sometimes ending in injury of their structure. Thus, those remedies which promote expectoration are of great consequence to health, though often neglected. The principal medicines of this class are antimony, squills, ipecacuan, and gum ammoniac. Syrup of squills is the preparation in greatest use. Carminatives are those medicines which produce the discharge of flatulence from the alimentary canal. This malady is more annoying than dangerous, though it rises occasionally to a most painful height. The warm essential oils, such as caraway, anise, or peppermint, and some aromatic stimulants, as cinnamon and ginger, are the best carminatives. are exceedingly mild in their operation, and are gene- | colds, and lodge there, causing difficult breathing, and rally employed merely to palliate the bad flavour of some stronger drug. The second kind of purgatives includes aloes, scammony, jalap, colocynth, senna, and rhubarb. The general character of all these has been given above, though the rhubarb possesses one remarkable distinction from the others. It is supposed to act on the muscular membrane of the bowels, producing a natural discharge simply, without altering the character of the feces. The principal neutral and metallic salts, which form the third order of purgatives, are sulphate of soda, Epsom salts (sulphate of magnesia), cream of tartar (super-tartarate of potash), phosphate of soda, and calomel (submuriate of mercury). The latter is the most universal in its application of all medicinal preparations. By proper regulation of the dose, and in conjunction with other drugs, it can be employed with benefit in almost every disease to which man is subject. But in proportion to its usefulness, so is its danger when misapplied. The dose should be very small at first, and cold ought always to be guarded against during its use. With respect to the others, little can be added to the general description already given, though it may be mentioned, that the pleasantest, though not the cheapest of all medicines, is the phosphate of soda, or tasteless salts. Sudorifics, or medicines which increase the cutaneous perspiration, form another important class of vital remedies. Certain substances received through the stomach into the blood, excite through it the vessels of the skin to action, and increase the natural discharge. The mode in which this result is effected is not well known; all we know is, that, during the operation, the heart, and the blood-vessels which terminate on the surface of the skin, are roused to unusual action. Among the most active sudorifics may be enumerated warm drinks; the warm bath; the preparations of antimony, including James's powder; Dover's powder (compound ipecacuan powder); the preparations of ammonia; and all medicines generally which nauseate the stomach. Probably of all these, Dover's powder is the best. Sudorifics, in almost all cases, when early used, prevent the effects of colds, which, when neglected, prove so often fatal in their consequences. All those classes of medicines which we have hitherto mentioned, are called evacuants, from the nature of their operation; and we may now describe another order of medicinal preparations, acting, like the former, through the medium of the circulation, but repressing instead of stimulating the powers of the sys tem. There are only two distinct classes of medicines of this kind, narcotics and antispasmodics, though the first of these has sometimes been divided into two, narcotics and sedatives. Narcotics are those substances which diminish the natural degree of action in the body, and tend to remove irritation or pain, inducing in general a state of repose. Before this quieting effect is produced, however, there is a primary excitement of short duration, which is well exemplified in the case of opium. Sedatives, viewed as a separate class, are believed to allay pain and promote sleep, without possessing any stimulating quali ties; but it is far from being clear that we have any simple sedative medicines at all. Opium, which is almost exclusively employed as a sedative, is universally ad mitted to have a primary exciting quality. Unless where excessive pain is present, narcotics may be regarded as a class of medicines only to be used with great caution, and never free from danger. Opium and its preparations, lettuce extract, henbane, foxglove, hemlock, and tobacco, are some of the strongest narcotics. It is difficult to say which of these is the safest, when a sedative is required, though probably the preparation from lettuce has the slightest stimulating powers. Morphia, a drug procured from opium, is said to possess the sedative without the exciting effect. Antispasmodics are used to remove spasms or con vulsive contractions of the muscular fibre in the body, and are so similar in their action to the last-mentioned class, as scarcely to require a separate notice. Opium, camphor, ammonia, valerian, and assafoetida, with most of the narcotics, are the antispasmodics generally in use. Emetics are another class of remedies, acting through the blood, and