prepared as before, until the liquid is nearly decoloured, or the alumina acquires a sufficiently dark tint. The first method is usually employed for acidulous solutions of colouring matter, or for those whose tint is injured by alkalies; the second, for those that are brightened, or at least uninjured, by alkalies; the third, for those colouring matters that have a great affinity for gelatinous alumina, and readily combine with it by mere agitation. By attention to these general rules, lakes may be prepared from almost all animal and vegetable colouring substances that yield their colour to water, many of which will be found to possess great beauty and permanence.

The precise process adapted to each particular substance may be easily ascertained by taking a few drops of its infusion or decoction, and observing the effects of alkalies and acids on the colour. The quant.i.ty of alum or of alumina employed should be nearly sufficient to decolour the dye liquor; and the quant.i.ty of carbonate of pota.s.sa should be so proportioned to the alum as to exactly precipitate the alumina without leaving free or carbonated alkali in the liquid. The first portion of the precipitate has the deepest colour, and the shade gradually becomes paler as the operation proceeds. A beautiful 'tone' of violet, red, and even purple, may be communicated to the colouring matter of cochineal by the addition of perchloride of tin; the addition of a.r.s.eniate of pota.s.sa (neutral a.r.s.enical salt) in like manner gives shades which may be sought for in vain with alum or alumina. After the lake is precipitated, it must be carefully collected, washed with cold distilled water, or the purest rain water, until it ceases to give out colour, and then carefully dried in the shade. In this state it forms a soft velvety powder. That of the shops is generally made up into conical or pyramidal drops (drop lake), which is done by dropping the moist lake through a small funnel on a clean board or slab, and drying it by a gentle heat as before. A very little clear gum water is commonly added to the paste to give the drops consistence when dry.

=Lake, Blue.= _Syn._ LACCA CRULEA, L. Prepared from some of the blue-coloured flowers; fugitive. The name is also applied to lump archil (lacca crulea), to moist alumina coloured with indigo, and to mixed solutions of pearlash and prussiate of potash, precipitated with another solution of sulphate of iron and alum. These are permanent and beautiful, but are seldom used, in consequence of indigo and Prussian blue supplying all that is wanted in this cla.s.s of colours.

=Lake, Brazil-wood.= _Syn._ DROP LAKE; LACCA IN GLOBULIS, L. _Prep._ 1.

Take of ground Brazil-wood, 1 lb.; water, 4 galls.; digest for 24 hours, then boil for 30 or 40 minutes, and add of alum, 1-1/2 lb., dissolved in a little water; mix, decant, strain, and add of solution of tin, 1/2 lb.; again mix well and filter; to the clear liquid add, cautiously, a solution of salt of tartar or carbonate of soda, as long as a deep-coloured precipitate forms, carefully avoiding excess; collect, wash, dry, &c., as directed above.

_Obs._ The product is deep red. By collecting the precipitate in separate portions, lakes varying in richness and depth of colour may be obtained.

The first portion of the precipitated lake has the brightest colour. An excess of alkali turns it on the violet, and the addition of cream of tartar, on the brownish red. The tint turns more on the violet red when the solution of tin is omitted. Some persons use less, others more, alum.

2. Add washed and recently precipitated alumina to a strong and filtered decoction of Brazil wood. Inferior to the last.

=Lake, Carminated.= _Syn._ COCHINEAL LAKE, FLORENCE L., FLORENTINE L., PARIS L., VIENNA L.; LACCA FLORENTINA, L. _Prep._ 1. The residuum of the cochineal left in making carmine is boiled with repeated portions of water, until it is exhausted of colour; the resulting liquor is mixed with that decanted off the carmine, and at once filtered; some recently precipitated alumina is then added, and the whole gently heated, and well agitated for a short time; as soon as the alumina has absorbed sufficient colour, the mixture is allowed to settle, after which the clear portion is decanted, the lake collected on a filter, washed, and dried, as before.

