ABIETIS^[318] RESINA. L. E. D. (Pinus Abies, Resina concreta.) Resin of the Spruce Fir.

Olim, Thus—Frankincense.^[319]

Qualities. Form, tears or small brittle masses: Odour, very fragrant when burning. It has all the chemical properties of a Resin, and is used only for external purposes: see Pix Arida. Officinal Preparations. Empl: Aromatic: D. Empl: Galban: comp: L. Empl: Opii L. Empl: Thuris. D.

ABSINTHIUM. (Artemisia Absinthium) Common Wormwood.

Qualities. Odour, strong and peculiar. Taste, intensely bitter, slightly pungent, and very unpleasant, as its name^[320] implies. Chemical Composition. Extractive, a small portion of resin, and a green essential oil; in the first of which its bitterness resides, in the last, a narcotic principle; hence the watery extract is not possessed of the nauseous flavour of the plant but retains its bitterness almost entire; the narcotic principle is therefore dissipated by decoction, but its tonic and anthelmintic properties are not impaired by that process. Medical Uses. The whole plant is powerfully antiseptic; and its bitterness renders it stomachic. Infused in ale it forms the beverage known by the name of Purl. Its powers as a vermifuge has bestowed upon it the name of Wormwood. Dose, ℈j, ℈ij; and of the infusion, (made in the proportion of ℥j of the plant to oj of water,) f℥i-f℥iss. Incompatible Substances. Precipitates are produced in the decoction or infusion by Sulphate of Iron, Acetate of Lead, and some other metallic salts. Tartarized Antimony is not in the least affected by it. Off: Prep: Extract: Absinth: D.

ACACIÆ GUMMI. L. (Acacia vera.) Mimosa. Nilotica. E. D. Gum Arabic.

Qualities. It is dry, semi-transparent, brittle and insipid; by exposure to the air it undergoes no other change than loss of colour. Specific Gravity, 1·515. Solubility. It is soluble in water in every proportion, forming a viscid solution, (mucilage). One part dissolved in water affords a fluid of the consistence of syrup; and in two parts, a medium well calculated for the union of dry powders. Gum is also soluble in pure alkalies and lime water, as well as in vegetable acids, especially vinegar, with which it forms a mucilage that may be used as a cement, like the watery solution, and with the additional advantage of not being susceptible of mouldiness.^[321] It is insoluble in alcohol, as well as in æther and oils. By strong sulphuric acid the gum is decomposed, and a considerable proportion of carbon deposited.^[322] For a farther history of its habitudes see Mucilago Acaciæ. Medicinal Uses. It is demulcent and nutritious; although it appears in certain states of the body to pass through the bowels without change. When triturated with gum-resins it assists their mechanical division, as in Form: 30. Officinal Preparations. Mucilago Acaciæ. L. E. D. Emulsio Mimosæ Niloticæ. E. Emulsio Arabica. D. Mist. Corn. ust. L. D. (O) Mist. Cretæ. L. D. (O) Mist. Moschi. L. (O) Confect. Amygdal. L. (O) Pulv. Cret. co. L. (O) Pulv. Tragacanth co. L. (B) Trochisci Carbonat. Calcis E. (O) Troch. Glycyrrh. Glab. E. (O) Troch. Glycyrrh. cum Opio E. (O) Troch. Gummos. E. (O). Adulterations. Gum Senegal is not unfrequently substituted for it, but this may be distinguished by its clammy and tenacious nature; whereas genuine gum arabic is dry and brittle; the fraud is of no consequence in a medical point of view. It is also occasionally mixed with the gum of plum and cherry trees; this fraud however, is to be easily detected, for such gum has peculiar properties by which it may be chemically distinguished; see Mucilago Tragacanth.

ACETICA. L.E.D. Preparations of Vinegar.

These preparations consist of vegetable principles dissolved in vinegar. Officinal Preparations. Acetum Aromaticum. E. Acidum Acetosum camphoratum. E. Medicated vinegars were formerly much extolled; the first London Dispensatory contained no fewer than ten, at present the number is reduced to two, viz. Acetum Colchici. L. Acetum Scillæ. L.E.D. which see.

ACETIS HYDRARGYRI. E. Acetas Hydrargyri. D. Acetate of Mercury.

