Chapter VI: Front Matter (6)

=LANTHOPINE.= C_{23}H_{25}NO_{4}. A base obtained by Hesse in small quantity, associated with other bases from the aqueous extract of opium. It is homologous with papaverine. Strong nitric acid dissolves it, giving rise to an orange red colour. Strong sulphuric acid gives with it a faint violet colour.

=LA′PIS.= [L.] A stone. The term was much employed by the old chemists, and is still commonly applied to several preparations used in medicine.

=Lapis Causticus.= See POTASSIUM.

=Lapis Divi′nus.= _Syn._ DIVINE STONE; LAPIS OPHTHALMICUS, L.; PIERRE DIVINE, Fr. _Prep._ 1. (Beer.) Verdigris, nitre, and alum, equal parts, melted together.

2. (P. Cod.) Alum, nitre, and blue vitriol, of each 3 oz.; camphor, 1 dr.; as last.

3. (Woolfuss.) Blue vitriol, nitre, alum, and camphor, equal parts, melted together, adding the camphor last. Astringent and detergent. 1 oz., dissolved in water, 1 pint, formed a once celebrated lotion. 1 dr. in water, 1 pint, is still used as a collyrium.

=Lapis Inferna′lis.= See NITRATE OF SILVER.

=Lapis Lazu′li.= See ULTRAMARINE.

=Lapis Lydius.= _Syn._ LYDIAN STONE. A siliceous slate, used as a touchstone by jewellers.

=Lapis Medicamento′sus.= _Syn._ MEDICINAL STONE; LAPIS MIRABILIS, L. _Prep._ (Ph. L. 1746.) Alum, litharge, and Armenian bole, of each 6 oz.; colcothar of green vitriol, 3 oz.; vinegar, 4 fl. oz.; mix, and evaporate to dryness. Formerly used to make an astringent and detergent lotion:——1 oz. to water, 1 pint. Once a popular application to ulcers, and in other cases; now disused.

=Lapis Vulnerar′ius.= Very similar to LAPIS DIVINUS.

=LARCH BARK.= The inner bark of the _Larix Europœa_, the common larch, has been lately introduced, under the form of a tincture, into the British Pharmacopœia.

Dr Stenhouse obtained from the bark a peculiar volatile constituent, possessed of acid properties for which the name of lariximic acid has been proposed. The other trees of the pine family are deficient in this acid. The young bark abounds most in it. Gum, starch, resin, and that variety of tannic acid, which forms olive green precipitates with the salts of iron, have also been found, in addition to other substances, in larch bark.

The inner bark, employed internally, has a special action on the mucous membranes, and acts as an astringent and mild stimulant. It is said to have been given with excellent results in hæmoptysis, as well as in bronchitis attended with copious expectoration, and in diseases of the urinary passages. Externally has been found serviceable in psoriasis, chronic eczema, and some other skin diseases. It is best to combine its extract or tincture with glycerin when it is to be used outwardly. See TINCTURE OF LARCH BARK.

=LARD.= _Syn._ HOG’S LARD, AXUNGE; ADEPS (Ph. L.), AXUNGIA (Ph. E.), A. SUILLUS (Ph. D.), A. PORCI, A. PRÆPARATUS (B. P.), L. The fat of the pig (_Sus scrofa_——Linn.) melted by a gentle heat, and strained through flannel or a hair sieve. The fat about the loins yields the whitest and hardest lard. “That which has been cured with chloride of sodium is not to be employed.” (Ph. L.) “It is not to be used without being first carefully washed with water.” (Ph. L. 1866.) Used chiefly to make ointments, and in cookery. See ADEPS.

=LARD′ING.= By many this is regarded as belonging to the higher style of cookery only, and too troublesome and extravagant to be adapted to the kitchens of the middle classes and the poor. This, we are assured, is not the case. On the contrary, “it is an economical process, and will make lean meat go much farther than without it.” The process of larding is as follows:——“Get what is called a larding needle, that is, a piece of steel from 6 to 9 inches long, pointed at one end, and having four slits at the other to hold a small strip of bacon when put between them. It will, perhaps, cost tenpence. Cut the bacon into pieces 2 or 3 inches long, and 1/4 to 1/2 an inch square; put each one after the other in the pin, insert it in the meat, and leave only about half an inch out; using 8 pieces to each pound.” (Soyer.)

=LARK.= The _Alauda arvensis_ (SKYLARK) and the _Alauda cristata_ (FIELD-LARK), with several other species of the same genus, form a light and nutritious article of food, by many esteemed a delicacy. The last, according to Galen and Dioscorides, eaten either roasted or boiled, ‘helps the colic.’ The heart, applied to the thigh, was also regarded to possess the same virtue.

=LARYNGITIS.= Inflammation of the larynx, or upper part of the windpipe. The symptoms that indicate this most dangerous malady are sore throat, accompanied with considerable pain in front of the throat, difficulty in breathing and swallowing, considerable hoarseness, change or loss of voice, a sense of suffocation, fever, restlessness, flushing of the face, and an eager desire for fresh air. We have described the accompaniments of this dread disease, in order that any one seized with an attack may know its nature, and at once send for his medical attendant. Should circumstances prevent his doing so immediately, as many leeches as possible should be applied to the centre of the throat.

=LAUD′ANUM.= This name is now understood to denote, exclusively, the common tincture of opium of the Pharmacopœia; but formerly the term was applied to several preparations of opium differing greatly from each other, both in their strength and mode of preparation. (See _below_.)

=Laudanum, Dutchman’s.= From the flowers of bull’s hoof or Dutchman’s laudanum (_Passiflora merucuja_——Linn.) infused in rum. Narcotic. Used as a substitute for tincture of opium in the West Indies.

=Laudanum, Ford’s.= This is merely the common tincture of opium aromatised with a little cloves and cinnamon.

=Laudanum, Houlton’s.= _Prep_. From opium 2-1/2 oz.; distilled vinegar, 1-1/2 pint; digested together for a week, the filtered tincture gently evaporated nearly to dryness, and then redissolved in weak spirit (1 of rectified spirit to 7 of water), 1 quart.——_Dose_, 10 to 60 drops.

=Laudanum, Neumann’s.= A fermented infusion of opium evaporated to the consistence of honey.