of very general use. It may be supposed, that, as they are received into the stomach, and act directly and speedily upon it, there is no absorption into the blood necessary. Tobacco, for instance, taken into the stomach, excites vomiting; but it is from its reception into the circulation; because, if the tobacco be laid on the arm, the same effect will be produced. Some emetics, indeed, appear to act principally on the muscular covering of the stomach, exciting it to contraction, and thereby causing the expulsion of the contents. Most of them, however, simply produce nausea, which causes the inversion of the receptacle of the food. The most active emetics employed in medicine are tartar-stomachics and tonics; the former increasing the diemetic, ipecacuan root, chamomile flowers, mustard, and blue or white vitriol. The two first of these are most commonly used; the latter being the gentlest, and perhaps on that account the safest in ordinary cases. Diuretics are those medicines which operate in promoting the flow of urine, by stimulating the action of the kidneys, the organs which secrete it. This class is very numerous, though the manner of their operation, like that of all the other vital agents, is not thoroughly understood. Those chiefly employed in practice are squills, foxglove, juniper-berries, potash, cream of tartar, acetate of ammonia, nitric ether, and Spanish flies. All these act powerfully on the urinary organs, those in highest repute being squills, foxglove, juniper, and cream of tartar. The first and the last of these are the most efficient, being more certain in their action than the others. Warm fomentations are useful accompaniments in all cases. Expectorants are used to promote the expulsion from the lungs of those fluids which are secreted during Stomachics.-There is another class of medicines, acting by absorption into the blood, or as vital agents, which cannot be ranked either amongst those which excite action or those which repress it. These are gestive powers of the stomach, the latter renovating the tone, or contractile energies, of the muscular fibre. They are slow in their operation, and augment the strength of the body without materially exciting its actions. As these two kinds of medicines are not very distinctly separable, it may be better to enumerate them together. Good nutriment is the most natural and best supporter of the bodily powers, but to effect this purpose, it is necessary that the function of diges tion should be in a proper condition. Gentian root, quassia, chamomile, columba, and canella, assist powerfully this object. Amongst the tonics, Peruvian and cascarilla barks, the preparations of iron, the sulphuric and nitric acids, are in greatest repute. With respect to the two kinds of medicinal agents, which act chemically and mechanically on the system, they are generally ranged into five classes-caustics, astringents, antiseptics, antacids, and demulcents. Caustics are a class of substances employed to create artificial sores or ulcers, for the purpose of relieving some deep-seated malady. The operation of caustics mon use. Is considered chemical, being the result of some attrac- | blood. When strong stimulants, such as mustard or tion between the animal body and the substance em- Spanish flies, are applied to the skin, they are supposed ployed. The same action takes place on the applica- to excite these minute vessels so powerfully, that those tion of caustics to a portion of the dead subject. Where which contain serum become filled with red globules. Euppuration is going on in any internal part, they are This can only be produced during an extraordinary exceedingly useful in creating a drain on the surface flow of blood to the part, and is the cause of the redof the body. The principal caustics employed in medi-ness consequent on the application of mustard catapcine, are potass, blue vitriol, nitrate of silver, arsenic, lasms or blisters. A blister is simply a rubefacient and some preparations of mercury. The nitrate of allowed to remain on the skin until a deeper layer of it silver, or lunar caustic, is the substance in most com- becomes affected, and pus or serum exudes. Like caustics, blisters are exceedingly useful in substituting a superficial inflammatory action for one existing in some deeper and more dangerous seat, and they are therefore called counter-irritants. The principal substances employed in exciting cutaneous inflammation are Spanish flies, mustard, tartarised antimony, ammonia, turpentine, and a few other drugs of a stimulant nature. The Spanish flies are almost exclusively used in blistering, and mustard, as a rubefacient, is held in a similar degree of estimation. Latterly a new and improved method of employing Spanish flies, or cantharides, has been introduced into practice. It consists in applying an extract which contains the essential powers of the material to the skin, by spreading it on paper. The blister so formed, which bears the name of tela vesicatoria (blistering tissue), produces a much more rapid effect than the common fly blister, and