Chapter XIX: Part IV: Acids and Alkalies (2)

The amount of acid in the stomach varies from moment to moment, and therefore it is not possible to say what the average acidity of gastric juice is. It has been shown that in the total absence of _free_ hydrochloric acid digestion may take place, because hydrochloric acid forms a compound with pepsin which acts as a solvent on the food. The amount of physiologically active acid varies with the food taken. It is smallest when carbohydrates are consumed, greatest with meat. The maximum amount that Jaksch found in his researches, when meat was ingested, was ·09 per cent. of hydrochloric acid. It is probable that anything above 0·2 per cent. of hydrochloric acid is either abnormal or owing to the recent ingestion of hydrochloric acid.

§ 72. =Influence of Hydrochloric Acid on Vegetation.=--Hydrochloric acid fumes, if emitted from works on a large scale, injure vegetation much. In former years, before any legal obligations were placed upon manufacturers for the condensing of the volatile products, the nuisance from this cause was great. In 1823, the duty on salt being repealed by the Government, an extraordinary impetus was given to the manufacture of hydrochloric acid, and since all the volatile products at that time escaped through short chimneys into the air, a considerable area of land round the works was rendered quite unfit for growing plants. The present law on the subject is, that the maximum quantity of acid escaping shall not exceed 2 grains per cubic foot of the air, smoke, or chimney gases; and, according to the reports of the alkali inspectors, the condensation by the improved appliances is well within the Act, and about as perfect as can be devised.

It appears from the reports of the Belgian Commission in 1855, when virtually no precautions were taken, that the gases are liable to injure vegetation to the extent of 2000 metres (2187 yards) around any active works; the more watery vapour the air contains, the quicker is the gas precipitated and carried to the earth. If the action of the vapour is considerable, the leaves of plants dry and wither; the chlorophyll becomes modified, and no longer gives the normal spectrum, while a thickening of the rind of trees has also been noticed. The cereals suffer much; they increase in stalk, but produce little grain. The leguminosæ become spotted, and have an air of dryness and want of vigour; while the potato, among plants utilised for food, appears to have the strongest resistance. Vines are very sensitive to the gas. Among trees, the alder seems most sensitive; then come fruit-trees, and last, the hardy forest-trees--the poplar, the ash, the lime, the elm, the maple, the birch, and the oak.[92]

[92] Those who desire to study more closely the effect of acids generally on vegetation may consult the various papers of the alkali inspectors contained in the Local Government Reports. See also Schubarth, _Die saueren Gase, welche Schwefelsäure- und Soda-Fabriken verbreiten_. _Verhandlungen des Vereins zur Beförderung des Gewerbefleisses in Preussen_, 1857, S. 135. Dingler’s _Journal_, Bd. 145, S. 374-427.

Christel, _Ueber die Einwirkung von Säuren-Dämpfen auf die Vegetation_.

_Arch. f. Pharmacie_, 1871, p. 252.

_Vierteljahrsschrift für gerichtliche Medicin_, 17 Bd. S. 404, 1872.

§73. =Action upon Cloth and Manufactured Articles.=--On black cloth the acid produces a green stain, which is not moist and shows no corrosion. On most matters the stain is more or less reddish; after a little time no free acid may be detected, by simply moistening the spot; but if the stain is cut out and boiled with water, there may be some evidence of free acid. The absence of moisture and corrosion distinguishes the stain from that produced by sulphuric acid.

§74. =Poisonous Effects of Hydrochloric Acid Gas.=--Eulenberg[93] has studied the effects of the vapour of this acid on rabbits and pigeons. One of these experiments may be cited in detail. Hydrochloric acid gas, prepared by heating together common salt and sulphuric acid, was passed into a glass shade supported on a plate, and a rabbit was placed in the transparent chamber thus formed. On the entrance of the vapour, there was immediate blinking of the eyes, rubbing of the paws against the nostrils, and emission of white fumes with the expired breath, while the respiration was irregular (40 to the minute). After the lapse of ten minutes, the gas was again introduced, until the atmosphere was quite thick; the symptoms were similar to those detailed above, but more violent; and in fourteen minutes from the commencement, the rabbit sank down on its right side (respirations 32). When twenty-two minutes had elapsed, the gas was again allowed to enter. The rabbit now lay quiet, with closed eyes and laboured respiration, and, finally, after half-an-hour of intermittent exposure to the gas, the animal was removed.

[93] _Gewerbe Hygiene_, Berlin, 1876, S. 51.

The cornea were opalescent, and the eyes filled with water; there was frequent shaking of the head and working of the forepaws. After three minutes’ exposure to the air, the respirations were found to be 128 per minute; this quickened respiration lasted for an hour, then gave place to a shorter and more superficial breathing. On the second day after the experiment, the rabbit suffered from laboured respiration (28 to the minute) and pain, and there was a rattling in the bronchial tubes. The animal died on the third day, death being preceded by slow respiration (12 to the minute).

The appearances twenty-four hours after death were as follows:--The eyes were coated with a thick slime, and both cornea were opalescent; there was strong rigidity of the body. The pia mater covering the brain was everywhere hyperæmic, and at the hinder border of both hemispheres appeared a small clot, surrounded by a thin layer of bloody fluid. The _plex. venos spin._ was filled with coagulated blood, and there was also a thin extravasation of blood covering the medulla and pons. The lungs were mottled bright brown-red; the middle lobe of the right lung was dark brown, solid, and sank in water; the lower lobe of the same lung and the upper lobe of the left lung were nearly in a similar condition, but the edges were of a bright red. The parenchyma in the darker places on section did not crepitate. On the cut surface was a little dark, fluid, weakly-acid blood; the tracheal mucous membrane was injected. The heart was filled with thick coagulated blood; the liver was congested, of a reddish-brown colour, and rich in dark, fluid blood: in the vena cava inferior was coagulated blood. The kidneys were not hyperæmic; the intestines were superficially congested.

