The process employed for correcting the acescency of wine is not precisely known. Some wines are easily corrected; Mérat found that a bottle of harsh wine, which had a sharp, bitterish, rather acrid taste, took up in forty-eight hours twelve grains of litharge, and became palatable.[[1279]] With other wines this simple method will not answer, because the colour is destroyed, and a taste is substituted which has no resemblance to that of the genuine wine. Thus Orfila remarked, that Burgundy, neutralized with litharge, acquired a saccharine taste and became pale-red, because the insoluble salts of lead which were formed, combined with and removed the colouring matter.[[1280]] On the whole, it is probable that the adulteration of wine with lead can only be practised with success on the common tart kinds, such as those used by the lower orders on the continent.
Some excellent observations have been published on this subject by Fourcroy. In order to render what he has said intelligible, it is necessary to premise, that in the course of the fermentation of wine, the bitartrate of potass, which accelerates the conversion of the sugar of the fruit into alcohol, is itself partly converted into malic acid; that in sound wine, therefore, there is a mixture of tartaric and malic acids; but that if the malic acid originally existed in the fruit in too great abundance, the fermentation of the sugar is imperfect, and the wine is consequently both too acid and too weak; and lastly, that all wines, if neglected, are apt to ferment too much, in consequence of which they pass the vinous stage of fermentation, and become impregnated with acetic acid.[[1281]]
Now Fourcroy found that the oxide and other preparations of lead correct acescency and harshness in wines, not so much by throwing down the acids, as by combining with them in solution, and imparting to the liquor the peculiar sweetness of lead. Hence tart wines, which owe their acidity to too great a proportion of tartaric acid or bitartrate of potass, cannot be improved by adulteration with oxide of lead. For the bitartrate of potass cannot act at all as a solvent on the oxides or carbonate of lead, and even pure tartaric acid takes up so little, that wine containing it, could not acquire the sweet taste which is the purpose of the adulteration. This statement I have confirmed. But the case is very different when the wine contains acetic acid, the presence of which is the general cause of spoiling or acidity. For Fourcroy remarked, that acetic acid dissolves not only oxide and carbonate of lead, but likewise the tartrate, notwithstanding its great insolubility in water or in its own acid. Hence the presence of tartaric acid in a wine spoiled by co-existence of the acetic, will not prevent the liquor from taking up oxide of lead in sufficient quantity to acquire an improved taste and flavour. Nay, an obvious mode of correcting excessive acidity, produced by too much tartaric acid, is to add tartaric acid, and then to treat the mixture with oxide of lead. Fourcroy farther thinks, that the malic acid possesses the same solvent power as the acetic over tartrate of lead, and that its presence may therefore be the reason why some tart wines, which do not contain the acetic acid, become nevertheless impregnated with the poison. The solvent power of acetic acid is increased by the presence of other vegetable principles in the wine.[[1282]] I may add, that I have found the citric acid to possess the same property with the acetic and malic acids. It dissolves so much of the tartrate of lead as to acquire a pleasant sweetness, unmixed with metallic astringency.
The practice of adulterating wine with lead does not seem to have been ever pursued to any material extent in Britain. Home-made wines may be adulterated in this way, as may be inferred from the receipt formerly quoted for preventing acescency. But I have never heard that any such adulteration has been suspected in the foreign wines usually drunk in this country. Considering, indeed, the nature of these wines, and the class of people who alone make use of them, it is not likely that adulteration with lead could be practised with success. If the foreign wines used in Britain should become acescent, lead could hardly restore their taste so thoroughly as to impose on the consumer.
Sometimes spirituous liquors and preserves have been adulterated with lead, in consequence of sugar of lead having been used to clarify them, or to render them colourless. Cadet de Gassicourt says it is a common practice in France to clarify honey and sugar of grapes, and to make brandy pale in this way; and M. Boudet has detected lead in many samples of these articles in Paris.[[1283]] Hollands has likewise been poisoned in the same manner. Dr. Shearman mentions his having detected an extensive adulteration of smuggled Geneva by an excise officer, which had been sold and dispersed over an extensive tract of country, and which committed great ravages among the inhabitants.[[1284]]
The adulterations hitherto noticed take place through means of the chemical action of the adulterated articles on lead or its oxide. Some other substances are occasionally contaminated by its compounds being merely mechanically mixed with them. There is no end to the number and variety of adulterations of this kind. But the following will serve as examples. Gaubius once detected an adulteration of butter with white lead at a time when it was very scarce in Flanders, owing to a dreadful mortality among cattle.[[1285]] An instance of poisoning with lead, in consequence of cheese having been mixed with red lead, is mentioned in the Repertory of Arts.[[1286]] This variety deserves to be remembered. Red lead was at one time a good deal used to communicate the peculiar reddish-yellow colour, which is supposed to characterize the finer qualities of certain kinds of English cheese. In the Transactions of the Medical Society of London, a singular instance has been related by Mr. Deering, of lead colic attacking a whole family, and proving fatal to two of them, in consequence of the insidious introduction of white lead into the body. Although the nature of the symptoms in the several cases left no doubt that lead was the cause of them, it was long before the source of the poison was discovered. Every vessel and article used in the kitchen was in vain examined; when at length it was discovered that the sugar used by the family had been taken from a barrel which had formerly contained white lead, and that, as the sugar from the centre of the barrel had been dug out, and given away to various friends, the outer part of it next the white lead was chiefly used by the family themselves.[[1287]]
Process for detecting Lead in Organic Mixtures.
In the first place, a little nitric acid should be added to the suspected matter before filtration; for nitric acid redissolves any insoluble compound formed by the salts of lead with albumen and other animal principles, as well as some of those formed with vegetable principles; and consequently renders it more probable, that the poison will be detected in the first part of the analysis, if present at all.[[1288]] This being done, sulphuretted-hydrogen gas is to be transmitted through the fluid part of the mixture; and if a dark-coloured precipitate is formed, the whole is to be boiled and filtered to collect the precipitate.
In order to ascertain that the precipitate positively contains lead, those who are accustomed to use the blowpipe may put the sulphuret into a little hole in a bit of charcoal, and reduce it by the fine point of a blowpipe-flame; when a single globule is procured, which is easily distinguished by its lustre and softness. A better process, for those not accustomed to the blowpipe, and perhaps a better test of the existence of lead in all circumstances, is to heat the sulphuret to redness in a tube, and to treat it with strong nitric acid, without heat or with the aid of a gentle heat only. The lead is thus dissolved without the sulphur being acted on. The solution is then to be diluted with water, filtered, evaporated to dryness, and gently heated to expel the excess of nitric acid. If the residue be dissolved in water, it will present the usual characters of a lead solution when subjected to the proper liquid tests. Of these the hydriodate of potass is to be preferred when the quantity is too small for trying more of them. But for this purpose care must be taken to expel all the excess of nitric acid, because an excess will strike a yellow colour with the test though lead be not present.
If the preceding process should not detect lead in the filtered part of the mixed fluid, then the insoluble matter left on the filter is to be incinerated, and the residuum dissolved in nitric acid, and tested as above. This branch, however, will be rarely required, if lead be present, because the precaution of adding nitric acid, previous to filtration, dissolves the lead from most of its compounds which are insoluble in water. The process of incineration in medico-legal analysis generally should be avoided if possible, as it is not easily managed by unpractised persons.—The present branch of the process of analysis will be particularly required for the contents of the stomach or vomited matter, when any sulphate or phosphate has been given as an antidote.