Mercury, in its metallic state, is never applied to any medical use,^[522] except in visceral obstruction, in hopes of forcing a passage by its gravity; but under various forms of preparation, it affords a series of very active remedies. Adulterations. With the exception of Peruvian Bark, there is perhaps no active article in the materia medica more shamefully adulterated; its impurity is at once indicated by its dull aspect; by its tarnishing, and becoming covered with a grey film; by its diminished mobility, in consequence of which its globules are unable to retain the spherical form, and therefore tail, as it is technically expressed. Lead is discovered by dissolving it in nitric acid, and adding to the solution water impregnated with sulphuretted hydrogen, when, if lead be present, a dark brown precipitate will ensue. Bismuth, by pouring the nitric solution into distilled water, when it will appear as a white precipitate. Zinc, by exposing the mercury to heat. Tin is detected by a dilute solution of nitro-muriate of gold, which throws down a purple precipitate. The presence of lead in mercury is a most dangerous circumstance; I have once witnessed a case of cholica pictonum in consequence of it. The usual mode of purifying quicksilver, by pressing it through chamois leather, will not separate the lead, if it be, as is generally the case, in combination with bismuth; for the manner in which the adulteration is effected, is by melting with a gentle heat these two metals, and adding the alloy to the mercury; and although this alloy should exceed one-fourth of the whole bulk, it will pass, together with the mercury, through chamois leather. On standing, the bismuth will be thrown upon the surface, in the form of a dark powder, but the lead will remain in solution. The greatest part of the mercury of commerce comes from Istria and Friuli, and from the Palatinate, and as it passes through the hands of the Dutch, we must expect to receive it in a state of alloy. On a superficial examination, it ought not, when shaken with water, to impart to it any colour; when agitated or digested with vinegar, it should not communicate a sweetish taste; and when exposed in an iron spoon to heat, it ought to evaporate entirely. The French are so well aware of the mischievous extent to which this metal is falsified, that in their late Codex they direct the reduction of the red oxyd in order to obtain it; the process however is too expensive for general adoption. The Italian Jews purify quicksilver for their barometers, by digesting it in dilute sulphuric acid, which is by no means an improper process. The mode directed for the purification of mercury by the London College, (Hydrargyrum Purificatum) is unable to separate it completely from its more deleterious contaminations. It is a general opinion in Germany, that mercury, boiled in water, will impart to it an anthelmintic virtue;^[523] this, if it happens, can only depend upon the impurities of the mercury; but large draughts of cold water are in themselves anthelmintic. Although metallic mercury in its fluid form exerts no effect upon the animal system, it, nevertheless, in a state of vapour, manifests considerable powers; and it is necessary for the practitioner to be informed that it assumes this condition at the ordinary temperature of the atmosphere. I have stated several experiments in proof of this fact in my work on Medical Jurisprudence, Art. “Aerial Poisons,” to which the reader may refer.

Qualities. Form, an impalpable powder of a snowy whiteness; Odour and Taste, none. Chemical Composition. It is a triple compound of oxide of mercury 81, muriatic acid 16, ammonia 3 parts. Solubility. It is insoluble in water, and in alcohol; when triturated with lime water it does not become black. It is now only used in combination with lard as an ointment; formerly it was administered internally, and Boerhaave strongly recommends it as a safe and mild mercurial, and as seldom, if ever, exciting copious salivation. Officinal Prep. Unguent. Hydrarg. præcipitati albi. L.D.

This is mercury slightly oxydized by trituration, and mixed with chalk. Grs. iij contain about one grain of mercury. Dose, grs. v to ʒss. It is a mild and excellent mercurial, and has been known to cure syphilitic affections, when the constitution had proved rebellious to every other form of preparation. Dr. George Fordyce committed a great error, when he denied to this compound any mercurial efficacy. The peculiar mildness of this preparation has been very justly attributed to the effects of the carbonate of lime, in neutralizing acid matter in the primæ viæ. In Mesenteric affections I have employed it with much advantage; in certain forms of Dysentery it is also a very valuable medicine.

