1. _Lime-Water_ throws down the binoxide of mercury in the form of a

heavy yellow powder. The precipitate first thrown down is lemon-yellow, an additional quantity of the test gives it a reddish-yellow tint, and a still larger quantity restores the lemon-yellow. This test is characteristic, but not so delicate as those already mentioned.—2. _Caustic Potass_ has precisely the same effect as lime-water, except that the tint of the precipitate is always yellow—3. _Caustic Ammonia_ causes a fine, white, flocculent precipitate of intricate composition, commonly called precipitate. It is a very delicate test; but ammonia likewise causes a white precipitate in other metallic solutions.—4. _Carbonate of Potass_ causes a brisk-red precipitate, by virtue of a double decomposition, the precipitate being carbonate of mercury.—5. The _Ferro-cyanate of Potass_ causes at first a white precipitate, the ferro-cyanide of mercury. The precipitate becomes slowly yellowish, and at length pale-blue, owing, it is believed, to the admixture of a small quantity of iron with the corrosive sublimate.—6. _A polished plate of Copper_ immersed in a solution of corrosive sublimate becomes in a few seconds tarnished and brownish; and in the course of half an hour a grayish-white powder is formed on its surface. This powder, according to Orfila,[837] is a mixture of calomel, mercury, and a copper amalgam. If it is wiped off, and the plate then rubbed briskly where tarnished, it assumes a white argentine appearance.—7. _A little Mercury_ put into a solution of corrosive sublimate is instantly tarnished on the surface; the solution in a few seconds becomes turbid, a heavy grayish precipitate is formed, and in no long time with the aid of agitation the whole corrosive sublimate is removed from the solution. The powdery precipitate is a mixture of finely divided mercury and calomel; the former being derived from the surface of the mercury, and the latter produced by the corrosive sublimate uniting with a larger proportion of the metal to form the protochloride.—8. _A solution of Albumen_ causes a white precipitate, which is soluble in a considerable excess of the reagent. The nature of this precipitate will be discussed presently.—A _slip of Gold_ aided by galvanism, becomes silver-white in the solution, in consequence of the formation of an amalgam. When the solution is concentrated, it may be thus tested by simply putting a few drops on a bit of gold, and touching the gold through the solution with an iron point, as recommended by Mr. Sylvester and Dr. Paris.[838] When the solution is very weak, a different method is necessary, and a process for the purpose has been proposed by M. Devergie, which appears so delicate, accurate, and at the same time simple, a mode of detecting traces of mercury in very weak solutions, as to deserve detailed notice. A thin plate of gold, and another of tin, a few lines broad, and two or three inches long, being closely applied to one another by silk threads at the ends, and then twisted spirally, this galvanic pile is left for twenty-four or thirty-six hours in the solution previously acidulated with muriatic acid; upon which the gold is found whitened, and mercury may be obtained in globules by heating the gold in a tube. Distinct indications may be obtained by this method, where the corrosive sublimate forms but an 80,000th of the water.[839] For facility of application, an important condition is, that the quantity of fluid should not exceed three or four ounces, because in a larger quantity the pile of the size stated above cannot remove the whole mercury. Somewhat similar to this is the galvanic method of Mr. Davy of Dublin. He proposes to place the suspected solution in a platinum crucible with hydrochloric acid, diluted with its own weight of water, to excite galvanic action by immersing in the fluid a plate of zinc, and to sublime and collect the reduced mercury, by washing the crucible, heating it over a spirit-lamp, and condensing the mercurial vapours on a plate of glass placed over the mouth of the crucible.[840] _Of the Tests for Corrosive Sublimate when mixed with Organic Fluids and Solids._ The process for detecting corrosive sublimate in mixtures of organic fluids and solids, such as the contents of the stomach, is now to be described. But some remarks are previously required on the chemical relations subsisting between this poison and various principles of the vegetable and animal kingdoms. These relations are important in a medico-legal point of view on several grounds. On the one hand, the chemical changes which corrosive sublimate undergoes often alter so much the action of its tests, as to render necessary a process of analysis materially different from any hitherto described. And on the other hand, these chemical changes, of which some take place rapidly, others slowly, will hinder the corrosive sublimate, more or less completely, from exerting its usual operation on the animal system; so that it may thus either accidentally fail to act as intended, or be checked in its operation by antidotes administered for the purpose. It appears from the researches of M. Boullay, confirmed by those of Professor Orfila, that various vegetable fluids, extracts, fixed oils, volatile oils and resins, possess the power of decomposing corrosive sublimate. According to M. Boullay, a part of the chlorine is gradually disengaged in the form of hydrochloric acid, and the salt is consequently converted into calomel, which is deposited in a state of mixture or combination with vegetable matter.