Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 12

=LA'BELS= capable of resisting the action of OILS, SPIRITS, WATER, SYRUPS and DILUTE ACIDS, may be obtained as follows:--Lay a coat of strained white of egg over the label (an ordinary paper one), and immediately put the vessel into the upper portion of a common steam-pan, or otherwise expose it to a gentle heat till the alb.u.men coagulates and turns opaque, then take it out and dry it before the fire, or in an oven, at a white heat of about 212 Fahr.; the opaque white film will then become hard and transparent. The labels on bottles containing STRONG ACIDS or ALKALINE SOLUTIONS should be either etched upon the gla.s.s by means of hydrofluoric acid, or be written with incorrodible ink. See ETCHING and INK.

=LAB'ORATORY.= _Syn._ LABORATORIUM, L. A place fitted up for the performance of experimental or manufacturing operations in chemistry, pharmacy, and pyrotechny. For full information respecting the best mode of fitting up a chemical laboratory, the reader is referred to works especially devoted to chemical manipulation.[11] Almost any well-lighted spare room may be fitted up as a small laboratory at very little expense.

The gas-furnaces and improved lamps introduced of later years have to a certain extent rendered chemists independent of brick furnaces. A strong working bench, fitted with drawers and cupboards, and having gas-pipes at intervals for attaching different kinds of jets, is an indispensable fixture. A close cupboard or closet, which is connected by a pipe with the chimney or the external air, is required to receive vessels emitting corrosive or evil-smelling vapours; the door of this closet should be of gla.s.s. A sink, with a copious supply of water, must be at hand, for washing apparatus. A gla.s.s, a stoneware barrel, with a tap of the same material, is required for holding distilled water. Shelves, supports for apparatus, and drawers, should be provided in abundance. The fine balances and other delicate instruments should be kept in a separate apartment.

With regard to apparatus, we may state that the articles most frequently required in a laboratory are the gas or alcohol lamps; iron pans for sand bath and water bath; evaporating dishes; precipitating jars, funnels, and wash-bottles; retorts, flasks, and test-tubes; mortars and pestles; retort- and filtering-stands; rat-tail and triangular files, and gla.s.s rod and tubing.

[Footnote 11: The latest and best work is the 'Handbook of Chemical Manipulation,' by Greville Williams. Faraday's famous work on the same subject has long been out of print.]

The princ.i.p.al philosophical instrument-makers sell chests or cabinets filled with apparatus and chemicals, under the name of 'PORTABLE LABORATORIES,' Those sold by Mr J. J. Griffin and by Messrs Jackson and Townson are, perhaps, the most complete. They are well adapted for ill.u.s.trating all the more valuable facts of chemical science, and performing all the ordinary operations of qualitative a.n.a.lysis.

=LABURNINE.= A poisonous alkaloid, found in the unripe seeds of the laburnum plant, a.s.sociated with another poisonous alkaloid called _Cytisine_.

=LAC.= _Syn._ LACCA, L. A resinous substance combined with much colouring matter, produced by the puncture of the female of a small insect, called the _Coccus lacca_ or _ficus_, upon the young branches of several tropical trees, especially the _Ficus Indica_, _Ficus religiosa_, and _Croton lacciferum_. The crude resinous exudation const.i.tutes the STICK-LAC of commerce. Sh.e.l.l-LAC or Sh.e.l.lAC is prepared by spreading the resin into thin plates after being melted and strained. SEED-LAC is the residue obtained after dissolving out most of the colouring matter contained in the resin.

Sh.e.l.l-lac is the kind most commonly employed in the arts. The palest is the best, and is known as 'orange-lac.' The darker varieties--'liver-coloured,' 'ruby,' 'garnet,' &c.--respectively diminish in value in proportion to the depth of their colour.

_Uses, &c._ Lac was formerly much used in medicine; its action, if any, is probably that of a very mild diuretic. It is now chiefly used in DENTIFRICES, VARNISHES, LACQUERS, and SEALING-WAX.

