XII.—Hydrocyanic Acid.

§ 251. Hydrocyanic Acid (hydric cyanide)—specific gravity of liquid 0·7058 at 18° C., boiling-point 26·5° (80° F.), HCy = 27.—The anhydrous acid is not an article of commerce, and is only met with in the laboratory. It is a colourless, transparent liquid, and so extremely volatile that, if a drop fall on a glass plate, a portion of it freezes. It has a very peculiar peach-blossom odour, and is intensely poisonous. It reddens litmus freely and transiently, dissolves red oxide of mercury freely, forms a white precipitate of argentic cyanide when treated with silver nitrate, and responds to the other tests described hereafter.

§ 252. Medicinal Preparations of Prussic Acid.—The B.P. acid is a watery solution of prussic acid; its specific gravity should be 0·997, and it should contain 2 per cent. of the anhydrous acid, 2 per cent. is also the amount specified in the pharmacopœias of Switzerland and Norway, and in that of Borussica (VI. ed.); the latter ordains, however, a spirituous solution, and the Norwegian an addition of 1 per cent. of concentrated sulphuric acid. The French prussic acid is ordered to be prepared of a strength equalling 10 per cent.

The adulterations or impurities of prussic acid are hydrochloric, sulphuric,[233] and formic acids. Traces of silver may be found in the French acid, which is prepared from cyanide of silver. Tartaric acid is also occasionally present. Hydrochloric acid is most readily detected by neutralising with ammonia, and evaporating to dryness in a water-bath; the ammonium cyanide decomposes and volatilises, leaving as a saline residue chloride of ammonium. This may easily be identified by the precipitate of chloride of silver, which its solution gives on testing with silver nitrate, and the deep brown precipitate with Nessler solution. Sulphuric acid is, of course, detected by chloride of barium; formic acid by boiling a small quantity with a little mercuric oxide; if present, the oxide will be reduced, and metallic mercury fall as a grey precipitate. Silver, tartaric acid, and any other fixed impurities are detected by evaporating the acid to dryness, and examining any residue which may be left. It may be well to give the various strengths of the acids of commerce in a tabular form:—

[233] A trace of sulphuric or hydrochloric acid should not be called an adulteration, for it greatly assists the preservation, and therefore makes the acid of greater therapeutic efficiency.

Per cent.
British Pharmacopœia, Switzerland, and Bor. (vj),2
France,10
Vauquelin’sAcid,3·3
Scheele’s„4 to 5[234]
Riner’s„10
Robiquet’s„50
Schraeder’s„1·5
Duflos’„9
Pfaff’s„10
Koller’s„25

[234] Strength very uncertain.

In English commerce, the analyst will scarcely meet with any acid stronger than Scheele’s 5 per cent.

Impure oil of bitter almonds contains hydric cyanide in variable quantity, from 5 per cent. up to 14 per cent. There is an officinal preparation obtained by digesting cherry-laurel leaves in water, and then distilling a certain portion over. This Aqua Lauro-cerasi belongs to the old school of pharmacy, and is of uncertain strength, but varies from ·7 to 1 per cent. of HCN.

§ 253. Poisoning by Prussic Acid.—Irrespective of suicidal or criminal poisoning, accidents from prussic acid may occur—

1. From the use of the cyanides in the arts.

2. From the somewhat extensive distribution of the acid, or rather of prussic-acid producing substances in the vegetable kingdom.

1. In the Arts.—The galvanic silvering[235] and gilding of metals, photography, the colouring of black silks, the manufacture of Berlin blue, the dyeing of woollen cloth, and in a few other manufacturing processes, the alkaline cyanides are used, and not unfrequently fumes of prussic acid developed.

[235] The preparation used for the silvering of copper vessels is a solution of cyanide of silver in potassic cyanide, to which is added finely powdered chalk. Manipulations with this fluid easily develop hydrocyanic acid fumes, which, in one case related by Martin (Aerztl. Intelligenzbl., p. 135, 1872), were powerful enough to produce symptoms of poisoning.

2. In the Animal Kingdom.—One of the myriapods (Chilognathen) contains glands at the roots of the hairs, which secrete prussic acid; when the insect is seized, the poisonous secretion is poured out from the so-called foramina repugnatoria.

3. In the Vegetable Kingdom.—A few plants contain cyanides, and many contain amygdalin, or bodies formed on the type of amygdalin. In the presence of emulsin (or similar principles) and water, this breaks up into prussic acid and other compounds—an interesting reaction usually represented thus—

C20H27NO11 + 2H2O = CNH + C7H6O + 2C6H12O6.

1 equivalent of amygdalin—i.e., 457 parts—yielding 1 equivalent of CNH or 27 parts; in other words, 100 parts of amygdalin yield theoretically 5·909 parts of prussic acid,[236] so that, the amount of either being known, the other can be calculated from it.

[236] According to Liebig and Wöhler, 17 grms. of amygdalin yield 1 of prussic acid (i.e., 5·7 per cent.) and 8 of oil of bitter almonds. Thirty-four parts of amygdalin, mixed with 66 of emulsin of almonds, give a fluid equalling the strength of acid of most pharmacopœias, viz., 2 per cent.

Greshoff[237] has discovered an amygdalin-like glucoside in the two tropical trees Pygeum parriflorum and P. latifolium. The same author states that the leaves of Gymnema latifolium, one of the Asclepiads, yields to distillation benzaldehyde hydrocyanide. Both Lasia and Cyrtosperma, plants belonging to the natural family of the Orontads, contain in their flowers potassic cyanide. Pangium edule, according to Greshoff, contains so much potassic cyanide that he was able to prepare a considerable quantity of that salt from one sample of the plant. An Indian plant (Hydnocarpus inebrians) also contains a cyanide, and has been used for the purpose of destroying fish. Among the Tiliads, Greshoff found that Echinocarpus Sigun yielded hydrocyanic acid on distillation. Even the common linseed contains a glucoside which breaks up into sugar, prussic acid, and a ketone.

[237] M. Greshoff—Erster Bericht über die Untersuchung von Pflanzenstoffen Niederländisch-Indiens. Mittheilungen aus dem chemisch-pharmakologischen Laboratorium des botan. Gartens des Staates, vii., Batavia, 1890, Niederländisch. Dr. Greshoff’s research indicates that there are several other cyanide-yielding plants than those mentioned in the text.

