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The trough is made of wood, lined with lead, or tinned copper. Any shape serves; but an oval form is generally found to answer best. It should be from 6 to 12 inches deep, from 20 to 28 inches long, and from 12 to 15 inches wide. A moveable shelf, E, nearly half the breadth of the trough, perforated with several large holes, or having a slit along the middle, is placed lengthwise in it, at the depth of at least two inches, and the trough is to be filled with water, at least one inch above the shelf. If the glass vessel, I), with its mouth downwards, be immersed in the tub, filled with water, and then placed inverted on the shelf, provided the mouth of the vessel be kept constantly below the surface of the water, it will remain full. This effect is produced by the pressure of the atmosphere, which sustains the water in the upper part of the glass, in the same manner as the mercury Is sustained in the barometer. If, however, common air, or any other elastic fluid of equal lightness and elasticity, and not greedily absorbed by water, be suffered to enter the glass vessel, it will rise to the top. On this principle, when ifis required to collect any gas or aeriform substance, the mouth of a tube, from Which it is to issue, is immersed in the water directly under the gtavs, D, when it rises

to the top, gradually displaces the water, and causes it to fall to the level of the water in the trough. When one glass is full, it may be slid along the shelf out of the way, and another placed over the ascending gas; or it may be wholly removed, by sliding it off the shelf into a saucer, held on a level with the shelf, and of course somewhat under the surface of the water. In this way any quantity of gas may be obtained, and employed for making experiments.

We come now to the method of pouring gas from one vessel into another. Our readers must all have observed, that if a tumbler or wineglass, in that state which is usually called empty, but in which it is, in fact, filled with air, be plunged into water with its mouth downwards, so that the air cannot escape, scarcely any water will rise in the glass, because its entrance is opposed by the air already contained in it; but if the mouth of the glass be turned upwards, the air immediately escapes in bubbles through the water, and the glass is filled with that fluid. If a vessel full of atmospheric air, or of any of the gases, be plunged in water in this manner, and its mouth turned up directly under the opening of the inverted glass, D, on the shelf, the included air can only escape into D, atmospheric air cannot find admittance, and, in this way, gases or air may be emptied from one vessel into another, without suffering any change. Gases which are considerably heavier than atmospheric air, or than the air they are to displace, may be poured like water into a vessel full of atmospheric air, or full of a gas lighter than themselves. Some gases, however, are absorbed by water, or water effects an alteration in them; and such gases are treated in the manner here described, mercury or quicksilver being substituted for the water. In this case, as the mercury is a costly article, a smaller trough is used, and as it is very weighty, the trough is hollowed out of a solid bloek of hard wood or marble; and a small rod is placed across the trough, a few inches above it, and by means of which, to prevent accidents, the jar filled with mercury may be supported.

This method of obtaining and confining a particular species of air, was invented by Dr. Mayow, and afterwards improved by Dr. Hales. To Dr. Priestly we are in* debted for the present pneumatic apparatus; and to him, Mr. Watt, ot Birmingham, and Lavoisier, the science owes most of the improvements that, in later times, have been made in the mode of operating on gases.

In making chemical experiments, great care is always requisite in making the joining of all the vessels, tubes, retorts, &c. air tight. For some purposes, it is sufficient if the glass vessels are made to fit close by being ground with emery; but in most cases this is effected by what the Chemists call lutes, and the operation is called luting. The lutes, with which the joinings of vessels are closed, are of different kinds, according to the nature of the operations to be made, and of the substances to be distilled in these vessels.

When vapours of watery liquors, and such as are not corrosive, arc to be contained, it is sufficient to surround the joining of the receiver to the nose^ofithc alembic,

or of the retort, with sups of paper or of linen, covered with (lour paste. In such cases also, slips of wet bladder answer very well.

When more penetrating and dissolving vapouts are to be contained, a lute is to be employed, of quick-lime slaked in the air, and beaten into a liquid paste with whites of eggs. This paste is td be spread upon linen slips, which are to be applied exactly to the joining of the vessels. This lute is very convenient, easily dries, becomes solid and sufficiently firm. Of this lute vessels may be formed hard enough to bear polishing on the wheel.

Lastly, when acid and corrosive vapours are to be contained, we must then have recourse to the lute called fat lute. This lute is made by forming into a paste some dried clay, finely powdered, sifted through a silken searce, and moistened with water; and then, by leating this paste well in a mortar with boiled linseed oil, which has been rendered drying, by litharge dissolved in it, and fit for the use of painters. This luto easily takes and retains the form given to it. It is generally rolled into cylinders of a convenient size. These are to be applied, by flatten* »ng them, to the joinings of the vessel, which ought to be perfectly dry, because the least moisture would prevent the lute from adhering. When the joinings are well closed with this fat lute, the whole is te be covered with slips of linen, spread with lute of lime and whites of eggs. These slips are to be fastened with packthread. The second lute is necessary to keep on the fat lute, because this latter remains soft, and does not beoomo solid enough to stick on alone.