I think there can be little doubt that the symptoms during life, and the appearances after death, in this case are perfectly consistent with the following view:--The vapour acts first as a direct irritant, and is capable of exciting inflammation in the lung and bronchial tissues; but besides this, there is a secondary effect, only occurring when the gas is in sufficient quantity, and the action sufficiently prolonged--viz., a direct coagulation of the blood in certain points of the living vessels of the lungs. The consequence of this is a more or less general backward engorgement, the right side of the heart becomes distended with blood, and the ultimate cause of death is partly mechanical. The hyperæmia of the brain membranes, and even the hæmorrhages, are quite consistent with this view, and occur in cases where the obstruction to the circulation is of a coarser and more obvious character, and can therefore be better appreciated.

§ 75. =Effects of the Liquid Acid.=--There is one distinction between poisoning by hydrochloric and the other mineral acids--namely, the absence of corrosion of the skin. Ad. Lesser[94] has established, by direct experiment, that it is not possible to make any permanent mark on the skin by the application even of the strongest commercial acid (40 per cent.). Hence, in any case of suspected poisoning by acid, should there be stains on the lips and face as from an acid, the presumption will be rather against hydrochloric. The symptoms themselves differ very little from those produced by sulphuric acid. The pathological appearances also are not essentially different, but hydrochloric is a weaker acid, and the extensive disorganisation, solution, and perforation of the viscera, noticed occasionally with sulphuric acid, have never been found in hydrochloric acid poisoning. We may quote here the following case:--

[94] Virchow’s _Archiv f. path. Anat._, Bd. 83, Hft. 2, S. 215, 1881.

A woman, under the influence of great and sudden grief--not unmixed with passion--drew a bottle from her pocket, and emptied it very quickly. She immediately uttered a cry, writhed, and vomited a yellow-green fluid. The abdomen also became enlarged. Milk was given her, but she could not swallow it, and death took place, in convulsions, two hours after the drinking of the poison.

The _post-mortem_ appearances were briefly as follows:--Mouth and tongue free from textural change: much gas in the abdomen, more especially in the stomach; the membranes of the brain congested; the lungs filled with blood. The stomach was strongly pressed forward, of a dark brown-red, and exhibited many irregular blackish spots, varying from two lines to half an inch in diameter (the spots were drier and harder than the rest of the stomach); the mucous membrane, internally, was generally blackened, and changed to a carbonised, shaggy, slimy mass, while the organ was filled with a blackish homogeneous pulp, which had no odour. The gullet was also blackened. A considerable quantity of hydrochloric acid was separated from the stomach.[95]

[95] _Preuss. Med. Vereinszeit. u. Friederichs Blätter f. gerichtl. Anthropologie_, 1858, Hft. 6, S. 70.

The termination in this instance was unusually rapid. In a case detailed by Casper,[96] in which a boy drank an unknown quantity of acid, death took place in seven hours. In Guy’s Hospital museum, the duodenum and stomach are preserved of a patient who is said to have died in nine and a half hours from half an ounce of the acid. The same quantity, in a case related by Taylor, caused death in eighteen hours. From these and other instances, it may be presumed that death from acute poisoning by hydrochloric acid will probably take place within twenty-four hours. From the secondary effects, of course, death may take place at a remote period, _e.g._, in a case recorded by Dr. Duncan (_Lancet_, April 12, 1890), a man drank about 1 oz. of HCl accidentally, was admitted to Charing Cross Hospital the same day, and treated with small quantities of sodium carbonate, and fed by the rectum. On the eighth day he brought up 34 oz. of blood; in a month he left apparently perfectly well, but was admitted again in about six weeks, and died of contraction of the stomach and stricture of the pylorus on the ninety-fourth day.

[96] Case 230.--_Gerichtliche Medicin_, 6th Ed., Berlin, 1876.

§76. =Post-mortem Appearances.=--The pathological appearances are very similar to those found in the case already detailed; though the skin of the face may not be eroded in any way by the acid, yet the more delicate mucous membrane of the mouth, gullet, &c., appears mostly to be changed, and is usually white or whitish-brown. There is, however, in the museum of the Royal College of Surgeons the stomach and gullet (No. 2386c.) of an infant thirteen months old; the infant drank a tea-cupful of strong hydrochloric acid, and died nine hours after the dose. The pharynx and the upper end of the gullet is quite normal, the corrosive action commencing at the lower end, so that, although the acid was concentrated, not the slightest effect was produced on the delicate mucous membrane of the throat and upper part of the gullet. The lower end of the gullet and the whole of the stomach were intensely congested; the rugæ of the latter were ecchymosed and blackened by the action of the acid. There were also small hæmorrhages in the lungs, which were ascribed to the action of the acid on the blood. Perforation of the stomach has not been noticed in hydrochloric acid poisoning.

In Guy’s Hospital museum (prep. 1799¹⁰), the stomach and duodenum of the case mentioned exhibit the mucous membrane considerably injected, with extravasations of blood, which, at the time when the preparation was first arranged, were of various hues, but are now somewhat altered, through long keeping in spirit. In St. George’s Hospital museum (ser. x. 43, d. 200) are preserved the stomach and part of the duodenum of a person who died from hydrochloric acid. The case is detailed in the _Medical Times and Gazette_ for 1853, vol. ii. p. 513. The whole inner surface appears to be in a sloughing state, and the larynx and lung were also inflamed.

A preparation, presented by Mr. Bowman to King’s College Hospital museum, exhibits the effects of a very large dose of hydrochloric acid. The gullet has a shrivelled and worm-eaten appearance; the stomach is injected with black blood, and was filled with an acid, grumous matter.[97]

[97] A drawing of parts of the gullet and stomach is given in Guy and Ferrier’s _Forensic Medicine_.

Looking at these and other museum preparations illustrating the effects of sulphuric and hydrochloric acids, I was unable (in default of the history of the cases) to distinguish between the two, by the naked eye appearances, save in those cases in which the disorganisation was so excessive as to render hydrochloric acid improbable. On the other hand, the changes produced by nitric acid are so distinctive, that it is impossible to mistake its action for that of any other acid. The nitric acid pathological preparations may be picked out at a glance.

Detection and Estimation of Free Hydrochloric Acid.