The following plants, with many others, all yield, by appropriate treatment, more or less prussic acid:—Bitter almonds (Amygdalus communis); the Amygdalus persica; the cherry laurel (Prunus laurocerasus); the kernels of the plum (Prunus domestica); the bark, leaves, flowers, and fruit of the wild service-tree (Prunus padus); the kernels of the common cherry and the apple; the leaves of the Prunus capricida; the bark of the Pr. virginiana; the flowers and kernels of the Pr. spinosa; the leaves of the Cerasus acida; the bark and almost all parts of the Sorbus aucuparia, S. hybrida, and S. torminalis; the young twigs of the Cratægus oxyacantha; the leaves and partly also the flowers of the shrubby Spiræaceæ, such as Spiræa aruncus, S. sorbifolia, and S. japonica;[238] together with the roots of the bitter and sweet Cassava.

[238] The bark and green parts of the Prunus avium, L., Prunus mahaleb, L., and herbaceous Spirææ yield no prussic acid.

In only a few of these, however, has the exact amount of either prussic acid or amygdalin been determined; 1 grm. of bitter almond pulp is about equal to 21⁄2 mgrms. of anhydrous prussic acid. The kernels from the stones of the cherry, according to Geiseler, yield 3 per cent. of amygdalin; therefore, 1 grm. equals 1·7 mgrm. of HCN.

§ 254. The wild service-tree (Prunus padus) and the cherry-laurel (Prunus Laurocerasus) contain, not amygdalin but a compound of amygdalin with amygdalic acid; to this has been given the name of laurocerasin. It was formerly known as amorphous amygdalin; its formula is C40H55NO24; 933 parts are equivalent to 27 of hydric cyanide—that is, 100 parts equal to 2·89.

In the bark of the service-tree, Lehmann found ·7 per cent. of laurocerasin (= ·02 HCN), and in the leaves of the cherry-laurel 1·38 per cent. (= 0·39 HCN).

Francis,[239] in a research on the prussic acid in cassava root, gives as the mean in the sweet cassava ·0168 per cent., in the bitter ·0275 per cent., the maximum in each being respectively ·0238 per cent., and ·0442 per cent. The bitter-fresh cassava root has long been known as a very dangerous poison; but the sweet has hitherto been considered harmless, although it is evident that it also contains a considerable quantity of prussic acid.

[239] “On Prussic Acid from Cassava,” Analyst, April 1877, p. 5.

The kernels of the peach contain about 2·85 per cent. amygdalin (= ·17 HCN); those of the plum ·96 per cent. (= ·056 HCN); and apple pips ·6 per cent. (= ·035 per cent. HCN).

It is of great practical value to know, even approximately, the quantity of prussic acid contained in various fruits, since it has been adopted as a defence in criminal cases that the deceased was poisoned by prussic acid developed in substances eaten.

§ 255. Statistics.—Poisoning by the cyanides (prussic acid or cyanide of potassium) occupies the third place among poisons in order of frequency in this country, and accounts for about 40 deaths annually.

In the ten years ending 1892 there were recorded no less than 395 cases of accidental, suicidal, or homicidal poisoning by prussic acid and potassic cyanide. The further statistical details may be gathered from the following tables:—

DEATHS IN ENGLAND AND WALES DURING THE TEN YEARS 1883-1892 FROM PRUSSIC ACID AND POTASSIC CYANIDE.

Prussic Acid (Accident or Negligence).
Ages,0-11-55-1515-2525-6565 and
above		Total
Males,...11112116
Females,11...27...11
Totals,121319127
Cyanide of Potassium (Accident or Negligence).
Ages, 1-55-1515-2525-6565 and
above		Total
Males, 1141...7
Females, 1......3...4
Totals, 2144...11
Prussic Acid (Suicide).
Ages, 15-2525-6565 and
above		Total
Males, 2315623202
Females, 513119
Totals, 2816924221
Potassium Cyanide (Suicide).
Ages, 5-1515-2525-6565 and
above		Total
Males, 16885100
Females, ...615122
Totals, 1121036122

To these figures must be added 10 cases of murder (2 males and 8 females) by prussic acid, and 4 cases of murder (3 males and 1 female) by potassic cyanide.

In order to ascertain the proportion in which the various forms of commercial cyanides cause death, and also the proportion of accidental, suicidal, and criminal deaths from the same cause, Falck collated twelve years of statistics from medical literature with the following result:—

In 51 cases of cyanide poisoning, 29 were caused by potassic cyanide, 9 by hydric cyanide, 5 by oil of bitter almonds, 3 by peach stones (these 3 were children, and are classed as “domestic,” that is, taking the kernels as a food), 3 by bitter almonds (1 of the 3 suicidal and followed by death, the other 2 “domestic”), 1 by tartaric acid and potassic cyanide (a suicidal case, an apothecary), and 1 by ferro-cyanide of potassium and tartaric acid. Of the 43 cases first mentioned, 21 were suicidal, 7 criminal, 8 domestic, and 7 medicinal; the 43 patients were 24 men, 14 children, and 5 women.

The cyanides are very rarely used for the purpose of murder: a poison which has a strong smell and a perceptible taste, and which also kills with a rapidity only equalled by deadly bullet or knife-wounds, betrays its presence with too many circumstances of a tragic character to find favour in the dark and secret schemes of those who desire to take life by poison. In 793 poisoning cases of a criminal character in France, 4 only were by the cyanides.

Hydric and potassic cyanides were once the favourite means of self-destruction employed by suicidal photographers, chemists, scientific medical men, and others in positions where such means are always at hand; but, of late years, the popular knowledge of poisons has increased, and self-poisoning by the cyanides scarcely belongs to a particular class. A fair proportion of the deaths are also due to accident or unfortunate mistakes, and a still smaller number to the immoderate or improper use of cyanide-containing vegetable products.

§ 256. Accidental and Criminal Poisoning by Prussic Acid.—The poison is almost always taken by the mouth into the stomach, but occasionally in other ways—such, for example, as in the case of the illustrious chemist, Scheele, who died from inhalation of the vapour of the acid which he himself discovered, owing to the breaking of a flask. There is also the case related by Tardieu, in which cyanide of potassium was introduced under the nails; and that mentioned by Carrière,[240] in which a woman gave herself, with suicidal intent, an enema containing cyanide of potassium. It has been shown by experiments, in which every care was taken to render it impossible for the fumes to be inhaled, that hydrocyanic acid applied to the eye of warm-blooded animals may destroy life in a few minutes.[241]

[240] “Empoisonnement par le cyanure de potassium,—guérison,” Bullet. général de Thérap., 1869, No. 30.