=Laudanum, Quince.= _Syn_. EXTRACTUM OPII CYDONIATUM, LAUDANUM CYDONIATUM, L. _Prep_. 1. Extract of opium made with quince juice; a few drops of the oils of cinnamon, cloves, and mace being added before the mass cools. Now seldom used.

2. LAUDANUM, LIQUID-QUINCE; (LAUDANUM LIQUIDUM CYDONIATUM, L.) (L. C. PARATUM FERMENTATIONE, L.) A fermented infusion of opium prepared with quince juice, aromatised with cloves, cinnamon, aloes wood, and yellow sandal wood, and evaporated so as to possess about twice the strength of the ordinary tincture. Now obsolete.

=Laudanum, Rousseau’s.= Wine of opium prepared by fermentation. See WINE.

=Laudanum, Smith’s Concentrated.= Resembles Battley’s LIQUOR OPII SEDATIVUS, but possesses about 6 times its strength.

=Laudanum, Swediaur’s.= _Prep_. From extract of opium, 2 parts, dissolved in a mixture of alcohol, 1 part, distilled water, 8 parts. Every 5 drops contain 1 gr. of opium.

=Laudanum, Sydenham’s Liquid.= _Syn_. LAUDANUM LIQUIDUM SYDENHAMI, L. Similar to WINE OF OPIUM——Ph. L., but rather stronger, and aromatised with a little cloves and cinnamon. Wine of opium is now always sold for it.

=Laudanum, Tartarised.= _Syn._ LAUDANUM LIQUIDUM TARTARIZATUM, L. A tincture of opium prepared with spirit alkalised with salt of tartar, and flavoured with aromatics. Obsolete.

=LAUGH′ING GAS.= See NITROUS OXIDE.

=LAUR′EL.= See CHERRY LAUREL, SWEET BAY, OIL, &c.

=LA′VA.= The matter thrown out by volcanoes. The beautiful ornamental vases, jugs, and other objects sold under the name, are a superior sort of unglazed coloured porcelain.

=LAVE′MENT.= See ENEMA.

=LAV′ENDER.= The flowers or flowering tops of _Lavandula vera_ or common garden lavender. An essential oil, spirit, and tincture, prepared from it, are officinal in the Pharmacopœias.

=Lavender Dye= (for COTTON). For 100 yards of material. Take 1 lb. of logwood, and 2 lbs. of sumach, and scald them separately. Then decant them into a proper sized tub, let them cool to 150° Fahr., and add 2 gills of vitriol. Winch the goods in this 20 minutes; lift, and run them slightly through acetate of iron; wash them in two waters; then give 1 lb. of logwood as before, raise with a pint of chloride of tin, wash in two waters; then in a tub of cold water put 4 oz. extract of indigo, enter and winch in this 15 minutes, lift; give one water, and dry.

=Lavender Dye= (for WOOL). Boil 5-1/2 lbs. of logwood with 2 lbs. of alum. Then add 10 oz. of extract of indigo. When cold put in the goods, and gradually raise to the boiling point. For 50 lbs.

=Lavender, Red.= See TINCTURE.

=Lavender, Smith’s British.= _Prep._ From English oil of lavender, 2 oz.; essence of ambergris, 1 oz.; eau de Cologne, 1 pint; rectified spirit, 1 quart. Very fragrant. See WATER (Lavender).

=Lavender, to Dye Silk.= (Mustpratt.) Into a vessel with warm water, as hot as the hand can bear, dissolve a little white soap, enough to raise a lather; then add one gill of archil liquor, and work the goods in this for fifteen minutes; ring out and dry.

Boil one ounce of cudbear, and add the solution to the soap and water instead of archil, which will give a lavender having a redder tint than with the archil. If a still redder shade of lavender be required the soap may be dispensed with.

=Lavender Water.= See SPIRITS, PERFUMED.

=LAX′ATIVES.= _Syn._ LENITIVES; LAXATIVA, LAXANTIA, LENITIVA, L. Mild purgatives or cathartics. The principal of these are——almond oil, cassia pulp, castor oil, confection of senna, cream of tartar, figs, grapes, honey, phosphate of soda, prunes, salad oil, tamarinds, &c.

=LAY′ERS.= Among gardeners, a mode of propagating plants, by laying down the shoots of young twigs, and covering a portion of them with the soil, without detaching them from the parent plant. To facilitate the rooting of such layers, the part beneath the soil is fractured by twisting or bruising it, or it is partly cut through with a sharp knife, immediately under a bud. When the layer has taken root, it is divided from the parent stem, and transplanted or potted. In this way, with a little care, nearly all plants may be multiplied.

=LEAD.= Pb. Eq. 207. _Syn._ PLUMBUM. This metal, like gold, silver, and iron, appears to have been known in the most remote ages of antiquity. The ore from which it is almost exclusively extracted, as being the only one found in abundance, is the native sulphide or sulphuret of lead, called by mineralogists galena.

_Prep._ On the large scale lead is obtained by roasting galena in a reverberatory furnace, and smelting the residue along with coal and lime. The lead thus obtained generally contains small quantities of both silver and gold, which it often pays to extract, by a method termed ‘Pattinson’s process.’ This process is founded on the circumstance that, when melted, lead containing silver is allowed to cool. The lead crystallises out first, leaving an alloy of lead and silver still fused. By removing the crystals of lead, as formed, until about four fifths are removed, the residue is an alloy of lead and silver much richer than the original. Repeated several times, this yields a rich alloy of silver and lead that is expelled and the silver obtained.

Another method for the removal of silver from lead is one employed in Glasgow, and known as the ‘Flack-Guillim’ process. It is thus described in ‘Dingler’s Polytechnic Journal,’ ccxxxv, 67-70, and in ‘Engineering’ for September 15th, 1876. “Eighteen tons of rich lead are melted, and one per cent. of zinc added. The molten mass then allowed to cool, the crust which forms is removed, and the lead sweated out in a small pot. The lead in the large pot is then treated with another half per cent. of zinc in the same way. A third addition of a quarter per cent. of zinc suffices to remove the greater part of the remaining silver, 5 dwts. being left in the lead per ton. This lead is then run into the improving pan, and the last traces of zinc oxidised out.”

Pure lead for chemical purposes may be obtained as follows, although the lead of commerce is nearly pure:

By reducing nitrate of lead with charcoal.

By heating the oxide left by igniting pure acetate of lead with black flux.