Qualities. Form, a crystalline mass, composed of very small prismatic crystals, which is easily pulverized, and undergoes a slight alteration by exposure to air, becoming on its surface opaque and pulverulent. Light, however, has no effect upon it, although a different opinion has existed, and it has accordingly been recommended to be kept in black bottles. Odour, none. Taste, very acrid, with a metallic astringency, occasioning a sensation of obstruction in the throat which continues for some time. Sp. gr. 5·1398. When pulverised and thrown upon burning coals, it is immediately volatilized, giving out a thick white smoke of a very pungent smell, which irritates the mucous membranes extremely, and is highly dangerous to those who inhale it. Chemical Composition. According to the latest views, it is a Bi-chloride of mercury, consisting of one proportional of mercury, to two proportionals of chlorine. In the French codex, it is termed “Deuto-Chloruretum Hydrargyri.” Solubility. It is soluble in eleven parts of cold, and in three of boiling water, and in half its weight of alcohol; it is also very soluble in æther; indeed this latter liquid has the curious property of abstracting it from its solution in water, when agitated with it. Its solubility in water is greatly increased by the addition of a few drops of rectified spirit, or of muriatic acid. In a solution of muriate of ammonia it is seventeen times more soluble than in water, no decomposition however arises; it is therefore probable that a triple salt is formed; it is also soluble in the sulphuric, nitric, and muriatic acids, and may be obtained again unaltered, by simply evaporating the solutions. Dr. Davy, in his late researches upon corrosive sublimate states that with muriatic acid, common salt, and some other muriates, it forms definite compounds remarkable for their solubility. Its watery solution is said to change vegetable blues to green, but this is an optical fallacy, (see page 306.) On exposure to light this solution slowly undergoes decomposition; but Dr. Davy has shewn that corrosive sublimate remains unaltered when exposed in solution in media having a strong affinity for it, as in alcohol, æther, muriatic acid, &c. and that decomposition only takes place under circumstances of complicated affinities, as in the instance of Liquor Hydrargyri Oxymuriatis, and in that of the aqueous solution; in which cases Calomel and Muriatic acid appear to be formed, and oxygen to be evolved. Incompatible Substances. The carbonates of the fixed alkalies precipitate it of a yellow hue, but the precipitates are not pure oxides; ammonia forms with it a white triple compound. Lime water decomposes it more perfectly than any alkaline body, occasioning a precipitate of a deep yellow colour,^[524] which is a per-oxyd of mercury containing a little muriatic acid; this result forms a useful lotion to ill conditioned ulcers, and has been long known under the title of Aqua Phagadenica; f℥j of lime water should be employed for the decomposition of two grains of the salt. Tartarized antimony, nitrate of silver, acetate of lead, sulphur, sulphuret of potass, and soaps, decompose it. Iron, lead, copper, bismuth, and zinc, in their metallic state, also decompose it, producing precipitates which consist of an amalgam of the metal employed, except in those cases where the metal in question refuses to amalgamate with mercury, when this latter metal appears as a metallic dew, composed of very minute globules, with calomel; hence mortars of glass or earthenware should be used for dispensing this article; when triturated with olive oil, the oil becomes white, and when boiled with it, calomel is precipitated; the same happens if sugar be substituted for oil. The volatile oils reduce it. When Oil of Turpentine was used, some traces of artificial camphor was discovered by Dr. Davy, and when the oils of Cloves and Peppermint, a purple compound distilled over, consisting of the oil employed and muriatic acid. The following vegetable infusions produce precipitates, viz. the infusions and decoctions of chamomile, horse-radish root, calumba root, catechu, cinchona, rhubarb, senna, simarouba, oak bark, tea and almond emulsion. Swediaur observes, that “many authors have recommended sublimate combined with bark, but that a reciprocal decomposition is thus produced, by which the energies of both remedies are alike annulled;” to this ignorance, however, he thinks that many patients have been indebted for their lives; for, says he, “I see every day examples of weak and very delicate persons of both sexes, to whom ignorant practitioners prescribe, and sometimes in very large doses, the corrosive sublimate, with a decoction of bark; certainly without curing the syphilis, but at the same time without occasioning those grave and dangerous symptoms, which that acrid medicine would certainly produce, if given alone, or without that decoction.” We have here presented the reader with the opinion of Swediaur; but it is just to state, that the experience of this country has rather tended to subvert, than to confirm, such a belief. That the corrosive sublimate of mercury is actually decomposed by the vegetable principles of the bark is sufficiently evident, but it would seem that the oxide thus developed, and recombined with vegetable extractive, is a very active mercurial, especially with respect to its alterative powers. The same observation will, to a certain extent, apply to the results of its decomposition by other agents; the fixed alkalies have been found by actual experiment to be incapable of disarming this salt of its virulence, because, as Orfila has stated, the oxide liberated is, in itself, an active poison. Mr. Rose has lately transmitted to me a formula for the preparation of “Alterative Drops,” which he states, from ample experience, to possess very considerable powers as a mercurial, and to excite ptyalism, with a quickness and certainty which characterize but few preparations of the same class. The principal ingredients are an alcoholic solution of corrosive sublimate and a vinous solution of tartarized antimony. It is scarcely necessary to observe that upon admixture a mutual decomposition takes place; the peroxide of mercury is precipitated by the alkaline element of the antimonial compound, whilst this latter salt, having its affinities thus overthrown, parts with the protoxide of antimony; so that the preparation holds a considerable quantity of insoluble matter in suspension, and which is to be carefully incorporated with the liquid by shaking the phial, whenever the drops are administered. Now there can be but little doubt but that the activity of this preparation is owing to the peroxide of mercury, thus diffused in a state of minute division, while at the same time the antimonial protoxide very probably disposes the stomach and system to be more readily influenced by it, for reasons which have been fully discussed in the first part of this work, p. 152. Med. Uses. It is one of the most acrid and active of all metallic preparations; in well directed doses, however, it is frequently of service in secondary syphilis, and in cases of anomalous disease, when it would be improper to administer the other forms of mercury.