albuminoids may be calculated out in terms of the original solids, which is doubtless a better guide to composition than the usual way of stating them. For example, calculating a malt, a "spirit-," and a "sugar "-vinegar in per cent. of the total solids, the results are as follows: Vinegar is often coloured with caramel; sometimes simply acetic acid thus coloured is sold as "vinegar." The estimation and detection of caramel has been worked out by C. Amthor* as follows:-10 cc. of the liquid are put into a flask with 30 to 50 cc. of paraldehyde, and absolute alcohol added until the liquids have mixed thoroughly. The flask is corked and allowed to remain undisturbed for twenty-four hours; by that time the caramel will have precipitated. To still further identify it, the liquid is decanted, the precipitate washed with a little alcohol, dissolved in hot water, and reduced by evaporation until it measures a cubic centimetre. On now treating the solution with phenylhydrazine, an insoluble compound is obtained. This is distinguished from the osazones of sugar by its amorphous appearance. Estimations of caramel are best made by imitating the colour of the paraldehyde precipitate; for this purpose the precipitate is dissolved in water, made up to 100, and a solution of known caramel content used as a comparison liquid. Possibly the phenylhydrazine compound could be weighed, but the limits of accuracy in this direction have not yet been defined, and the formula of caramel is not accurately known. A. Sabaneef and J. Antushevitch† believe, from cryoscopic researches, that its formula is CH188080 125 * Zeit. f. anal. Chemie, xxiv., 30-33. J. Russ. Chem. Soc., xxv., 23-31. BIBLIOGRAPHY. ALLEN, A. H., and BODMER, R.-Experiments on the Determination of -On Vinegar. Analyst, Jany. and Feb., 1894. BROWN, J. ADRIAN.-The Chemical Action of pure Cultivations of Bacterium aceti. J. Chem. Soc. (Trans.), 1886, xlix. 172. -On an Acetic Ferment which forms cellulose. Ib., 432. CAUVET.-Examen et analyse des vinaigres. Ann. d'Hyg. et de Méd Lég., 2e série, 1874, t. xli. CHEVALLIER, GOBLEY, et JOURNELL.-Essais sur le vinaigre, ses falsifica- GAULTIER DE CLAUBRY.-Ann. d'Hyg. et de Méd. Lég., 1841, t. xxvij. 1877, p. 105. PASTEUR. Études sur le vinaigre." Paris, Svo, 1868. 203. Analyst, i., Analyst, ii., 1878, 163, LEMON JUICE AND LIME JUICE. $290. Lemon juice is the expressed juice of the Citrus limonum, and lime juice that of the Citrus acida and Citrus limetta. The Board of Trade standard for lemon juice is a density of 1.030 [when dealcoholised], and an acidity equivalent to 30 grains per ounce of citric acid. The British pharmacopoeia directs that lemon juice should have a specific gravity of 1·039, and should contain 32.5 grains of citric acid per ounce. Lemon, lime, and bergamot juice are all similar in their composition, containing citric acid as the predominant free acid, and small quantities of acetic, formic, and other organic acids, together with albumen, sugar, mucilage, and extractive matters. The mineral matter is very small, and contains 54 per cent. of its weight in potash and 15 per cent. of phosphoric acid. The juice is expressed in England, and also in Sicily, where the method of preparation is to mix one ounce of brandy with ten ounces of the juice, and over the surface of the liquid to pour a layer of olive oil. This crude process of preservation is effectual, but is now being supplanted by more modern methods. The following table shows the specific gravity, free acid, and combined organic acid of the citric commercial juices, the acid being expressed in terms of crystallised citric acid [Allen] :— § 291. Adulterations and Analysis of Citric Juices.