_Prop., &c._ The general properties of lead are too well known to require notice here. The sp. gr. of that of commerce is about 11·35; but in a state of absolute purity its greatest density is 11·45. It melts at about 600° Fahr., and when very slowly cooled, crystallises in octahedrons. At a white heat it boils, and is volatilised. When exposed to moist air, it soon becomes covered with a grey film. It is scarcely acted on by hydrochloric or sulphuric acids, although after some time both coat it with a film of chloride or sulphate. It is rapidly acted on by nitric acid, with formation of the nitrate. Pure water put into a leaden vessel and exposed to the air soon corrodes it, and dissolves the newly formed oxide; but river and spring water have little action upon lead, provided there is no free carbonic acid present, the carbonates and sulphates in such water destroying their solvent powers. It has been found that a very small amount of phosphate of sodium or of iodide of potassium, dissolved in distilled water, prevents its corrosive action on this metal. The lead in contact with such water gradually becomes covered with a superficial film of an insoluble salt of lead, which adheres tenaciously, and prevents further change. From this it appears that ordinary water (‘hard water’), which abounds in mineral salts, may be more or less safely kept in leaden cisterns; but distilled water and rain water, and all other varieties that contain scarcely any saline matter, speedily corrode, and dissolve a portion of lead, when kept in vessels of that metal. When, however, leaden cisterns have iron or zinc fastenings or braces, a galvanic action is set up, the preservative power of saline matter ceases, and the water speedily becomes contaminated with lead, and unfit for consumption as a beverage. Water containing carbonic anhydride also acts on lead, and this is the reason why the water of some springs (although loaded with saline matter), when kept in leaden cisterns, or raised by leaden pumps, possesses unwholesome properties.

M. Fordos, in a communication to the ‘Journal de Pharmacie et de Chimie,’ xix, 20, states that in the course of some experiments on the applicability of lead for water pipes and cisterns he could not detect a trace of lead in ten litres of river water taken from the leaden cistern of one of the Paris hospitals. But upon shaking pure water with shot and air, a coating of carbonate of lead was formed on the sides of the bottle, which almost rendered the glass opaque. On dissolving the film in nitric acid, and estimating the lead, it was found that one litre of water had produced five milligrammes of the carbonate. Wine and vinegar would also dissolve that film; and as shot is commonly used for cleaning wine bottles, lead frequently finds its way into wines, a fact which may account for many of the cases of chronic poisoning by lead which occur in large towns. The detection of small quantities of lead in forensic investigation would afford, therefore, no proof of any intentional poisoning.

Orfila’s erroneous statement that lead is a normal constituent of the human organism may also be accounted for in this way.

Free carbonic acid is evolved during the fermentation or decay of vegetable matter, and hence the absolute necessity of preventing the leaves of trees falling into water-cisterns formed of lead. The ‘eau de rose’ and the ‘eau d’orange’ of commerce, which are pure distilled water holding in solution small quantities of essential oil, and are imported in leaden canisters, always contain a small quantity of lead, and deposit a sediment, which is not the case when they are kept in glass or incorrodible vessels.

Lead and all its preparations are highly poisonous; and whether imbibed in almost infinitesimal quantities with our daily beverages and food, or swallowed in larger and appreciable doses, is productive of the most disastrous consequences, the real cause being unfortunately seldom suspected.

Mr G. Bischof[13] writes:——Some eight months ago a tube was passed in my laboratory, which is supplied with water by the New River Company, into the slate cistern so as to act as a syphon to supply some apparatus with water. The external surface of the tube inside the cistern was therefore alternately exposed to the action of air and water, according to the level of water in the cistern.

[Footnote 13: ‘Journal of the Chemical Society,’ April, 1867.]

Recently I noticed a white efflorescence on the greater part of the tube inside the cistern. An adjoining cistern of sheet lead, with a lead overflow pipe fixed into the bottom, shows nowhere any such corrosion.

On cutting the tube it became evident that it is a composition tube, that is to say, a lead tube, containing some antimony. On analysis it was found to be composed of——

Lead 98·3
Antimony 1·7
————
100·0

Although the external diameter of the tube is only half an inch, 0·29 gram of efflorescence was obtained per foot by gentle rubbing. This dried at 100° C. contained 1·02 per cent. of sulphuric acid, corresponding with 4·1 per cent. of sulphate of lead. The remainder, except 1·13 per cent. of a residue insoluble in nitric acid, is carbonate of lead.

The alternate exposure to air and water appears not essential to the corrosion, as I have observed a similar effect when the same tubing remained constantly under water. The interior of the tube has also been corroded, although of course no permanent efflorescence could be formed, owing to the rapid flow of the water.

The frequent practice of plumbers of using composition tubing in connection with water supplies is therefore highly reprehensible, being fraught with considerable danger to the health of those using the water for drinking or cooking.

Mr Louis Siebold detected lead in eight out of ten samples of concentrated solution of acetate of ammonia as well as in a sample of the ordinary solution of the British Pharmacopœia. In pursuing his investigations Mr Siebold found that solutions of acetate of ammonium are capable of dissolving lead from glass. He therefore advises that all forms of the solution, more particularly the concentrated liquor employed by many chemists for making the weaker solutions, should be kept in bottles free from lead.

With the acids lead or its oxides form salts, usually white in colour, and in the majority nearly insoluble in water, but readily soluble in acids.

_Tests._ The oxides and salts of lead, mixed with a little carbonate of soda, and exposed on a charcoal support to the reducing flame of the blowpipe, readily yield a soft and ductile globule of metallic lead, and the charcoal, at the same time, becomes covered with a yellowish incrustation of oxide of lead. Both metallic lead and its oxides are soluble in nitric acid, furnishing a solution which may be examined with ease.