does not give the same pain to the patient. Astringents. The action of this class of medicines is rather obscure. Their power appears to depend in a great measure on the presence of the principle called tannin, and they produce their effect by bringing into closer contact the particles of the body to which they are applied, without, in other respects, affecting its mechanical structure. They are believed to be often of service in restoring tone to the stomach, and it is evident that their astringency will be of great advantage when any laxity of the surface of that organ exists. All the vegetable astringents contain tannin, and those most generally employed are gall-nuts, catechu, kino, oak-bark, and logwood. A number of the acids, and some of the salts, those particularly in which the acid preponderates over its base, as in alum, which | is a compound of vitriol and the earth alumina, possess astringent properties, although they contain no tannin. Some of the metallic salts, as superacetate of lead (sugar of lead), and sulphate of zinc (white vitriol), are ranked in this class. Cold is also a direct astringent, and is often employed in this character with great advantage in checking bleedings. Antiseptics, though still ranked as a distinct class of medicines, are very little trusted to in the present day. They were great favourites with the ancients, and were supposed to possess the property of resisting putrefaction, or that tendency to mortification which sometimes appears towards the termination of fevers and other complaints. Peruvian bark is commonly believed to have antiseptic qualities, and, with the exception of alcohol and vinegar, is the only drug of this class worthy of notice. Antacids. The stomach of many individuals is liable to a continued conversion of their food, particularly vegetable food, into a species of acid, which produces the annoying feeling called heartburn. This acid may be neutralised by any of the earths or alkalies, and the process of relief is as purely chemical as if it were performed in a glass of water for experiment. The three alkalies, potass, soda, and ammonia, the alkaline earth magnesia, and carbonate of lime (chalk), are the most useful medicines of this description. The relief obtained from them is, as might be expected, merely temporary, since they do not prevent the generation of the acid anew. Demulcents are a class of medicinal agents, the operation of which seems entirely mechanical. A poultice is applied externally to soften an inflamed or irritated part, and with exactly the same views are demulcents used to soothe any irritation of the alimentary canal. Solutions of gum, and syrups, with barley water, and other farinaceous drinks, are employed for this purpose. Iceland moss (lichen Islandicus), liquorice root, almonds, sugar, marshmallow, and others, are included in the class of demulcents. These are all the classes of medicines that can be said to have a chemical or mechanical action on the stomach; and to complete this brief view of the principal articles used in medical practice, of the order in which they are arranged, and the nature of their action, some account may be given of rubefacients, as they are called, from reddening or inflaming the skin, and of blisters. Counter-Irritants.-The extremities of the vessels which convey the blood from the heart over the body, are supposed, when they terminate on the skin, to divide into minute tubes, one kind of which carries the red globules, and another the colourless serum of the The principal medicines employed at the present day for the alleviation or cure of disease, have been now enumerated in an arrangement which may show their several properties and modes of operation. Each university of importance has a list of medicinal preparations drawn up for the guidance of its own members and pupils, and this list is termed its Pharmacopeia : with the enumeration is given a full account of the processes by which the various substances are prepared for use. This paper, which gives a pharmacopeia of a simple and popular kind, will have the effect, we humbly imagine, of dissipating some portion of that veil of mysticism which enveloped the art of medicine, and of showing what are the rational objects to be expected from the action of drugs upon the animal frame. In regard to the quantities of medicine to be employed as doses, that is a branch of the subject which we leave entirely in the hands of the medical practitioners properly empowered to administer them. It may here, however, be mentioned, as an interesting fact, that the action of the dose by no means corresponds with the quantity. The general rule seems to be, that when a too large dose of a medicine is taken, nature makes an effort to expel it, and it is accordingly vomited without doing the intended good. A dose of a moderate size pushes its way to the bowels, which it irritates and causes to act with a degree of violence. A dose of a smaller size will act only on the stomach. The action of medicines in the stomach is by absorption into the system; and as the stomach is always less or more filled with fluid materials, it follows that the medicines received are diluted, and have a correspondingly weak or at least slow influence on the absorbents. Thus it has been found that a few drops of certain medicaments dropped on the tongue, by which they are absorbed at once into the system, have as powerful an effect as twenty times the quantity poured into the stomach. Mineral Waters.