Fine porcelain clay, mixed with a solution of borax, is well adapted to iron vessels, the part received into an aperture being smeared with it


The very subtile nature of the

two poisons, the names of which

stand at the head of this article and the recent use made of one of them, and of a preparation of the other, in a neighbouring kingdom, to destroy life, under the expectation, we are glad to say vain expectation, of escaping punishment, by the poisons leaving no trace of their operation, may give rise to objections as to our propagating a knowledge of their existence and properties. We foresee that those who have no confidence in the virtues of mankind, and who live under the influence of the agonizing theory of man being naturally the enGmy of man, and who suppose that the species arc ready at all times to prey on one another, will cry out against us for putting the means of perpetrating mischief into the hands of a race which they are always ready to call wicked and detestable. Monuments of piety, examples of splendid virtue, or long continued patience and self-denial, have no influence over those whose minds are imbued with a theory of man being contaminated by that matter he renders subservient to his improvement. His continued progress towards a better state of things, bis repeated triumphs over the elements, bis brilliant discoveries of hidden properties, by which he makes the ocean the footpath of nations, and the winds the messengers of his will ;Jthe trophies of his conquests and his power, which are every where around us, showing that there is nothing which art and industry cannot achieve, and nothing except that Great Power which created both man and the elements, superior to him ;—all are lost on them, and they can never place any confidence in a race which they persist in denominating, in spite of all these facts, fallen and degraded. Belonging themselves to this race, is not sufficient to stop their calumnies. Thej would have no limits to their own. power or their own knowledge ; for each one amongst them holds himself to be an exception to the general laws they propound with so much selfcomplaccnc}'. a.* guiding the conduct of other men; hut all other

men they would have kept in ignorance and darkness, as if they were anxious, for the sake of their own reputation, to realize their theories of the wicked nature of man. Such people will be apt to exclaim, " What! when you see every day attempts made to destroy life, by administering various corrosive poisons; when the almost certainty of detection and the dread of punishment cannot stay the arm of the murderer—will you spread among the people a knowledge of poisons equally efficacious in destroying life, but effecting it by such hidden means, that the most skilful chemists and the best instructed physicians differ in their opinions as to the visible effects of such substances, and doubt the possibility of detecting them when administered 1" Though we do not ourselves share in these fears, and do not think one more life will be destroyed by a more extensive knowledge of the means by which this diabolical purpose may be effected, yet as we foresee that an objection of this kind may be, and will be made to the present article, we reply to it beforehand. We shall disarm our opponents, by showing them that they cannot use their weapons to our annoyance.

It is a fact, that such substances as these exist in nature, or may be and have been prepared by art; and a knowledge of the means of preparing them cannot be extirpated. Of their employment we have a recent example. In the month of November li»st year, a Doctor Castaing was tried and executed at Paris, for one of the most diabolical murders on record. He was the friend and medical adviser of two brothers, who had been brought up to the profession of the law, and who possessed considerable property. They both died, one after the other, within a few months, while under his care, leaving him the heir to considerable property. liy the death of the first, the second brother acquired all his wealth, and whether he shared the guilt of Castaing in, the liist instance, or was totally ignorant of that crime by which be profited for a season, does not appear, but he continued to live on good terms with Castaing. At length, however, he too fell a victim to the arts of this man; but, as his death was sudden and unexpected, it gave rise to several suspicions, and they being confirmed by Doctor Castaing's conduct as to the property, he was taken up and tried. After a minute investigation, he was acquitted of the charge of murdering the brother who died first, because his death had taken place some time before, and no investigation having then been made, no conclusive proof could be brought against him, though there was strong reason to suspect him of having also perpetrated that; but he was found guilty of murdering the second, by administering to him doses of Emetine and of acetat of Morphia. Dr. Castaing, it appeared on the trial, had long been in the habit of making experiments on poisons, with a view of ascertaining what substances unite with their poisonous qualities the treachery of leaving no trace of their operation; and so effectually had he succeeded, as almost to realize the stories which were once circulated of the famous woman at Home, and whose skill was afterwards imported into Paris, who could poison whom she pleased, and no trace be left of the means by which she accomplished her murderous purpose. Having free access to his victims, and having them, in fact, almost under his exclusive superintendence and management, he was able to operate on them as he pleased; and so artfully did he contrive it, administering the poison in small doses, and keeping his patient constantly sick till be died, that no suspicion was caused by the death of the first brother, and no conclusive evidence could be produced that he had poisoned the other. Suspicion alighted on him from his conduct betraying a consciousness of guilt, and no certain proof was brought forward at the trial, either that he had ad

ministered poison, or that his victim had died of poison. The most celebrated chemists and physicians of Paris, and amongst them the original discoverers of one of these substances, were employed to examine the body, and were called up as witnesses on the .trial, and they differed in their opinions as to the possibility of detecting these poisons when mixed with alimentary matters, or ascertaining their visible effects on the organization of the frame.