Qualities. Form, small flaky crystals; Colour, silvery white; Taste, acrid. Chemical Composition. Acetic Acid, and Oxyd of Mercury. Solubility. It is soluble in hot, but very sparingly in cold water, and quite insoluble in Alcohol. Forms of Exhibition. It should be always given in pills,^[323] it is however seldom used. Dose, gr. j. As an external application, a solution of it, in the proportion of grs. j. to f℥i of rose water, has been commended as a cosmetic.

Qualities. Taste, grateful, austere and acidulous. Chemical Composition. All its qualities depend upon the presence of Super-oxalate of Potass. In France the plant is commonly cultivated for the use of the table.

The qualities of this plant, like those of the preceding, depend upon Super-oxalate of Potass.

Qualities. Too well known to require description.^[324] Chymical Composition. Acetic acid largely diluted with water, vegetable gluten, mucilage, sugar, extractive matter, and frequently malic and tartaric acids, together with small proportions of sulphate of lime, sulphate of potass, and alcohol. Its composition however varies according to the fermented liquor from which it is obtained:^[325] e. g. wine yields a paler, purer, and stronger acid than fermented malt liquors or solutions of sugar, hence the superiority of that prepared in France and Italy. Vinegar is liable to spontaneous decomposition, or to become mouldy, and consequently for the purposes of pharmacy it should be distilled; as however the change depends upon the presence of gluten, it may if boiled be kept for a much longer time, and if powdered animal^[326] charcoal be previously added, it will become quite colourless like distilled vinegar, and that without being impaired in strength, whereas it always becomes much weaker by distillation. It is a curious circumstance that this is the only vegetable acid, except the Prussic, that rises in distillation in combination with water.

Adulterations. Sulphuric acid, as it does not produce any turbid appearance in vinegar, is generally the acid selected for sharpening it; but it must be remembered, that the maker is allowed by law, to mix one thousandth of its weight of Sulphuric acid^[327] with it; so that the muriate of baryta when added to such vinegar may be expected to produce 1⅕ grain of insoluble sulphate in every fluid-ounce; if a more considerable quantity of precipitate occurs, we may infer that an excessive proportion of sulphuric acid is present; although some allowance ought perhaps to be made for the presence of the sulphates of potass and lime, which are always contained in vinegar. Of this vinegar 1000 grains should saturate 148 grains of crystallized sub-carbonate of soda; a fluid-ounce of the same, 68–3/4 grains.^[328] For the purpose of making the vinegar appear stronger, acrid vegetables, as grains of Paradise, berries of Spurge Flax, Capsicum, Pellitory of Spain, &c. are sometimes infused in it, but by tasting it with attention, the pungency of such substances may be easily detected. For the other adulterations, see Acidum Aceticum.

The purest vinegar which I have ever examined is that manufactured from malt, by Mr. Mackintosh of Glasgow. The strongest malt vinegar is termed proof vinegar, and is called by the manufacturer No. 24; it is estimated to contain 4·73 per cent. of real acetic acid.^[329] Its strength in relation to the other forms of acetic acid, will be seen by referring to the Medicinal Dynameter, and to the table inserted under the article Acidum Aceticum Fortius. In the former Editions of this work it was stated, that a Vinegar had of late years appeared in the market produced from the distillation of wood, (Pyroligneous Acid.) This article has now come into very general use; and the manufacturers have at length succeeded in divesting it of that empyreumatic flavour which had so long rendered it objectionable. See Acidum Aceticum Fortius e Ligno destillatum.

Vinegar appears to be a solvent of the acrid and medicinal principle which resides in the bulb of this plant. Dose fʒss to fʒij. in any bland fluid. See Colchici Radix.

This preparation is an acetic solution of the acrid matter of the Squill, upon which its medicinal efficacy depends.^[330] Dose fʒss to fʒij. in cinnamon or mint water. See Scillæ Radix. Form. 107, 114. Alkalies and their carbonates are chemically incompatible with these Vinegars. This preparation, as well as the Oxymel, deposites when long kept a precipitate consisting of citrate of lime and tannin, but its medicinal efficacy is not on that account impaired.