[841] Some vegetable fluids produce this change at once, others not for some hours, others not for days, and only when aided by a temperature approaching ebullition. For example, a strong infusion of tea, mixed with a solution of a few grains of corrosive sublimate, becomes immediately muddy, and an insoluble cloud separates in half an hour. But the remaining fluid slowly becomes muddy again, and in eight days a considerable precipitate is formed. Both precipitates contain mercury; the former, I find, contains 31 per cent. On the other hand, an infusion of galls in like circumstances does not become muddy for six or seven hours. A solution of sugar does not undergo any change after being mixed with a solution of corrosive sublimate for months at the ordinary temperature of the atmosphere; but at the temperature of ebullition Boullay has found that the usual changes ensue, though to no great extent. The experiments of Professor Taddei of Florence have farther shown, that the property of decomposing corrosive sublimate is possessed in an eminent degree by one of the vegetable solids, gluten. If the salt in solution is properly mixed with a due proportion of gluten of wheat, that is, about four times its weight, the water will be found no longer to contain any mercury, while the gluten becomes whitish, brittle, hard, and not prone to putrefaction. A ternary compound is formed, the protochloride of mercury and gluten.[842] This change is effected with rapidity. The researches of Berthollet,[843] repeated and extended by Professor Orfila,[844] have also shown that the same property is possessed by most animal fluids and solids. Among the soluble animal principles, albumen, caesin, osmazôme, and gelatin possess it in a high degree, but above all albumen, the action of which has been examined with some care, as it supplies the physician with the most convenient and effectual antidote against the effects of the poison. If a solution of albumen, for example that procured by beating white of eggs in water, is dropped by degrees into a solution of corrosive sublimate, a white flaky precipitate is immediately thrown down, which when separated and dried forms horny masses, hard, brittle, and pulverizable. The precipitate is soluble in a considerable excess of albumen; so that wherever albumen abounds in any fluid, to which corrosive sublimate has been added, a portion of the mercury will always be found in solution. The precipitate is also soluble in a considerable excess of corrosive sublimate. The dry precipitate I have found to contain 6 per cent. of metallic mercury. The action of casein as it exists in milk is precisely the same. A solution of corrosive sublimate, poured into a large quantity of milk, causes no change; but if the proportion of salt be considerable, a flaky coagulum is formed, and the milk becomes clear. The principles, osmazôme and gelatin, are similar in their effects, though not quite so powerful. Urea has no chemical action with corrosive sublimate. Of the compound animal fluids, blood and serum have the same effects as albumen. Many insoluble animal principles, as well as all the soft solids of the animal body, act in the same manner with vegetable gluten. Fibrin, for example, coagulated albumen, or coagulated casein, acts precisely in the same way. Muscular fibre, the mucous and serous membranes, the fibrous textures, and the brain, have all the same effect: they become firmer, brittle, white, and a white powder detaches itself from their surface, which contains mercury and animal matter. This chemical action, which Taddei has proved to take place in the living[845] as well as in the dead body, is the source of the corrosive property of the poison, as was first pointed out by Berthollet in his essay formerly quoted. In all of the compounds thus formed by vegetable and animal substances, the presence of mercury is easily proved by boiling the powder in a solution of caustic potass. The organized matter is dissolved; a heavy, grayish-black powder is formed, which is protoxide of mercury; and if this be collected in the way formerly described, it forms running quicksilver when heated. A difference of opinion prevails as to the nature of the changes effected by the mutual action of corrosive sublimate and organic matter. For example, in the instance of the action of albumen, which has been most carefully examined, Berzelius and Lassaigne[846] regard the precipitate as a compound of bichloride of mercury with albumen. Professor Rose and Dr. Geoghegan[847] have proved it, in their opinion, to be a compound of binoxide of mercury and albumen without any chlorine. And according to Boullay it is composed of albumen in union with calomel.[848] Lassaigne says he has found it to be a compound of ten equivalents of albumen with one of mercury, or 93·33 per cent. of the former, and 6·67 of the latter.[849] The compound with fibrin he considers to be analogous in composition. With regard to the changes induced by these effects of organized matter on the operation of the liquid tests for corrosive sublimate, it will in the first place be manifest that the poison may thus be wholly removed from their sphere of action: it may be thrown down as an insoluble substance, on which any process by liquid tests hitherto mentioned will of course fail to act. But secondly, even when a moderate quantity does remain in solution, the operation of the liquid tests, as formerly noticed under the head of each, will be materially modified. It is of some moment for the medical jurist to remember, that by reason of the slowness with which the changes in question sometimes takes place, the poison may exist abundantly in solution at one time, and yet be present only in small quantity after an interval of some hours or days. _Process for Organic Mixtures._—Various processes have been proposed for detecting corrosive sublimate in organic mixtures. The first I shall mention is one proposed by myself in former editions of this work. It is a double one; of which