Solution of lead salts may be recognised by the following reactions:——Sulphuretted hydrogen, sulphydrate of ammonium, and the alkaline sulphides, give black precipitates, insoluble in the cold dilute acids, alkalies, alkaline sulphides, and cyanide of potassium. Potassium and sodium hydrates give a white precipitate, soluble in excess. Ammonia (except with the acetate) gives a white precipitate, insoluble in excess. The carbonates of potassium, sodium, and ammonium, give a white precipitate, insoluble in excess. Dilute sulphuric acid (in excess), and solutions of the sulphates give a white precipitate, sparingly soluble in dilute acids, but soluble in a hot boiling solution of potassium carbonate. Chromate and bichromate of potassium give yellow precipitates insoluble in dilute nitric acid, and soluble in solution of potassium hydrate. Iodide of potassium gives a yellow precipitate, soluble in great excess by heat, and separating in small, brilliant, golden-yellow scales, as the liquid cools. A piece of polished zinc precipitates metallic lead in an arborescent form, hence called the lead tree. To prepare for these tests, a solid supposed to contain lead should be digested in nitric acid, when the solution, evaporated to dryness and redissolved in water, may be tested as above.

_Estim._ This has been already referred to under previous heads. The ores of lead (galena) may be digested in nitric acid, when the solution may be treated with sulphuric acid, and the lead estimated from the weight of the precipitated sulphate. This is called an assay in the wet way. The method adopted by practical mineralogists is an assay in the dry way, and is conducted as follows:——A small but powerful air-furnace, charged with coke, is brought to as high a temperature as possible, and a conical wrought-iron crucible plunged into the midst of it; as soon as the crucible has attained a dull-red heat, 1000 gr. of the galena, reduced to powder, are thrown into it, and stirred gently with a long piece of stiff iron wire flattened at the one end, in order to expose as large a surface of the powdered ore to the air as possible, observing now and then to withdraw the wire, to prevent it becoming red hot, in which case some of the ore would permanently adhere to it, and be reduced before the intended time; the roasting is completed in 3 or 4 minutes, and any portion of the ore adhering to the stirrer being detached by a knife, and returned into the crucible, the latter is covered up, and allowed to attain a full cherry-red heat, when about 2 or 3 spoonfuls of reducing flux are added, and the whole brought to a full white heat; in 12 to 15 minutes, the portion of metal and scoria adhering to the sides of the crucible are scraped down into the melted mass with a small stick of moist green wood, after which the crucible is again covered, and the heat urged for 2 or 3 minutes longer, so as to keep the mass in a perfectly liquid state during the whole time; the crucible is then removed from the fire with the crucible-tongs, and adroitly tilted so as to discharge its contents into a small, ingot-mould of brass, observing to rake the scoria from the surface to the sides of the crucible, so as to allow the molten lead to be poured out without it; the scoria is then reheated in the crucible with about 1/2 spoonful of flux, and after being cleansed with a piece of green wood, as before, is at once poured into a second mould, which is instantly inverted; the little button of lead thus obtained is added to the lead in the other mould, and the whole is accurately weighed. The weight, divided by 10, gives the per-centage of lead (including silver, if present) in the ore examined.

One half of the lead thus obtained is put into a dry cupel of bone ash, and placed in the cupelling furnace, and treated as described in the article on assaying; the metallic button left on the cupel is then detached and weighed. The weight, divided by 5, gives the per-centage of pure silver.

_Obs._ The flux commonly employed in the above assay is composed of red argol, 6 parts; nitre, 4 parts; borax, 2 parts; fluor spar, 1 part; well pulverised and thoroughly mixed together. When the ore is very refractory, about a spoonful of carbonate of potassium should be added for each 1000 grains of ore, in which case the roasting may be dispensed with. The quantity of silver in argentiferous galena varies from 3/10000 to 1/3 part of the whole. Whenever this ore contains above 2 parts of silver in the 1000, it is found to be profitable to extract the latter. Indeed, by Pattison’s process it is found that as small a proportion as 1 in 8000 can be extracted with profit.

_Uses._ The uses of lead in the arts are well known. It enters into the composition of many important alloys (pewter, type-metal, shot-metal, solder, &c.), it furnishes us with several valuable pigments (chrome yellow, &c.), and it is extensively used in dyeing. Some of its preparations are employed in medicine.

_Ant., &c._ Administer an emetic of sulphate of zinc or sulphate of copper, and, if necessary, tickle the fauces with the finger or a feather, to induce vomiting. Should this not succeed the stomach-pump may be had recourse to. Epsom or Glauber’s salts, or alum, dissolved in water, or water acidulated with sulphuric acid, followed by tea, water gruel, or barley water, are the proper antidotes, and should be taken as soon after the poison has been swallowed as possible. In poisoning by white lead, Dr Alfred Taylor recommends the administration of a mixture of sulphate of magnesium and vinegar, as preferable to the sulphate alone. When the symptoms are those of painter’s colic, the treatment recommended under that head should be adopted. In paralysis arising from lead, small doses of strychnine and its preparations may be cautiously administered. A symptom of poisoning by lead is the formation of a narrow leaden blue line, from 1/20th to 1/6th of an inch wide, bordering the edges of the gums, attached to the neck of two or more teeth of either jaw. (Dr Burton.) This discoloration may often be detected or rendered more conspicuous by rinsing the mouth out with water holding a little sulphuretted hydrogen or sulphydrate of ammonium in solution. Chevallier and Rayer recommend the use of sulphurous or hepatic mineral waters, or of artificial solutions of sulphuretted hydrogen or alkaline sulphides in water, both in cases of acute and chronic poisoning by lead; but the practical success of this plan does not appear to have been in proportion to theoretical anticipations. The moist and freshly precipitated sulphides of iron are said by their advocates to be infallible if taken sufficiently early.

=Lead in Aerated Water.= Some time since Sir Robert Christison condemned the use of syphons for lemonade, owing to the action of free tartaric acid upon lead, and the rapidity with which waters containing any free acid become charged with lead in syphons. According to Professor Miller, 0·0175 gr. of lead per gallon is not an unusual amount for average cistern water. Mr John S. Thompson, however, reports to the Edinburgh University Chemical Society that, after such water has been aerated and put into a syphon, the amount of lead dissolved in it begins to rise in a rapid manner. Thus in potash water, drawn from a syphon, 0·0408 grain of lead per gallon was found to be present, being nearly 25 times the quantity found in the same water before it entered the syphon. Pure aerated water again drawn in a similar manner from a syphon gave 0·0816 gr. of lead per gallon, or exactly double the amount found in the potash water, showing at once the well-known protective action that salts of the alkalies and alkaline earths have on lead. “Although,” says the ‘Medical Journal,’ “these results are sufficiently high and alarming; still, when the water is drawn off in small quantities at a time, as is frequently the case with invalids, the results are found to be still higher; thus, when potash water was so treated, 0·0455 gr. of lead per gallon was found, while aerated water, drawn off in small quantities, gave 0·0933 gr. of lead per gallon, showing a very marked rise in both cases. The cause of this increase in quantity of the lead appears to be owing, not so much to the lengthened period of contact between the liquid and the metal as to the fact that the nozzle of the syphon, being exposed to the atmosphere in a moist state, becomes rapidly oxidised or carbonated, and is left in the most suitable condition for entering into solution, so that, when merely small portions of the liquid are drawn off each time, a comparatively concentrated solution of lead is obtained. These results,” continues the same authority, “compare accurately with those which were obtained by Messrs Savory and Moore, in examining the contents of a series of syphons of aerated water for Dr George Owen Rees, F.R.S., whose attention was drawn to the subject by detecting symptoms of lead-poisoning in himself after he had been in the habit for some time of drinking such aerated water.”