^[525] In obstinate cutaneous diseases its administration in small doses is often very serviceable; I have, however, seen extreme emaciation and hectic fever produced by its too long continued exhibition, although ptyalism was never occasioned. Its application also as a lotion to leprous affections, in the proportion of about one grain to a fluid-ounce and a half of some liquid vehicle, I have frequently seen highly beneficial; in directing the use of so acrid a lotion, we should caution the patient not to touch his eyes until his hands have been washed; in consequence of a neglect of this kind I have seen a very severe ophthalmia produced. The practitioner should also remember that the system may become affected by such external applications; a case stands recorded in which a girl of five years old became salivated, and died, in consequence of an application made to the head for the cure of Tinea, which consisted of Pomatum rubbed up with a few grains of this salt. Its internal exhibition should be accompanied with mucilaginous drinks; when an overdose has been taken, the white of egg, diluted with water, is the best antidote, for Orfila has found that albumen decomposes it, reducing it to the state of mild muriate, whilst the compound which it forms with it is inert. Many examples are recorded of the success of this practice. In the Transactions of the King and Queen’s College of Physicians in Ireland, an interesting case of this kind is related by Dr. Lendrick; it is, however, at the same time but justice to state, that there are instances also of the failure of this antidote. In the 41st volume of the London Medical and Physical Journal, p. 204, the reader will find the case of a girl, who was poisoned by a drachm of Sublimate, and who, notwithstanding the copious ingestion of albumen, died in ninety hours. More recently vegetable gluten, as existing in wheat-flower, is said to answer as well as albumen; for the administration of which all that is required is to give wheat-flower and water. Dose, gr. 1/8 to ½, see Liquor Hydrargyri Oxymuriatis, and Form. 142. Adulterations. It ought to be volatilized by heat; it is frequently met with in commerce contaminated with muriate of iron, sometimes with arsenic; the presence of calomel is at once discovered from its insolubility. Tests of its Presence. If any powder be suspected to contain this salt, expose it to heat in a coated tube, as directed in the treatment of arsenic, but without any carbonaceous admixture, when corrosive sublimate, if present, will rise and line the interior surface with a shining white crust. This crust is then to be dissolved in distilled water, and assayed by the following tests; 1st, lime water will produce, if the suspected solution contains this salt, a precipitate of an orange yellow colour. 2d, a single drop of a dilute solution of sub-carbonate of potass will at first produce a white precipitate, but on a still farther addition of the test, an orange-coloured sediment will be formed. 3rd, sulphuretted water will throw down a dark coloured precipitate, which when dried and strongly heated may be volatilized without any alliaceous odour. 4th, ammonia produces a white precipitate, which is an insoluble triple salt, composed of muriatic acid, ammonia, and oxide of mercury, which, on being heated, grows yellow; it passes afterwards to a red, and gives out ammoniacal gas, nitrogen, calomel, and metallic mercury. In this operation the oxide is supposed to be decomposed by the hydrogen which results from a portion of the ammonia. 5th, Nitrate of tin, according to Dr. Bostock, is capable of detecting the three-millionth part of a grain; a single drop will occasion an immediate and copious dark-brown precipitate. All the above precipitates, if rubbed on a bright plate of copper, will render its surface very white. Where the salt is mixed with various coloured liquids, we must proceed as directed under the head of Arsenic. A very ingenious application of galvanic electricity has been also proposed by Mr. Silvester, for the detection of corrosive sublimate, which will exhibit the mercury in a metallic state. A piece of zinc or iron wire about three inches in length, is to be twice bent at right angles, so as to resemble the Greek letter Π, the two legs of this figure should be distant about the diameter of a common gold wedding ring from each other, and the two ends of the bent wire must afterwards be tied to a ring of this description. Let a plate of glass, not less than three inches square, be laid as nearly horizontal as possible, and on one side drop some sulphuric acid, diluted with about six times its weight of water, till it spreads to the size of a halfpenny. At a little distance from this, towards the other side, next drop some of the solution supposed to contain corrosive sublimate, till the edges of the two liquids become joined; and let the wire and ring, prepared as above, be laid in such a way that the wire may touch the acid, while the gold ring is in contact with the suspected liquid. If the minutest quantity of corrosive sublimate be present, the ring in a few minutes will be covered with mercury on the part which touched the fluid. This experiment may be beautifully simplified in the following manner; drop a small quantity of solution containing corrosive sublimate on a piece of gold, and bring into contact a key, or some piece of iron, so as to form a galvanic circuit, when the gold will be immediately whitened. A solution of nitrate of silver will, under similar circumstances, occasion on the gold a white precipitate, but as no amalgamation takes place, it is readily wiped off, and cannot possibly occasion any fallacy.^[526]

