Chapter LXXII: Section I: Of the Chemical History and Tests for the Preparations of (2)

Another fact of some practical consequence, which flows from the experimental conclusions stated above is, that although it may be perfectly safe to keep some waters in leaden cisterns, it may be very unsafe to use covers of this metal, because the water which condenses on the covers must be considered as pure as distilled water. It has been found that white lead forms in much larger quantity on the inside of the covers of cisterns than on the cisterns themselves, where both are constructed of lead. A remarkable illustration of this is mentioned in a paper read before the Academy of Sciences at Paris in 1788 by the Comte de Milly. About a year after getting two leaden cisterns erected in his house, to keep the water of the Seine for general domestic purposes, he was attacked with severe and obstinate colic; which led him to examine his cisterns. He found that the sides, where they were occasionally left exposed by the subsidence of the water, and more especially the leaden cover, were lined with a white liquid, which was constantly dropping from the lid into the cistern, like the drops in caverns where stalactites are formed. The water was in consequence so strongly impregnated with lead as to give a dark precipitate with liver of sulphur.[1259] The reason of this occurrence is, that the water in the cistern is a solution of preventive salts, but what reaches the lid is in a manner distilled. In Edinburgh the lids of the cisterns are invariably made of wood, whether on account of its superior cheapness merely, or because a leaden cover had been found perishable, I have not been able to discover.

It may be well to conclude these remarks on the action of spring waters on lead with a general summary of the chief circumstances to be adverted to in using lead for keeping or conveying water; to which may be added a few hints for preventing action where it is found to have taken place.

The general results of the preceding inquiries are that rain or snow-water for culinary use should not be collected from leaden roofs, nor preserved nor conveyed in lead;—that the same rule applies to spring waters of unusual purity, where for example the saline impregnation does not exceed a 15,000th of the water;—that spring water which contains a 10,000th or 12,000th of salts may be safely conveyed in lead pipes, if the salts in the water be chiefly carbonates and sulphates;—that lead pipes cannot be safely used, even where the water contains a 4000th of saline matter, if this consist chiefly of muriates;—that spring water, even though it contain a large proportion of salts, should not be kept for a long period in contact with lead;—and that cisterns should not be covered with lids of this metal.

Where action is observed to take place in the instance of particular waters, it may in some cases be impossible to prevent it by any attainable means. But the inquiries detailed above suggest two modes by which a remedy may be generally found. It appears that, where a crust of carbonate is allowed to form slowly and quietly on the surface of lead, even distilled water ceases to have any material action; and that the action is reduced almost to nothing if a crust be thus formed in a solution containing a minute quantity of some powerfully protecting salt, such as phosphate of soda. It appears to me then that a remedy may be often found in the instance of unusually pure spring waters—either by leaving the new pipes filled with the water for a few months, care being taken not draw any water from them in the interval,—or perhaps even more effectually by filling the pipes for a similar period with a solution containing about a 25,000th of phosphate of soda. I had determined to try the latter plan with the pipes in the Dumfries-shire case mentioned above, but recommended that in the first instance the pipes should be left for a few months full of the water of the spring, and the stop-cocks kept carefully shut; and on this being done for three or four months, it was found that the water afterwards passed with scarcely any impregnation of lead, and what little was contracted at first gradually diminished in the course of time.—Probably neither of these methods will be of more than temporary use, when the chief or only salt present is chloride of sodium, even though the proportion be considerable. Both plans seemed to answer for a time in the instance which occurred at Lord Aberdeen’s (p. 411); but after a while the action recommenced, probably owing to the deposited carbonate being slowly dissolved. At the time of publication of my paper in the Transactions of the Royal Society of Edinburgh, the cure appeared complete, and was there represented to be so.

I should add that an effectual remedy has been lately introduced by a patent invention for covering lead pipes both externally and internally with a thin coating of tin.