-These waters, which are expelled from the earth as springs, form a distinct order of medicaments, prepared in the great laboratory of nature, and depending for their character on circumstances over which mankind have no control. Mineral waters are generally divided into four classes-acidulated or carbonated, saline, chalybeate or ferruginous (that is, containing iron), and sulphureous. Some are thermal, or hot; others are cold. "The substances which have been found in mineral waters are extremely numerous, but those which most frequently occur are oxygen, nitrogen, carbon, and sulphur, in different combinations; lime, iron, magnesia, &c. The saline springs consist in general of salts of soda and lime, or of mag nesia and lime, with carbonic acid and oxide of iron. The principal are those of Pyrmont, Seidlitz, Epsom, &c. The ferruginous waters have a decided styptic taste, and are turned black by an infusion of gall-nuts. The iron is sometimes in the state of an oxide, held in solution by carbonic acid, sometimes exists as a sul phate, and sometimes both as a sulphate and carbonate. The waters of Spa, Cheltenham, Tunbridge, Pittsburg, &c., are among them. The acidulous waters are characterised by an acid taste, and by the disengagement of fixed air. They contain five or six times their volume of carbonic acid gas; the salts which they contain are muriates and carbonates of lime and magnesia, carbonate and sulphate of iron, &c. The waters of Bath, Buxton, Bristol, Seltz, &c., are acidulous. The sulphureous waters are easily recognised by their dis. agreeable odour, and their property of tarnishing silver and copper. The springs at Saratoga and Ballston, Harrowgate, Moffat, Aix-la-Chapelle, and numerous others, are of this class."-Conversations Lexicon. The thermal or hot springs most frequented in Europe are those at Bath, and in the grand-dutchies of Nassau and Baden (there called brunnens). In the town of Baden-Baden, there is a saline spring, called the Ursprung, which gushes out at a temperature of 1534 degrees of our Fahrenheit thermometer, which is too hot to be either immediately drunk or bathed in. The quantity ejected by the spring is enormous. For two thousand years, which is as far back as any thing is known of the place, there have been thrown up, by the Ursprung alone, at the rate of three millions of cubic inches of water every twenty-four hours, and always, night or day, of exactly the same steaming heat and the same taste and composition. According to the analysis of Dr Koelruter, quoted by Granville, a pint of water, weighing 7392 grains, contains 23 3-20ths grains of solid matter, the principal ingredient of which is common sea-salt, there being not less than sixteen grains of that substance present. Next in importance are the sulphate, muriate, and carbonate of lime, which altogether amount to six and a half grains. The remainder consists of a small portion of magnesia and traces of iron, with about half a cubic inch of carbonic acid gas in addition. Artificial mineral waters are now prepared of different kinds by chemists, for by analysing these waters, their properties can be imitated. The article called soda water, usually sold in bottles, is well known. Its chief ingredients are carbonate of soda and tartaric acid. CHEMICAL ANALYSIS. The art of analysing the compounds of matter, or, in other words, of resolving them into the various elements of which they are framed, constitutes one of the most difficult yet important branches of chemical science. More particularly is it important in relation to numberless practical purposes of life. There are few trades which do not owe much of the success with which they are conducted, in an advanced state of society, to the light which chemistry has thrown on the nature of the substances employed in them, and the consequent improvements therein introduced. To the highest moral interests, even, of the social body, chemical analysis is of vital moment. It is the basis of medical jurisprudence. Without the knowledge of poisons possessed by the professors of that science, and their ability to separate by analysis the most minute portions of these from any compounds with which they may have been mixed, innocence might often perish under the erring severity of the laws, and guilt escape the penalty justly incurred. The mode in which chemical analysis, so important in every respect, is conducted, may best be explained by individual examples; but a few general observations will not be out of place. As respects the apparatus necessary for the chemical analyst in his laboratory, notice has already been taken of it; and it is only necessary to