sometimes the first part, sometimes the second, sometimes both may be required. The first removes the corrosive sublimate undecomposed from the mixture, which may be accomplished when its proportion is considerable; the second, when the proportion of corrosive sublimate is too small to admit of being so removed, separates from the mixture metallic mercury; and the analyst will know which of the two to employ by using the protochloride of tin as a trial-test in the following manner. A fluid mixture being in the first instance made, if necessary, by dividing and bruising all soft solids into very small fragments, and boiling the mass in distilled water, a small portion is to be filtered for the trial. If the protochloride of tin causes a pretty deep ash-gray or grayish-black colour, the first process may prove successful; if the shade acquired is not deep, that process may be neglected, and the second put in practice at once. _First branch of the Process._—In order to remove the corrosive sublimate undecomposed, the mixture, without filtration, is to be agitated for a few minutes with about a fourth part of its volume of sulphuric ether; which possesses the property of abstracting the salt from its aqueous solution. On remaining at rest for half a minute or a little more, the etherial solution rises to the surface, and may then be removed by suction with the pipette (Fig. 8). It is next to be filtered if requisite, evaporated to dryness, and the residue treated with boiling water; upon which a solution is procured that will present the properties formerly mentioned as belonging to corrosive sublimate in its dissolved state. This branch of the process is derived from one of Orfila’s methods. _Second branch of the Process._—If the preceding method should fail, or shall have been judged inapplicable, as will very generally be the case, the mixture is to be treated in the following manner. In the first place, all particles of seeds, leaves, and other fibrous matter of a vegetable nature, are to be removed as carefully as possible. This being done, the mixture, without undergoing filtration, is to be treated with protochloride of tin as long as any precipitate or coagulum is formed. If there were solid animal matters in the mixture, besides being cut and carefully bruised as directed above, they should also be brought thoroughly in contact with the salt of tin by trituration. The mixture, even if it contains but a very minute proportion of mercury, will acquire a slate-gray tint, and become easily separable into a liquid and coagulum. The coagulum is to be collected, washed and drained on a filter; from which it is then to be removed without being dried; and care should be taken not to tear away with it any fibres of the paper, as these would obstruct the succeeding operations. The mercury exists in it in the metallic state for reasons formerly mentioned. The precipitate is next to be boiled in a moderately strong solution of caustic potass contained in a glass flask, or still better in a smooth porcelain vessel glazed with porcelain; and the ebullition is to be continued till all the lumps disappear. The animal and vegetable matter, and oxide of tin united with them, will thus be dissolved; and on the solution being allowed to remain at rest, a heavy grayish-black powder will begin to fall down in a few seconds. This is chiefly metallic mercury, of which, indeed, globules may sometimes be discerned with the naked eye or with a small magnifier. In order to separate it, leave the solution at rest under a temperature a little short of ebullition for fifteen or twenty minutes, or longer, if necessary. Fill up the vessel gently with hot water without disturbing the precipitate, so that a fatty matter, which rises to the surface in the case of most animal mixtures, may be skimmed off first with a spoon, and afterwards with filtering paper. Then withdraw the whole supernatant fluid, which is easily done on account of the great density of the black powder. Transfer the powder into a small glass tube, and wash it by the process of affusion and subsidence till the washings do not taste alkaline. Any fibrous matter which may have escaped notice at the commencement of the process, and any lumpy matter which may have escaped solution by the potass, should now be picked out. The black powder is the only part which should be preserved. If the quantity of powder is very minute, an interval of twelve hours should be allowed for each subsidence, and the tube represented in Fig. 7 should be used. Lastly, the powder is to be removed, heated, and sublimed, as in the last stage of the process described in page 293, for detecting corrosive sublimate in a pure solution. The second branch of this process is very delicate. I have detected by it a quarter of a grain of corrosive sublimate mixed with two ounces of beef, or with five ounces of new milk, or porter, or tea made with a liberal allowance of cream and sugar. I have also detected a tenth part of a grain in four ounces of the last mixture, that is in 19,200 times its weight. It may be applied successfully and without difficulty to a very large majority of medico-legal cases. The only difficulty in the way of applying it to all organic mixtures whatever arises from the occasional presence of some vegetable matters, such as seeds, leaves, ligneous fibre and the like, which are insoluble in caustic potass, and which may therefore be left behind with the mercurial precipitate, and obstruct the subsequent sublimation of the metal. This difficulty may be sometimes got rid of, as recommended above, by picking such matters out of the mixture before the protochloride of tin is added. No mercury is lost by so doing, for none of it is united with these vegetable matters: corrosive sublimate does not