Acid of Lemons prepared in the Large Way.

XIII.

43

On the Preparation of concrete Acid of Lemons. By DIZE, Apothecary in Chief to the French Army, charged with the Inspection of the General Magazine of Medicines *.

THOUGH nature prefents us with the citric acid nearly in a difengaged state, it is nevertheless confounded in lemon juice with an extractive mucilaginous matter, which oppofes the union of its cryftallizable particles, and which cannot be feparated by the fimple process of evaporation and exposure to crystallize.

Scheele was the first who obtained this acid in the folid form. In the year 1774, Georgius in Sweden, and afterwards Du Buiffon in France, published obfervations on the method of concentrating and preferving lemon juice. Although their labours, as well as the experiment of Stahl and Guyton, could not determine the crystallization of this acid, it is nevertheless certain that their researches were very useful to affift Scheele in his discovery of the process he has left us.

I availed myself of an opportunity to repeat the process of Scheele in the large way, and to infift on an effential obfervation, which that chemift has not fufficiently developed; for It is one of the neceffary conditions for fuccefs in the cryftallization of this vegetable acid. Scheele, after feveral unfavourable attempts, advises the feparation of the extractive and mucilaginous matter of lemon juice, by uniting the citric acid to the bafis of calcareous carbonate, with which it forms a citrate of lime, that precipitates on account of its sparing folubility, while the extractive and mucous matter remains diffolved in the fluid. This citrate of lime is afterwards decompofed by a fufficient quantity of fulphuric acid diluted with water, with the precaution to add an excefs of this last acid. The fulphuric acid feizes the lime from the citric acid, and forms a fulphate, which falls to the bottom because nearly infoluble; while the citric acid, being fet at liberty, is diffolved in the water with which the fulphuric acid was diluted.

Filtration and washing with cold water feparate the citric acid entirely from the fulphate of lime, and it may be afterwards obtained in the concrete state by evaporation in stoneware veffels, at the temperature of boiling water. I have observed that it is very useful to fufpend the evaporation every two days, in order to permit the fulphate of lime, which is fufpended by the affiftance of the citric acid, to fall down.

The citric acid which I have prepared is the product of feveral chefts of lemons. The mafs of calcareous citrate which was decompofed was fomewhat confiderable, and the ope ration was performed in large stone-ware veffels. The fulphate of lime obtained by the decompofition of the calcareous citrate was well washed in tubs of white wood. The dif ferent liquors were united together for evaporation in ftone-ware veffels, at the temperature of boiling water. They were clear, light-yellow, and contained an excess of fulphuric acid.

As foon as the liquors were fufficiently concentrated by evaporation, the fulphuric acid exerted its action, and the yellow colour became brown, and even blackifh at the end of

* Read to the National Institute of France, and copied in the Journal de Physique, published to fupply the defect of the number for September 1794.

44

Purification of the Acid of Lemons.

the evaporation. The mafs of crystals which was taken out, after cooling and three days repofe, was confiderable and black.

I fuffered this faline mass to drain in ofier baskets, while the evaporation and crystallization of the remaining fluid were performed. When this first operation was ended, the whole of the faline mass was re-diffolved in a fufficient quantity of cold water, and filtered through ftrainers of linen, covered with filtering paper.

The folution which paffed the filter was clear, but of a dirty brown, and the greatest quantity of the matter which had blackened the crystals remained behind. This was again evaporated, left to cryftallize, and in this manner exhaufted of the citric acid. The crystals were now yellow, and more regularly figured. By a third folution, filtration, and evaporation, the crystals were again obtained white, regular, and of the greatest purity. The black matter depofited on the filter was fo trifling that it formed a very flight covering.

Scheele, who was content with having proved the poffibility of obtaining this vegetable acid in a concrete ftate, could not determine its natural form, because he operated on fuch fmall quantities.

My results afforded crystals as large as are usually obtained from the ordinary proceffes of faline folution, and as eafily to be defcribed. They prefent, on simple inspection, rhomboidal prisms, the fides of which are inclined to each other in angles of about 120 and 60 degrees, terminated at each end by four trapezoidal faces which include the folid angles.

I have before remarked, that Scheele had obferved, as one of the conditions effential to the ready crystallization of the citric acid, to add a fmall quantity of fulphuric acid in excefs beyond the exact quantity neceffary to decompofe the calcareous citrate. The remark of this chemift not being followed by any explanation, my trials in the large way have proved the great difcernment of the chemist of Gottingen; and that, if he had operated on a quantity of lemon juice equal to that which I purified, he would have ascertained the reasons why this excefs of acid was found to be neceffary in his more confined expe

riments.