add, that in performing analyses, the prin cipal tests and preparations are also required. The latter articles amount in number to about sixty or seventy. They consist chiefly of the sulphuric, nitric, and hydrochloric acids; sulphur, phosphorus, iodine; the principal alkalies and earthis, with their most important compounds; mercury, iron, lead, tin, cobalt, antimony, gold, silver, and a few other ictals, pure or in a compound state; with a few of the vegetable acids, such as the tartaric and oxalic. Tests and testpapers, most important matters in chemical experiments, are also to be procured. By boiling red cabbage, one blue solution of this character is obtain, d, which detects acids and alkalies, uncombined or in excess, the former turning the blue to a red, and the latter to a green. Boiled litmus gives another solution, which acids redden; and turmerie in solution is changed from yellow nearly to red by alkalies. Slips of paper, soaked in these solutions, and then dried un the dark, require only to be touched by the dissolved alkali or acid, to show the change of colour at once. Iron, again, is instantly detected by infusion of galls. The presence of acids and alkalies, in almost every compound in nature, renders these tests of vast consequence in analytic chemistry. In taking up any body of unknown composition for analysis, very minute quantities only, finely divided and weighed, are used. The body is then, if possible, dissolved, commonly in water, that the particles may be further separated as widely as possible, which is the most favourable condition for the action of other bodies upon it, and display of chemical affinities. It is possible that the body may be insoluble, or but partially soluble in water at a common temperature. In these cases, the processes of infusion, digestion, or decoction, will be tried by the analyst, heat adding powerfully to the solvent powers of water. Lixiviation and maceration are also resources of the chemist. Sometimes alcohol or other solvents must be employed, and at times several solvents require to be used in succession, each having the power to take up something insoluble in the others. Once dissolved, the body, or portions of it separately, can be treated with tests; and, happily, there is not one substance in nature which has not such affinities for one or more substances, in preference to all others, as readily to betray its own nature. The common results of adding one body as a test to another in solution, are either alteration of colour, or precipitation, or gasefaction. In the first case, the two bodies may form a compound, soluble, but of new colour; in the second place, an insoluble substance may be thrown down to the bottom of th solution; and, in the third, a gas may be set free. A of these results may be combined in some cases. Tie experimenter may, moreover, vaporise and crysta lise: fusion and condensation are processes also at hi command. When simple solution can be effected in no way, and at no temperature, the experimenter may then have recourse to other agents. Chemical action may be induced by pressure, by electricity, and sonictimes by light. These are the general ways and means by which the chemical analyst prosecutes his investigations. By way of particular example, let us take a case in the department of medical jurisprudence. Let us suppose a medical man called upon to examine a case of poisoning, where the only cause of death that can be suspected is the use of copper vessels when cerroded by articles of food. The object, then, is to an lyse the vegetable or animal fluids remaining on th stomach, or preserved otherwise, in order to deter the copper, if it exists. Being boiled, the fluid in tion is treated or mixed with diluted acetic acid o vinegar, which dissolves out the copper from among the other matters present. Well aware that sulphon has so strong an affinity for copper as to unite wil it whenever they meet favourably in solution, forming a compound of both, called a sulphuret of copper, Professor Christison then directs the introduction of sulphur, in the shape of sulphureted hydrogen gas, after the following preparations have first been made:-"The | marked as those of fluids or solids, and can be as readily suspected mixture having been prepared by the addition of acetic acid, is to be subjected to filtration, and any matter left on the filter is to be washed, collected, and dried, the washings being, of course, added to the faid which first passed through. The process here divides itself into two; for the oxide of copper may be left on the filter in the form of an insoluble salt, or it may have passed through in solution. But it may be observed in passing, that very few of the salts of copper are insoluble in diluted acetic acid, so that if copper is present at all in a suspected mixture, there are many chances in favour of its being found by the first branch of the analysis. The water, next day, gave no tinge with the tincture, showing the iron to be principally in the state of a carbonate. detected. For example, the gas called