=Lac, Bleached.= _Syn._ WHITE LAC; LACCA ALBA, L. By dissolving lac in a boiling lye of pearlash or caustic pota.s.sa, filtering and pa.s.sing chlorine through the solution until all the lac is precipitated; this is collected, well washed and pulled in hot water, and, finally, twisted into sticks, and thrown into cold water to harden. Used to make pale varnishes and the more delicate coloured sealing-wax.

=LAC DYE.= _Syn._ LAC, LAC-LAKE, INDIAN COCHINEAL. A colouring substance used to dye scarlet, imported from India.

_Prep._ By dissolving out the colour of ground stick-lac by means of a weak alkaline solution, and then precipitating it along with alumina by adding a solution of alum.

_Obs._ To prepare the lac for dyeing, it is ground and mixed with diluted 'lac spirit,' and the whole allowed to stand for about a week. The 'cloth'

is first mordanted with a mixture of tartar and 'lac spirit,' and afterwards kept near the boil for three quarters of an hour, in a bath formed by adding a proportion of the prepared lac dye to the mixture used for mordanting. Lac dye is only applicable to woollen and silk. The colours it yields are similar to those obtained from cochineal, but less brilliant.

=LAC SPIRIT.= See TIN MORDANTS.

=LACE.= This decorative fabric is made by interweaving threads of linen, cotton, or silk, into various patterns and designs. Although in some instances lace is made by hand, the greater part is now manufactured by machinery worked by steam or water. The hand-made lace was called bone, pillow, or bobbin lace, these two latter names having been given it from its having been woven upon a pillow or cushion by means of a bobbin. The manufactured article is bobbin net. Lace and the machinery by which it is produced is of so complex a nature that Dr Ure says of one particular form of it "it is as much beyond the most curious chronometer in the multiplicity of mechanical device as that is beyond a common roasting jack."

Owing to the improvements in machinery introduced of late years, it may be mentioned that a piece of lace which twenty years since could only be produced at a cost of 3s. 6d. for labour, may now be turned out for 1d., and a quant.i.ty of the fabric which sold for 17, now realizes only 7s. A pair of curtains, each four yards long, may be made in one frame in two hours.

The following statistics relating to the British lace industry are of interest:--"In 1843 there were 3200 twist net and 800 warp frames, returning 2,740,000 that year; in 1851, 3200 bobbin net and 800 warp, giving a return of 3,846,000; and in 1866, 3552 bobbin and 400 warp, returning 5,130,000. There has since been no actual census, but about the same number is now at work, and the returns and profits are greatly increased by improved quality and patterns of goods produced. The returns of 1872 were certainly 6,000,000 at least; and from advancing wages and demand for Lever's laces, must still rapidly increase. Men are now earning by making them from 4 to 6 for 56 hours' weekly labour."[12]

[Footnote 12: 'British Manufacturing Industries.' Stanford.]

=Lace, Gold and Silver, to Clean.= Reduce to fine crumbs the interior of a 2-lb. stale loaf, and mix with them 1/4 lb. of powder blue. Sprinkle some of this mixture plentifully on the lace, afterwards rubbing it on with a piece of flannel. After brushing off the crumbs rub the lace with a piece of crimson velvet.

=Lace, to Scour.= Take a perfectly clean wine bottle; wind the lace smoothly and carefully round it; then gently sponge it in tepid soap and water; and when clean, and before it becomes dry, pa.s.s it through a weak solution of gum and water. Next pick it out and place it in the sun to dry. If it be desired to bleach the lace, it should be rinsed in some very weak solution of chloride of lime, after removal from which it must be rinsed in cold water. Starch and expose it; then boil and starch, and again expose it if it has not become sufficiently white.

The following method is also said to whiten lace:--It is first ironed slightly, then folded and sewn into a clean linen bag, which is then placed for 24 hours in pure olive oil. Afterwards the bag, with the lace in it, is to be boiled in a solution of soap and water for 15 minutes, then well rinsed in lukewarm water, and finally dipped in water containing a small quant.i.ty of starch. The lace is then to be taken from the bag, and stretched on pins to dry.