=Lead, Acetate of.= Pb(C_{2}H_{3}O_{2})_{2}. _Syn._ PLUMBIC ACETATE, SUGAR OF LEAD, PLUMBI ACETAS. (B. P.) _Prep._ Litharge (in fine powder) 24; acetic acid, 40; distilled water, 20; mix the acetic acid and the water, add the litharge, and dissolve with the aid of a gentle heat, filter, evaporate until a pellicle forms, and crystallise. Drain and dry the crystal.

Acetic acid (sp. gr. 1·0843), 23 parts, is gently heated in a copper boiler rendered electro-negative by means of a large flat piece of lead soldered within it, and litharge (pure, and in fine powder), 13 parts, is sprinkled in; the heat is then continued, with constant stirring, until the acid is saturated, when the mother-waters of a former process, if any, are added, and the whole is heated to the boiling point, and allowed to settle until cold; the clear portion is now decanted, and evaporated in a similar vessel until the liquor has the sp. gr. 1·266 or 1·267, when it is run into salt-glazed stone-ware vessels (the edges of which have been well smeared with candle grease), and allowed to crystallise. The product is 38 to 38-1/2 parts of crystallised sugar of lead. It is found to be advantageous to preserve a very slight excess of acid during the boiling and crystallisation, to prevent the formation of any basic acetate the presence of which impedes the formation of regular crystals.

From litharge, 112 lbs.; acetic acid (sp. gr. 1·057), 128 lbs. _Prop._ 180 to 184 lbs.

_Prop._ Pure acetate of lead forms colourless, transparent, prismatic crystals, slightly efflorescent in dry air; it is soluble in 8 parts of alcohol and in 1-1/4 part of cold water; the aqueous solution has a sweet astringent taste, and feebly reddens litmus, but turns turmeric and the juice of violets green; when gently heated, it melts in its water of crystallisation; by continuing the heat, the whole of the water is expelled, and the dry acetate obtained; at a higher temperature the salt suffers decomposition, and acetic acid, acetone, &c., is given off. Commercial acetate of lead is in general a confused crystalline mass, somewhat resembling broken lump sugar. It is powerfully astringent and poisonous.

When pure it is completely soluble in distilled water acidulated with acetic acid forming a transparent colourless solution, “38 grains dissolved in water require for complete precipitation 200 grains measures of the volumetric solution of oxalic acid.” (B. P.)

_Uses, &c._ Acetate of lead is extensively employed in dyeing and calico-printing. In _medicine_ it is used as an astringent, styptic, and hæmostatic; in pulmonary, uterine, and intestinal hæmorrhage, colliquative diarrhœa, phthisical sweats, &c. It is usually combined with morphia or opium, and with acetic acid to prevent it passing into the state of the poisonous carbonate in the stomach.——_Dose_, 1/2 gr. to 2 gr. (Collier); 1 to 2 gr. to 8 or 10 gr., twice or thrice a day (Pereira); 3 gr. to 10 gr., every 6 or 8 hours (A. T. Thomson). _Externally_, as a collyrium, 10 gr. to water, 8 fl. oz. (A. T. Thomson); as a lotion, 20 gr. (A. T. Thomson), 1 dr. (Collier) to water, 8 or 10 fl. oz.; as an injection, 40 gr. to rose water, 1/2 pint. The lotion is cooling and sedative, and is commonly used in excoriations, local inflammations, &c.

=Basic Acetates.= There are several of these salts, but only one is of any importance.

=Tribasic Lead Acetate or Double Plumbic Acetate, and Dioxide.= Pb(C_{2}H_{3}O_{2})_{2} 2PbO. _Syn._ SUBACETATE OF LEAD; BASIC LEAD CITRATE; GOULARD’S ACETATE OF LEAD; PLUMBI SUBACETAS (B. P.). _Prep._ Litharge, 7; acetate of lead, 10; and distilled water, 40; are boiled half an hour, and evaporated down, and allowed to crystallise out of contact with air.

Used under the form of “Plumbi subacetas liquor” v. (B. P.)

=Lead, Arse′′niate of.= Pb_{3}(AsO_{4})_{2}. _Syn._ ARSENATE OF L.; PLUMBI ARSENIAS, L. _Prep._ Gradually add a solution of acetate of lead to another of arseniate of sodium. A white, insoluble powder. Proposed as an external application in certain forms of cancer.

=Lead, Bro′mide of.= PbBr_{2}. _Syn._ PLUMBI BROMIDUM, L. _Prep._ By precipitating a solution of neutral acetate or nitrate of lead with a solution of bromide of potassium. A white, crystalline powder, sparingly soluble in water. It fuses by heat into a red liquid, which turns yellow when cold. It has been used in the same cases as iodide of lead.

=Lead, Car′bonate of.= PbCO_{3}. _Syn._ PLUMBI CARBONAS, L. _Prep._ By precipitating a cold solution of either acetate or nitrate of lead with a solution of an alkaline carbonate, observing to well wash the precipitate and dry it in the shade. This preparation is seldom employed, the commercial carbonate (WHITE LEAD) being substituted for it. See WHITE PIGMENTS.

=Lead, Chloride of.= PbCl_{2}. _Syn._ CHLORIDE LEAD; PLUMBI CHLORIDUM (Ph. L. 1836). _Prep._ (Ph. L. 1836). Dissolve acetate of lead, 19 oz., in boiling water, 3 pints; next dissolve chloride of sodium, 6 oz., in boiling water, 1 pint; mix the two solutions, and when cold wash and dry the precipitate. A white, crystalline powder.