carbonic acid, present so largely in nature, has such an affinity for lime, that, on contact, it is at once absorbed by limewater, and renders that liquid turbid. By trials with a graduated glass tube, where the gas or air containing carbonic acid is brought into contact with lime-water, the loss of the acid gas by absorption may be measured, and the proportion of it present in the examined air at once determined. So with other gases, when tested in relation to their respective affinities. Having satisfied himself about the gases present in the spring of Fordel, Mr Robertson then tried the following preliminary experiments to determine the substances contained :First branch. The solution is to be examined first," Even when recent, it did not perceptibly redden tineboth because it is the more likely quarter in which to ture of litmus, though the tint was compared with the Lud the copper, and because the analysis is more easy colour of the tincture diluted to a similar extent. than that of the solid matter. The solution, then, is to It did not affect the colour of Brazil wood or turmebe treated in the usual way with a stream of sulphuric test-paper. With tincture of galls it gave a slight rted hydrogen, and immediately boiled to expel the tinge of purple, and ultimately a scanty purplish-brown excess of gas. If a brownish-black, or even pale-brown flocculent precipitate, showing the presence of iron, and precipitate is then thrown down, there is a presump-by the purplish tinge, also, the presence of earthy or tion in favour of the existence of copper: if there is alkaline salts. to precipitate or brown colouration, there is no copper the fluid. In order to ascertain precisely the nature f the precipitate, which is some metallic sulphuret, De superincumbent fluid, after ebullition and subsince of the precipitate, is to be cautiously withdrawn, d its place supplied with water; and when the wash- The water, upon being boiled, gave a considerable g has been several times repeated in the same man- yellowish-white precipitate, indicating carbonates. This r, the precipitate is to be transferred into a watch-precipitate was soluble, with considerable effervescence, tlass, or, still better, into a white porcelain cup, and in nitric acid. dried. It is next to be collected, and incinerated in a tiass tube, to destroy any adhering vegetable or animal matter. The last step in this branch of the process is to convert the sulphuret into the sulphate by the action of a few drops of nitric acid, aided by a gentle heat; and then to add to an excess of ammonia, either withat or with previous filtration, according to the degree of muddiness in the nitrous solution. If copper is [resent, the usual deep violet-blue tint will be struck. Second branch.-If copper is not detected in the fillered part of the suspected matter, it will be necessary examine also what remained on the filter. This proceeding, which constitutes the second branch of the aralysis, will be seldom required in ordinary medicogal researches, being rendered necessary only by the possibility of the oxide of copper having, either origitally or after mixture with the suspected matter, asBuded the form of an inorganic salt, insoluble in water acetic acid. The matter on the filter is first to be well dried, and then heated to redness in a crucible till it be completely tharred. The copper which is thus reduced to the metalic state, is next to be treated with nitric acid, sluted with its weight of water, and aided in its action gentle heat. A solution is then procured, which is to be removed by filtration, and tested with ammonia, ad the other liquid tests.' Ammonia, or hartshorn, as a strong affinity for copper, and when added to a eine solution of the latter, throws down a deep blue perder, called the ammoniuret of copper. The analysis of mineral waters, where the nature and amount of the whole ingredients, and not of one 23, form the subject of inquiry, is a task of very great 4ficulty. Generally, however, non-professional experimenters upon liquids of this description, are anxious merely to ascertain the existence or non-existence of rtain ingredients, without entering into minute protional quantities, or the like details. The report of a case where a clergyman, the Rev. W. Robertson, Ear, of Inverkeithing, examined a mineral spring Fordel, now lies before us, having been communiEled to the Philosophical Journal of Professor JameIt may give a fair idea of the way of going to work under such circumstances. A gas bubbled up through the spring, which Mr Robertson first examined. The elementary as well as Empound gases have properties and affinities as well When the water was evaporated by a gentle heat, flocculi of oxide of iron were deposited. The water decanted off from this precipitate gave no tinge with tincture of galls, but, on boiling it with a few drops of nitric acid, to peroxidise the iron which it might contain, the excess of acid being afterwards neutralised by ammonia, it gave unequivocal traces of iron, by a darkish tinge with the tincture. From this it was inferred