In the remarks now made on the action of water on lead no account has been taken of the effect of the galvanic fluid in promoting it. This, however, is a most important co-operating agent, or rather perhaps it ought to be considered a distinct power; for it acts with energy where water alone acts least, namely, when there is saline matter in solution, because then a galvanic current of greater force is excited. In general it is necessary that two different metals be present in the water before galvanic action be excited; but a very slight difference may be sufficient. For example, it seems enough that the lead contain here and there impurities, constituting alloys slightly different from the general mass of the pipe or cistern. It is probable that galvanic action may be thus excited by the joinings being soldered with the usual mixture of lead and the more fusible metals. At least I have seen pipes deeply corroded externally, when made of sheets of lead rolled and soldered; and the action was deepest on each side of the solder, which had itself entirely escaped corrosion. Even inequalities in the composition of the lead may have the same effect. Sheet lead long exposed to air or water is sometimes observed to be corroded in particular spots; and these will always be found in the neighbourhood of parts of the metal differing in colour, hardness or texture from the general mass. I have not analyzed such spots; but I conceive the supposition now made is exceedingly probable, and supplies a ready explanation of the corrosion. Similar effects may arise simply from fragments of other metals lying long in contact with the lead. They may also arise from portions of mortar being allowed to lie on the lead; but the action here is not galvanic.

I have no doubt that many of the instances of unusually rapid corrosion of lead by water, such as that mentioned by Dr. Wall [p. 410] are really owing, not to the simple action of water, but to an action excited obscurely in one or other of the ways now mentioned.

_Of the Action of Acidulous Fluids on Lead and its Oxide._

Water acidulated with various acids acts on lead with different degrees of rapidity.

The effect of acidulation with _carbonic acid_ has not yet been accurately ascertained. The effect of _sulphuric acid_ is peculiar. Distilled water feebly acidulated with that acid acts much less rapidly on lead than when quite pure. Thus I have found that, if it contained a 4000th or even only a 7000th of sulphuric acid, fifty grains of lead kept in it for thirty-two days gained a seventh or a twelfth of a grain in weight, and were covered with beautiful crystals of sulphate of lead. A minute trace of lead could be detected in the water. _Hydrochloric acid_ is somewhat more active as a solvent. Distilled water containing a 3000th of that acid acquired in thirty-two days a sweetish taste, and yielded by evaporation a considerable quantity of muriate of lead, while the lead rods lost weight, and were covered with acicular crystals of the same salt.

It is much more important, however, to consider the effects of the vegetable acids on lead and its oxide, because their solvent power is a fruitful source of the accidental as well as intentional adulteration of many articles of food and drink.

_Acetic acid_ in the form of common vinegar, even when much diluted, attacks and dissolves metallic lead, if by exposing the surface of the fluid to the air, a constant supply of oxygen be maintained to produce oxidation. The _citric acid_ will attack it under the same circumstances, but acts more slowly. In a solution of five grains of citric acid in twenty-four parts or two drachms of water, three lead rods lost two grains in weight in nine weeks. The greater part of the citrate of lead separated slowly in white powdery crystals; but a small portion was dissolved by the excess of acid, and imparted to the fluid a pleasant sweetness. _Tartaric acid_ acts much less energetically. In a comparative experiment with the last, the lead gained nearly half a grain in weight by acquiring a crystalline coat of tartrate of lead. But I could not detect any lead in solution; and there was no loose powder. The tartrate of lead is very sparingly soluble in an excess of its acid, so that a sweet taste cannot be communicated by it to a fluid acidulated with tartaric acid. _Malic acid_, according to MM. Chevallier and Ollivier, acts so quickly as a solvent, that if a solution be kept in a lead vessel for three hours, the metal may be detected in the fluid by any of its ordinary tests.[1260]

The acids act with greater rapidity on the protoxide of lead than on the metal; and the presence of air is of course not required to enable them to effect its solution.

The solvent power of the acids is liable to be counteracted by various substances; the operation of which, however, has not been well ascertained. It appears that substances containing gallic acid or tannin throw down the lead; and on this account various adulterations which would otherwise take place are either prevented or corrected. It has been also ascertained by Proust, that the vegetable acids do not attack lead when it is alloyed with tin. For as the latter metal has a stronger attraction than the former for acids, no lead can be oxidated before the tin undergoes that change.[1261]

From what has been said of the action of the vegetable acids, it follows that the preparation or preservation of articles of food and drink in leaden vessels is fraught with danger. For, if they contain a vegetable acid, more particularly the acetic, as many of them do, and if they are allowed to remain in the vessel for a moderate length of time, they will be apt to be impregnated with the metal. In this way lead has been often insidiously introduced into the food of man.

Thus milk has been poisoned by being kept in leaden troughs. An instance of the kind has been related by Dr. Darwin. A farmer’s daughter used to wipe the cream from the edge of the milk which was kept in leaden cisterns, and being fond of cream, had a habit of licking it from her finger. She was seized in consequence with the symptoms of lead colic, afterwards with paralytic weakness of the hands, and she died of general exhaustion.[1262] The circumstances under which the lead is acted on have not been carefully examined. It appears to be sometimes used with safety. It will of course be dissolved, if the milk should become sour.