[241] N. Gréhant, Compt. rend. Soc. Biol. [9], xi. 64, 65.

With regard to errors in dispensing, the most tragic case on record is that related by Arnold:[242]—A pharmaceutist had put in a mixture for a child potassic cyanide instead of potassic chlorate, and the child died after the first dose: the chemist, however, convinced that he had made no mistake, to show the harmlessness of the preparation, drank some of it, and there and then died; while Dr. Arnold himself, incautiously tasting the draught, fell insensible, and was unconscious for six hours.

[242] Arnold, A. B., “Case of Poisoning by the Cyanide of Potassium,” Amer. Journ. of Med. Scien., 1869.

§ 257. Fatal Dose.—Notwithstanding the great number of persons who in every civilised country fall victims to the cyanides, it is yet somewhat doubtful what is the minimum dose likely to kill an adult healthy man. The explanation of this uncertainty is to be sought mainly in the varying strength of commercial prussic acid, which varies from 1·5 (Schraeder’s) to 50 per cent. (Robiquet’s), and also in the varying condition of the person taking the poison, more especially whether the stomach be full or empty. In by far the greater number, the dose taken has been much beyond that necessary to produce death, but this observation is true of most poisonings.

The dictum of Taylor, that a quantity of commercial prussic acid, equivalent to 1 English grain (65 mgrm.) of the anhydrous acid, would, under ordinary circumstances, be sufficient to destroy adult life, has been generally accepted by all toxicologists. The minimum lethal dose of potassic cyanide is similarly put at 2·41 grains (·157 grm.). As to bitter almonds, if it be considered that as a mean they contain 2·5 per cent. of amygdalin, then it would take 45 grms., or about 80 almonds, to produce a lethal dose for an adult; with children less—in fact, 4 to 6 bitter almonds are said to have produced poisoning in a child.

§ 258. Action of Hydric and Potassic Cyanides on Living Organisms.—Both hydric cyanide and potassic cyanide are poisonous to all living forms, vegetable or animal, with the exception of certain fungi. The cold-blooded animals take a larger relative dose than the warm-blooded, and the mammalia are somewhat more sensitive to the poisonous action of the cyanides than birds; but all are destroyed in a very similar manner, and without any essential difference of action. The symptoms produced by hydric and potassic cyanide are identical, and, as regards general symptoms, what is true as to the one is also true as to the other. There is, however, one important difference in the action of these two substances, if the mere local action is considered, for potassic cyanide is very alkaline, possessing even caustic properties. I have seen, e.g., the gastric mucous membrane of a woman, who had taken an excessive dose of potassic cyanide on an empty stomach, so inflamed and swollen, that its state was similar to that induced by a moderate quantity of solution of potash. On the other hand, the acid properties of hydric cyanide are very feeble, and its effect on mucous membranes or the skin in no way resembles that of the mineral acids.

It attacks the animal system in two ways: the one, a profound interference with the ordinary metabolic changes; the other, a paralysis of the nervous centres. Schönbein discovered that it affected the blood corpuscles in a peculiar way; normal blood decomposes with great ease hydrogen peroxide into oxygen and water. If to normal venous blood a little peroxide of hydrogen be added, the blood at once becomes bright red; but if a trace of prussic acid be present, it is of a dark brown colour. The blood corpuscles, therefore, lose their power of conveying oxygen to all parts of the system, and the phenomena of asphyxia are produced. Geppert[243] has proved that this is really the case by showing, in a series of researches, that, under the action of hydric cyanide, less oxygen is taken up, and less carbon dioxide formed than normal, even if the percentage of oxygen in the atmosphere breathed is artificially increased. The deficiency of oxygen is in part due to the fact that substances like lactic acid, the products of incomplete combustion, are formed instead of CO2.

[243] Geppert, Ueber das Wesen der CNH-Vergift; mit einer Tafel, Berlin, 1889; Sep.-Abdr. aus Ztschr. f. klin. Med., Bd. xv.

At the same time the protoplasm of the tissues is paralysed, and unable to take up the loosely bound oxygen presented. This explains a striking symptom which has been noticed by many observers, that is, if hydrocyanic acid be injected into an animal, the venous blood becomes of a bright red colour; in warm-blooded animals this bright colour is transitory, but in cold-blooded animals, in which the oxidation process is slower, the blood remains bright red.

§ 259. Symptoms observed in Animals.—The main differences between the symptoms induced in cold-blooded and warm-blooded animals, by a fatal dose of hydric cyanide, are as follows:—

The respiration in frogs is at first somewhat dyspnœic, then much slowed, and at length it ceases. The heart, at first slowed, later contracts irregularly, and at length gradually stops; but it may continue to beat for several minutes after the respiration has ceased. But all these progressive symptoms are without convulsion. Among warm-blooded animals, on the contrary, convulsions are constant, and the sequence of the symptoms appears to be—dyspnœa, slowing of the pulse, giddiness, falling down, then convulsions with expulsion of the urine and fæces; dilatation of the pupils, exophthalmus, and finally cessation of the pulse and breathing. The convulsions also frequently pass into general paralysis, with loss of reflex movements, weak, infrequent breathing, irregular, quick, and very frequent pulse, and considerable diminution of temperature.