The decanted liquor, if still coloured, is now treated with fresh alumina until exhausted, and thus a lake of a second quality is obtained. Very fine.

2. To the coloured liquor obtained from the carmine and cochineal as above, a solution of alum is added, the filtered liquor precipitated with a solution of carbonate of pota.s.sa, and the alum or alumina; this brightens the lake collected and treated as before. Scarcely so good as the last.

_Obs._ Some makers mix a little solution of tin with the coloured liquor before adding colour. The above lake is a good glazing colour with oil, but has little body. It may be made directly from a decoction of cochineal. (See _below_.)

=Lake, Cochineal.= _Prep._ 1. Cochineal (in coa.r.s.e powder), 1 oz.; water and rectified spirit, of each 2-1/2 oz.; digest for a week, filter, and precipitate the tincture with a few drops of solution of tin, added every two hours, until the whole of the colouring matter is thrown down; lastly, wash the precipitate in distilled water, and dry it. Very fine.

2. Digest powdered cochineal in ammonia water for a week, dilute the solution with a little water, and add the liquid to a solution of alum, as long as a precipitate falls, which is the lake. Equal to the last.

3. Coa.r.s.ely powdered cochineal, 1 lb.; water, 2 galls.; boil 1 hour, decant, strain, add a solution of salt of tartar, 1 lb., and precipitate with a solution of alum. By adding the alum first, and precipitating the lake with the alkali, the colour will be slightly varied. All the above are sold as CARMINATED or FLORENCE LAKE, to which they are often superior.

=Lake, Green.= Made by mixing blue and yellow lake together. Seldom kept in the shops, being generally prepared extemporaneously by the artist on his palette.

=Lake, Lac.= _Prep._ Boil fresh stick-lac in a solution of carbonate of soda, filter the solution, precipitate with a solution of alum, and proceed as before.

=Lake, Lichen.= See ORCEIN.

=Lake, Madder.= _Syn._ LACCA RUBIae, L. COLUMBINA, L. _Prep._ 1. (Sir H. C.

Inglefield.) Take of Dutch grappe or crop madder, 2 oz.; tie it in a cloth, beat it well in a pint of water in a stone mortar, and repeat the process with fresh water (about 5 pints) until it ceases to yield colour; next boil the mixed liquor in an earthen vessel, pour it into a large basin, and add of alum 1 oz., previously dissolved in boiling water, 1 pint; stir well, and while stirring, pour in gradually of a strong solution of carbonate of pota.s.sa ('oil of tartar'), 1-1/2 oz.; let the whole stand until cold, then pour off the supernatant yellow liquor, drain, agitate the residue with boiling water, 1 quart (in separate portions), decant, drain, and dry. _Product_, 1/2 oz. The Society of Arts voted their gold medal to the author of the above formula.

2. Add a little solution of acetate of lead to a decoction of madder, to throw down the brown colouring matter, filter, add a solution of tin or alum, precipitate with a solution of carbonate of soda or of pota.s.sa, and otherwise proceed as before.

3. (Ure.) Ground madder, 2 lbs.; water, 1 gall.; macerate with agitation for 10 minutes, strain off the water, and press the remainder quite dry; repeat the process a second and a third time; then add to the mixed liquors, alum 1/2 lb., dissolved in water, 3 quarts; and heat in a water bath for 3 or 4 hours, adding water as it evaporates; next filter, first through flannel, and, when sufficiently cold, through paper; then add a solution of carbonate of pota.s.sa as long as a precipitate falls, which must be washed until the water comes off colourless, and, lastly, dried.

If the alkali be added in 3 successive doses, 3 different lakes will be obtained, successively diminishing in beauty. See MADDER, MADDER, RED, &c.