§ 77. (1) =Detection.=--A large number of colouring reagents have been proposed as tests for the presence of free mineral acid; among the best is _methyl-aniline violet_ decolorised by a large amount of hydrochloric acid; the violet turns to green with a moderate quantity, and to blue with a small quantity.

=Tropæolin= (00), in the presence of free mineral acid, strikes a ruby-red to a dark brown-red.

=Congo-red= is used in the form of paper dyed with the material; large amounts of free hydrochloric acid strike blue-black, small quantities blue.

=Günzburg’s test= is 2 parts phloroglucin and 1 part vanillin, dissolved in 100 parts of alcohol. Fine red crystals are precipitated on the addition of hydrochloric acid. To test the stomach contents for free hydrochloric acid by means of this reagent, equal parts of the fluid and the test are evaporated to dryness in the water-bath in a porcelain dish. If free hydrochloric acid be present, the evaporated residue shows a red colour; 1 mgrm. of acid can by this test be detected. The reaction is not interfered with by organic acids, peptones, or albumin.

Jaksch speaks highly of _benzopurpurin_ as a test. Filter-paper is soaked in a saturated aqueous solution of benzopurpurin 6 B (the variety 1 or 4 B is not so sensitive), and the filter-paper thus prepared allowed to dry. On testing the contents of the stomach with the reagent, if there is more than 4 parts per 1000 of hydrochloric acid the paper is stained intensely blue-black; but if the colour is brown-black, this is from butyric or lactic acids, or from a mixture of these acids with hydrochloric acid. If the paper is washed with pure ether, and the colour was due only to organic acids, the original hue of the paper is restored; if the colour produced was due to a mixture of mineral and organic acids, the brown-black colour is weakened; and, lastly, if due to hydrochloric acid alone, the colour is not altered by washing with ether. Acid salts have no action, nor is the test interfered with by large amounts of albumins and peptones.

A. Villiers and M. Favolle[98] have published a sensitive test for hydrochloric acid. The test consists of a saturated aqueous solution of colourless aniline, 4 parts; glacial acetic acid, 1 part; 0·1 mgrm. of hydrochloric acid strikes with this reagent a blue colour, 1 mgrm. a black colour. The liquid under examination is brought by evaporation, or by the addition of water, to 10 c.c. and placed in a flask; to this is added 5 c.c. of a mixture of equal parts of sulphuric acid and water, then 10 c.c. of a saturated solution of potassic permanganate, and heated gently, conveying the gases into 3 to 5 c.c. of the reagent contained in a test-tube immersed in water. If, however, bromine or iodine (one or both) should be present, the process is modified as follows:--The hydracids are precipitated by silver nitrate; the precipitate is washed, transferred to a small flask, and treated with 10 c.c. of water and 1 c.c. of pure ammonia. With this strength of ammonia the chloride of silver is dissolved easily, the iodide not at all, and the bromide but slightly. The ammoniacal solution is filtered, boiled, and treated with SH₂; the excess of SH₂ is expelled by boiling, the liquid filtered, reduced to 10 c.c. by boiling or evaporation, sulphuric acid and permanganate added as before, and the gases passed into the aniline. The process is inapplicable to the detection of chlorides or hydrochloric acid if cyanides are present, and it is more adapted for traces of hydrochloric acid than for the quantities likely to be met with in a toxicological inquiry.

[98] _Comptes Rend._, cxviii.

(2) =Quantitative estimation of Free Hydrochloric Acid.=--The contents of the stomach are diluted to a known volume, say 250 or 500 c.c. A fractional portion is taken, say 10 c.c., coloured with litmus or phenol-phthalein, and a decinormal solution of soda added drop by drop until the colour changes; this gives total acidity. Another 10 c.c. is shaken with double its volume of ether three times, the fluid separated from ether and titrated in the same way; this last titration will give the acidity due to mineral acids and acid salts;[99] if the only mineral acid present is hydrochloric acid the results will be near the truth if reckoned as such, and this method, although not exact for physiological research, is usually sufficient for the purpose of ascertaining the amount of hydrochloric acid or other mineral acids in a case of poisoning. It depends on the fact that ether extracts free organic acids, such as butyric and lactic acids, but does not extract mineral acids.

[99] To distinguish between acidity due to free acid and acid salts, or to acidity due to the combined action of acid salts and free acids, the method of Leo and Uffelmann is useful. A fractional portion of the contents of the stomach is triturated with pure calcium carbonate; if all the acidity is due to free acid, the fluid in a short time becomes neutral to litmus; if, on the other hand, the acidity is due entirely to acid salts, the fluid remains acid; or, if due to both acid and acid salts, there is a proportionate diminution of acidity due to the decomposition of the lime carbonate by the free acid. A quantitative method has been devised upon these principles. See Leo, _Diagnostik der Krankheiten der Verdauungsorgane_, Hirschwald, Berlin, 1890.

The free mineral acid, after extracting the organic acid by ether, can also be saturated with cinchonine; this hydrochlorate of cinchonine is extracted by chloroform, evaporated to dryness, and the residue dissolved in water acidified by nitric acid and precipitated by silver nitrate; the silver chloride produced is collected on a small filter, washed, and the filter, with its contents, dried and ignited in a porcelain crucible; the silver chloride, multiplied by 0·25426, equals HCl.

The best method of estimating free hydrochloric acid in the stomach is that of Sjokvist as modified by v. Jaksch;[100] it has the disadvantage of its accuracy being interfered with by phosphates; it also does not distinguish between actual free HCl and the loosely bound HCl with albuminous matters,--this in a toxicological case is of small importance, because the quantities of HCl found are likely to be large.

[100] _Klinische Diagnostik_, Dr. Rudolph v. Jaksch, Wien u. Leipzig, 1892. _Clinical Diagnosis_. English Translation, by Dr. Cagney. Second Edition. London: Charles Griffin & Co., Limited.

The method is based upon the fact that if carbonate of baryta be added to the contents of the stomach, the organic acids will decompose the barium carbonate, forming butyrate, acetate, lactate, &c., of barium; and the mineral acids, such as hydrochloric acid, will combine, forming salts of barium.