To scour point lace proceed as follows:--"Fix the lace in a prepared tent, draw it tight and straight, make a warm lather of Castile soap, and with a fine brush dipped in rub over the lace gently, and when clean on one side do the same on the other; then throw some clean water on it, in which a little alum has been dissolved, to take off the suds; and, having some thin starch, go over with it on the wrong side, and iron it on the same side when dry; then open with a bodkin and set it in order. To clean the same, if not very dirty, without washing, fix it as before, and go over with fine bread, the crust being pared off, and when done, dust out the crumbs." (Ernest Spon.)

Black lace may be cleaned by pa.s.sing it through warm water containing some ox-gall, rinsing it in cold water, and then pa.s.sing it through water in which a small quant.i.ty of glue has been previously dissolved by means of heat; it should then be taken out, clapped between the hands, and dried on a frame.

=LAC'QUER.= A solution of sh.e.l.l-lac in alcohol, tinged with saffron, annotta, aloes, or other colouring substances. It is applied to wood and metals to impart a golden colour. See VARNISH.

=LACTALBU'MEN.= See CASEIN.

=LAC'TATE.= _Syn._ LACTAS, L. A salt of lactic acid. The lactates are characterised by yielding an enormous quant.i.ty of perfectly pure carbonic oxide gas when heated with 5 or 6 parts of oil of vitriol. Most of these salts may be directly formed by dissolving the hydrate or carbonate of the metal in the dilute acid.

=LACTA'TION.= See INFANCY, NURSING, &c.

=LACTIC ACID.= H_{2}C_{6}H_{10}O_{6}. _Syn._ ACID OF MILK; ACIDUM LACTIc.u.m, L. A sour, syrupy liquid, discovered by Scheele in whey. It is also found in some other animal fluids, and in several vegetable juices, especially in that of beet-root.

Lactic acid is by no means an unimportant const.i.tuent of the human organism. It is contained in the gastric juice, and is frequently formed in the sweat. It has also been detected in the saliva of persons suffering from diabetes. A modification of the acid, termed sarkolactic acid, occurs in the fluids of the muscular tissue.

It is likewise a product of the fermentation of many vegetable juices, such as turnips, carrots, beet-root, and cabbage, which latter vegetable, after undergoing the lactic fermentation, becomes converted into the sauer kraut of the Germans.

In the form of calcic lactate it occurs in nux vomica.

_Prep._ 1. Dissolve lactate of barium in water, precipitate the barium with dilute sulphuric acid, carefully avoiding excess, and gently evaporate to the consistence of a syrup, or until it acquires the density 1215. Lactate of calcium may be used instead of lactate of barium, in which case a solution of oxalic acid must be employed as the precipitant.

Pure. (See No. 5.)

2. Milk (skimmed or stale), 1 gall.; bicarbonate of sodium, 1/2 lb.; dissolve and expose the liquid to the air for some days, until it becomes sour, then saturate the excess of acid with some more bicarbonate of sodium, and again expose it to the air; repeat this as often as the liquid becomes sour; next heat the liquid to the boiling point, filter, evaporate to dryness (or nearly), and exhaust the residuum with rectified spirit; filter the alcoholic solution, which contains lactate of sodium, add sulphuric acid as long as it causes a precipitate to form, again filter, and concentrate the clear liquid by evaporation.

3. (Boutron and Fremy.) Milk, 3 or 4 quarts; sugar of milk, 200 to 300 gr.; mix, and expose for 2 or 3 days in an open vessel at 70 to 80 Fahr., then saturate with bicarbonate of sodium, again expose at a moderate temperature, saturate with more bicarbonate of sodium, and repeat the process until the whole of the sugar of milk is decomposed; then coagulate the casein by heat, filter, evaporate, extract the acid lactate of sodium by alcohol of sp. gr. 810, and decompose it by the cautious addition of dilute sulphuric acid; again filter, distil off the alcohol, and evaporate as before.