Dissolve finely powdered litharge in boiling dilute hydrochloric acid, and set aside the filtered solution to cool. Brilliant colourless needles.

_Prop._ Soluble in 135 parts of cold and in 22 parts of boiling water; it melts when heated, and solidifies on cooling, forming a horn-like substance (horn lead; plumbi corneum).

_Uses, &c._ In the Ph. L. 1836, chloride of lead was ordered to be employed in the preparation of ‘hydrochlorate of morphia.’ Mr Tuson highly recommends it in cancerous affections, to allay pain and restrain morbid action, either in the form of a lotion or ointment.

Various mixtures of lead chlorides and oxide are employed as a white pigment under the name of ‘Pattison’s white.’ It is prepared by rapidly mixing a boiling solution of lead chloride with an equal volume of lime water. Another similar compound is called ‘patent yellow’ or ‘Turner’s yellow.’

=Lead, Chromate of.= PbCrO_{4}. _Syn._ LEMON YELLOW, LEIPSIG YELLOW, PARIS YELLOW. _Prep._ By adding a filtered solution of acetate or nitrate of lead to a like solution of chromate of potassium, as long as the precipitate forms, which is collected, washed with water, and dried. For information respecting the manufacture of this substance on the large scale, as a colouring substance (chrome yellow), see YELLOW PIGMENTS.

=Lead, Dichromate of.= _Syn._ CHROME ORANGE, CHROME RED. PbCrO_{4}.PbO. _Prep._ By adding to a solution of nitrate or acetate of lead a solution of chromate of potassium, to which an equivalent of potassa has been added. This compound is of a splendid scarlet colour. See RED PIGMENTS.

=Lead, Cy′anide of.= PbCy_{2}. _Syn._ PLUMBI CYANIDUM, L. _Prep._ By adding hydrocyanic acid to a solution of acetate of lead, as long as a precipitate forms, which, after being washed with distilled water, is dried by a very gentle heat, and preserved from the light and air. Sometimes used as a source of medicinal hydrocyanic acid.

=Lead, Iodide of.= PbI_{2}. _Syn._ LEAD IODIDE; PLUMBI IODIDUM (B. P., Ph. L. E. D.). _Prep._ (B. P.) Nitrate of lead, 4; iodide of potassium, 4; distilled water, a sufficiency. Dissolve with the aid of heat the nitrate of lead in 30 of water, and the iodide of potassium in 10 of water, mix, collect the precipitate, wash, and dry at a gentle heat.

_Prop., &c._ A rich yellow-coloured powder, soluble in acetic acid, alcohol, and boiling water; when heated, it fuses and volatilises in yellow vapour, but with a higher degree of heat, violet vapours of iodine are evolved, leaving a residuum (lead) which is wholly soluble in nitric acid.——_Dose_, 1/4 gr. to 4 gr. or more, made into a pill; as a deobstruent and resolvent, in enlargements of the cervical, axillary, and mesenteric glands, and in scrofulous affections and scirrhous tumours.

=Lead, Nitrate of.= Pb(NO_{3})_{2}. _Syn._ PLUMBI NITRAS, L. (B. P., Ph. E. D.)

_Prep._ (Ph. D.) Litharge (in fine powder), 1 oz.; pure nitric acid, 2 fl. oz., diluted with water, 1/2 pint; mix, apply a sand-heat, and evaporate to dryness, occasionally stirring; boil the residuum in water, 2-1/2 pints; filter, acidulate with a few drops of nitric acid, evaporate to a pellicle, and set the liquid aside to cool; lastly, dry the deposited crystals on bibulous paper, and preserve them in a well closed bottle.

(Commercial.) By dissolving white lead in dilute nitric acid, and crystallising.

_Uses, &c._ This salt is extensively used in calico printing, and in the preparation of the iodide and other salts of lead. It was formerly much esteemed in asthmas, hæmorrhages, and epilepsy. It is now often used in an external application in cancer, ulcers, wounds, and various cutaneous affections. It is the basis of Liebert’s celebrated ‘cosmétique infallible,’ and of Ledoyen’s ‘disinfecting fluid.’ A very weak solution is an excellent application to chapped nipples, lips, hands, &c.——_Dose_, 1/2 to 1 gr.; in the form of pill or solution, washed down with a tablespoonful of water very slightly acidulated with nitric acid.

=Lead, Nitro-sac′charate of.= _Syn._ PLUMBI NITROSACCHARAS, L. _Prep._ (Dr S. E. Hoskins.) Nitric acid, 1 part; water, 19 parts; mix; in this dilute acid saccharate of lead (in fine powder) is to be dissolved, and set aside that crystals may form, which are to be dried by pressure between the folds of bibulous paper. A weak solution of the salt, acidulated with saccharic acid, has been employed by Dr Hoskins as a solvent for phosphatic calculi, with apparent success.

=Lead, Oxide of.= PbO. _Syn._ MONOXIDE OF LEAD, PROTOXIDE OF LEAD, YELLOW OXIDE OF LEAD, PLUMBI OXYDUM (B. P.) _Prep._ This substance is obtained perfectly pure by expelling the acid from nitrate of lead, by exposing it to heat in a platinum crucible; or, still better, by adding ammonia to a cold solution of nitrate of lead until the liquid becomes faintly alkaline, washing the precipitate with cold water, drying it, and heating it to moderate redness for 1 hour.

_Prop., &c._ Pure protoxide of lead has a lemon-yellow colour, and is the best of all the salts of lead. It is very heavy, slightly soluble in water, and freely so in acids, particularly when in the hydrated state; the aqueous solution has an alkaline reaction; at a red heat it melts, and assumes a semi-crystalline form on cooling; in the melted state it rapidly attacks and dissolves siliceous matter, with which it unites to form glass (flint glass); when heated along with organic substances of any kind, it is easily reduced to the metallic state.

On the commercial scale, this oxide is prepared by heating the grey film or dross that forms on the surface of melted lead when freely exposed to the air. When the process is arrested, as soon as the oxide acquires a uniform yellow colour, it is called massicot; when the heat is still further increased, until it fuses or partially vitrifies, it forms litharge of which there are several varieties. See LITHARGE, MASSICOT.