Qualities. Odour, fainter and less agreeable than common vinegar (Acetum): Taste, less acid; Colour, none. Specific Gravity; Mr. Phillips states, that when prepared according to the directions of the Pharmacopœia, it varies from 1·007 to 1·009; and that 1000 grains of the latter require for their saturation, 145 grains of crystallized sub-carbonate of soda. I apprehend, however, that it will be found quite impossible to obtain a dilute acetic acid equal in strength or specific gravity, to that last mentioned, by the process of the London College;^[331] it may even be doubted whether it can be produced of the specific gravity 1·007. The general run of distilled vinegar as found in the shop of the druggist, varies from 1·005 to 1·006, and contains from 2·80 to 2·826 per cent. of real acid; when of the specific gravity of 1·009 it would contain about 4·73 per cent. Dr. Powell states (Translation of the Pharmacop: of London, 1815) that “one fluid-ounce ought to dissolve at least thirteen grains of white marble;” or, what is equivalent to it, 39·67 grains of crystallized Sub-carbonate of Soda; acid of this strength corresponds very nearly with six degrees of the Revenue Acetometer, the proportions being as follow, 100 grains of Pharmacopœia strength will saturate 8·68 grains of crystallized Sub-carbonate of Soda; 100 grains of acid of 6° of the Acetometer will saturate 8·70 grains of the salt. Chemical Composition. Acetic Acid more largely diluted than that in vinegar, with very minute portions of uncombined mucilage and extractive. Solvent Powers. It is capable of dissolving all those vegetable principles which are soluble in water, and in some cases, as in Squill, Colchicum, and in several Aromatics and Narcotics, its acid appears to extend its solvent powers; at the same time it often modifies or diminishes the medicinal virtues of the substances, as for instance those of Narcotics; this circumstance considerably limits its pharmaceutical application; when however it is employed, a portion of spirit should be always added, in order to counteract the spontaneous decomposition to which it is liable, and the acetic compound should be preserved in stopped bottles. Acetic acid does not dissolve true resins, but it has some action on gum resins. Medicinal Uses. It is refrigerant, and may be advantageously administered in hemorrhage; especially in cases where the acetate of lead has been given, since the solubility of this latter substance is increased by it. See Form. 57; externally, it may be a convenient adjunct to lotions containing lead. See Form. 147. In consequence of its chemical action upon osseous matter, it has been much employed at the Gloucester Infirmary to hasten exfoliation of carious bone. Adulterations. Sulphuric Acid may be detected by a precipitate being produced on the addition of acetate of baryta: this test however will not answer for its detection in common vinegar, for the reason stated under that article. See Acetum. Sulphurous Acid may be recognised by drawing a little of the vapour into the lungs. The presence of Nitric Acid may be discovered by saturating the suspected sample with pure potass, evaporating to dryness, and then treating the product with a highly concentrated alcohol, the acetate of potass will be thus dissolved, but as it exerts no action on the Nitrate it will be found in the residuum, and may be recognised by its deflagration, when thrown upon burning charcoal;^[332] Copper may be detected by the acid assuming a blue colour, when supersaturated with ammonia; and Lead, by a solution of sulphuretted hydrogen, producing a dark coloured precipitate. Tin however is the metal with which distilled vinegar is more usually contaminated, for no vegetable acid will act upon lead while any tin is present in the mixture, since the latter, being more oxidable than the former, is exclusively dissolved.

The acetic acid from wood has been very generally introduced to supersede the use of distilled vinegar for the purposes of Medicine and the Arts.^[333] It is at length found to be capable of such complete separation from all foreign matter as to afford a perfectly pure acetic acid, invariable in its acidifying power, and immutable in its chemical properties. In justice to the skill and industry of Messrs. Beaufoy and Co. of South Lambeth, I beg to state that I have examined various specimens of this acid from their manufactory, and that I find it free from those impurities which have hitherto constituted an insuperable objection to its introduction into the Materia Medica. The purified Pyroligneous acid, manufactured by this company, and sold under the name of “Improved Distilled Vinegar,” is perfectly free from any unpleasant taste, as well as colour and sediment; and it forms a limpid and colourless solution with ammonia. The common distilled vinegar of the shops varies essentially in strength as well as purity, differing in acidifying power from 30 to 40 per cent. in value: it is sometimes 7 degrees, and at others less than 5, by the Revenue Acetometer;^[334] and hence has arisen the difficulty of procuring an uniform article for medical application, a difficulty which the introduction of the pyroligneous acid seems calculated to overcome, as it may be procured from the manufacturers of any degree of concentration,^[335] from 6 degrees of the Acetometer, or 2·826 per cent. of real acetic acid to 130 degrees, or 61·49 per cent. of acid; and even of still higher strength if required; their common, or Proof acid is about equivalent in strength to that of the best Malt Vinegar, of which 100 grains will saturate 14½ grains of crystallized Sub-carbonate of Soda, and consequently contains 4·73 per cent. of real acid, and will require at least one half part of water to reduce it to the strength of the best common distilled vinegar. It is found that acetic acid of 45 per cent. real acid, or of 95° of acetometer strength, dissolves Camphor and the Essential Oils very readily.