Certain metals likewise decompose solutions of this salt, by virtue of superior affinity; in those cases where the precipitating metal is capable of forming a direct union with Mercury, we shall find the precipitates to consist of an amalgam of the metal employed; where no such combination takes place, the mercury will be frequently seen standing on the surface as a metallic dew. This is particularly striking where iron or steel has been employed; these metals are also at the same time blackened by it.

Brugnatelli^[527] has proposed the following method of distinguishing corrosive sublimate from arsenic—Take a quantity of fresh wheat starch, mix with water, and add a sufficient quantity of iodine to give the liquid a blue colour; if corrosive sublimate or arsenic be added to this liquor, the colour is alike destroyed and it becomes reddish, but if the change has been effected by the latter substance, a few drops of sulphuric acid will restore the blue colour, but if by the former it is not recoverable by such means.^[528]

This preparation has been known in pharmacy for upwards of two centuries under a variety of fanciful names, such as Draco mitigatus; Aquila alba; Aquila mitigata; Manna metallorum; Panchymagogum minerale; Panchymagogus quercetanus; Sublimatum dulce; Mercurius dulcis sublimatus; Calomelas; and yet there is not a name in this list that is so objectionable as the one at present adopted by our colleges: for whether we adhere to the theory of muriatic acid being the simple body, or accede to the new views of chlorine, the name is equally inappropriate; if we regard it as a compound of muriatic acid and oxyd of mercury, it is not a sub-muriate, but as much a muriate as the corrosive sublimate; the only difference depending upon the degree of oxidizement of the mercury, which is at a minimum in calomel, and at a maximum in sublimate. According to the new views respecting chlorine, calomel must consist of one proportional of chlorine with one proportional of metal, and is therefore a chloride of mercury. (“Proto-chloruretum Hydrargyri.” Codex Med. Paris.)