On ignition, chloride of barium will be unaffected, while the organic salts of barium will be converted into carbonate of barium, practically insoluble in carbonic acid free water.

The contents of the stomach are coloured with litmus, and barium carbonate added until the fluid is no longer acid (as shown by the disappearance of the red colour); then the contents are evaporated to dryness in a platinum dish, and ignited at a dull red heat; complete burning to an ash is not necessary. After cooling, the burnt mass is repeatedly exhausted with boiling water and filtered; the chloride of barium is precipitated from the filtrate by means of dilute sulphuric acid; the barium sulphate filtered off, washed, dried, and, after ignition, weighed; 233 parts of barium sulphate equal 73 parts of HCl.

A method somewhat quicker, but depending on the same principles, has been suggested by Braun.[101] A fractional part, say 10 c.c., of the fluid contents is coloured by litmus and titrated with decinormal soda. To the same quantity is added 2 or 3 more c.c. of decinormal soda than the quantity used in the first titration; this alkaline liquid is evaporated to dryness and ultimately ignited. To the ash is now added exactly the quantity of decinormal sulphuric acid as the decinormal soda last used to make it alkaline--that is to say, if the total acidity was equal to 3·6 d.n. soda, and 5·0 d.n. soda was added to the 10 c.c. evaporated to dryness and burned, then 5·6 c.c. of d.n. sulphuric acid is added to the ash. The solution is now warmed to get rid of carbon dioxide, and, after addition of a little phenolphthalein, titrated with d.n. soda solution until the change of colour shows saturation, the number of c.c. used, multiplied by 0·00365, equals the HCl.

[101] _Op. cit._, S. 157.

§78. In investigating the stains from hydrochloric acid on fabrics, or the leaves of plants, any free hydrochloric acid may be separated by boiling with water, and then investigating the aqueous extract. Should, however, the stain be old, all free acid may have disappeared, and yet some of the chlorine remain in organic combination with the tissue, or in combination with bases. Dr. Angus Smith has found weighed portions of leaves, &c., which had been exposed to the action of hydrochloric acid fumes, richer in chlorides than similar parts of the plants not thus exposed.

The most accurate method of investigation for the purpose of separating chlorine from combination with organic matters is to cut out the stained portions, weigh them, and burn them up in a combustion-tube, the front portion of the tube being filled with caustic lime known to be free from chlorides; a similar experiment must be made with the unstained portions. In this way a considerable difference may often be found; and it is not impossible, in some instances, to thus detect, after the lapse of many years, that certain stains have been produced by a chlorine-holding substance.

III.--Nitric Acid.

§ 79. =General Properties.=--Nitric acid--commonly known in England as _aqua fortis_, chemically as _nitric acid_, _hydric nitrate_, or _nitric monohydrate_--is a mono-hydrate of nitrogen pentoxide (N₂O₅), two equivalents, or 126 parts, of nitric acid containing 108 of N₂O₅, and 18 of H₂O. Anhydrous nitric acid, or nitrogen pentoxide, can be obtained by passing, with special precautions, dry chlorine over silver nitrate; the products are free oxygen and nitrogen pentoxide, according to the following equation:--

Silver Chlorine. Silver Nitrogen Oxygen.
Nitrate. Chloride. Pentoxide.
Ag₂O,N₂O₅ + 2Cl = 2AgCl + N₂O₅ + O

By surrounding the receiver with a freezing mixture, the acid is condensed in crystals, which dissolve in water, with emission of much heat, forming nitric acid. Sometimes the crystals, though kept in sealed tubes, decompose, and the tube, from the pressure of the liberated gases, bursts with a dangerous explosion.

Pure nitric acid has a specific gravity of 1·52, and boils at 98°. Dr. Ure examined the boiling point and other properties of nitric acid very fully. An acid of 1·5 specific gravity boils at 98·8°; of specific gravity 1·45, at 115·5°; specific gravity 1·40, at 118·8°; of specific gravity 1·42, at 122·8°. The acid of specific gravity 1·42 is the standard acid of the British Pharmacopœia. It can always be obtained by distilling either strong or moderately weak nitric acid; for, on the one hand, the acid on distillation gets weaker until the gravity of 1·42 is reached, or, on the other, it becomes stronger.

There is little doubt that acid of 1·42 gravity is a definite hydrate, consisting of 1 atom of dry acid and 4 atoms of water; it corresponds to 75 per cent.[102] of the liquid acid HNO₃. There are also at least two other hydrates known--one an acid of 1·485 specific gravity, corresponding to 1 atom of dry acid and 2 of water, and an acid of specific gravity 1·334, corresponding to 1 atom of dry acid and 7 atoms of water.

[102] The British Pharmacopœia states that the 1·42 acid equals 70 per cent. of HNO₃; but this is not in accordance with Ure’s Tables, nor with the facts.

In Germany the officinal acid is of 1·185 specific gravity, corresponding to about 30 per cent. of HNO₃. The dilute nitric acid of the Pharmacopœia is a colourless liquid, of specific gravity 1·101, and should contain about 17·4 per cent. of acid. The acids used in various industries are known respectively as _dyers’_ and _engravers’_ acid. _Dyers’_ acid has a specific gravity of 1·33 to 1·34 (66° to 68° Twad.), that is, strength from 56 to 58 per cent. of HNO₃. _Engravers’_ acid is stronger; being of 1·40 specific gravity (80° Twad.); and contains 70 per cent. of HNO₃. Although the _pure_ acid of commerce is (and should be) almost colourless, most commercial specimens are of hues from yellow up to deep red. An acid saturated with red oxides of nitrogen is often known as “fuming nitric acid.”

§ 80. =Use in the Arts.=--Nitric acid is employed very extensively in the arts and manufactures. The dyer uses it as a solvent for tin in the preparation of valuable mordants for calico and other fabrics; the engraver uses it for etching copper. It is an indispensable agent in the manufacture of gun-cotton, nitro-glycerin, picric acid, and sulphuric acid; it is also used in the manufacture of tallow, in preparing the felt for hats, and in the gilding trades. It is said to be utilised to make yellowish or fawn-coloured spots on cigar leaves, so as to give them the appearance of age and quality. It is also used as a medicine.