that the iron in it was in the state of protoxide. A portion of this water, after being thus treated, also gave a red tinge, with sulpho-cyanate of potash. With ferro-cyanate of potashi, and a drop of muriatic acid, the water, when recent, gave a whitishi precipitate, becoming blue by exposure to the air, indicating iron in the state of protoxide. With lime-water, the recent water gave a copious flocculent precipitate, the lime uniting with the excess of the carbonic acid, and the whole of the carbonates falling down together. This precipitate was redissolved, on adding more of the mineral water, which showed a considerable excess of carbonic acid; and it was also soluble with effervescence in dilute acetic acid. With the bicarbonate of potash there was no precipitate, the whole being kept dissolved by the excess of carbonic acid. With ammonia, and also with potash, a flocculent white precipitate took place, partly owing to the abstraction of free carbonic acid. With the carbonates of potash, soda, and ammonia, there were similar precipitates, but more scanty; they were all soluble in a dilute acetic acid. With a solution of soap in alcohol, a great milkiness. With acetate of lead, a considerable milkiness, and a precipitate insoluble in acetic acid. With oxalate of ammonia, a considerable precipitate, indicating lime. With carbonate of ammonia and phosphate of soda, an immediate milkiness, and a precipitate, after standing, indicating magnesia; the precipitate soluble in acetic acid. With carbonate of ammonia or phosphate of soda, separately, no milkiness, after standing for the same length of time. With muriate of baryta, a slight precipitate, insoluble in muriatic acid, indicating sulphuric neid. With nitrate of silver, a copious precipitate, white while secluded from the light, becoming rapidly purple on exposure to light, indicating muriatic acid. Two ounces of the water, evaporated to dryness, gave, with nitro-muriate of platinum, slight traces of potach, The water, very much concentrated by evaporation, gave, with starch and sulphuric acid, no trace of iodine. From the above indications, it was concluded that the water contained sulphuric, muriatic, and carbonic acids, together with protoxide of iron, lime, magnesia, and a little potash. The presence of alumina was inferred to be incompatible with that of the earthy carbonates, neither could any be subsequently detected." The determination of the quantities of each substance present was the next object with Mr Robertson; but it is not necessary here to carry our notice of the subject beyond generalities. The agricultural chemist proceeds in a similar way and with similar instruments. He has the advantage, generally, of knowing beforehand the probable character of the matters on which he operates, and the point is to determine in what proportions they exist in the particular soil under examination. Where a less exact analysis will suit the purposes of the agriculturist, the following simple plan of ascertaining the qualities of soils may be adopted. We quote, with some slight alterations, from Mr Young's "Letters of Agricola." "In the field to be examined, take earth a little below the surface, from four separate places, about a quarter of a pound from each. Mix them together, and again separate them into four quantities of a quarter of a pound each. Then take one quantity and expose it to the sun, or before the fire, till completely dry; and turn it over frequently, that it may be well mixed together. Being thus powdered, pass it through a fine sieve, which will allow all the particles of sand and gravel to escape, but which will hold back stones, small fibrous roots, and decayed wood. Weigh the two parts-the fine and the rough-separately, and take a note of each. The stones and other bulky materials are then to be examined apart from the roots and wood. If they are hard and rough to the touch, and scratch glass easily, they are silicious and flinty; if they are without much difficulty broken to pieces by the fingers, and can be scraped by a knife to powder, they are aluminous or clayey; or if, when put in a wine-glass, and common vinegar poured upon them, small air-bubbles ascend to the top of the liquid, they are calcareous. The finely divided matter which ran through the sieve, must next undergo the test of experiment. After being weighed, agitate the whole in water, till the earth be taken up from the bottom and mechanically suspended, adding water till this effect be produced. Allow the mass then to settle for two or three minutes, and in that time the sandy particles will sink to the bottom. Pour off the water, which will then contain the clay in suspension, and the insoluble earth arising from animal and vegetable decomposition. The sand should be first attended to, and if from inspection it be thought either silicious or calcareous in its nature, the requisite tests may be instantly applied. By this time the mixture in the poured-off water will leave deposited at the bottom of the vessel the clay and other earths, with the insoluble animal and