Qualities. Form. A semi-transparent mass, consisting of short prismatic crystals;^[530] inodorous, insipid, and of an ivory colour, which deepens by exposure to light. Solubility. It is considered as being insoluble, since according to Rouelle, one part requires 1152 of water, at 212° for its solution. Incompatible Substances. Alkalies and lime water decompose it and turn it black, in consequence of precipitating the black oxyd of the metal; it is also decomposed by soaps, sulphurets of potass and antimony; and by iron, lead, and copper; hence it is improper to employ any metallic mortar for dispensing medicines which contain it. There seems to be reason for supposing that this preparation may undergo decomposition in transitu, and that therefore some substances may be chemically, and yet not be medicinally incompatible with it. If calomel be boiled for a few minutes in distilled water to which alcoholized potass has been added, it is completely decomposed, a muriate of potass and black oxyd of mercury being the new products. Calomel is not affected by sulphuric acid in the cold, but, at a boiling temperature, corrosive sublimate, and deuto-sulphate of mercury are formed. Medicinal Uses.^[531] This mercurial preparation is more extensively and more usefully employed than almost any other article of the materia medica. It is capable of curing syphilis in every form, provided it does not run off by the bowels; and in obstructions and hepatic affections, it is in well-regulated doses a most valuable remedy; in combination, it probably merits the appellation of Dirigens, more decidedly than any other remedy with which we are acquainted, for when combined with certain diuretics, it is diuretic, (Form. 103, 104) and in diaphoretic arrangements, it is diaphoretic: it moreover imparts force to many of the mild, and moderates the severity of drastic medicines: whenever we wish a strong and permanent impression to be made on the alimentary canal, and through it on the neighbouring viscera or the system generally, Calomel by universal consent is adopted for such a purpose. (Form. 81, 88, 119, 161.) In larger doses it is one of the most efficient purgatives which we possess, especially when in combination with other cathartics: it appears to be particularly eligible in the diseases of children; and it is singular that infants can generally bear larger doses of it than adults. Dose, as an alterative, from gr. ss to j, night and morning; as a purgative, from gr. ij to gr. x, or in some cases even to gr. xv, or ℈j. Forms of Exhibition. That of pill; its insolubility and specific gravity render any other form ineligible. Officinal Preparations. Pil. Hydrargyri submuriat. comp: L. Impurities. Corrosive sublimate may be detected by precipitation being produced, by the carbonate of potass, in a solution made by boiling the suspected sample with a small portion of muriate of ammonia, in distilled water; calomel ought also, when rubbed with a fixed alkali, to become intensely black, and not to exhibit any trace of an orange hue.

Howard’s or Jewel’s Hydro-sublimate. Instead of subliming so as to obtain the calomel in a concrete state, as directed by the Pharmacopœia, the salt in the act of sublimation is exposed to aqueous vapour, and received in water. Being in a state of very minute division, it is lighter than common calomel in the proportion of three to five, and it cannot contain any corrosive sublimate. The French in their late codex have introduced a similar formula, under the title of “Murias Mercurii dulcis mediante aqua subtilissime divisus, juxta Methodum Josiæ Jewel.”

This Patent Calomel of Howard is undoubtedly to be preferred, and appears, in consequence probably of its minute division, to affect the system more readily than that made according to the Pharmacopœias.

Sub-murias Hydrargyri Præcipitatus. E.D. This is produced by precipitating a nitrate of mercury by muriate of soda; the preparation will generally contain a small portion of sub-nitrate, and it is on that account more liable to run off by the bowels in small doses: in other respects it is essentially the same as that procured by sublimation.

Qualities. Form, a red crystalline cake, inodorous, insipid, and insoluble in water, alcohol, acids, and alkalies, although these bodies decompose it when melted with it; it is also decomposed by nitro-muriatic acid, which unites with the metal, and disengages the sulphur. Chemical Composition. It is a bi-sulphuret of Mercury, i. e. it consists of two proportionals of sulphur and one of mercury. Uses.^[533] It is now only used for the purpose of mercurial fumigation, which is done by inhaling the fumes, produced by throwing ʒss of it on red hot iron; the effect which is generally produced is violent salivation; this however does not depend upon the action of the substance as a sulphuret, but upon its decomposition, and the volatilization of the metallic mercury with a portion of sulphate and sulphureous vapour. Mr. Pearson observes that it is useful in those cases of venereal ulcers in the mouth, throat, and nose, where it is an object to put a sudden stop to the progress of the disease, but that mercury must at the same time be introduced into the constitution, by inunction, just as much as if no fumigations had been made use of. Ulcers and excrescencies about the pudendum and anus in women are particularly benefitted by it; and in these cases it is conveniently applied by placing a red hot heater at the bottom of a night-stool pan, and after sprinkling on it a few grains of the sulphuret, placing the patient upon the stool. Adulterations. Red Lead^[534] may be discovered by digesting it in acetic acid, and by adding sulphuret of ammonia, which will produce a black precipitate; or by burning a small portion of the suspected sample on a piece of bread in the candle, when metallic globules will announce its presence; for the oxide of mercury, although revived by this process, will at the same time be volatilized. The bread, by combustion, affords the carbon by which the metallic reduction is effected. Dragon’s Blood, by its giving a colour to alcohol when digested with it; Chalk, by its effervescence, on the addition of an acid. It is known in the arts under the name of Vermillion; and by the following simple expedient its presence may, in very minute quantities, be easily recognised; boil a portion with sulphuric acid in a platina spoon, and lay the sulphate thus produced, in a drop of muriatic acid, on a piece of gold, and bring a piece of metallic tin in contact with both, when the white mercurial stain will be produced.