The commencement of the symptoms in animals is extremely rapid, the rapidity varying according to the dose and the concentration of the acid. It was formerly thought that the death from a large dose of the concentrated acid followed far more quickly than could be accounted for by the blood carrying the poison to the nervous centres; but Blake was among the first to point out that this doubt was not supported by facts carefully observed, since there is always a sufficient interval between the entry of the poison into the body and the first symptoms, to support the theory that the poison is absorbed in the usual manner. Even when Preyer injected a cubic centimetre of 60 per cent. acid into the jugular vein of a rabbit, twenty-nine seconds elapsed before the symptoms commenced. Besides, we have direct experiments showing that the acid—when applied to wounds in limbs, the vessels of which are tied, while the free nervous communication is left open—only acts when the ligature is removed. Magendie describes, in his usual graphic manner, how he killed a dog by injecting into the jugular vein prussic acid, and “the dog died instantly, as if struck by a cannon ball,” but it is probable that the interval of time was not accurately noted. A few seconds pass very rapidly, and might be occupied even by slowly pressing the piston of the syringe down, and in the absence of accurate measurements, it is surprising how comparatively long intervals of time are unconsciously shortened by the mind. In any case, this observation by Magendie has not been confirmed by the accurate tests of the more recent experimenters; and it is universally acknowledged that, although with strong doses of hydric cyanide injected into the circulation—or, in other words, introduced into the system—in the most favourable conditions for its speediest action, death occurs with appalling suddenness, yet that it takes a time sufficiently long to admit of explanation in the manner suggested. This has forensic importance, which will be again alluded to. Experiments on animals show that a large dose of a dilute acid kills quite as quickly as an equivalent dose of a stronger acid, and in some cases it even seems to act more rapidly. If the death does not take place within a few minutes, life may be prolonged for hours, and even, in rare cases, days, and yet the result be death. Coullon poisoned a dog with prussic acid; it lived for nineteen days, and then died; but this is quite an exceptional case, and when the fatal issue is prolonged beyond an hour, the chance of recovery is considerable.

§ 260. The length of time dogs poisoned by fatal doses survive, generally varies from two to fifteen minutes. The symptoms are convulsions, insensibility of the cornea, cessation of respiration, and, finally, the heart stops—the heart continuing to beat several minutes after the cessation of the respirations.[244] When the dose is short of a fatal one, the symptoms are as follows:—Evident giddiness and distress; the tongue is protruded, the breath is taken in short, hurried gasps, there is salivation, and convulsions rapidly set in, preceded, it may be, by a cry. The convulsions pass into paralysis and insensibility. After remaining in this state some time, the animal again wakes up, as it were, very often howls, and is again convulsed; finally, it sinks into a deep sleep, and wakes up well.

[244] N. Gréhant, Compt. rend., t. 109, pp. 502, 503.

Preyer noticed a striking difference in the symptoms after section of the vagus in animals, which varied according to whether the poison was administered by the lungs, or subcutaneously. In the first case, if the dose is small, the respirations are diminished in frequency; then this is followed by normal breathing; if the dose is larger, there is an increase in the frequency of the respirations. Lastly, if a very large quantity is introduced into the lungs, death quickly follows, with respirations diminished in frequency. On the other hand, when the poison is injected subcutaneously, small doses have no influence on the breathing; but with large doses, there is an increase in the frequency of the respirations, which sink again below the normal standard.

§ 261. Symptoms in Man.—When a fatal but not excessive dose of either potassic or hydric cyanide is taken, the sequence of symptoms is as follows:—Salivation, with a feeling of constriction in the throat, nausea, and occasionally vomiting. After a few minutes a peculiar constricting pain in the chest is felt, and the breathing is distinctly affected. Giddiness and confusion of sight rapidly set in, and the person falls to the ground in convulsions similar to those of epilepsy. The convulsions are either general, or attacking only certain groups of muscles; there is often true trismus, and the jaws are so firmly closed that nothing will part them. The respiration is peculiar, the inspiration is short, the expiration prolonged,[245] and between the two there is a long interval ever becoming more protracted as death is imminent. The skin is pale, or blue, or greyish-blue; the eyes are glassy and staring, with dilated pupils; the mouth is covered with foam, and the breath smells of the poison; the pulse, at first quick and small, sinks in a little while in frequency, and at length cannot be felt. Involuntary evacuation of fæces, urine, and semen is often observed, and occasionally there has been vomiting, and a portion of the vomit has been aspirated into the air-passages. Finally, the convulsions pass into paralysis, abolition of reflex sensibility, and gradual ceasing of the respiration. With large doses these different stages may occur, but the course is so rapid that they are merged the one into the other, and are undistinguishable. The shortest time between the taking of the acid and the commencement of the symptoms may be put at about ten seconds. If, however, a large amount of the vapour is inhaled at once, this period may be rather lessened. The interval of time is so short that any witnesses generally unintentionally exaggerate, and aver that the effects were witnessed before the swallowing of the liquid—“As the cup was at his lips”—“He had hardly drunk it,” &c. There is probably a short interval of consciousness, then come giddiness, and, it may be, a cry for assistance; and lastly, there is a falling down in convulsions, and a speedy death. Convulsions are not always present, the victim occasionally appears to sink lifeless at once. Thus, in a case related by Hufeland, a man was seen to swallow a quantity of acid, equivalent to 40 grains of the pure acid—that is, about forty times more than sufficient to kill him. He staggered a few paces, and then fell dead, without sound or convulsion.

[245] In a case quoted by Seidel (Maschka’s Handbuch, p. 321), a man, 36 years of age, four or five minutes after swallowing 150 mgrms. anhydrous HCN in spirits, lay apparently lifeless, without pulse or breathing. After a few minutes was noticed an extraordinary deep expiration, by which the ribs were drawn in almost to the spine, and the chest made quite hollow.

§ 262. The very short interval that may thus intervene between the taking of a dose of prussic acid and loss of consciousness, may be utilised by the sufferer in doing various acts, and thus this interval becomes of immense medico-legal importance. The question is simply this:—What can be done by a person in full possession of his faculties in ten seconds? I have found from experiment that, after drinking a liquid from a bottle, the bottle may be corked, the individual can get into bed, and arrange the bedclothes in a suitable manner; he may also throw the bottle away, or out of the window; and, indeed, with practice, in that short time a number of rapid and complicated acts may be performed. This is borne out both by experiments on animals and by recorded cases.

In Mr. Nunneley’s numerous experiments on dogs, one of the animals, after taking poison, “went down three or four steps of the stairs, saw that the door at the bottom was closed, and came back again.” A second went down, came up, and went again down the steps of a long winding staircase, and a third retained sufficient vigour to jump over another dog, and then leap across the top of a staircase.

In a remarkable case related by Dr. Guy,[246] in which a young man, after drinking more wine than usual, was seized by a sudden impulse to take prussic acid, and drank about 2 drachms, producing symptoms which, had it not been for prompt treatment, would, in all probability, have ended fatally—the interval is again noteworthy. After taking the poison in bed, he rose, walked round the foot of a chest of drawers, standing within a few yards of the bedside, placed the stopper firmly in the bottle, and then walked back to bed with the intention of getting into it; but here a giddiness seized him, and he sat down on the edge, and became insensible.

[246] Forensic Medicine, 4th ed., p. 615.