Such being the state of the case, it becomes a question, whether it is right to diffuse a knowledge of these substances through the community, or whether attempts should be made to confine that knowledge to a select few. We have answered to ourselves this question in the affirmative, and we shall briefly state why.

In the first place, we say that the great motive which restrains such men as may otherwise be disposed to commit atrocious crimes, is, of course, the fear of detection. Now, as long as society is generally ignorant of the existence of any such subtle poisons as are here described, it is clear that those who possess a knowledge of them may poison people unsuspected; and that the most powerful check which can be devised against such an employment of' these materials, is to put people on their guard against them. Suspicion will, in such a case, be in proportion to knowledge; and thus, by making the whole matter known, we generate in those who may now possess this knowledge, a fear of being suspected, which, without this, could never arise, and every one would be confident of escaping detection. We say that this knowledge, as far as it can be employed' for evil, already exists; and that by making it more general, we only multiply the means of preventing that particular application of it which is here alluded to.

But is there any reason to believe it will be so applied to any extent? We answer. No; for as soon as the matter is generally known, all temptation to employ these poisons in preference to others, disappears. Leaving the secret in possession of a few individuals would give them a power of perpetrating any crimes they pleased; but no man will commit an action of which he believes every one will suspect him. Independent of this, these substances are powerful and very useful medicines; and shall we be withheld from making their properties known, because some persons may misapply them? Why, there is not a single weapon or a single instrument invented by man, which may not be mischievously employed; and if we were to act on this principle of limiting man's knowledge and powers, because he may abuse them, we should tie every man's hand to prevent them all turning pickpockets. We leave such precautions and such principles to those who have a worse opinion than we have of our fellow.creatures; and shall never attempt, either by our silence or our reprobation, to check the diffusion of any species of knowledge; ^-except, indeed, the diffusion of, such unsound theories as lead men, to place an overweening confidence in themselves, and cherish the darkest mistrust of all other men.

Emetine is extracted from the drug called Ipecacuanha, and is so named because it constitutes the part of this medicine which occasions vomiting. It was first extracted from it by Messrs. Majendie and Pelletier, French Chemists, by the following method, which is still employed:—Ipecacuanha was digested first iu sulphuric ether, and then in alcohol. The solution in alcohol was evaporated to dryness, r.e-dissolved in water, and acetat of lead dropped in the solution. A copious precipitate fell, which being edulcorated and diffused through water, was exposed to a current of sulphuretted hydrogen gas. The lead was precipitated in the state of sulphuret, and the emetine dissolved in water. The liquid being -filtered and evaporated to dryness, the residue con

sisted of emetine in a state of purity. It possesses the following properties:—It consists of transparent scales of a brownish red colour, having no smell, and being of a bitter and acrid, but not nauseous taste. When exposed to-a heat greater than that of boiling water, it swells, blackens, and is decomposed: furnishing water, carbonic acid,alittle oil and ace tic acid, a very light coal remaining behind.* When exposed to damp air, it becomes moist, and it dissolves readily in water, but cannot be made to crystallize. It is soluble in alcohol, and insoluble in sulphuric ether. Concentrated sulphuric acid chars and destroys it. Nitric acid, either hot or cold, dissolves it, and forms a fine red coloured solution, which gradually becomes yellow; while nitrous gas exhales, and crystals of oxalic acid are formed, but no yellow bitter principle. Muriatic and phosphoric acid dissolve it without alteration, and let it fall again when they are saturated with an alkali. Acetic acid is one of the best solvents of it. Gallic acid precipitates it of a dirty white colour. Half a grain of Emetine, when swallowed, occasions severe vomiting, followed by sleep, and the animal awakens in a state of health. Six grains produce vomiting, followed by sleep and death. In such cases, a violent inflammation takes place in the lungs and intestinal canal, which appears to be the proximate cause of death. It appeared, however, on the trial of Doctor Castaing, that this substance might be administered in such small doses as not to occasion this inflammation, and yet produce death, more particularly when its effects are modified by small doses of the acetat of Morphia, one ingredient of which is extracted from opium.

• Dr. Thompson and other chemical writers state, that there is no azot in this substance; but by a later and more correct analysis of Messrs.Dumas and Pelletier, published in the Annales Phys. ch. for October 1823, it appears there is a considerable quantity of azot in this as well as all the other vegetable alkalies.

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