Qualities. Form, a very black, impalpable, insipid, and inodorous powder. Chemical Composition. It is a Sulphuret of Mercury, i. e. it consists of one proportional of sulphur, and one proportional of mercury; when heated in contact with the air it is converted into a bi-sulphuret. Solubility. It is entirely soluble in a solution of pure potass, from which the acids precipitate it unchanged; it is insoluble in nitric acid. Med. Uses. It is supposed to be alterative, and has been given for such a purpose, in doses from gr. v. to ʒss, but its medicinal virtues are very questionable. Adulterations. It is frequently imperfect, globules of mercury being still discoverable in it by a magnifying glass, or by its communicating a whiteness to a portion of gold upon which it is rubbed; ivory black may be discovered by the residue, after throwing a suspected sample on a red hot iron; it is also sometimes mixed with equal parts of crude antimony.

Qualities. This plant, when recent, has a strong fetid, and narcotic odour; properties which are nearly lost by exsiccation. Chemical Composition. Resin, mucilage, extractive matter, gallic acid, and some salts; an alkaline element (Hyoscyama) is said to constitute its active principle. This principle differs from other vegetable alkalies, in being able to resist a low red heat, without undergoing decomposition. Solubility. Water freely extracts the narcotic powers of this plant, and decoction destroys them; diluted alcohol is the best menstruum. Incompatibles. Precipitates are produced by acetate of lead, nitrate of silver, and sulphate of iron; vegetable acids weaken its narcotic powers. The extract or inspissated juice is the best form in which it can be exhibited; see also the Tincture; its leaves form an anodyne cataplasm, and the smoke from its seeds, when applied by a funnel to a carious tooth, is recommended in severe fits of odontalgia. The root of this plant is poisonous.^[535] In Dr. Molyneux’s appendix to Threlkeld’s “Synopsis Stirpium Hibernicarum” are related several cases of its effects on persons who had eaten them instead of Skirrets. Officinal Prep. Extract: Hyoscyam: Tinct: Hyoscyam: L.E.D.

The following kinds, imported from St. Petersburg, are found in the market. Short Staple; Long Staple; Book; and Leaf. Picking the Staple, as it is called, is a peculiar art practised by persons in this town, who gain a very good livelihood by it; they engage to return the same weight of isinglass in shreds, as they receive in Staple; this in itself secures very fair profit, for by damping the isinglass in order to pick it, it gains considerable weight; these persons moreover are in the habit of adulterating it with pieces of bladder, and the dried skin of soles; such frauds however are easily detected by their insolubility, for pure isinglass will dissolve entirely, and yield a clear and transparent jelly; a single grain will produce, with an ounce of water, a solution of considerable thickness; it is also soluble in acids and alkalies; and although insoluble in alcohol, yet it is not precipitated by it from its watery solutions, unless when added in a very considerable quantity; it is coagulated by the infusions and decoctions of vegetable astringents; carbonate of potass likewise throws down a precipitate. 100 parts of good isinglass consist of 98 of gelatine, and 2 of the phosphates of soda and lime. Its solutions soon putrefy. Uses. It is now rarely used except as a nutrient; its mechanical application in fining wines and turbid liquors is well known, and its mode of operation is equally obvious, for by forming a skin, or fine network, which gradually precipitates, it acts just like a filtre, with this difference, that in this case the filtre passes through the liquor, instead of the liquor through the filtre.

These are watery solutions of vegetable matter, obtained by maceration, either in cold or hot^[536] water without the assistance of ebullition. In selecting and conducting the operation, the following general rules should be observed.

I. Infusion should always be preferred to decoction, where the medicinal virtues of the vegetable substance reside in volatile oil, or in principles which are easily soluble; whereas, if they depend upon resino-mucilaginous particles, decoction is an indispensable operation.