A case related by Taylor is still stronger. A woman, after swallowing a fatal dose of essence of almonds, went to a well in the yard, drew water, and drank a considerable quantity. She then ascended two flights of stairs and called her child, again descended a flight of stairs, fell on her bed, and died within half an hour from the taking of the poison.

Nevertheless, these cases and similar ones are exceptional, and only show what is possible, not what is usual, the rule being that after fatal doses no voluntary act of significance—save, it may be, a cry for assistance—is performed.[247]

[247] Dr. J. Autal, a Hungarian chemist, states that cobalt nitrate is an efficacious antidote to poisoning by either HCN or KCN. The brief interval between the taking of a fatal dose and death can, however, be rarely utilised.—Lancet, Jan. 16, 1894.

§ 263. Chronic poisoning by hydric cyanide is said to occur among photographers, gilders, and those who are engaged daily in the preparation or handling of either hydric or potassic cyanides. The symptoms are those of feeble poisoning, headache, giddiness, noises in the ears, difficult respiration, pain over the heart, a feeling of constriction in the throat, loss of appetite, nausea, obstinate constipation, full pulse, with pallor and offensive breath. Koritschoner[248] has made some observations on patients who were made to breathe at intervals, during many weeks, prussic acid vapour, with the idea that such a treatment would destroy the tubercle bacilli. Twenty-five per cent. of those treated in this way suffered from redness of the pharynx, salivation, headache, nausea, vomiting, slow pulse, and even albuminuria.

[248] Wiener klin. Woch., 1891.

§ 264. Post-mortem Appearances.[249]—If we for the moment leave out of consideration any changes which may be seen in the stomach after doses of potassic cyanide, then it may be affirmed that the pathological changes produced by hydric and potassic cyanides mainly coincide with those produced by suffocation. The most striking appearance is the presence of bright red spots; these bright red spots or patches are confined to the surface of the body, the blood in the deeper parts being of the ordinary venous hue, unless, indeed, an enormous dose has been taken; in that case the whole mass of blood may be bright red; this bright colour is due, according to Kobert, to the formation of cyanmethæmoglobin. The lungs and right heart are full of blood, and there is a backward engorgement produced by the pulmonic block. The veins of the neck and the vessels of the head generally are full of blood, and, in like manner, the liver and kidneys are congested. In the mucous membrane of the bronchial tubes there is a bloody foam, the lungs are gorged, and often œdematous in portions; ecchymoses are seen in the pleura and other serous membranes; and everywhere, unless concealed by putrefaction, or some strong-smelling ethereal oil, there is an odour of hydric cyanide.

[249] Hydric cyanide has, according to C. Brame, a remarkable antiseptic action, and if administered in sufficient quantity to animals, preserves them after death for a month. He considers that there is some more or less definite combination with the tissues.

Casper has rightly recommended the head to be opened and examined first, so as to detect the odour, if present, in the brain. The abdominal and chest cavities usually possess a putrefactive smell, but the brain is longer conserved, so that, if this course be adopted, there is a greater probability of detecting the odour.

The stomach in poisoning by hydric cyanide is not inflamed, but if alcohol has been taken at the same time, or previously, there may be more or less redness.

In poisoning by potassic cyanide, the appearances are mainly the same as those just detailed, with, it may be, the addition of caustic local action. I have, however, seen, in the case of a gentleman who drank accidentally a considerable dose of potassic cyanide just after a full meal, not the slightest trace of any redness, still less of corrosion. Here the contents of the stomach protected the mucous membrane, or possibly the larger amount of acid poured out during digestion sufficiently neutralised the alkali. Potassic cyanide, in very strong solution, may cause erosions of the lips, and the caustic effect may be traced in the mouth, throat, gullet, to the stomach and duodenum; but this is unusual, and the local effects are, as a rule, confined to the stomach and duodenum. The mucous membrane is coloured blood-red, reacts strongly alkaline,[250] is swollen, and it may be even ulcerated. The upper layers of the epithelium are also often dyed with the colouring-matter of the blood, which has been dissolved out by the cyanide. This last change is a post-mortem effect, and can be imitated by digesting the mucous membrane of a healthy stomach in a solution of cyanide. The intensity of these changes are, of course, entirely dependent on the dose and emptiness of the stomach. If the dose is so small as just to destroy life, there may be but little redness or swelling of the stomach, although empty at the time of taking the poison. In those cases in which there has been vomiting, and a part of the vomit has been drawn into the air-passages, there may be also inflammatory changes in the larynx. If essence of almonds has been swallowed, the same slight inflammation may be seen which has been observed with other essential oils, but no erosion, no strong alkaline reaction, nor anything approaching the effects of the caustic cyanide.

[250] The following case came under my own observation:—A stout woman, 35 years of age, the wife of a French polisher, drank, in a fit of rage, a solution of cyanide of potassium. It was estimated that about 15 grains of the solid substance were swallowed. She died within an hour. The face was flushed, the body not decomposed; the mouth smelt strongly of cyanide; the stomach had about an ounce of bloody fluid in it, and was in a most intense state of congestion. There was commencing fatty degeneration of the liver, the kidneys were flabby, and the capsule adherent. The contents of the stomach showed cyanide of potassium, and the blood was very fluid. The woman was known to be of intemperate habits.

In poisoning by bitter almonds no inflammatory change in the mucous membrane of the coats of the stomach would be anticipated, yet in one recorded case there seems to have been an eroded and inflamed patch.

§ 265. Tests for Hydrocyanic Acid and Cyanide of Potassium.—(1.) The addition of silver nitrate to a solution containing prussic acid, or a soluble cyanide,[251] produces a precipitate of argentic cyanide. 100 parts of argentic cyanide are composed of 80·60 Ag and 19·4 CN, equivalent to 20·1 HCN. It is a white anhydrous precipitate, soluble either in ammonia or in a solution of cyanide of potassium. It is soluble in hot dilute nitric acid, but separates on cooling. A particle of silver cyanide, moistened with strong ammonia, develops needles; silver chloride treated similarly, octahedral crystals. It is insoluble in water. Upon ignition it is decomposed into CN and metallic silver, mixed with a little paracyanide of silver.

[251] In the case of testing in this way for the alkaline cyanides, the solution must contain a little free nitric acid.