Rum has been also supposed to be sometimes adulterated with lead by being left in contact with the metal. The dry belly-ache of the West Indies, which appears to be the same disease with the lead colic, has been ascribed by some to the same cause. But on this subject precise information is still wanted. Dr. J. Hunter has stated, that an epidemic colic, which attacked three of our regiments in Jamaica during the years 1781 and 1782, and which seized almost every man of them, was traced by him to the presence of lead in the rum; and he endeavours to show that the spirit might dissolve the lead in passing through the leaden worms of the distilling apparatus.[1263] He adds in another work, that, according to information communicated by Dr. Franklin, the legislature of Massachusetts passed an act in 1723, prohibiting the use of leaden still-heads and worms in the distillation of spirituous liquors.[1264] It is certain that rum has been often impregnated with lead; but it is by no means clear that Dr. Hunter has successfully accounted for the mode in which the adulteration is effected.

Wine has been accidentally impregnated in like manner, in consequence of the bottles having been rinsed with shot, and some of the shot left behind. An interesting example of this has been related in the Philosophical Magazine. Severe abdominal symptoms were caused by a bottle of wine; and the cause was discovered to be the action of the wine on some shot in the bottom of the bottle. The shot had been so completely dissolved, that it crumbled when squeezed between the fingers.[1265] The illness in this instance must have been owing to the arsenic contained in the shot, because the quantity of lead was hardly sufficient to excite violent symptoms.—At one time home-made British wines must have been frequently adulterated with lead, from the makers being ignorant of the dangerous nature of the adulteration. Sir G. Baker quotes the following receipt in a popular cookery book of his time: “_To hinder wine from turning._—Put a pound of melted lead in fair water into your cask, pretty warm, and stop it close.”[1266]

But by far the most remarkable adulteration of the kind now under review is that of cider. At one time a disease in every respect the same as the lead colic used to prevail in some of the south-west counties of England at the cider season; and it was generally ascribed, in consequence apparently of the opinion of Huxham, to the working people indulging too freely in their favourite beverage during the season of plenty. The subject, however, was carefully investigated in 1767 by Sir George Baker, who succeeded in proving, that the disease arose from the cider being impregnated with lead, sometimes designedly for the purpose of correcting its acescency when spoiled, but chiefly by accident, in consequence of the metal being used for various purposes in the construction of the cider-house apparatus. The substance of his researches is,—that a disease in all respects the same with the lead colic was in his time so prevalent in Devonshire as to have supplied 289 cases to the Exeter Hospital in five years, and 80 to the Bath Infirmary in a single season (1766); while, on the contrary, it was little, if at all, known in the adjoining counties of Gloucester, Worcester, and Hereford, although cider is there an equally common drink among all ranks:—that in the latter counties lead was seldom or never used in constructing the apparatus of the cider-houses, while in Devonshire it was used sometimes for lining the presses, but more commonly for fastening the iron cramps, and filling up the stone joinings of the grinding troughs, and for conveying the liquor from vessel to vessel:—that lead did not exist in the cider of Herefordshire, but might be detected both in the ripe cider, and more especially in the must, of Devonshire:—that from eighteen bottles of cider, a year in bottle, 4½ grains of metallic lead were procured.[1267] The accuracy of these facts, and the soundness of the conclusions which Sir George Baker drew from them have been universally admitted; and lead is now, I believe, completely excluded from the cider apparatus.

Notwithstanding the notoriety of these facts, accidents from adulterated cider seem still to occur occasionally in France. So recently as 1841 a set of cases which presented the incipient symptoms of lead colic were traced by MM. Chevallier and Ollivier to cider having been adulterated with lead to the amount of nearly two grains and a half per quart, in consequence of a publican having kept his cider for two days in a vessel lined with lead.[1268]

If lead is previously oxidated, the presence of vegetable acids in articles kept in contact with it is still more likely to give rise to a poisonous impregnation, than in the case of lead itself.