=Lake, Or'ange.= _Prep._ Take of the best Spanish annotta, 4 oz.; pearlash, 3/4 lb.; water, 1 gall.; boil for half an hour, strain, precipitate with alum, 1 lb., dissolved in water, 1 gall., observing not to add the latter solution when it ceases to produce an effervescence or a precipitate; strain, and dry the sediment in small squares, lozenges, or drops. The addition of some solution of tin turns this lake on the LEMON YELLOW; acids redden it. See LAKE, YELLOW.

=Lake, Red.= _Prep._ Take of pearlash, 1 lb.; clean shreds of scarlet cloth, 3-1/2 lbs.; water, 5 galls.; boil till the cloth is decoloured, filter the decoction, and precipitate with a solution of alum, as before.

See the LAKES noticed above (Brazil-wood, Carminated, Cochineal, and Madder).

=Lake, Yellow.= _Prep._ 1. Boil French berries, quercitron bark, or turmeric, 1 lb., and salt of tartar, 1 oz., in water, 1 gall., until reduced to one half, then strain the decoction, and precipitate with a solution of alum.

2. Boil 1 lb. of the dye-stuff with alum, 1/2 lb.; water, 1 gall., as before, and precipitate the decoction with a solution of carbonate of potash. See LAKE, ORANGE (_above_).

=LAMB= in its general qualities closely resembles mutton, of which, indeed, it is merely a younger and more delicate kind. It is well adapted as an occasional article of food for the convalescent and dyspeptic; but it is unequal for frequent use, more especially for the healthy and robust, to the flesh of the adult animal.

=LAMBS, DISEASES OF.= Among other diseases, these animals are particularly p.r.o.ne to one affecting the lungs, in consequence of the existence of parasites (_Strongylus bronchialis_) in the air-pa.s.sages. See PARASITES.

=LAMP.= A contrivance for producing artificial light or heat by the combustion of inflammable liquids. The term 'lamp' is also applied to a portable gas-burner (GAS-LAMP), and to a tubular candle-holder, which, by the aid of a simple mechanical device, keeps the flame at one height (CANDLE-LAMP).

OIL LAMPS were employed for illumination among the nations of antiquity, at the earliest period of which any record exists. The a.s.syrian, Greek, and Roman lamps preserved in our museums are generally n.o.ble specimens of art-workmanship. Though elegant in form, and rich in external embellishment, the ancient lamp was simply a vessel to contain the oil, with a short depression or spout on the one side, in which the wick is laid. Lamps of this rude construction are still in common use in many countries.

No important improvement in the principle and construction of lamps as a source of light occurred until a comparatively recent date; the smoke, dirt, and disagreeable odour of the common lamp having previously led to its disuse among the superior cla.s.ses in favour of candles. At length, in 1789, M. Argand made a revolution in illumination by the invention and introduction of the well-known lamp which bears his name. In the ARGAND LAMP a hollow tubular wick of woven cotton replaces the solid bundles of fibres, and is so arranged that air pa.s.ses through it into the interior of the flame. Over the burner is placed a cylindrical gla.s.s chimney, open at the bottom, and surrounding the flame at a short distance from it, by which another current of air is made to act on the exterior portion of the flame. In this way a due supply of oxygen is secured, and sufficient heat generated for the perfect combustion of the gaseous products of the oil, and the smoke and soot which escape from the ordinary lamp are converted into a brilliant and smokeless flame.

The earliest table-lamps constructed on Argand's principle had one serious defect--the oil vessels had to be placed almost on a level with the burners, in a position which caused them to cast objectionable shadows.

This defect was almost entirely removed by making the oil vessel in the form of a flattish ring, connected by slender tubes with the burner. The more elegant contrivances, known as the MODERATOR LAMP and CARCEL LAMP, which are now so much used for burning colza and similar oils, cast no shadow. In these the oil, instead of being sucked up by the wick, or descending to it by the force of gravity, is driven up by mechanical means from the oil-reservoir contained in the foot or pedestal. A spiral spring, acting upon a piston, elevates the oil in the 'moderator,' while a little pump worked by clockwork does the same duty in the 'Carcel.' The burner and wick in each are formed on Argand's principle.