§ 81. =Statistics of Poisoning by Nitric Acid.=--In the ten years 1883-1892 no case of murder was ascribed to nitric acid, but it caused accidentally 25 deaths, and was used in 27 cases of suicide.

The following tables give the age and sex distribution of these deaths:--

DEATHS IN ENGLAND AND WALES DURING THE TEN YEARS ENDING 1892 FROM NITRIC ACID.

ACCIDENT OR NEGLIGENCE.

Ages, 1-5 5-15 15-25 25-65 65 and Total
above
Males, 6 2 1 9 ... 18
Females, 3 ... ... 4 ... 7
--------------------------------------
Totals, 9 2 1 13 ... 25
--------------------------------------

SUICIDE.

Ages, 15-25 25-65 65 and Total
above
Males, 3 14 1 18
Females, 1 8 ... 9
----------------------------
Totals, 4 22 1 27
----------------------------

§ 82. =Fatal Dose.=--The dose which causes death has not been ascertained with any exactness. As in the case of sulphuric acid, we may go so far as to say that it is possible for a few drops of the strong acid to be fatal, for if brought into contact with the vocal apparatus, fatal spasm of the glottis might be excited. The smallest dose on record is 7·7 grms. (2 drachms), which killed a child aged 13.

§ 83. =Action of Nitric Acid on Vegetation.=--Nitric acid acts on plants injuriously in a two-fold manner--viz., by direct corrosive action, and also by decomposing the chlorides which all plants contain, thus setting free chlorine, which decomposes and bleaches the chlorophyll. The action is most intense on soft and delicate leaves, such as those of clover, the cabbage, and all the cruciferæ. The tobacco plant is particularly injured by nitric acid. Next to all herbaceous plants, trees, such as the apple, pear, and fruit trees, generally suffer. The coniferæ, whether from their impregnation with resin, or from some other cause, possess a considerable resisting-power against nitric acid vapours, and the same is true as regards the cereals; in the latter case, their siliceous armour acts as a preserving agent.

§ 84. =Nitric Acid Vapour.=--The action of nitric acid in a state of vapour, as evolved by warming potassic nitrate and sulphuric acid together, has been studied by Eulenberg. A rabbit was placed under a shade into which 63 grains of nitric acid in a state of vapour were introduced. From the conditions of the experiment, some nitric peroxide must also have been present. Irritation of the external mucous membranes and embarrassment in breathing were observed. The animal in forty-five minutes was removed, and suffered afterwards from a croupous bronchitis, from which, however, it completely recovered in eleven days. A second experiment with the same animal was followed by death. On inspection, there was found strong injection of the cerebral membranes, with small extravasations of blood; the lungs were excessively congested; the right middle lobe especially was of a liver-brown colour, and empty of air: it sank in water.

O. Lassar[103] has also made a series of researches on the influence of nitric acid vapour, from which he concludes that the acid is not absorbed by the blood, but acts only by its mechanical irritation, for he could not trace, by means of an examination of the urine, any evidence of such absorption.

[103] Hoppe-Seyler’s _Zeitschrift f. physiol. Chemie_, Bd. i. S. 165-173, 1877-78.

There are a few instances on record of the vapour having been fatal to men; for example, the well-known case of Mr. Haywood, a chemist of Sheffield, may be cited. In pouring a mixture of nitric and sulphuric acids from a carboy of sixty pounds capacity, the vessel broke, and for a few minutes he inhaled the mixed fumes. He died eleven hours after the accident, although for the first three hours there were scarcely any symptoms of an injurious effect having been produced. On inspection, there was found intense congestion of the windpipe and bronchial tubes, with effusion of blood in the latter. The lining membrane of the heart and aorta was inflamed; unfortunately, the larynx was not examined.[104]

[104] _Lancet_, April 15, 1854, p. 430.

A very similar case happened in Edinburgh in 1863.[105] Two young men were carrying a jar of nitric acid; the jar broke, and they attempted to wipe up the acid from the floor. The one died ten hours after the accident, the other in less than twenty-four hours. The symptoms were mainly those of difficult breathing, and it is probable that death was produced from suffocation. Dr. Taylor relates also, that having accidentally inhaled the vapour in preparing gun-cotton, he suffered from severe constriction of the throat, tightness in the chest, and cough, for more than a week.[106]

[105] _Chemical News_, March 14, 1863, p. 132.

[106] _Principles and Practice of Medical Jurisprudence_, vol. i., 1873, p. 218.

§ 85. =Effects of Liquid Nitric Acid.=--Poisoning by nitric acid, though still rare, is naturally more frequent than formerly. At the beginning of this century, Tartra[107] wrote a most excellent monograph on the subject, and collated all the cases he could find, from the first recorded instances related by Bembo[108] in Venetian history, down to his own time. The number of deaths in those 400 years was but fifty-five, while, in our century, at least fifty can be numbered. Most of these (74 per cent.) are suicidal, a very few homicidal, the rest accidental. In one of Tartra’s cases, some nitric acid was placed in the wine of a drunken woman, with fatal effect. Osenbrüggen[109] relates the case of a father murdering his six children by means of nitric acid; and C. A. Büchner[110] that of a soldier who poured acid into the mouth of his illegitimate infant. A curious case is one in which a man poisoned his drunken wife by pouring the acid into her right ear; she died after six weeks’ illness. All these instances prove again, if necessary, that the acid is only likely to be used with murderous intent in the case of young children, or of sleeping, drunken, or otherwise helpless people.

[107] Tartra, A. E., Dr., _Traité de l’Empoisonnement par l’Acide Nitrique_, Paris, An. 10 (1802), pp. 300.

[108] _Bembo Cardinalis, Rerum Venetarium Historiæ_, lib. xii., lib. i. p. 12, Paris Ed., 1551.

[109] _Allgem.-Deutsche Strafrechtszeitung, herausgeg. v. Frz. v. Holtzendorff_, 5 Jahrg., 1865, Hft. 5, S. 273.

[110] Friederich’s _Blätter f. ger. Med._, 1866, Hft. 3, S. 187.