The “Acidum Aceticum Fortius,” which is now introduced into the Materia Medica of the London College, is directed to have a specific gravity of 1·046.^[336] It is exactly six times the strength of Proof vinegar, or the strong Malt vinegar manufactured, but it requires to be diluted with nine times its weight of water to reduce it to the strength of the ordinary samples of distilled vinegar. Mr. Phillips states, that he has not met with acetic acid of greater specific gravity than 1·043,^[337] being five times the strength of vinegar of specific gravity 1·009.^[338] The strongest acid that can be procured is the Glacial acid, which exists in a crystallized state under 50° Fah. It contains 79 per cent. of real acid, and is consequently of the strength of 167·5 of the Acetometer. If this acid be kept perfectly still, it may be reduced several degrees below its crystallizing point in a fluid state, when the slightest agitation of the vessel instantly occasions it to solidify. It will greatly facilitate our inquiries into the strength of different samples of acetic acid to know, that the representative numbers of acetic acid and pure white marble coincide on the scale of equivalents; it therefore follows that the weight of marble dissolved by a hundred grains of any acetic acid, will at once represent the percentage of real acid in such a sample.

The Impure Pyroligneous acid, as it first comes over, contaminated with Tar, has, it is said, been very successfully employed as a lotion in Lepra, scrophulous ulcerations, chronic inflammation of the eyes, and edges of the eye-lids, and for promoting digestion of irritative ulcers, or those connected with carious bone. It has also been injected into sinuses to produce healthy discharge and adhesive inflammation.^[339] M. Monge discovered that this acid has the property of preventing the decomposition of animal substances; it is sufficient to plunge meat for a few moments in this acid, even slightly empyreumatic, to preserve it as long as you please. “Putrefaction,” it is said, “not only stops but retrogrades.” To the empyreumatic oil a part of this effect has been ascribed, and hence has been explained the agency of wood smoke in the preservation of tongues, hams, herrings, &c.

The process for this preparation has not retained its place in the London Pharmacopœia, as it is now universally superseded by the Acetic acid distilled from wood. Since however it possesses peculiar chemical habitudes, it claims some notice in this work. The concentrated acid obtained from the decomposition of acetic salts, by the action of sulphuric acid, is pungent, acrid, and volatile, and when heated with free access of air, it takes fire very readily. Its solvent powers are much greater than those of distilled vinegar; it is capable of dissolving camphor, resins, and essential oils^[340] copiously, but they are precipitated by dilution; it combines with alcohol, and forms a species of ether; with water it unites in any proportion, heat being evolved by the mixture. Gold, platinum, glass, and earthenware, can alone retain this acid without being corroded. It blisters the skin immediately.

I shall conclude this article by the introduction of a Table, which I have constructed with considerable care, for the use of the practical Chemist. The accuracy of the results may be depended upon, since it has been tested by several different modes of enquiry. The Medicinal Dynameter will give the equivalents in any other denomination that may be required.

The reader will observe an anomaly with regard to the specific gravity of the acid of 145 of the acetometer, when compared with the glacial acid. The fact is, that by diluting this latter preparation with a small portion of water we augment its specific gravity, a circumstance peculiar to this acid.

Qualities. Form, small feathery crystals of a brilliant white colour, which are not brittle, but possess a kind of ductility and elasticity, and, on being rubbed in a mortar, assume the consistence of paste. Odour. As generally met with, it possesses a peculiar aromatic smell, but this depends upon the oily matter which adheres to it, for Mr. Guise informs us, that on dissolving the benzoic acid in as little alcohol as possible, filtering the solution, and precipitating by water, the acid will be obtained pure, and void of smell, the odorous oil remaining dissolved in the spirit. Taste, rather acrid and sour; Specific Gravity, ·667. It is not altered by exposure to air. Solubility. Four hundred parts of cold water dissolve but one, although the same quantity of boiling water dissolves twenty parts, nineteen of which separate on cooling; in alcohol it is soluble in a much greater proportion. Medicinal Uses. It is said to be stimulant and expectorant; in certain cases of tracheal irritation, a pill, composed of two grains of Benzoic acid, and three of Extract of Poppy, has been found serviceable. Officinal Preparations. Tinctura Camphoræ Composita, L.D. Tinct: Opii Ammoniat: E. Impurities. The crystals ought not to be discoloured; they should dissolve without residuum in alcohol, and when subjected to heat, ought to be entirely volatilized.