A very neat process for the identification of cyanide of silver is the following:—Place the perfectly dry cyanide in a closed or sealed tube, containing a few crystals of iodine. On heating slightly, iodide of cyanogen is sublimed in beautiful needles. These crystals again may be dissolved in a dilute solution of potash, a little ferrous sulphate added, and hydrochloric acid, and in this way Prussian blue produced. If the quantity to be tested is small, the vapour of the acid may be evolved in a very short test-tube, the mouth of which is closed by the ordinary thin discs of microscopic glass, the under surface of which is moistened with a solution of nitrate of silver; the resulting crystals of silver cyanide are very characteristic, and readily identified by the microscope.

(2.) If, instead of silver nitrate, the disc be moistened with a solution of sulphate of iron (to which has been added a little potash), and exposed to the vapour a short time, and then some dilute hydrochloric acid added, the moistened surface first becomes yellow, then green, lastly, and permanently, blue. No other blue compound of iron (with the exception of Prussian blue) is insoluble in dilute hydrochloric acid.

(3.) A third, and perhaps the most delicate of all, is the so-called sulphur test. A yellow sulphide of ammonium, containing free sulphur, is prepared by saturating ammonia by SH2, first suspending in the fluid a little finely-precipitated sulphur (or an old, ill-preserved solution of sulphide of ammonium may be used). Two watch-glasses are now taken; in the one the fluid containing prussic acid is put, and the second (previously moistened with the sulphide of ammonium described) is inverted over it. The glasses are conveniently placed for a few minutes in the water-oven; the upper one is then removed, the moist surface evaporated to dryness in the water-bath, a little water added, and then a small drop of solution of chloride of iron. If hydrocyanic acid is present, the sulphocyanide of iron will be formed of a striking blood-red colour.

(4.) The reaction usually called Schönbein’s, or Pagenstecher and Schönbein’s[252] (but long known,[253] and used before the publication of their paper), consists of guaiacum paper, moistened with a very dilute solution of sulphate of copper (1 : 2000). This becomes blue if exposed to the vapour of hydrocyanic acid. Unfortunately, the same reaction is produced by ammonia, ozone, nitric acid, hypochlorous acid, iodine, bromine, chromate of potash, and other oxidising agents, so that its usefulness is greatly restricted.

[252] Neues Repert. de Pharm., 18, 356.

[253] This reaction (with tincture of guaiacum and copper) has been long known. “I remember a pharmaceutist, who attended my father’s laboratory, showing me this test in 1828 or 1829.”—Mohr’s Toxicologie, p. 92.

(5.) A very delicate test for prussic acid is as follows:—About one-half centigrm. of ammonia, ferrous sulphate (or other pure ferrous salt), and the same quantity of uranic nitrate, are dissolved in 50 c.c. of water, and 1 c.c. of this test-liquid is placed in a porcelain dish. On now adding a drop of a liquid containing the smallest quantity of prussic acid, a grey-purple colour, or a distinct purple precipitate is produced.[254]

[254] M. Carey Lea, Amer. Journ. of Science [3], ix. pp. 121-123; J. C. Society, 1876, vol. i. p. 112.

(6.) A hot solution of potassic cyanide, mixed with picric acid, assumes a blood-red colour, due to the formation of picro-cyanic acid. Free HCN does not give this reaction, and therefore must first be neutralised by an alkali.

(7.) Schönbein’s Test.—To a few drops of defibrinated ox-blood are added a few drops of the carefully-neutralised distillate supposed to contain prussic acid, and then a little neutral peroxide of hydrogen is added. If the distillate contains no prussic acid, then the mixture becomes of a bright pure red and froths strongly; if, on the other hand, a trace of prussic acid be present, the liquid becomes brown and does not froth, or only slightly does so.

(8.) Kobert’s Test.—A 1-4 per cent. solution of blood, to which a trace of ferridcyanide of potassium is added, is prepared, and the neutralised distillate added to this solution. If hydric cyanide be present, then the liquid becomes of a bright red colour, and, examined spectroscopically, instead of the spectrum of methæmoglobin, will be seen the spectrum of cyanmethæmoglobin. Kobert proposes to examine the blood of the poisoned, for the purpose of diagnosis, during life. A drop of blood from a healthy person, and a drop of blood from the patient, are examined side by side, according to the process just given.

§ 266. Separation of Hydric Cyanide or Potassic Cyanide from Organic Matters, such as the Contents of the Stomach, &c.—It is very necessary, before specially searching for hydric cyanide in the contents of the stomach, to be able to say, by careful and methodical examination, whether there are or are not any fragments of bitter almonds, of apples, peaches, or other substance likely to produce hydric cyanide. If potassic cyanide has been taken, simple distillation will always reveal its presence, because it is found partly decomposed into hydric cyanide by the action of the gastric acids. Nevertheless, an acid should always be added, and if, as in the routine process given at [p. 48], there is reasonable doubt for suspecting that there will be no cyanide present, it will be best to add tartaric acid (for this organic acid will in no way interfere with subsequent operations), and distil, as recommended, in a vacuum. If, however, from the odour and from the history of the case, it is pretty sure to be a case of poisoning by hydric or potassic cyanide, then the substances, if fluid, are at once placed in a retort or flask, and acidified with a suitable quantity of sulphuric acid, or if the tissues or other solid matters are under examination, they are finely divided, or pulped, and distilled, after acidifying with sulphuric acid as before. It may be well here, as a caution, to remark that the analyst must not commit the unpardonable error of first producing a cyanide by reagents acting on animal matters, and then detecting as a poison the cyanide thus manufactured. If, for example, a healthy liver is carbonised by nitric acid, saturated with potash, and then burnt up, cyanide of potassium is always one of the products; and, indeed, the ashes of a great variety of nitrogenous organic substances may contain cyanides—cyanides not pre-existing, but manufactured by combination. By the action of nitric acid even on sugar,[255] hydric cyanide is produced.

[255] Chemical News, 68, p. 75.

The old method of distillation was to distil by the gentle heat of a water-bath, receiving the distillate in a little weak potash water, and not prolonging the process beyond a few hours. The experiments of Sokoloff, however, throw a grave doubt on the suitability of this simple method for quantitative results.

N. Sokoloff[256] recommends the animal substances to be treated by water strongly acidified with hydric sulphate, and then to be distilled in the water-bath for from two to three days; or to be distilled for twenty-four hours, by the aid of an oil-bath, at a high temperature. He gives the following example of quantitative analysis by the old process of merely distilling for a few hours, and by the new:—

[256] Ber. d. deutsch. chem. Gesellsch., Berlin, ix. p. 1023.