vegetable matter. After pouring off the water, dry the sediment, and apply a strong heat by placing it on the bottom of a pot ignited to redness, and the animal and vegetable matter will fly off in aëriform products. The remainder lying in the bottom will be found to consist of clay, lime, or magnesia. To obtain accuracy, another quarter of a pound may be taken, and the whole process gone over a second, a third, or even a fourth time, so that the operator may rectify any blunders he had previously committed, and be satisfied as to the results of the experiment. He should provide himself with a pair of fine scales, and a set of weights divided at least into half and quarter ounces and drachms. Although vinegar will detect lime by effervescence, it does not dissolve it so effectually as the nitric or muriatic acids, small quantities of which may be obtained from the druggists at a small pense." ving ascertained by these, or any other inquiries, the composition of the soil, a pretty accurate notion, other things considered, may be obtained respecting its capacity for productive husbandry. If it be necessary to enter on a course of improvement, the defect in composition may be remedied by the application of materials of an opposite quality-an excess of calcareous matter being counteracted by sand and clay, an excess of clay by the admixture of sand, or an excess of sand by the application of clay, peat, &c. An excellent soil for bearing wheat has been found to contain in 100 parts-carbonate of lime, 28; silica, 32; alumina, 29; and of animal and vegetable matter, with moisture, 11. Oxide of iron, to the extent of 2 or 3 in the 100 parts, is not unusual in good soils. COMBUSTIBLES. The class of combustibles in the manufacture of which a knowledge of chemistry is more particularly required, includes gunpowder, fulminating powders, the material of Congreve and sky rockets, bomb-shells, percussioncaps, rapidly igniting matches, and of fireworks generally. The term Pyrotechny (from pur, fire, and techne, art) has been applied to the art of making and compounding these substances. Of each of them we shall present a short account, with an explanation of the principles on which they fulminate and explode. The leading ingredients in most explosive combustibles are charcoal, saltpetre or nitre, and sulphur. In making fireworks of a varied kind, however, numerous other substances are employed. The chief are chlorate of potass, fulminating silver, and mercury, preparations of steel, copper, and other metals, with various oils, spirits, and resins. Charcoal, as is mentioned in the preceding sheet, is simply wood reduced to a charred condition (pure carbon), by being burnt to a kind of blackened cinder in a vessel closed from the atmosphere. For making gunpowder, light woods, such as the willow and alder, are the best, and the pieces are stripped of their bark before being used. In preparing this kind of charcoal, it is important that the vapours be allowed freely to escape, otherwise its combustibility will be impaired. The preparation is usually effected by iron retorts over furnaces; and by a connecting tube the vapour escapes, and is condensed into a tarry acid, from which pyroligneous acid is afterwards distilled. After being thus prepared, the charcoal is ground to a fine powder. It has been properly charred if it burns without leaving any residuum. Saltpetre, nitre, or nitrate of potass, is abundant in nature, but may be also compounded by the artificial union of its two ingredients, nitric acid and potass. It is procured largely from India, and also from Egypt, Spain, and other countries, where it is found on the surface of limestones, marls, and chalky strata, being spontaneously generated and reproduced there by some atmospheric influence not well understood. The slight silky tufts of the nitre are swept up with a broom, and are lixiviated, allowed to settle, evaporated, and crystallised. In this state it is exported; but the impurities which it contains require its subjection to successive solutions and crystallisations, ere it can be formed into gunpowder. The last process is that of fusion, in iron pots at a regulated heat. Nothing can surpass, in these respects, the nitre prepared in the government powderworks at Waltham Abbey. It is tested by adding to its solution in distilled water nitrate of silver, with which it occasions no perceptible opalescence. Sulphur is procured in many volcanic countries, and the great emporium for it is Sicily. At the gunpowder works, it is purified for use either by distillation or by fusion. In the first instance, the pure part is distilled over, and, in the second, skimmed off, the impurities being left behind. Gunpowder. The three ingredients, charcoal, nitre, and sulphur, being duly prepared by trituration, and passed through fine sieves, they are ready to be mixed. There appears to be a great difference of opinion and practice in determining the relative proportions of the ingredients. The following is a scale of proportions in 100 parts, adopted by different gunpowder makers:— |