Although this acid is commonly procured from the resinous substance called Benzoin, yet it exists extensively in other vegetable, and in some animal substances. In the Tonca bean (Dipterix odorata) it is frequently to be seen beautifully crystallized on its surface. It exists also in vanello; cinnamon; cloves; ambergris; in the urine of children, and sometimes in that of adults, and always in that of quadrupeds living on grass and hay.

Qualities. Form, crystals which are right rhombic prisms, white, semi-transparent, and persistent. Taste, extremely acid, almost caustic. Solubility, f℥j of cold water dissolves ʒx, but of boiling, ℥ij. ʒx of the crystals dissolved in a pint of water, are about equivalent to one pint of lemon juice, the solution however if kept is liable to spontaneous decomposition. The following table of equivalents may be found of practical use; the author is aware that they do not exactly agree with the proportions of Dr. Haygarth, but they are the results of careful and repeated experiments, and as such they are submitted with confidence.

These alkaline citrates are decomposed by the oxalic, tartaric, and the stronger mineral acids, and by the solutions of lime and barytes. Form. 107, 123, 137, 168.

Citric acid decomposes the following salts, viz. The Alkaline, Earthy, and Metallic Carbonates; the Alkaline and Metallic Acetates; the Sulphurets of Earths and Alkalies, and Alkaline Soaps. It is also incompatible with Tartrate of Potass, which it converts into citrate and super-tartrate of potass. It curdles the milk of most animals, but it does not produce that effect on human milk, whether applied hot or cold. Adulterations. Tartaric Acid, with which it is sometimes mixed, may be detected by adding to the solution an excess of Potass, which will instantly form with it an insoluble super-tartrate, and precipitate in granular crystals, or, if a little of the suspected acid be saturated with potass, and then boiled with a dilute solution of muriate of Platinum, if tartaric acid be present, a black protoxide of Platinum will be precipitated. If we add the tartrate of potass for this purpose, we may be deceived, for the citric acid, by neutralizing a portion of its base, will convert the remainder into super-tartrate. See Potassæ Tartras. Sulphuric Acid is known by the acetate of lead producing a precipitate, insoluble in nitric acid. Muriatic Acid may be discovered in the same manner, substituting only an acidulous solution of nitrate of silver for the acetate of lead. The presence of Oxalic Acid may be inferred, if the solution, when added to that of sulphate of lime, produce a precipitate. Malic acid has the power of precipitating silver, mercury, and lead, from their solutions in nitric acid, but no doubt or difficulty can arise from this circumstance, for the fact of its forming a soluble salt with lime will prevent every chance of accidental intrusion, and its price at once secures us against its fraudulent introduction; it might moreover be easily detected by throwing the suspected precipitate upon burning coals, when it would be decomposed. Where the presence of lime is suspected, it may be known by dissolving some of the crystals in water, saturating the solution with ammonia, and then treating it with the oxalate of that alkali, which, if lime be present, will immediately separate it in a palpable form. The juices of many other fruits besides the lemon and lime, will furnish the citric acid in abundance, and may be obtained from them by a similar process; e. g. Vaccinium oxycoccus, the Cranberry; Prunus Padus, the Bird’s Cherry; Dulcamara Solanum, the berry of the Nightshade; Cynosbatus, vel Rosa Canina, the hep or fruit of the Wild Briar. There are many plants whose juices contain combinations of the Citric and Malic acids in considerable abundance, such as Fragaria Vesca, the Wood Strawberry, and the common Raspberry; Ribes Rubrum the Red Gooseberry; Vaccinium Myrtillus, the Bilberry; Cratægus Aria, the Hawthorn; Prunus Cerasus, the Black Cherry, &c. This fact is interesting, since the juices of such fruits have been long known to possess the property of dissolving the tartareous incrustations on the teeth.