As an example of the way in which accidents are brought about by heedlessness, may be cited the recent case of a woman who bought a small quantity of aqua fortis for the purpose of allaying toothache by a local application. She attempted to pour the acid direct from the bottle into the cavity of the tooth; the acid went down her throat, and the usual symptoms followed. She threw up a very perfect cast of the gullet (preserved in University College museum), and rapidly died. Nitric acid has been mistaken for various liquids, and has also been used by injection as an abortive, in every respect having a toxicological history similar to that of sulphuric acid.

§ 86. =Local Action.=--When strong nitric acid comes in contact with organic matters, there is almost constantly a development of gas. The tissue is first bleached, and then becomes of a more or less intense yellow colour. Nitric acid spots on the skin are not removed by ammonia, but become of an orange-red when moistened with potash and a solution of cyanide of potassium. The yellow colour seems to show that picric acid is one of the constant products of the reaction; sulphide of ammonium forms a sort of soap with the epidermis thus attacked, and detaches it.

§ 87. =Symptoms.=--The symptoms and course of nitric acid poisoning differ in a few details only from those of sulphuric acid. There is the same instant pain and frequent vomiting, destruction of the mucous membranes, and, in the less severe cases, after-contraction of the gullet, &c.

One of the differences in the action of nitric and sulphuric acids is the constant development of gas with the former. This, without doubt, adds to the suffering. Tartra made several experiments on dead bodies, and showed that very considerable distension of the intestinal canal, by gaseous products, was the constant result; the tissues were corroded and almost dissolved, being transformed, ultimately, into a sort of greasy paste. The vomited matters are of a yellow colour, unless mixed with blood, when they are of a dirty-brown hue, with shreds of yellow mucus, and have the strong acid reaction and smell of nitric acid. The teeth may be partially attacked from the solvent action of the acid on the enamel. The fauces and tongue, at first blanched, soon acquire a citron-yellow, or even a brown colour; the whole cavity may swell and inflame, rendering the swallowing of liquids difficult, painful, and sometimes impossible. The air passages may also become affected, and in one case tracheotomy was performed for the relief of the breathing.[111] The stomach rejects all remedies; there are symptoms of collapse; quick, weak pulse, frequent shivering, obstinate constipation, and death (often preceded by a kind of stupor) in from eighteen to twenty-four hours. The intellectual faculties remain clear, save in a few rare instances.

[111] Arnott, _Med. Gaz._, vol. xii. p. 220.

C. A. Wunderlich has recorded an unusual case, in which the symptoms were those of dysentery, and the large intestine was found acutely inflamed, while the small one was little affected. The kidneys had the same appearance as in Bright’s disease.[112] The smallest fatal dose given by Taylor is from 2 drachms, which killed a child aged 13 years. Should the dose of nitric acid be insufficient to kill at once, or, what amounts to the same thing, should the acid be immediately diluted with water, or in some way be neutralised, the patient, as in the case of sulphuric acid, may yet die at a variable future time from stenosis of the gullet, impaired digestion, &c. For example, in an interesting case related by Tartra,[113] a woman, who had swallowed 42 grms. (1·5 oz.) of nitric acid, feeling acute pain, took immediately a quantity of water, and three hours afterwards was admitted into hospital, where she received appropriate treatment. At the end of a month she left, believing herself cured; but in a little while returned, and was re-admitted, suffering from marasmus, extreme weakness, and constant vomiting; ultimately she died. The _post-mortem_ examination revealed extreme contraction of the intestinal canal throughout. The lumen would hardly admit a penholder. The stomach was no larger than an ordinary intestine, and adherent to adjacent organs; on its internal surface there were spots, probably cicatrices; there were also changes in the gullet, but not so marked. A somewhat similar case is related by the same author in his thirteenth observation. In the Middlesex Hospital there is preserved the stomach (No. 1363) of a man who died forty days after swallowing 2 ozs. of nitric acid diluted in a tumbler of water. The stomach is contracted, the mucous membrane of the lower part of the gullet, the lesser curvature, and the pyloric end of the stomach is extensively corroded, showing ulcerated patches commencing to cicatrize.

[112] _De Actionibus quibusdam Acidi Nitrici Caustico in Corpus Humanum immissi. Programma Academ._, Lipsiæ, 1857, 4.

[113] _Op. cit._

§ 88. =Post-mortem Appearances.=--The pathological changes in the tongue, gullet, and stomach can be readily studied from the preparations in the different museums. The staining by the nitric acid appears unchanged to the naked eye for many years; hence, most of the nitric acid preparations are in an excellent state of preservation. A very good example of the pathological changes is to be found in Nos. 1049 and 1050, University College museum.

No. 1049 presents the tongue, pharynx, and larynx of a man who had
swallowed a tea-cupful of nitric acid. The epithelium of the
œsophagus is for the most part wanting, and hangs in shreds; the
dorsum of the tongue, in front of the circumvallate papillæ, is
excavated, and over its central part superficially ulcerated; in
other places the tongue is encrusted with a thick, loose,
fawn-coloured layer, formed probably of desquamated epithelium. The
whole of the mucous surface is stained of a dirty yellow.

No. 1050 is a preparation showing the tongue, gullet, and stomach of
a person who died from the effects of nitric acid. The tongue in
places is smooth and glazed; in others, slightly depressed and
excavated. On the anterior wall and lower portion of the gullet two
large sloughs exist.

Although perforation of the stomach is not so common with nitric as
with sulphuric acid, such an accident may occur, as shown in a
preparation at Guy’s Hospital, in which there is a perforation at
the cardiac end. All the mucous membrane has disappeared, and the
inner surface is for the most part covered with flocculent shreds.
Three ounces of nitric acid are said to have been swallowed, and the
patient lived seventeen hours. There is the usual staining. There is
also in the Middlesex Hospital (No. 1364) the œsophagus and stomach
of a woman aged 30, who died six hours after swallowing 2 to 3 ozs.
of strong nitric acid. The inner coats of the mucous membrane of the
gullet and stomach are in part converted into opaque yellow and
black eschars, and in part to a shreddy pulpy condition. At the most
depending part of the stomach is a large ragged perforation, with
pulpy margins, which allowed the contents of the stomach to escape
into the peritoneal cavity.