Having ascertained that the black matter remaining on the filters in this process is charcoal, it follows that it could not have been afforded but at the expence of a confiderable portion of the mucilaginous matter of the lemon juice, which the citric acid had carried with it in its combination with the base of the calcareous carbonate; and that afterwards when the citrate is decompofed, the excefs of fulphuric acid is required to decompofe this mucilage, and precipitate the carbone, as foon as the fluid begins to be condensed by evaporation. The ingenious experiments of Fourcroy and Vauquelin prove the nature of the action of fulphuric acid on vegetable matter, and strongly confirm my inductions *.

Lemon

*For the fe important experiments fee Philof. Journal I. 385.-In order to fhew that mucilage enters into the citrate of lime, and that it is decompofed by fulphuric acid, it seems neceffary to make the experiment with only a very minute excess of the latter. Scheele thought the acid (Effays, p. 362.) in the citrate to be pure, aud he required an excess of fulphuric acid to be added to insure the saturation of the whole of the lime. I would propofe to the confideration of the learned author of this paper, to afcertain whether it be not a portion of the acid itself which is altered and made to depofit carbone. If fo, the lefs the furplus of fulphuric acid the better:

buc,

Purification of the Acid of Lemons.

45

Lemon juice separated from all the mucous matter which falls down by exposure to the contact of the air for a few hours, that is to fay, fuch as it ought to be for ufe in medicine or the arts, marks five degrees of density by the areometer for falts of Baumé (specific gravity 1.034). One hundred pounds of this juice require for faturation fix pounds four ounces of calcareous carbonate. The citrate of lime, after being well washed and dried,, weighs twenty pounds.

One pound of pure crystallized acid of lemons diffolved in a fufficient quantity of water, demands one pound of carbonate of lime for its faturation. In this experiment the weight of calcareous citrate has diminished the mass rather more than one-fourth part, instead of increasing it upwards of two-thirds, as in the foregoing combination. Whence it may be concluded, that one hundred pounds of lemon juice faithfully prepared, and of the strength of five degrees by Baumé's areometer for falts, contain fix pounds four ounces of pure concrete acid. This ferves to explain two phenomena; that is to say, the increase of 13lbs. 12oz. in the calcareous citrate from lemon juice, and the prefence of mucilaginous matter. diffolved in that liquid, which enters into the combination of the calcareous citrate, and is afterwards decomposed by the excess of fulphuric acid necessary to be added when that citrate is decompofed.

One ounce of distilled water diffolves an ounce and two drams of citric acid, and produces 13 degrees (R.) of cold by the folution. A like quantity of diftilled water diffolves twice its weight of this acid, when it is heated to 80 degrees, or the boiling temperature. One hundred parts of citric acid diffolved in a sufficient quantity of diftilled water, boiling hot, diffolve 50 parts of calcareous citrate.

pure

A lemonade of the most agreeable taste and appearance may be had by diffolving 40 grains of citric acid in a pint of water, with the addition of a fufficient quantity of fugar. It may be rendered fragrant by diffolving a small quantity of oleo-faccharum, prepared by rubbing a lemon on a lump of fugar. The fugar imbibes the volatile oil of the lemon, and renders it foluble. It is easy by this means to preserve the whole of the volatile oil of a number of lemons. The oleo-faccharum thus obtained may be mixed in a mortar with a sufficient quantity of fugar. The mixture is then to be dried by a gentle: heat, and preferved in well clofed glafs veffels. This method of procuring the flavour of lemons at all times is preferable to employing the volatile oil obtained by distillation. The action of fire communicates to this laft an acrid flavour, easily distinguished by a delicate: tafte.

I fhall finish my obfervations by enumerating fome of the characters of this acid, when mixed with different earthy and metallic folutions.

Solutions of the acetites of magnefia, lime, alumine, of the muriates of barytes, lime,. alumine, and magnesia, and of the nitrates and fulphates of thefe fame fubftances, do not undergo any change by the presence of the citric acid.

The muriates and nitrates of zinc, the fulphate, muriate, nitrate, and acetite of

copper,

but, on the other hand, if his inference be correct, the furplus must be a definite quantity, namely, fufficient so deftroy the mucilage. The difference of weight in the citrates formed by the crude and the purified acids with equal doses of lime, as mentioned in a fubfequent paragraph, may arife either from the prefence of mucilage in the former acid, or a change of affinity for lime produced by the re-action of the excess of fulphuric acid on the latter: but experiment muft determine which. N.

and

and the nitrate of lead, are not decompofed, but the acetite of lead is immediately decompofed and precipitated in a white powder. The nitrate and acetite of mercury are alfo decompofed, and the mercurial citrate which falls down is a flaky falt, of a brick-dust colour, more or lefs red. The citric acid gives a green tinge to the solution of the acetite and fulphate of iron.

The quantity of citric acid which I obtained being confiderable, I intend hereafter to give an account of the phenomena it exhibits in its different combinations.

