CIT

CIT ( 2.90 )

cryftallizing when evaporated nearly to dry-nefs.

Lemon-juice is clarified partly by being putfor a day or two in a cold cellar, remaining per-fectly at reft. Much of the mucilage thenfubfides, and the clear juice poured off, bottled,and carefully corked, will then keep for a con-fiderable time. It is better if brifkly boiled fora minute or two before it is put afide to clarify,but this fomewhat impairs the flavour, andgives one that is not agreeable. In the Medi-terranean, oil is poured over it to prevent theaftion of the air, which has a temporary effect,but after a while the juice beneath becomesmuddy, bitter, mouldy, and befides gets a ranktafte from the oil. Concentration by freezingis fometimes ufed with fome fuccefs. If themucilage is firft feparated as much as may beby ftanding in a cool place, and the clear juicethen expofed to a cold of from 23 0 to 26° thewatery part alone freezes, and the remainingunfrozen liquor, of courfe, contains the acid ina condenfed ftate. By continuing to removethe ice, till it begins to grow four from the aciditfelf freezing, lemon juice may be concentratedto about one-eighth of its former bulk, and isthen clear, intenfely four, and will keep in acool climate for feveral years unaltered. 0 Stillhowever the extradt entirely remains and partof the mucilage, and therefore in tropical cli-mates even this concentrated juice fpoils in nogreat length of time, d befides the capital defedtin the utility of the procefs, that the cold whichit requires can never be obtained naturally inthe countries where the fruit grows, and at thefeafon in which it is moft likely to fpoil.

Sometimes certain mixtures are added tolemon juice to preferve it. Forfter found inCook’s Voyage to the South Pole that thejuice mixed with a fifth part of brandy or rum,in well clofed calks, kept very well for thirty-two months. Brugnatelli* propofes to clarifythe juice by alcohol. Frelh lemon juice wasmixed with fome ftrong alcohol and bottled.In a few days a llimy mucilage had feparated,and the liquor filtered through paper, containedthe purified juice with alcohol, which laft maybe feparated by evaporation. But it is obviousthat this only very partially clarifies the juice,for the clear liquor, evaporated llowly to dry-nefs, (fives no cryftals, but only a four extradt.Befides, the expenfe forbids its being ufed in thegreat way. Some perfons add fulphuric or fomeother mineral acid to the juice, partly to pre-ferve and partly to adulterate it. The juice is

• Georgi from the A£ta Sot. Petropol. * Proull.,

indeed kept a long time from moulding by thisaddition, but the adulteration is often a feriousinconvenience and lofs. Evaporation is cer-tainly the belt method of preferving the juice inhot climates in its natural ftate, that can bepractifed in the large way. This juice cannotbe purified like vinegar by diftillation, for, beinglefs volatile than water, it will not rife in vapourwith a heat lefs than will decompofe it; but ifthe frelh juice limply ftrained be expofed to avery gentle heat, the greater part of the waterflies off without carrying away any of the acid,and when the liquor has nearly a fyrupy con-fluence (before it acquires a burnt tafte), it isthen intenfely four, and will keep in bottles formany years, with very little alteration, and evenretaining much of its original flavour. Thisinfpiffated juice or Rob of Lemons , as it iscalled, if intended for the table, may be imme-diately mixed with dry white fugar, which isknown to preferve all vegetable matter fromcorruption, and it will then keep for almoft anylength of time unimpaired, and is excellent forfea voyages and domeftic ufe. In hot climatesthe heat of the fun is made to aflift confiderablyin the evaporation.

But the pure citric acid cannot be obtainedby fuch Ample methods, but a double procefsof chemical affinity is required, firft, by adding-an intermede to feparate it from the other partsof the juice, and next to obtain it free from this-addition in its cryftallized form. This veryingenious procefs was difeovered by Scheele f ,and fince has been followed by all fucceedingchemifts, with only a flight variation in the pro-portions and minutiae of the procefs. The in-termede which this admirable chemift ufed waslime added in the form of chalk, the fame thathe had before employed for a fimilar purpofein preparing the concrete acid of Tartar .

The mode he recommends is in a few wordsthe following: Saturate boiling lemon juicewith chalk in powder added gradually, till nomore effervefcence arifes. The compoundthence arifing is a grey infoluble mafs, thecitrat of lime, which readily fettles, leaving themucilage, extradt, and other ingredients of thejuice in the fupernatant liquor, which is thrownaway, and the calcareous precipitate well waffied-with cold water till it is colourlefs. Then add;to the precipitate a quantity of dilute fulphuricacid, diluted with ten times its bulk of water,and equal in weight to the chalk ufed, and boilfor a few minutes. This by ftronger affinity,unites with the lime, forming a fulphat of lime

• A»nali dLChemia, vol.ii. Ph.Mag, vol, ii„ 1 EiTaye