-Lime juice has been rather extensively adulterated, and at the present time it is by no means uncommon to meet with a wholly fictitious article under this name. Sulphuric, hydrochloric, and nitric acids are the main foreign ingredients to be sought for. The general principles of the detection of these acids in a free state are entirely the same as in vinegar, and the remarks with regard to the alkalinity of vinegar-ash when genuine apply equally to the ash from the citric juices. (See p. 584.) Good juice contains insignificant traces of sulphates and chlorides, so that the mere addition of silver nitrate or of barium chloride will at once show whether there has been any tampering with the liquid. Nitric acid may be detected by the ordinary tests for that acid. The juice may be boiled with metallic copper, when red fumes will appear, should nitric acid be present. Or, it may be much diluted and filtered, and one portion be made neutral with burnt magnesia, and boiled to expel all free ammonia; afterwards, by acting upon the liquid with a copper zinc couple, any nitrates may be turned into ammonia, distilled over, and titrated in the usual way. F. Scribani* adds to the suspected lemon juice an aqueous solution of ferrous chloride, strongly acidified with hydrochloric acid and free from ferric salt. The liquid is boiled for a few minutes, and then a little sulphocyanide is added. If nitric acid has been present, it will have oxidised the ferrous salt into a ferric salt, and a deep blood-red colour will be produced by the test. § 292. The Analysis of Lime Juice, with a view to ascertain its strength, is confined to the determination of the amount of citric acid and citrates. The amount of citric acid is determined frequently for technical purposes by the aid of a special hydrometer, called "a citrometer," but this method is not exact enough for the purposes of the food-analyst. Nevertheless, it will always be well to take the specific gravity of the juice by a specific gravity bottle, or by any other reliable method, first boiling off any alcohol which the juice may contain, and making it up to the same bulk as before the dealcoholisation. The amount of free acid may be estimated by means of decinormal soda. A known quantity of the juice is taken and coloured with phenol-phthalein, and then d. n. soda is run in until the colour changes. About 10 cc. of the ordinary raw juice may be taken and diluted to 50 cc.; but the concentrated juice must be much diluted before titration. The free acid known, the next step is to determine the amount of citrates and other organic acids combined with bases. For this purpose, the measured quantity of the juice which has already been neutralised by soda, is evaporated down, charred, and the charred mass treated with a known volume of decinormal *Gaz. Chim. Ital., viii. 294. sulphuric acid, which must be sufficient to more than neutralise the carbonates. The acid solution is filtered and neutralised by d. n. soda; this will give the necessary data from which to calculate the amount of sulphuric acid used by the carbonates produced by the action of heat on the organic acids. This amount is equivalent to the total amount of organic acid; if expressed as citric acid, forty-nine parts of sulphuric are equal to seventy of 2H,CH,O,H2Ŏ, or sixty-seven of HC,H,O,H20. The amount of free acid already obtained is now subtracted from the total acid, the difference being that which is combined with bases. To ascertain the amount of real citric acid present in the juice, it must be determined as citrate of lime, for it need hardly be said that the process given above does not distinguish between malates, meconates, or any other organic acids converted by heat into carbonates. To determine the real citric acid, Mr. Warington* recommends the following process: from 15 to 20 cc. of raw lime juice are exactly neutralised by d. n. soda, the whole made up to about 50 cc., and heated to boiling. While boiling, so much of a solution of chloride of calcium is added as is known to be rather more than equivalent to the total amount of organic acids present. The boiling must be continued for half an hour, and the precipitate collected and washed with hot water. The filtrate and washings are evaporated to a small bulk (not more than 15 cc.), and a little ammonia added to exact neutralisation, if the liquid gives an acid reaction; a further precipitation takes place, and this second precipitate must be collected on a filter. The filters are dried and burnt up at a low heat, and their neutralising power with regard to acid is determined. For this purpose, the ash may be dissolved in standard hydrochloric acid, and titrated back; each cc. of normal HCl neutralised is equivalent to 070 grm. of crystallised citric acid. If either oxalic or tartaric acids should be present, the results are, of course, inaccurate. *Journ. Chem. Soc., 1875, 934. |