Old Process.—(1.) Body of a hound—age, 2 years; weight, 5180 grms.; dose administered, 57 mgrms. HCN; death in fifteen minutes. After five days there was found in the saliva 0·6 mgrm., stomach 3·2 mgrms., in the rest of the intestines 2·6 mgrms., in the muscles 4·1—total, 10·5.

(2.) Weight of body, 4000 grms.; dose given, 38 mgrms.; death in eleven minutes. After fifteen days, in the saliva 0·8, in the stomach 7·2, in the rest of the intestines 2·2, in the muscles 3·2—total, 13·4.

New Process.—Weight of body, 5700 grams; dose, 57 mgrms.; death in twenty-four minutes. After fifteen days, in the saliva 1·1 mgrm., in the stomach 2·6, in the rest of the intestines 9·6, in the muscles 31·9, and in the whole, 45·2 mgrms. Duration of process, thirteen hours.

From a second hound, weighing 6800 grms.; dose, 67 mgrms.; 25·1 mgrms. were separated three days after death.

From a third hound, weighing 5920 grms.; dose, 98 mgrms.; after forty days, by distillation on a sand-bath, there were separated 2·8 mgrms. from the saliva, 4·8 from the stomach, 16·8 from the intestines, 23·6 from the muscles—total, 48 mgrms.

It would also appear that he has separated 51·2 mgrms. of anhydrous acid from the corpse of a dog which had been poisoned by 57 mgrms. of acid, and buried sixty days.[257]

[257] Without wishing to discredit the statements of M. Sokoloff, we may point out that a loss of half-a-dozen mgrms. only appears rather extraordinary.

From another canine corpse, three days laid in an oven, and left for twenty-seven days at the ordinary temperature, 5·1 mgrms. were recovered out of a fatal dose of 38 mgrms.

The estimation was in each case performed by titrating the distillate with argentic nitrate, the sulphur compounds having been previously got rid of by saturating the distillate with KHO, and precipitating by lead acetate.

Venturoli[258] has, on the contrary, got good quantitative results without distillation at all. A current of pure hydrogen gas is passed through the liquid to be tested and the gas finally made to bubble through silver nitrate. He states that the whole of the hydric cyanide present is carried over in an hour. Metallic cyanides must be decomposed by sulphuric acid or tartaric acid. Mercury cyanide must be decomposed with SH2, the solution acidified with tartaric acid, neutralised with freshly precipitated calcic carbonate to fix any ferro- or ferri-cyanides present, and hydrogen passed in and the issuing gases led first through a solution of bismuth nitrate to remove SH2 and then into the silver solution.

[258] L’Orosi. xv. 85-88.

§ 267. How long after Death can Hydric or Potassic Cyanides be Detected?—Sokoloff appears to have separated prussic acid from the body of hounds at very long periods after death—in one case sixty days. Dragendorff recognised potassic cyanide in the stomach of a hound after it had been four weeks in his laboratory,[259] and in man eight days after burial. Casper also, in his 211th case, states that more than 18 mgrms. of anhydrous prussic acid were obtained from a corpse eight days after death.[260] Dr. E. Tillner[261] has recognised potassic cyanide in a corpse four months after death. Lastly, Struve[262] put 300 grms. of flesh, 400 of common water, and 2·378 of KCy in a flask, and then opened the flask after 547 days. The detection was easy, and the estimation agreed with the amount placed there at first. So that, even in very advanced stages of putrefaction, and at periods after death extending beyond many months, the detection of prussic acid cannot be pronounced impossible.

[259] Dragendorff, G., Beitr. zur gericht. Chem., p. 59.

[260] Casper’s Pract. Handbuch der gerichtlichen Medicin, p. 561.

[261] Vierteljahr. f. gerichtl. Med., Berlin, 1881, p. 193.

[262] Zeitschrift f. anal. Chemie, von Fresenius, 1873, xii. p. 4.

§ 268. Estimation of Hydrocyanic Acid or Potassic Cyanide.—In all cases, the readiest method of estimating prussic acid (whether it be in the distillate from organic substances or in aqueous solution) is to saturate it with soda or potash, and titrate the alkaline cyanide thus formed with nitrate of silver. The process is based on the fact that there is first formed a soluble compound (KCy, AgCy), which the slightest excess of silver breaks up, and the insoluble cyanide is at once precipitated. If grains are used, 17 grains of nitrate of silver are dissolved in water, the solution made up to exactly 1000 grain measures, each grain measure equalling ·0054 grain of anhydrous hydrocyanic acid. If grammes are employed, the strength of the nitrate of silver solution should be 1·7 grm. to the litre, each c.c. then = ·0054 hydrocyanic acid, or ·01302 grm. of potassic cyanide.

Essential oil of bitter almonds may also be titrated in this way, provided it is diluted with sufficient spirit to prevent turbidity from separation of the essential oil. If hydrocyanic acid is determined gravimetrically (which is sometimes convenient, when only a single estimation is to be made), it is precipitated as cyanide of silver, the characters of which have been already described.

§ 269. Case of Poisoning by Bitter Almonds.—Instances of poisoning by bitter almonds are very rare. The following interesting case is recorded by Maschka:—

A maid-servant, 31 years of age, after a quarrel with her lover, ate a quantity of bitter almonds. In a few minutes she sighed, complained of being unwell and faint; she vomited twice, and, after about ten minutes more had elapsed, fell senseless and was convulsed. An hour afterwards, a physician found her insensible, the eyes rolled upwards, the thumb clenched within the shut fists, and the breathing rattling, the pulse very slow. She died within an hour-and-a-half from the first symptoms.

The autopsy showed the organs generally healthy, but all, save the liver, exhaling a faint smell of bitter almonds. The right side of the heart was full of fluid dark blood, the left was empty. Both lungs were rich in blood, which smelt of prussic acid. The stomach was not inflamed—it held 250 grms. of a yellow fluid, containing white flocks smelling of bitter almond oil. In the most dependent portion of the stomach there was a swollen patch of mucous membrane, partially denuded of epithelium. The mucous membrane of the duodenum was also swollen and slightly red. The contents of the stomach were acid, and yielded, on distillation, hydride of benzole and hydric cyanide. Residues of the almonds themselves were also found, and the whole quantity taken by the woman from various data was calculated to be 1200 grains of bitter almonds, equal to 43 grains of amygdalin, or 2·5 grains of pure hydric cyanide.