XIV.

Useful Notices refpecting various Objects.—Governor for regulating the Motions of SteamEngines.-Amelioration of Oil.

1. Governor for regulating the Motions of Steam-Engines.

THE apparatus mentioned page 424 of the prefent work by the name of a Governor, is

there supposed to be the invention of Mr. Watt. My fuppofition was grounded upon no other fact than that of having seen it in his engines. It was invented by Bunce, Efq. of the Admiralty, who applied it to a crane feveral years ago, the construction of which was communicated to the Society of Arts, soon after which period it was adopted in steamengines. I cannot now refer to the volume, as I do not poffefs the set. But I had the information from the inventor himself.

2. Amelioration of Oil.

EVERY one who has occafion to use lamps must be fenfible that the colour of the light, as well as the quantity and kind of difagreeable vapour emitted from the flame, depends greatly on the quality of the oil. When oil is kept in an open veffel, it gradually becomes more and more oxygenated, and at the fame time less fluid. For both these reasons it is lefs fit for ufe. It is lefs combuftible, and lefs adapted to pafs between the fibres of the wick. These observations point out the expediency of keeping oil in well-closed veffels. The fluidity of whale-oil, and the facility of its combuftion, may be confiderably augmented by an addition of cold-drawn linseed oil.

It is well known that oil may be rendered purer by agitation with water, more particularly with the addition of an acid. The effect of this procefs is ftated to be, that it carries off a portion of mucilage, which is not adapted to answer the purposes to which oil is applied. It may easily be imagined, however, that oil thus treated will retain a portion of aqueous or faline matter, which may render it unfit to be applied to the moving parts of inftruments for the purpose of diminishing friction. Some clock and watch makers expofe olive-oil to the atmosphere in frosty weather; and select that portion which they find to continue fluid after a confiderable part is frozen. This proceeding is grounded on the fuppofition, that the oil may confift of two different fluids, one of which is supposed to congeal in a less heat than the other; and that this congelation is the principal evil which happens to the oil in

time-pieces. It does not feem probable that either of these fuppofitions are well founded.

For

Purification of Oil.-New Publication.

47

For the whole of the oil will freeze, if time be allowed; and the thickening of this fluid appears to be produced by chemical change, and not by mere cooling. Mathematical inftrument-makers, directed, as I imagine, by experience only, find that oil is greatly improved by exposure to light, which it is afferted caufes it to depofit mucilage. A very exquifite regulator having the dead-beat scapement of Graham, which requires oil on the pallets, was found to go much more fteadily when this oil was ufed, instead of the oil commonly applied to fuch inftruments.

Most of the facts here stated respecting oil were communicated to me by an intelligent cultivator of the fciences, whofe name I forbear to add because I neglected to afk permiffion for that purpose.

NEW PUBLICATION.

Reports of the late Mr. John Smeaton, F. R. S. made on various Occafions in the Course of his Employment as an Engineer. Printed for a Select Committee of Civil Engineers. Sold by Faden in London. Quarto. 412 pages, rather closely printed, with a Portrait of the Author, and 2 plates.

THAT Smeaton was a man of strong natural powers and great industry, that his expe

rience and obfervations were extenfive, and his fuccefs highly to the credit of himself and his country, are too well known to be infifted upon. This firft volume of his Reports is published at the expence of Sir J. Banks, Capt. J. Huddart, Wm. Jeffop, Robert Milne, and John Rennie, Efqrs. conditionally that the profits fhould be given to Mr. Smeaton's reprefentatives. If this liberal effort, by which the nation is benefited by so valuable a mass of practical information, fhould be attended with fuccefs, another volume will appear, containing the remainder of the Profeffional Reports of this great engineer. I fhall take the earliest opportunity of communicating the general principles ufed and adopted by Smeaton, in a paper I intend to draw up refpecting the relative value and effect of firft movers, and other elementary objects of daily ufe to engineers; and in the mean time shall avail myself of the Preface, nearly verbatim, to thefe Reports, to give fome account of the Society of Civil Engineers.

The origin of the Society of Civil Engineers took its rife from the following circumstances:-Before or about the year 1760, a new era in all the arts and sciences, learned and polite, commenced in this country. Every thing which contributes to the comfort, the beauty, and the prosperity of a country, moved forward in improvement fo rapidly and fo obviously as to mark that period with particular distinction.

The learned Societies extended their views, their labours, and their objects of research. The profeffors of the polite arts affociated together for the first time; and they now enjoy a protection favourable to improvement, and not lefs honourable to real merit than to the Public and the Throne, which have with one'accord promoted their prosperity.

Nor have these exertions failed of producing the adequate effects, comparing the present with the paft ftate of things.

Military and naval establishments were made or enlarged, to promote and extend the true knowledge on which thefe fciences depend.