=Lead, Red Oxide of.= _Syn._ RED LEAD, MINIUM. _Prep._ This is prepared by exposing unfused protoxide of lead to the air for a long time, at a dull red heat. It is a very heavy powder, of a fine red colour, decomposed by a strong heat into protoxide of lead, and oxygen gas, which is evolved. Somewhat uncertain in its composition, but is generally of the composition Pb_{3}O_{4} or PbO_{2}2PbO. See RED PIGMENT.

=Lead, Dioxide.= PbO_{2}. _Syn._ BINIODIDE OF LEAD, PEROXIDE OF LEAD, PUCE OXIDE OF LEAD. _Prep._ By digesting red oxide of lead in dilute nitric acid; or by infusing a mixture of protoxide of lead and chlorate of potassium at a heat a little below redness, and washing the powdered mass in water; or by transmitting a current of chlorine gas through a solution of neutral acetate of lead. This oxide gives up half its oxygen at a red heat; acids also decompose it. Its chief use is in chemical analysis, to separate sulphurous acid from certain gaseous mixtures, which it converts into sulphuric acid, which it at the same time absorbs, forming sulphate of lead. It has recently been employed as an oxidising agent in the manufacture of the ANILINE DYES.

=Lead, Pyrolig′nite of.= Sugar of lead made with rough pyroligneous acid. Used in dyeing, chiefly for the preparation of acetate of alumina.

=Lead, Sac′charate of.= _Syn._ PLUMBI SACCHARAS, L. _Prep._ (Dr S. E. Hoskins.) Nitric acid, 2 parts; water, 10 parts; mix in a porcelain capsule, add of sugar, 1 part; and apply heat until reaction ceases; then dilute the liquid with distilled water, neutralise it with powdered chalk, filter, and add to the filtrate a solution of acetate of lead, as long as a precipitate (saccharate of lead) forms; lastly, collect the precipitate on a filter, wash and dry it. Used to make nitro-saccharate of lead, and as a source of saccharic acid.

=Lead, Sul′phate of.= PbSO_{4}. _Syn._ PLUMBI SULPHAS, L. This salt occurs native in transparent octohedra (lead vitriol), and is obtained in large quantities as a by-product in the preparation of acetate of aluminum for dyeing.

_Prep._ By adding dilute sulphuric acid to a solution of a soluble salt of lead. It is very sparingly soluble in water and in dilute sulphuric acid, soluble in strong hydrochloric acid and bitartrate of ammonium.

=Lead, Sul′phide of.= PbS. _Syn._ PLUMBI SULPHIDE. This occurs abundantly in nature in the form of GALENA.

_Prep._ By fusing metallic lead with sulphur or by passing sulphuretted hydrogen through a solution of a salt of lead.

=Lead, Tan′nate of.= _Syn._ PLUMBI TANNAS, L. _Prep._ Precipitate a solution of acetate of lead with an infusion of galls, and wash and dry the precipitate. Astringent, sedative, and hæmostatic.——_Dose_, 1 gr. and upwards, made into a pill. It has been highly recommended in the form of ointment and cataplasms, in bed-sores, chronic ulcers of the feet, white swellings, &c.

=Lead, Tar′trate of.= _Syn._ PLUMBI TARTRAS, L. _Prep._ By precipitating acetate of lead, by tartrate of ammonium, washing and drying.

=LEAD DUST.= _Syn._ PULVIS PLUMBI, PLUMBUM DIVISUM, L. _Prep._ By melting new lead, adding bruised charcoal, mixing with violent agitation, which must be continued until the metal ‘sets,’ and then pounding and washing away the charcoal. Used by potters.

=LEAD, GRANULATED.= _Prep._ By melting new lead, and pouring it in a small stream from an iron ladle with a hole drilled in its bottom, into a pail of water. Used to make solutions and alloys.

=LEAD, RED.= See RED PIGMENTS.

=LEAD, WHITE.= See WHITE PIGMENT.

=LEAD PYROPH′ORUS.= See PYROPHORUS.

=LEATH′ER.= _Syn._ CORIUM, CORIUS, L. Leather is the skin of animals which has been prepared by one or other of several processes adopted for the purpose, having the common object of preventing its spontaneous destruction by putrefaction, besides other objects, which are more or less peculiar to each variety of this useful substance.

Leather is only prepared on the large scale, and primarily either by the process of ‘TANNING’ or ‘TAWING,’ in the manner briefly described under these heads.

CURRIED LEATHER is leather which has been tanned, and sold to the currier, who, after soaking it in water, and rubbing it to soften it, pares it even with a broad, sharp knife, rubs it with a piece of polished stone or wood, and, whilst still wet, besmears it with oil or grease (DUBBING), which gradually penetrates the leather as the moisture evaporates. It next undergoes the operation of ‘waxing,’ which consists of first rubbing it on the flesh side with a mixture of oil and lamp black; it is then ‘black-sized’ with a brush or sponge, and, when dry, is lastly ‘tallowed’ with a proper cloth, and ‘slicked’ upon the flesh side with a broad and polished lump of glass. Leather curried on the hair or grain side, termed ‘black on the grain,’ is blackened by wetting it with iron liquor, and rubbing it with an iron ‘slicker’ before applying the oil or grease. The grain is finally raised by the ‘pommel’ or ‘graining board’ passed over it in various directions.

Leather is dyed or stained by the application, with an ordinary brush, of any of the strong liquid dyes, in the cold or only gently heated, to the surface of the skin previously stretched on a board. The surface, when dry, is commonly finished off with white of egg and the pommel or smoothing stick. Bookbinders generally employ copperas water as a black stain or sprinkle; a solution of indigo as a blue one; and a solution of salt of tartar or common soda, as a brown one.

Leather, before being japanned or varnished, as in the preparation of what is called ‘ENAMELLED’ and ‘PATENT LEATHER,’ is carefully freed from grease by the application of absorbent substances or hard pressure between rollers, and the surface is nicely shaved, smoothed, and polished by appropriate tools, the varnish is then applied to the grain side for the former, and the flesh side of the skin for the latter, which is previously stretched out tight on a board to receive it. The whole is, lastly, submitted to a gentle stove-heat to harden the varnish; and the process is repeated, if necessary.