Poisonous Cyanides other than Hydric and Potassic Cyanides.

§ 270. The action of both sodic and ammonic cyanides is precisely similar to that of potassic cyanide. With regard to ammonic cyanide, there are several experiments by Eulenberg,[263] showing that its vapour is intensely poisonous.

[263] Gewerbe Hygiene, p. 385.

A weak stream of ammonic cyanide vapour was passed into glass shades, under which pigeons were confined. After a minute, symptoms of distress commenced, then followed convulsions and speedy death. The post-mortem signs were similar to those produced by prussic acid, and this substance was separated from the liver and lungs.

§ 271. With regard to the double cyanides, all those are poisonous from which hydric cyanide can be separated through dilute acids, while those which, like potassic ferro-cyanide, do not admit of this decomposition, may be often taken with impunity, and are only poisonous under certain conditions.

Sonnenschein records the death of a colourist, after he had taken a dose of potassic ferro-cyanide and then one of tartaric acid; and Volz describes the death of a man, who took potassic ferro-cyanide and afterwards equal parts of nitric and hydrochloric acids. In this latter case, death took place within the hour, with all the symptoms of poisoning by hydric cyanide; so that it is not entirely true, as most text-books declare, that ferro-cyanide is in no degree poisonous. Carbon dioxide will decompose potassic ferro-cyanide at 72°-74°, potass ferrous cyanide being precipitated—K2Fe2(CN)6. A similar action takes place if ferro-cyanide is mixed with a solution of peptone and casein, and digested at blood heat[264] (from 37° to 40° C.), so that it is believed that when ferro-cyanide is swallowed HCN is liberated, but the quantity is usually so small at any given moment that no injury is caused: but there are conditions in which it may kill speedily.[265]

[264] Autenrieth, Arch. Pharm., 231, 99-109.

[265] The presence of ferro-cyanide is easily detected. The liquid is, if necessary, filtered and then acidified with hydrochloric acid and a few drops of ferric chloride added; if the liquid contains ferro-cyanide, there is immediate production of Prussian blue. It may happen that potassic or sodic cyanide has been taken as well as ferro-cyanide, and it will be necessary then to devise a process by which only the prussic acid from the simple cyanide is distilled over. According to Autenrieth, if sodium hydrocarbonate is added to the liquid in sufficient quantity and the liquid distilled, the hydric cyanide that comes over is derived wholly from the sodium or potassium cyanide. Should mercury cyanide and ferro-cyanide be taken together, then this process requires modification; bicarbonate of soda is added as before, and then a few c.c. of water saturated with hydric sulphide; under these circumstances, only the hydric cyanide derived from the mercury cyanide distils over. If the bicarbonate of soda is omitted, the distillate contains hydric cyanide derived from the ferro-cyanide.

Mercuric cyanide, it has been often said, acts precisely like mercuric chloride (corrosive sublimate), and a poisonous action is attributed to it not traceable to cyanogen; but this is erroneous teaching. Bernard[266] declares that it is decomposed by the gastric juice, and hydric cyanide set free; while Pelikan puts it in the same series as ammonic and potassic cyanides. Lastly, Tolmatscheff,[267] by direct experiment, has found its action to resemble closely that of hydric cyanide.[268]

[266] Substances Toxiques, pp. 66-103.

[267] “Einige Bemerkungen über die Wirkung von Cyanquecksilber,” in Hoppe-Seyler’s Med. Chem. Untersuchungen, 2 Heft, p. 279.

[268] Mercury cyanide may be detected in a liquid after acidifying with tartaric acid, and adding a few c.c. of SH2 water and then distilling. S. Lopes suggests another process: the liquid is acidified with tartaric acid, ammonium chloride added in excess, and the liquid is distilled. A double chloride of ammonium and mercury is formed, and HCN distils over with the steam.—J. Pharm., xxvii. 550-553.

Silver cyanide acts, according to the experiments of Nunneley, also like hydric cyanide, but very much weaker.

Hydric sulphocyanide in very large doses is poisonous.

Potassic sulphocyanide, according to Dubreuil and Legros,[269] if subcutaneously injected, causes first local paralysis of the muscles, and later, convulsions.

[269] Compt. rend., t. 64, 1867, p. 561.

Cyanogen chloride (CNCl) and also the compound (C3N3Cl3)—the one a liquid, boiling at 15°, the other a solid, which may be obtained in crystals—are both poisonous, acting like hydric cyanide.

Methyl cyanide is a liquid obtained by distillation of a mixture of calcic methyl sulphate and potassic cyanide. It boils at 77°, and is intensely poisonous. Eulenberg[270] has made with this substance several experiments on pigeons. An example of one will suffice:—A young pigeon was placed under a glass shade, into which methyl cyanide vapour, developed from calcic methyl sulphate and potassic cyanide, was admitted. The pigeon immediately became restless, and the fæces were expelled. In forty seconds it was slightly convulsed, and was removed after a few minutes’ exposure. The pupils were then observed not to be dilated, but the respiration had ceased; the legs were feebly twitching; the heart still beat, but irregularly; a turbid white fluid dropped out of the beak, and after six minutes life was extinct.

[270] Gewerbe Hygiene, p. 392.

The pathological appearances were as follows:—In the beak much watery fluid; the membranes covering the brain weakly injected; the plexus venosus spinalis strongly injected; in the region of the cervical vertebra a small extravasation between the dura mater and the bone; the right lung of a clear cherry-red colour, and the left lung partly of the same colour, the parenchyma presented the same hue as the surface; on section of the lungs a whitish froth exuded from the cut surface. In the cellular tissue of the trachea, there were extravasations 5 mm. in diameter; the mucous membrane of the air-passages was pale; the right ventricle and the left auricle of the heart were filled with coagulated and fluid dark red blood; liver and kidneys normal; the blood dark red and very fluid, becoming bright cherry-red on exposure to the air; blood corpuscles unchanged. Cyanogen was separated, and identified from the lungs and the liver.

Cyanuric acid (C3O3N3H3), one of the decomposition products obtained from urea, is poisonous, the symptoms and pathological effects closely resembling those due to hydric cyanide. In experiments on animals, there has been no difficulty in detecting prussic acid in the lungs and liver after poisoning by cyanuric acid.