This peculiar acid exists in a great variety of native combinations in the vegetable kingdom,^[341] and imparts to them certain properties which have been long known, and esteemed in medicine. It is, however, only lately, that it has been administered in its simple but diluted form. As few practitioners will choose to prepare the acid, it seems unnecessary in the present work to dwell upon the merits of the different processes which have been proposed for its preparation; for a full account of them, as well as for other details of importance, the practitioner is advised to consult a work by Dr. Granville, entitled “An Historical and Practical Treatise on the use of Prussic Acid. Second Edition. London, 1820.”

Qualities. A colourless transparent liquid, although it occasionally exhibits a yellow tinge; Odour like that of bitter almonds; Taste bitterish and peculiar: these properties however are soon lost by exposure to air and light, and the acid undergoes spontaneous decomposition. Chemical Composition. The true nature of Prussic acid was not ascertained until 1815, when Gay Lussac presented to the Royal Institute of France, a memoir which at once developed its real chemical constitution; and it is now admitted to consist of a peculiar gaseous and highly inflammable compound of carbon and nitrogen, to which the name Cyanogene has been assigned, and of hydrogen; the latter body acting as the acidifying principle, whence the term Hydro-cyanic acid is well contrived to express its composition. The medicinal, or diluted acid, however, contains but a small proportion of this concentrated compound; according to M. Majendie, one part of the acid of Gay Lussac and eight parts and a half of water, by weight, or one part of acid with six times its volume of water, constitute the preparation which should be used in medicine; and which, to avoid the possibility of mistake, ought always to be prescribed as the Acidum Hydro-cyanicum dilutum, and is, in fact, the Prussic acid of Scheele. Dr. Ure, who has lately taken considerable pains upon this subject, has constructed a table exhibiting the relations between the specific gravities, and quantities of real acid, in preparations of different strength; from these experiments it would appear that an acid of specific gravity 0·996 or 0·997 is such as is usually prescribed in medicine.^[342] Medical Uses. In a sufficient dose, hydro-cyanic acid instantly destroys life by extinguishing the nervous energy of the body;^[343] but it has at the same time been observed that animals submitted to its action would often continue to breathe for several hours freely, and to circulate their blood, although no trace of sensibility or muscular contractility could be found after its application. This remarkable property of extinguishing the general sensibility, without any ostensible injury to respiration and circulation, naturally led to a belief that the hydro-cyanic acid, or prussic acid, might be advantageously used in cases of excessive sensibility and irritation, particularly when these two morbid states are likely to affect either the respiratory organs or the circulation generally. This kind of analogical reasoning, it is said, induced Professor Brera, ten years ago, to administer it in cases of high pulmonary and other inflammations, in doses of four drops twice a day; when, as we are told, the violence of the disease was quickly subdued. The remedy, however, does not appear to have excited much attention, until after the first essay of Dr. Majendie, who deserves whatever credit may belong to its introduction. Seven years of trial have elapsed, and the general sense of the medical profession with respect to its utility may now be collected. As a palliative in certain spasmodic coughs, there is reason for supposing that it may sometimes be useful, but in that species of pulmonary irritation for which it was at first so greatly extolled, I will venture to assert that it is far inferior in efficacy to well directed doses of Conium. But there is another class of diseases in which its exhibition is said to prove useful, in dyspeptic affections attended with heartburn; where it is supposed to be capable of reducing the morbid irritability of the stomach, and thereby of enabling the juices of that organ to be more slowly secreted and of a more healthy character. Dr. Elliotson has published the result of his treatment of stomach complaints with this medicinal agent, and would appear to appropriate to himself the merit of originating the practice, a claim which Mr. Thomson, in the third edition of his Dispensatory, refuses to concede.^[344] As a local remedy, prussic acid has also received no small share of commendation, and it has been said that it is the only application that can be depended upon for allaying the cutaneous irritation so frequently attendant upon certain impetiginous affections. It must, however, be confessed that this medicine is rapidly declining in popularity.