sulphates was found in gin by the Commission of the 'Lancet.' This adulteration is detected by means of chloride of barium, or nitrate of baryta, which occasion in the liquor a precipitate of sulphate of baryta, insoluble in nitric acid. If the acid is combined with zinc, ammonia and sulphuretted hydrogen will produce a precipitate of white sulphuret of zinc; if it is combined with alumina, in the form of alum, evaporate to dryness, dissolve the residue in water, and proceed as directed at p. 20. Free sulphuric acid is also occasionally added to spirits.

Lead.-Should acetate of lead have been used to adulterate spirits, concentrate the liquor, and test as directed at p. 41 for lead, and p. 43 for acetic acid.

The samples of spirits examined by the Commission of the Lancet' yielded from 22.35 to 48.80 per cent. of alcohol; this great variation in their strength being, doubtless, principally attributable to dilution with water. They found from 3 oz. 4 dr. 23 gr. to 13 oz. 4 dr. 13 gr. of sugar per gallon of gin; two of the analysed samples contained oil of cinnamon, or, more probably, of cassia; seven of the samples yielded cayenne pepper, some of them in very large quantity. They failed to detect free sulphuric acid in gin, the spirits being neutral to test paper; but most of the samples were found to contain sulphates, mostly derived from the water and alum used in the adulteration and clarification of the spirit.

VINEGAR.

Vinegar being the result of a peculiar fermentation, I shall conclude the present chapter with a short account of this article of diet, and its adulterations.

Vinegar is the product of the phenomenon known as the

acetous fermentation. When a solution of sugar is mixed with a ferment, and allowed to stand undisturbed, freely exposed to the atmosphere, it is converted into alcohol; but if the fermentation be allowed to continue longer, the alcohol rapidly disappears, and, in its place, vinegar is found.

In France, vinegar is usually prepared from wine. At Paris, the wine destined for this purpose is mixed with wine-lees, transferred into cloth sacks, and strained by pressure. The fluid is next exposed to the heat of the sun in summer, or to that of a stove in winter. Fermentation supervenes in a few days; in a few days; in summer, the process is usually completed in a fortnight; in winter, double the time is requisite. The vinegar is then run off into barrels, which contain chips of birch wood. In about a fortnight, it is found to be clarified, and is then fit for the market. In this country vinegar is usually made from an infusion of malt mixed with the barm of beer; the fluid is collected in casks placed upright, and supplied with a false cover pierced with holes, which is fixed at about a foot from their bottom. The liquor is poured into another barrel every twenty-four hours; and, towards the end of the fermentation, rape or refuse from the maker of British wine, or a quantity of low-priced raisins, are added to communicate flavour.

Finally, vinegar has been long prepared by the distillation of wood; oak, ash, birch, and beech being used for this purpose. The crude products of distillation are rectified by a second distillation in a copper still; and then, by mixing the fluid with lime, evaporating it to dryness, roasting gently the residue, decomposing the calcarious salt with sulphuric acid, and distilling the mixture; a perfectly colourless and grateful vinegar distils over. French vinegar is distinguished from all those varieties made in

Britain, by the action of ammonia, which occasions a purplish muddiness and precipitate in the former. The latter, or British vinegars, are either unaltered by ammonia, or produce with it a dirty brownish precipitate.

Chemical analysis of vinegar. - Vinegar owes its active properties to an organic acid called acetic acid, it is important that we should possess satisfactory and prac tical means of estimating the proportion of this acid in a given quantity of vinegar. The most convenient method is to use a normal solution of carbonate of soda, and to add the fluid, drop by drop, until the mixture, when tested with blue litmus paper, has ceased to turn it red. 97 grains of the pure hydrated acid (sp. gr. 1063) are neutralized by nearly 242 grains of crystallized carbonate of soda. As in the analysis in question, the colour of the test paper might be affected by the carbonic acid evolved from the carbonate of soda, it will be advisable to dry the test paper after each immersion; if the red colour is owing to free carbonic acid, the paper, when dry, will reassume its blue appearance. Should free sulphuric acid have been found present in the vinegar under examination, it will be necessary to distil the liquid nearly to dryness, and then determine the amount of anhydrous acetic acid contained in the distillate. French wine vinegar yields from 3:46 to 5.10 per cent. of pure acetic acid (Dr. Hassall).

Adulterations of vinegar.-According to Dr. Christison, vinegar may be adulterated with water, sulphuric acid, copper, lead, and acrid vegetable substances; to these; Dr. Hassall adds pyroligneous acid and burnt sugar.

Water. To determine how much water there exists in a given quantity of vinegar, ascertain first the amount

of pure hydrated acid which it contains (see page 138); then evaporate to dryness another weighed sample of the fluid, and weigh the residue, thereby obtaining the total amount of fluid in the vinegar; by subtracting the weight of the pure acetic acid from the total amount of fluid lost. by evaporation in the second operation, the weight of the water will be obtained.

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Sulphuric acid.-The addition of one part of sulphuric acid to a thousand of British vinegar is permitted by law; so that, unless the quantity should exceed this, it is not to be considered as an illegal adulteration. In some cases, however, the Commission of the Lancet' have found samples of vinegar to consist of little else than sulphuric acid, coloured with burnt sugar. This adulteration is not uncommonly met with in low coffee-houses and oyster-stalls. Test (see page 94) The quantitative determination of sulphuric acid may be obtained with a normal solution of chloride of barium, prepared in such a way that 1·2 grain of chloride of barium be dissolved in 100 grains of distilled water, a quantity which represents half a grain of commercial sulphuric acid. Five hundred grains of vinegar should be poured into a beaker, and the solution gradually added so long as any precipitate forms. A more exact method is to add an excess of chloride of barium to a weighed sample of the vinegar, to collect the precipitate of sulphate of baryta on a filter, burn the filter, and determine the weight of the ashes. If sulphuric acid should be present in vinegar in the form of a sulphate, by evaporating some of the vinegar to dryness and igniting the residue, the ashes dissolved in distilled water will yield, with chloride of barium, a precipitate insoluble in nitric acid.

Burnt sugar-For the detection of this adulteration, evaporate the vinegar to dryness, treat the residue with

water, and test the aqueous solution as directed at p. 9. Burnt sugar is sometimes used for colouring vinegar. Copper and lead.-These substances may find their way into vinegar. Test: The adulteration is detected by sulphuretted hydrogen, which occasions a black precipitate in the vinegar. If copper be present, ammonia will produce a blue colour in the fluid; iodide of potassium will occasion a yellow precipitate of iodide of lead, in vinegar containing a comparatively large quantity of this metal.