form any chemical compound with them as it does with other vegetable matters soluble in caustic potass, and with the soft animal solids. When the particles are too small to admit of being thus removed, or cannot be afterwards removed during the process of washing the black powder, which is left after the action of potass—the analyst must be content with the increased facility of sublimation derived from the abstraction of other vegetable and animal admixtures, and take care to use a tube of greater length and with a larger ball than usual. If the sublimate is too much obscured by empyreumatized matter to exhibit distinctly its metallic, globular appearance, the portion of the tube is to be broken off, and scraped, washed, and boiled with a little rectified spirit in a tube. If the globules do not then become visible, a second sublimation will render them distinct. This supplemental operation, however, will be very seldom required; and the process given above will be found to apply to a great majority of instances. Various objections brought against this process by reviewers and others were noticed in previous editions of this work. The result of the investigation is, that, though not by any means a perfect process, it is one of the most convenient and certain, and least fallacious of all yet proposed. The first step for separating corrosive sublimate by ether in the undecomposed state,—which is borrowed from a suggestion of Professor Orfila, will seldom succeed; for the poison is seldom present in sufficient quantity. It must be observed that this as well as every other method yet proposed for discovering corrosive sublimate in compound mixtures merely indicates the presence of mercury, and does not point out its state of combination. More especially, in the case of the contents of the stomach, if mercury be not obtained from the filtered fluid, it is impossible to know whether what is detected in the solid matter only may not have proceeded from calomel given medicinally. This objection can be obviated solely by sufficient evidence that calomel was not administered; at least the different criterions laid down by Professor Orfila for distinguishing calomel in the alimentary canal from the products of the decomposition of corrosive sublimate do not appear sufficiently precise, or commonly applicable.[850] Various processes for detecting corrosive sublimate in organic mixtures have been proposed by others. But none of these seem to me preferable to the method detailed above, with the exception of one which has been lately proposed by Professor Orfila, and which is particularly deserving of notice, because, although complex, he has found it sufficiently manageable and delicate for detecting mercury in the animal textures and secretions, into which it has obtained admission through the medium of absorption in cases of poisoning with the compounds of mercury. Like the previous process, however, it merely detects mercury, and cannot point out the state of combination in which mercury was administered, or mixed with the substance examined. If the suspected matter be sufficiently liquid, boil for a few minutes and filter; acidulate the product with a few drops of hydrochloric acid; and immerse some slips of copper-leaf in it for a few hours. Should they be tarnished, dissolve oxide and chloride of copper from the surface by means of ammonia; wash them and press them between folds of filtering paper; cut them in pieces, and heat these in a glass tube. Globules of mercury may be obtained or not. In either case, let the liquid, in which the plates were first immersed, be evaporated to dryness over the vapour-bath; add to the residue a sixth of sulphuric acid in a retort with a receiver; and heat gently till a nearly dry carbonaceous mass be obtained. Boil this with an ounce and a half of nitro-hydrochloric acid [Edin. Pharm.], until the charcoal be again nearly dry. Heat what remains with boiling distilled water, filter, apply to a small part of the liquid the copper test as just described, and try whether corrosive sublimate can be detached from the remainder by means of sulphuric ether (p. 299). The distilled fluid in the receiver may contain corrosive sublimate in considerable proportion, relatively to what existed in the subject of analysis. In order to discover it, boil the liquid for fifteen minutes with nitro-hydrochloric acid; transmit chlorine gas for an hour, filter, and evaporate to dryness over the vapour-bath; dissolve the residue in water, and search for corrosive sublimate both by copper plates, and by agitation with ether. If mercury be not thus detected, proceed to the solid matter left on the filter, by which the subject of analysis was in the first instance separated into a liquid and solid part. Examine this by evaporation to dryness over the vapour-bath, and charring with sulphuric acid in a retort with a receiver attached; and then subject the product to the same steps as those detailed above for the dried residuum of the liquid part. If the materials for analysis be soft solids, especially the stomach, intestines, liver, and the like, commence at once with the process of charring with sulphuric acid. In the case of the urine, examine both the liquid and sediment. Filter the liquid, transmit chlorine to excess, let the product rest twenty-four hours, filter, evaporate to dryness, dissolve the residue in water acidulated with hydrochloric acid, and test the solution both with copper-leaf and by agitation with ether. Heat the sediment with nitro-hydrochloric acid as directed above, and then proceed as with the liquid portion of the urine.[851] Some other processes, but probably inferior to that of Professor Orfila, will be found in the last edition of this work. It seems unnecessary to reproduce them here.