In St. Bartholomew’s museum, there is a very good specimen (No.
1870) of the appearances in the gullet and stomach after poisoning
by nitric acid. The case is detailed in _St. Bartholomew’s Hospital
Reports_, vol. v. p. 247. A male died in fifteen hours after
swallowing 1 oz. of nitric acid. The whole mucous membrane is
wrinkled, or rather ploughed, into longitudinal furrows, the yellow
discoloration stops abruptly, with an irregular border, at the
commencement of the stomach, the epithelial and mucous coats of
which are wanting--its surface being rough and of a brownish-red
colour.

The following preparations are to be found in the museum of the
London Hospital:--A. b. 1. and A. b. 8.--A. b. 1. shows the pharynx,
œsophagus, larynx, and stomach of a young woman, who, after taking
half an ounce of nitric acid, died in eight hours. The staining is
very intense; as an unusual feature, it may be noted that the larynx
is almost as yellow as the œsophagus. The abrasion or solution of
the epithelium on the dorsum of the tongue has dissected out the
circumvallate and fungiform papillæ, so that they project with
unusual distinctness. The lining membrane of the gullet throughout
is divided into minute squares by longitudinal and transverse
furrows. The mucous membrane of the stomach appears wholly
destroyed, and presents a woolly appearance.

A. b. 8. shows a very perfect cast of the œsophagus. The case was
that of a woman, aged 35, who swallowed half an ounce of nitric
acid. The symptoms for the first four days were the usual pain in
the throat and stomach, which might be expected; the bowels were
freely open, and the stools dark and offensive. On the sixth day,
there was constant vomiting with offensive breath; on the ninth, the
appearance of the patient was critical, and she threw up the cast
preserved. She died on the tenth day after the taking of the acid.
The gullet, stomach, trachea, and larynx were found after death much
inflamed.

The following preparations are in St. Thomas’ Hospital:--P. 5.--a
stomach with gullet attached. The stomach is covered with
yellowish-green patches of false membrane and deposit; the gullet
has the usual longitudinal furrows so characteristic of corrosive
fluids.

P. 6. is also from a case of nitric acid poisoning. It shows the
lining membrane of the stomach partly destroyed and shreddy, yet but
little discoloured, the hue being a sort of delicate fawn.

To these may be added a case described and figured by Lesser; to a
baby, a few days old, an unknown quantity of fuming nitric acid was
given; the child made a gurgling, choking sound, and died in a few
minutes. The corpse, nine days after death, showed no signs of
decomposition. The tongue and gums were yellow, the gullet less so,
the stomach still less, and the small intestine had no yellow tint;
the whole of the mouth, gullet, and stomach showed the corrosive
action of the acid. The graduation of tint, Lesser remarks, is what
is not seen when the yellow colour is due to poisoning by chromic
acid or by strong solution of ferric perchloride; in such cases,
wherever the liquid has gone, there is a yellowness.[114]

[114] A. Lesser, _Atlas der gerichtlichen Medicin_, Berlin, 1884, Tafel i. fig. 2.

§ 89. =Detection and Estimation of Nitric Acid.=--The detection either of free nitric acid or of its salts is not difficult. Free nitric acid, after preliminary estimation of the total acidity by decinormal soda, may be separated by the cinchonine process given at p. 100. On precipitation by ammonia or soda solution, the nitrate of ammonia or soda (and, it may be, other similarly combined acids) remain in solution. If free nitric acid is present in small quantity only, it may be necessary to evaporate the filtrate from the quinine nearly to dryness, and to test the concentrated liquid for nitric acid. The ordinary tests are as follows:--

(1.) Nitrates, treated with mercury or copper and strong sulphuric acid, develop nitric oxide, recognised by red fumes, if mixed with air or oxygen.

(2.) A nitrate dissolved in a small quantity of water, with the addition of a crystal of ferrous sulphate (allowed to partially dissolve), and then of strong sulphuric acid--poured through a funnel with a long tube dipping to the bottom of the test-tube, so as to form a layer at the bottom--strikes a brown colour at the junction of the liquid. When the test is properly performed, there will be three layers--the uppermost being the nitrate solution, the middle ferrous sulphate, and the lowest sulphuric acid; the middle layer becomes of a smoky or black hue if a nitrate is present. Organic matter interferes much with the reaction.

(3.) Nitrates in solution, treated in the cold with a zinc copper couple, are decomposed first into nitrites, and then into ammonia. The nitrites may be detected by a solution of metaphenyldiamine, which strikes a red colour with an infinitesimal quantity. Hence, a solution which gives no red colour with metaphenyldiamine, when submitted to the action of a zinc copper couple, and tested from time to time, cannot contain nitrites; therefore, no nitrates were originally present.

(4.) Nitrates, on being treated with strong sulphuric acid, and then a solution of indigo carmine dropped in, decolorise the indigo; this is a useful test--not conclusive in itself, but readily applied, and if the cinchonine method of separation has been resorted to, with few sources of error.

There is a process of separating nitric acid direct from any organic tissue, which may sometimes be useful:--Place the substance in a strong, wide-mouthed flask, closed by a caoutchouc cork, and in the flask put a small, short test-tube, charged with a strong solution of ferrous chloride in hydrochloric acid. The flask is connected to the mercury pump (see fig. p. 47), and made perfectly vacuous by raising and lowering the reservoir. When this is effected, the tube SS′P is adjusted so as to deliver any gas evolved into a eudiometer, or other gas-measuring apparatus. By a suitable movement of the flask, the acid ferrous chloride is allowed to come in contact with the tissue, a gentle heat applied to the flask, and gases are evolved. These may be carbon dioxide, nitrogen, and nitric oxide. On the evolution of gas ceasing, the carbon dioxide is absorbed by passing up under the mercury a little caustic potash. When absorption is complete, the gas, consisting of nitrogen and nitric oxide, may be measured. A bubble or two of oxygen is now passed into the eudiometer; if nitric oxide is present, red fumes at once develop. On absorbing the excess of oxygen and the nitric peroxide by alkaline pyrogallate, and measuring the residual gas, it is easy to calculate how much nitric oxide was originally present, according to the principles laid down in “Foods,” p. 587.