4. (Scheele.) Evaporate sour whey to 1/8th of its bulk, saturate with slaked lime, filter, add 3 or 4 times the quant.i.ty of water, cautiously precipitate the lime with a solution of oxalic acid, filter, and gently evaporate to dryness in a warm bath; digest the residuum in strong rectified spirit, and again filter and evaporate.

5. (Wackenroder.) Sugar of lead, 25 parts; finely powdered chalk, 20 parts; skimmed milk, 100 parts; water, 200 parts; digested together at about 75 Fahr. In six weeks the chalk will be dissolved; the whole is then heated, but not to boiling; the cheese is strained off, pressed, and the decanted liquid is clarified by alb.u.men and evaporated, to let the lactate of calcium crystallise; the salt is recrystallised and decomposed, either by sulphuric acid or by the exact quant.i.ty of oxalic acid. This is, perhaps, the most effective mode of preparing lactic acid.

6. (Wholesale.)--_a._ Good raw cane-sugar, 7 lbs., is dissolved in milk (skimmed or stale), 2 galls., and cheese (in a moist or putrescent state), 1/2 lb., and chalk, 4 lbs., previously rubbed to a cream with water, 1-1/2 gall., is then added; the mixture is then exposed in a loosely covered jar, at a temperature of 80 to 86 Fahr., with occasional stirring, for 2 or 3 weeks, or until the whole is converted into a semi-solid ma.s.s of crystals of lactate of calcium; this is purified either by draining off and expressing the liquid portion, dissolving the residue in water, and evaporating the solution for crystals; or the whole is put into a stoneware vessel and heated to the boiling-point, by which the casein is coagulated, and the lactate of calcium is dissolved; the solution filtered whilst hot, furnishes the salt in crystals on cooling; these crystals are subsequently dissolved in water, and the filtered solution decomposed by oxalic acid, as before.

_b._ From cane-sugar, 4 parts; moist cheese, 1 part; chalk, 3 parts; water, 20 parts; as the last.

_Obs._ Lactic acid prepared by any of the used formulae may be rendered quite pure by dilution with water, saturation with baryta, evaporation, crystallisation, re-solution in water, and the careful addition of dilute sulphuric acid, as in No. 1; the liquid is, lastly, again filtered and evaporated. Another plan is to convert the acid into lactate of zinc, by the addition of commercial zinc-white, and to redissolve the new salt in water, and then decompose the solution with a stream of sulphuretted hydrogen. In all cases the evaporation should be conducted at a very gentle heat, and, when possible, finished over sulphuric acid, or _in vacuo_. For particular purposes this last product must be dissolved in ether, filtered, and the ether removed by a very gentle heat. Care must also be taken to remove the solid lactate of calcium at the proper period from the fermenting liquid, as otherwise it will gradually redissolve and disappear, and on examination the liquid will be found to consist chiefly of a solution of butyrate of calcium.

_Prop._ The product of the above formulae is a solution of lactic acid. It may be concentrated _in vacuo_ over a surface of oil of vitriol until it appears as a syrupy liquid of sp. gr. 1215; soluble in water, alcohol, and ether; exhibiting the usual acid properties, and forming salts with the metals, called LACTATES. Heated in a retort to 266 Fahr.; a small portion distils over, and the residuum on cooling concretes into a yellowish, solid, fusible ma.s.s, very bitter, and nearly insoluble in water. This is lactic acid, which has lost half (1 equiv.) of its basic water. By long boiling in water this substance is reconverted into lactic acid. Heated to 480 Fahr., it suffers decomposition, lactide (the anhydrous, concrete, or sublimed lactic acid of former writers) and other products being formed. This new substance may be purified by pressure between bibulous paper and solution in boiling alcohol from which it separates in dazzling white crystals on cooling. By solution in hot water and evaporation to a syrup, it furnishes common lactic acid.

_Uses._ Lactic acid has been given in dyspepsia, gout, phosphatic urinary deposits, &c. From its being one of the natural const.i.tuents of the gastric juice, and from its power of dissolving a considerable quant.i.ty of phosphate of calcium, it appears very probable that it may prove beneficial in the above complaints.--_Dose_, 1 to 5 gr.; in the form of lozenges, or solution in sweetened water.