^[345] Any prejudice raised against it, upon the ground of its poisonous activity in large doses, is too absurd to be believed; the knife and the caustic are unquestionably powerful, and may therefore become dangerous instruments; but who ever blames the surgeon for employing a sharp knife or an active caustic, seeing that both are to be directed by his eye, and guided by his hand? Forms of Exhibition. It may be conveniently administered in any liquid vehicle, as distilled water, camphor mixture, or in some vegetable infusion. See Supplementary Formulæ, 1, 2, 3. A question has lately arisen whether the effects of the prussic acid might not be more conveniently ensured by the administration of some vegetable^[346] in which it exists as a native ingredient; a company of associated Physicians, Surgeons, and Naturalists at Florence, have accordingly expressed their joint opinion, that the essential oil of the Prunus Lauro Cerasus is to be preferred in medical practice to all other preparations which contain the hydro-cyanic acid; for, say they, unlike the distilled water of the plant, and pure prussic acid, it contains the same proportion of active matter, and of the same power, whether recently prepared or not; whether made in one place or another; or whether it has been exposed or not to the air, light, or heat. They are also of opinion that olive oil forms the best vehicle for its exhibition in the proportion of one ounce to twelve drops of the essential oil. Other practitioners again prefer Laurel Water, made by distilling two drachms of the fresh leaves chopped, with four ounces of water, recommitting the distilled water twice afterwards on the same quantity of fresh leaves, and making ultimately four ounces of the menstruum, of which from ♏︎xxx to fʒj every six hours may be given until a sedative effect is produced. See Oleum Amygdalæ Amaræ. Incompatible Substances. Hydro-cyanic acid is decomposed by most of the oxydes usually employed in medicine, particularly by those of Mercury and Antimony. The alkalies do not appear to diminish its efficacy. Nitrate of Silver, and the salts of iron occasion precipitates; nor ought the sulphurets, the mineral acids, or chlorine to enter with it into prescriptions. Dose. Of the medicinal, or diluted hydro-cyanic acid, ♏︎ij,–viij. There is however considerable difficulty with regard to the strength of the dilute acid employed in medicine, since the density is a criterion of greater nicety than can be conveniently used by the majority of practitioners; in fact, as Dr. Ure has observed, the liquid at 0·996, contains about double the quantity of real acid, which it does at 0·998. Dr. Ure has accordingly proposed another test of the strength of this powerful and dangerous medicine, which is not only easier in use, but more delicate in its indications;^[347] it is as follows. To 100 grains, or any other convenient quantity of the prussic acid, contained in a small phial, add in succession, small quantities of the peroxide of mercury, (the common red precipitate of the shops) in fine powder, till it ceases to be dissolved on agitation. The weight of the red precipitate taken up, being divided by four, gives a quotient representing the quantity of real prussic acid present. By weighing out before hand, on a piece of paper, or a watch glass, forty or fifty grains of the peroxide, the residual weight of it shews at once the quantity expended. The operation may always be completed in five minutes, for the red precipitate dissolves as rapidly in the dilute prussic acid, with the aid of slight agitation, as sugar dissolves in water. Adulterations. If, says Dr. Ure, the presence of muriatic acid be suspected, then the specific gravity of the liquid compared with the gravity of the peroxide dissolved, will shew how far the suspicion is well founded; thus if 100 grains of acid, specific gravity 0·996, dissolve more than 12 grains of the red precipitate, we may be sure that the liquid has been contaminated with muriatic acid. Nitrate of Silver, in common cases, so valuable a reagent for muriatic acid, is unfortunately of little use here, for it gives with prussic acid, a flocculent white precipitate, soluble in water of ammonia, and insoluble in nitric acid, which may easily be mistaken by common observers, for the chloride of that metal. But the difference in the volatility of prussiate and muriate of ammonia may be had recourse to with advantage; the former exhaling at a very gentle heat, the latter requiring a subliming temperature of about 300° Fah. After adding ammonia in slight excess to the prussic acid, if we evaporate to dryness at a heat of 212°, we may infer from the residuary sal ammoniac, the quantity of muriatic acid present.

Antidotes. To counteract the poisonous effect of prussic acid, Orfila recommends, after full vomiting has been excited, the exhibition of three or four spoonsful of oil of turpentine, in the infusion of coffee, at intervals of half an hour. M. Virey conceives that sulphate of iron in solution is the best antidote, he having observed that the salt restored a cow that was nearly killed by the essential oil of bitter almonds. When an overdose has been taken, hot brandy and water, and the ammoniated tincture of iron are recommended by Mr. Thomson; on the former I should rely with much greater confidence than upon the latter antidote, or, in other words, it is from vital agents, counteracting its sedative influence, rather than from chemical substances, changing its composition, that we can expect any benefit upon such an occasion. For the chemical processes by which the presence of this acid may be ascertained, the reader may consult my work on Medical Jurisprudence, vol. 2, p. 408.