_Uses, &c._ These are well known, and are all but universal. The leather manufacture of Great Britain is equal in importance and utility to any other department of our industry, and inferior in point of value and extent only to those of cotton, wool, and iron. “If we look abroad on the instruments of husbandry, on the implements used in most of the mechanic trades, on the structure of a multitude of engines and machines; or if we contemplate at home the necessary parts of our clothing——breeches, shoes, boots, gloves——or the furniture of our houses, the books on our shelves, the harness of our horses, or even the substance of our carriages; what do we see but instances of human industry exerted upon leather? What an aptitude has this single material in a variety of circumstances for the relief of our necessities, and supplying conveniences in every state and stage of life! Without it, or even without it in the plenty we have it, to what difficulties should we be exposed?” (Dr Campbell.) Leather is a kind of natural felt, but of much closer and firmer texture than that of artificial origin. “The thinner and softer kinds of leather are sometimes used as body-clothing; but its special and proper purpose is the manufacture of coverings for the feet, to protect them from cold and water.” (Eras. Wilson.) See JAPANNING, VARNISH, &c.

=Leather, destruction of, by Gas.= It is well-known that the binding of books suffer considerable damage, when the books are kept in apartments lighted by coal gas. That the cause of this deterioration is due, as was believed, to the combustion of the bisulphide of carbon contained in the gas, and its consequent oxidation into sulphuric acid, is exemplified by the following interesting communication from Professor Church, published in the ‘Chemical News’ for October 19th, 1877. He says:——“Vellum seems unaffected; morocco suffers least; calf is much injured, and russia still more so. The disintegration is most rapid with books on the upper shelves of a library, whither the heated products of combustion ascend, and where they are absorbed and condensed.

By comparing specimens of old leather, with specimens of new, it is quite clear that the destructive influence of gas is due mainly to its sulphur.

True there are traces of sulphates in the dye and size of new leather bindings, but the quantity is insignificant and there is practically no free sulphuric acid. That leather may be destroyed by the oil of vitriol produced by the burning of gas in a library is proved by the following observations and analyses.

The librarian of one of our public libraries forwarded to me the backs of several volumes, which had been ‘shed’ by the books on the upper shelves in an apartment lighted by gas. The leather of one of these backs (a volume of the ‘Archæologia’) was carefully scraped off so as to avoid any paper or size from underneath. This task of scraping was easy enough, for the leather was reduced to the consistency of Scotch snuff. On analysis of the watery extract of this leather, the following figures were obtained:——

Free sulphuric acid in decayed
leather 6·21 per cent.
Combined 2·21 ”
————
8·42

=LEAV′EN.= Dough which has become sour or run into a state of incipient putrefaction. When a small quantity of it is added to recent dough, it excites fermentation, but is apt to produce a disagreeable taste and odour in the bread. It is now superseded by yeast. Both these substances are used in the same way.

=LEAVES (Medicated).= _Syn._ FOLIA MEDICATA, L. On the Continent several preparations of this kind are in use. In many cases the leaves of tobacco deprived of nicotine, by soaking them in water, are dried, and then moistened or steeped in a tincture or infusion of the medicinal substance. In this way belladonna, camphor, and henbane, are often administered. Cruveilhier recommends opiated belladonna leaves for smoking in troublesome coughs, phthisis, spasmodic asthmas, &c., to be prepared as follows:——Belladonna leaves, 1 oz., are steeped in an infusion of opium, 10 gr., in water, 1 fl. oz. (or less), and are then carefully dried in the shade. “MUSTARD LEAVES (Riggollot’s) consist of mustard moistened with water, spread on paper, and dried.” (Squire.) See CIGARS (in _pharmacy_), and VEGETABLES.

=Leaves, How to Dissect.= “For the dissection of leaves,” says Mrs Cussons, “I find the process of maceration too long and tedious, to say nothing of the uncertainty as to the results. I have therefore adopted the use of alkali in saturated solution, the specimens to be introduced while the liquid is heated to the boiling point; the time of immersion to be regulated by the character of the various leaves and the nature of the epidermis to be removed. When the specimen is freed from epidermis and cellular tissue, it must be subjected to the action of chlorine to destroy the colouring matter. The introduction of peroxide of hydrogen not only serves to render the lace-like specimen purer in colour, but also preserves it. In destroying the colouring matter in ferns this also is invaluable; added to the chlorine it gives a solidity to the bleached fronds, and appears to equalise the action of the chlorine. For skeletonising capsules the slow process of maceration by steeping in rain-water is alone available; a moderate heat may be applied to hasten the process, but alkali is useless. The only known flower which can be dissected is the _Hydrangea japonica_. The fibrous nature of the petals renders it easy to skeletonise in the perfect truss in which it grows. Skeletonised leaves and capsules appear to gain in the process a toughness and durability not possessed by them in their natural state.”

=LECANOR′IC ACID.= See ORSELLINIC ACID.

=LEECH.= _Syn._ HIRUDO (B. P., Ph. L. & D.), L. The officinal leech of the Pharmacopœias is the _Sanguisuga medicinalis_ (_Hirudo medicinalis_——Cuv.), familiarly known as the ‘old English’ or ‘speckled leech.’ It is also occasionally called the ‘Hamburg grey’ or ‘Russian leech,’ from being imported from those parts. Its characteristics are——Back, greenish or olive green, sometimes almost black or intense brown, with 6 rusty-red or yellowish longitudinal stripes, which are mostly spotted with black.——Belly, dirty yellow or light olive green, spotted more or less with black. The spots are very variable in size and number; in some cases few, in others so numerous as to form the prevailing tint of the belly. This variety, which is the most valuable of the commercial leeches, is chiefly imported from Hamburg.

Another variety of leech, the _Sanguisuga officinalis_, familiarly known as the ‘Hamburg’ or ‘French green leech,’ is imported from Bordeaux, Lisbon, and Hamburg. Its characteristics are——Back, brownish olive-green, with 6 reddish or rusty yellow longitudinal bands.——Belly, light dirty pea-green, or yellowish green, free from spots, but exhibiting two lateral stripes. This leech is vastly inferior to the preceding variety, and some of those imported from France and Portugal are absolutely useless, from their indisposition to bite, arising from the fraud practised by the collectors and dealers of gorging them with blood to improve their appearance before sending them to market. The above are the species of leech commonly employed in medicine in this country, but many others are noticed by writers on the subject.