Of accidental adulterations of this kind the most important is that which arises from the action of vegetable acids on the glazing of earthenware. This glaze is well known to contain generally a considerable quantity of oxide of lead, and in consequence is more or less easily dissolved by vegetable acids. A good example has been noticed by Dr. Beck.[1269] A family in Massachusetts, consisting of eight persons, were all seized with spasmodic colic, obstinate costiveness, and vomiting; and the disease was satisfactorily traced to a store of stewed apples, which had been kept some months in an earthenware vessel and had corroded the lead glazing. Another interesting example has been described by Dr. Hohnbaum of Hildburghausen. A family of five persons were all violently affected for a long time with spasmodic colic, and some with partial palsy. After examining many articles of food, Dr. Hohnbaum at last found that the vinegar for dressing their salads was kept in a large earthenware vessel capable of holding eight or ten quarts, and glazed with lead; that an ounce of vinegar remaining in the vessel contained no less than nine grains of lead; and that the whole glazing of the vessel was completely dissolved.[1270] Accidents like this appear from the statements of the same author to have been common in Germany not long ago. Luzuriaga attributes the great prevalence of colic in Madrid and the neighbourhood to the general use in the kitchen of earthenware glazed with lead.[1271] Jacob imputes it to the same cause.[1272] But others have doubted the accuracy of this explanation.

The effect of acids on lead glazing appears to be variable. Sometimes they hardly act on it at all.[1273] The difference probably depends on differences in the composition of the glaze. Gmelin says, that if there is little oxide of lead present, acids and fat do not corrode it; but that potters often use too much, to render the glaze more fusible; and that then it is easily corroded.[1274] Westrumb states, that, if the lead glaze is thoroughly vitrified and not cracked, the strongest acids do not attack it.[1275] Farther experiments are still required to elucidate this subject.

It is not, however, by accident only that the food or drink of man is subject to be poisoned with lead. Many articles are adulterated with it designedly for a variety of purposes. These adulterations it is necessary for the medical jurist to study.

No kind of adulteration with lead is more common than that of wine; which, when too acid and harsh from the first, or rendered acescent by decay, may be materially improved in taste by the addition of litharge.

The practice of correcting unsound wines in this way seems to have been well known at an early period. Betwixt the years 1498 and 1577, various decrees were passed against it by the German emperors; and in some provinces the crime was even punished capitally.[1276] For some time afterwards the dangerous effects of the practice appear to have been lost sight of in Germany. But towards the close of the seventeenth century, the attention of physicians and legislators in that country was pointedly directed to the subject by various writers in the _Acta Germanica_.[1277] The same practice has been long prevalent in France. The famous endemic colic of Poitou, which appeared in 1572, and raged for sixty or seventy years, has been with justice ascribed in modern times to the adulteration of wine with lead, and has given to the lead colic its scientific name of _colica pictonum_. More recently, the practice became exceedingly prevalent in Paris. About the year 1750, the farmers-general found that for some years before that, 30,000 hogsheads of sour wine were annually brought into Paris for the alleged purpose of making vinegar, while the previous yearly imports did not exceed 1200. An inquiry was accordingly set on foot; which led to the discovery, that the vinegar merchants corrected the sour wines with litharge, and thus made them marketable.[1278] Notwithstanding the active system of medical police in the French capital, the crime is not yet eradicated. Indeed the small tart wines used so abundantly there by all ranks, hold out great encouragement and facilities to its perpetration.

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.

A process different from the preceding, and analogous to those for detecting copper and antimony in complex organic mixtures, has lately been proposed by Professor Orfila, especially for those cases in which lead is to be sought for in the textures of the body, where death is supposed to have been occasioned by it. The subject of analysis, such as the liver, spleen, or kidneys, being cut into small pieces, and boiled in distilled water, and the filtered decoction being evaporated to dryness, the extract is to be carbonized with nitric acid as directed under the head of copper (p. 357); and care must be taken that the heat be not raised to redness, so as to inflame the mass. The residuum is then to be boiled with nitric acid; the solution being evaporated to dryness to expel the excess of acid, the saline matter left is to be redissolved and acted on by hydrosulphuric acid gas; and the sulphuret thus formed may be recognized by the means mentioned above.[1289]

A question has been recently started, whether all the processes for detecting lead in the tissues of the human body are not rendered fallacious by the alleged existence of lead in the healthy animal textures. In the first place, however, it is doubtful, as will be seen presently, whether lead ever exists naturally in the animal organs. But besides, the fallacy, if a real one, is obviated by the process of Orfila; who states that lead, naturally combined in the animal tissues, cannot be indicated by his method, if the animal matter be charred by nitric acid without deflagration. And farther, in regard to the tissues of the stomach in cases of acute poisoning with the preparations of lead, it appears that in most instances there may be seen on the villous coat little white points, which are blackened by hydrosulphuric acid, a phenomenon never occasioned by lead naturally contained in the substance of the membrane. [See p. 439.]