It is also obvious that, by treating nitric oxide with oxygen, and absorbing the nitric peroxide present by an alkaline liquid of known strength and free from nitrates or ammonia, the resulting solution may be dealt with by a zinc copper couple, and the ammonia developed by the action of the couple directly estimated by titration by a decinormal hydrochloric acid, if large in quantity, or by “_nesslerising_,” if small in quantity. Crum’s method of estimating nitrates (“Foods,” p. 568) in the cases of minute stains on fabrics, &c., with a little modification, may be occasionally applicable.

IV.--Acetic Acid.

§ 90. In the ten years ending 1893 nine deaths (four males and five
females) occurred in England and Wales from drinking, by mistake or
design, strong acetic acid.

A few cases only have been recorded in medical literature although
there have been many experiments on animals.

The symptoms in the human subject consist of pain, vomiting, and
convulsions.

In animals it causes colic, paralysis of the extremities, bloody
urine, and œdema of the lungs. The lethal dose for plant-eating
animals is about 0·49 gramme per kilo.

There should be no difficulty in recognising acetic acid; the odour
alone is, in most cases, strong and unmistakable. Traces are
detected by distilling, neutralising the distillate by soda,
evaporating to dryness, and treating the residue as follows:--A
portion warmed with alcohol and sulphuric acid gives a smell of
acetic ether. Another portion is heated in a small tube of hard
glass with arsenious acid; if acetic acid is present, or an acetate,
a smell of kakodyl is produced.

V.--Ammonia.

§ 91. Ammonia, (NH₃), is met with either as a vapour or gas, or as a solution of the pure gas in water.

=Properties.=--Pure ammonia gas is colourless, with a strong, irritating, pungent odour, forming white fumes of ammonic chloride, if exposed to hydric chloride vapour, and turning red moist litmus-paper strongly blue. By intense cold, or by a pressure of 6½ atmospheres at the ordinary temperature, the gas is readily liquefied; the liquid ammonia boils at 38°; its observed specific gravity is ·731; it freezes at -57·1°. Ammonia is readily absorbed by water; at 0° water will take up 1000 times its own volume, and at ordinary temperatures about 600 times its volume. Alcohol also absorbs about 10 per cent. Ammonia is a strong base, and forms a number of salts. Ammonia is one of the constant products of the putrefaction of nitrogenous substances; it exists in the atmosphere in small proportions, and in everything that contains water. Indeed, water is the only compound equal to it in its universality of diffusion. The minute quantities of ammonia thus diffused throughout nature are probably never in the free state, but combinations of ammonia with hydric nitrate, carbon dioxide, &c.

§ 92. =Uses.=[115]--A solution of ammonia in water has many applications in the arts and industries; it is used in medicine, and is an indispensable laboratory reagent.

[115] Sir B. W. Richardson has shown that ammonia possesses powerful antiseptic properties.--_Brit. Med. Journal_, 1862.

The officinal caustic preparations of ammonia are--_ammoniæ liquor fortior_ (_strong solution of ammonia_), which should contain 32·5 per cent. of ammonia, and have a specific gravity of ·891.

_Liquor ammoniæ_ (_solution of ammonia_), specific gravity ·959, and containing 10 per cent. of ammonia. There is also a _liniment of ammonia_, composed of olive oil, 3 parts, and ammonia, 1 part.

_Spiritus Ammoniæ Fœtidus_ (_fœtid spirit of ammonia_).--A solution of assafœtida in rectified spirit and ammonia solution, 100 parts by measure, contains 10 of strong solution of ammonia.

Strong solution of ammonia is an important ingredient in the “_linimentum camphoræ composita_” (_compound liniment of camphor_), the composition of which is as follows:--camphor, 2·5 parts; oil of lavender, ·125; strong solution of ammonia, 5·0; and rectified spirit, 15 parts. Its content of strong solution of ammonia is then about 22·6 per cent. (equivalent to 7·3 of NH₃).[116]

[116] There is a common liniment for horses used in stables, and popularly known as “white oil.” It contains 1 part of ammonia, and 4 parts of olive or rape oil; not unfrequently turpentine is added. Another veterinary liniment, called “egg oil,” contains ammonia, oil of origanum, turpentine, and the yelks of eggs.

_The carbonate of ammonia_ is also caustic; it is considered to be a compound of acid carbonate of ammonium, NH₄HCO₃, with carbamate of ammonium, NH₄NH₂CO₂. It is in the form of colourless, crystalline masses; the odour is powerfully ammoniacal; it is strongly alkaline, and the taste is acrid. It completely volatilises with heat, is soluble in water, and somewhat soluble in spirit.

The officinal preparation is the “_spiritus ammoniæ aromaticus_,” or aromatic spirit of ammonia. It is made by distilling in a particular way ammonic carbonate, 4 ozs.; strong solution of ammonia, 8 ozs.; rectified spirit, 120 ozs.; water, 60 ozs.; volatile oil of nutmeg, 4½ drms.; and oil of lemon, 6½ drms. Aromatic spirit of ammonia is a solution in a weak spirit of neutral carbonate, flavoured with oil of lemon and nutmeg; the specific gravity should be 0·896.

_Smelling salts_ (_sal volatile_) are composed of carbonate of ammonia.

§ 93. =Statistics.=--Falck has found throughout literature notices of thirty cases of poisoning by ammonia, or some of its preparations. In two of these it was used as a poison for the purpose of murder, and in eight with suicidal intent; the remainder were all accidental. The two criminal cases were those of children, who both died. Six out of eight of the suicidal, and twelve of the twenty accidental cases also terminated fatally.

Ammonia was the cause of 64 deaths (39 male, 25 female) by accident and of 34 (18 male, 16 female) by suicide, making a total of 98 during the ten years 1883-1892 in England and Wales. At present it occupies the seventh place among poisons as a cause of accident, the ninth as a means of suicide.