=LAC'TIC FERMENTA'TION.= The peculiar change by which saccharine matter is converted into lactic acid. Nitrogenous substances, which in an advanced state of putrefactive change act as alcohol-ferments, often possess, at certain periods of their decay, the property of inducing an acid fermentation in sugar, by which that substance is changed into lactic acid. Thus, the nitrogenised matter of malt, when suffered to putrefy in water for a few days only, acquires the power of acidifying the sugar which accompanies it; whilst in a more advanced state of decomposition it converts, under similar circ.u.mstances, the sugar into alcohol. The gluten of grain behaves in the same manner. Wheat flour, made into a paste with water, and left for four or five days in a warm situation, becomes a true lactic acid ferment; but if left a day or two longer, it changes its character, and then acts like common yeast, occasioning the ordinary panary or vinous fermentation. Moist animal membranes, in a slightly decaying condition, often act energetically in developing lactic acid. The rennet employed in the manufacture of cheese furnishes a well-known example of this cla.s.s of substances.

In preparing lactic acid from milk, the acid formed, after a time, coagulates and renders insoluble the casein, and the production of the acid ceases. By carefully neutralising the free acid by carbonate of sodium, the casein becomes soluble, and resuming its activity, changes a fresh quant.i.ty of sugar into lactic acid, which may be also neutralised, and by a sufficient number of repet.i.tions of this process all the sugar of milk present may, in time, be acidified. This is the rationale of the common process by which lactic acid is obtained. Cane-sugar (probably by previously becoming grape-sugar) and the sugar of milk both yield lactic acid; the latter, however, most readily, the grape-sugar having a strong tendency towards the alcoholic fermentation. If the lactic fermentation be allowed to proceed too far, the second stage of the process of trans.m.u.tation commences, hydrogen gas and carbonic acid gas are evolved, and the butyric fermentation, by which oily acids are formed, is established.

Pasteur ascribes the lactic fermentation to the agency of a specific kind of ferment, which occurs in the form of a greyish layer deposited upon the surface of the sediment formed during the fermentation of the sugar, casein, and chalk (see Lactic acid, _b_), in the manufacture of lactic acid.

If to a mixture of yeast, or any nitrogenous substance, and water, sugar, and then chalk, be added, and finally a very small quant.i.ty of this greyish substance, taken from a portion of a liquid undergoing active lactic fermentation, lactic acid fermentation is almost immediately set up, the chalk disappears owing to the formation of calcic lactate, and the greyish substance is copiously deposited. When placed under the microscope this ferment is seen to be composed of "little globules, or very short articulations, either isolated or in threads, const.i.tuting irregular flocculent particles, much smaller than those of beer yeast, and exhibiting a rapid gyratory motion." If these little particles be washed thoroughly in pure water, and then placed in a solution of sugar, lactic acidification immediately commences in the saccharine liquid, and goes on steadily until stopped by the excess of free acid.

=LAC'TIDE.= See LACTIC ACID.

=LAC'TIN.= See SUGAR OF MILK.

=LAC'TOMETER.= _Syn._ GALACTOMETER. An instrument for ascertaining the quality of milk. Milk may be roughly tested by placing it in a long graduated tube sold for the purpose, and allowing it to remain until all the cream has separated and measured, then decanting off the clear whey, and taking its specific gravity; the result of the two operations, when compared with the known quant.i.ty of cream and the density of the whey of an average sample of milk, gives the value of the sample tested. See MILK.

A little instrument called a 'milk-tester' is sold in London at a low price. It is essentially a hydrometer which sinks to a given mark on the stem in pure water, and floats at another mark at the opposite end of the scale in pure milk. The intermediate s.p.a.ce indicates the quant.i.ty of water (if any) employed to adulterate the article. As the sp. gr. of pure milk varies, the indications of the 'tester' cannot be depended on.