II. The temperature employed must be varied according to the circumstances of each case;^[537] an infusion made in the cold, is in general more grateful, but less active, than one made with heat.

III. The duration of the process must likewise be regulated by the nature of the substances, or the intention of the prescriber; for the infusion will differ according to the time in which the water has been digested on the materials; thus, the aroma of the plant is first taken up, then, in succession, the colouring, astringent, and gummy parts.

Infusions are liable to undergo decompositions by being kept, and therefore, like decoctions, they must be regarded as extemporaneous preparations. Unless the dose of them be otherwise stated, it is generally from f℥j to f℥ij.

Infusum Anthemidis. L.E. It is a good stomachic; and when exhibited warm, is well calculated to assist the operation of emetics: (Form. 66): the cold infusion, i. e. made with cold water, is more grateful. Incompatibles. All soluble preparations of iron; nitrate of silver; oxy-muriate of mercury; acetate, and sub-acetate of lead; solutions of isinglass; infusion of yellow cinchona bark. Dose, f℥j-f℥ij.

Infusum Calumbæ. L.E. See Calumbæ Radix. This infusion is more perishable than that of other bitters; in twenty-four hours a copious precipitation takes place in it, and in two days it becomes ropy, and even musty. Form. 155. Dose, f℥i-f℥ij.

Infusum Caryophyllorum. L. f℥j. of this infusion holds in solution the active matter of grs. vj of cloves. Incompatibles. Precipitates are produced by sulphate of iron; sulphate of zinc; acetate of lead; nitrate of silver; tartarized antimony; lime water, and yellow cinchona. Dose, f℥j-f℥ij.

Infusum Rosæ Compositum. L.E.D. This is an infusion of the petals of the red rose, rendered astringent and refrigerant,^[538] by the addition of dilute sulphuric acid. By referring to the Dynameter, it will be seen that f℥j; does not contain more than four and a half minims of dilute acid, which are equivalent to three-sevenths of a minim of the strong concentrated acid. Wherever therefore we expect any advantage from this latter ingredient, the quantity must be increased by extemporaneous addition. Incompatibles. All those bodies which are decomposed by the sulphuric acid; the sulphates of iron and zinc do not immediately alter the infusion, but they slowly decompose it, producing precipitates of a dark colour. Dr. Clarke of Cambridge detected iron in the petals;^[539] may not the presence of this metal enhance the tonic powers of the infusion? It affords a most elegant vehicle for the exhibition of cathartic salts.

Infusum Sennæ Compositum. L.E.D. A pint of water will take up the active matter of ℥j of senna, but nothing beyond that proportion; hence there is an unnecessary waste in the London process. The quantity of infusion directed to be made at one time, is also injudicious, since by simple exposure to the air for only a few hours, in consequence of the powerful affinity of its extractive matter for oxygen, a yellow precipitate takes place, and the infusion loses its purgative quality, and excites tormina in the bowels; in preparing it therefore, we see the necessity of conducting the process in covered vessels, and of making only such a portion as may be required for immediate use; indeed, notwithstanding every precaution, the extractive will to a certain extent become oxidized, and the infusion have a tendency to gripe.^[540] Dr. Cullen used to say that Senna was one of the best purgatives, if it could only be divested of its griping quality; this however he was unable to obviate, because he was not aware of its cause, and therefore conjoined it with various aromatics, instead of those salts^[541] which might be capable of increasing the solubility of its oxidized extractive, or the purgative activity of the infusion; see page 150, and 161. Soluble tartar and alkaline salts are its most useful adjuncts; it is however rarely prescribed in practice without the addition of other cathartics. (Form. 70, 76, 90.) Sydenham’s favourite “potio cathartica lenitiva,” consisted of an infusion of tamarinds, senna leaves, and rhubarb, with the addition of manna and syrup of roses. The addition of tamarinds renders the infusion more grateful but less active; when made with bohea tea, it is in a great degree deprived of its nauseous taste; a decoction of guaiacum increases its powers, and is said at the same time to render it milder. Bitters also very considerably exalt its efficacy, see page 153. A pint of the infusion with a drachm of jalap forms an excellent combination for a purgative enema. Incompatibles. The infusion is disturbed by strong acids; lime water; nitrate of silver; oxy-muriate of mercury; acetate of lead; tartarized antimony; and by an infusion of yellow cinchona. Dose, f℥j-f℥ij.