For burning the hydrocarbon oils distilled from coal and petroleum, lamps of very simple construction are used. These oils, in consequence of their diffusive character, rise to a considerable height up a wick, and therefore do not require mechanical lamps. The wicks of HYDRO-CARBON LAMPS are usually flat, but sometimes circular. To cause perfect combustion, a strong draught of air is created by placing over the flame a tall gla.s.s chimney, usually much contracted above the flame. A metallic cap, with an orifice the shape of the flame, is placed over the burner, its use being to deflect the currents of air upon the flame. The reservoirs of hydro-carbon lamps ought always to be constructed of some bad conductor of heat, as gla.s.s or porcelain.

[Ill.u.s.tration]

For chemical operations, many forms of lamp are used. The ordinary gla.s.s SPIRIT-LAMP, fitted with a ground-gla.s.s cap, is quite indispensable for minor experiments. (See _engr._ 1.) Stoneware wick-holders are preferable to those of bra.s.s, which become greatly heated, and endanger the splitting of the gla.s.s. "An effective spirit-lamp may at any time be constructed out of a vial having a gla.s.s tube pa.s.sing through the cork, a cover being formed from a test-tube inverted over the wick, and fitting with moderate tightness on the superior extremity of the cork" (Greville Williams).

Alcohol or wood spirit is the fuel used.

The ARGAND LAMP, when intended as a source of heat for chemical purposes, is so modified as to adapt it to burn either oil, spirit of wine, or wood-spirit, and the combustion is greatly aided by the chimney, which in this case is made of copper. (See _engr._ 2 and 3.) The lamp itself is also made of metal, and furnished with ground caps to the wick-holder and aperture by which the spirit is introduced, in order to prevent loss of spirit by evaporation when the lamp is not in use. When in use this aperture must always be left open, otherwise an accident is sure to happen, as the heat expands the air in the lamp, and the spirit is forcibly expelled.

In those situations in which coal-gas is cheap, it may be used with great economy and advantage as a source of heat in most chemical operations.

Retorts, flasks, capsules, and other vessels, can be thus exposed to an easily regulated and constant temperature for many successive hours. Small platinum crucibles may be ignited to redness by placing them over the flame on a little wire triangle. Of the various gas-lamps now used in the laboratory, the first and most simple consists of a common Argand gas-burner fixed on a heavy and low foot, and connected with a flexible gas-tube of caoutchouc or other material. (See _engr._ 4.) With this arrangement it is possible to obtain any degree of heat, from that of the smallest blue flame to that which is sufficient to raise a moderately large platinum crucible to dull redness. When gas mixed with a certain proportion of air is burnt, a pale blue flame, free from smoke, and possessing great heating power, is obtained. A lamp for burning the mixture may easily be made by fitting a close cover of fine wire gauze over the top of the chimney of the last-mentioned contrivance. The gas is turned on, and after a few minutes ignited above the wire gauze. (See page 946). The ingenious and useful burners of Bunsen and Griffin are so constructed that gas and air mixed in any proportions, or gas alone, may be burnt at pleasure. Bunsen's is a most efficient and convenient form of burner. (See ill.u.s.tration on next page.) It consists of a gas jet, surrounded by a metal tube, about 6 to 9 inches high and about 1/2 inch in diameter; having at the bottom four large holes. On the admission of air, when the gas is turned on, the air rushes in by these orifices, and mingling with the gas, the mixture ascends to the top of the tube and is there ignited, giving rise to a flame of great heat, but without luminosity, owing to the simultaneous combustion of the carbon and the hydrogen. The burner, however, is so contrived that by shutting off the supply of air entirely, or limiting it, the flame may be made more or less luminous at pleasure. To distribute the flame, a rosette burner is placed on the top of the tube.

[Ill.u.s.tration]

An improved variety of this burner has been designed by Bunsen, and is figured below.

[Ill.u.s.tration: FIG. 1.]