Arsenic (through Lat. from Gr. arsenikon) is the name popularly given to a well-known poison, arsenious acid, but, strictly speaking, the term is restricted to the metal, of which the symbol is As, and the atomic weight 75. The metal arsenic is rarely found free in nature, but in a state of combination it occurs largely. The most important of all arsenical minerals, because of their use as ores of arsenic, for the preparation of white arsenic, or arsenious acid, are those in which arsenic is combined with nickel and cobalt. The chief of these are arsenical pyrites, or leucopyrite, nickeline, cobaltine, and smaltine, which are found in Cornwall and the continent of Europe, as well as in other parts of the world. The last-named two are used for the preparation of blue colours for porcelain or stoneware. The presence of arsenic in a mineral may commonly be detected by the alliaaceous odour which it emits before the blowpipe.
The metal is generally prepared from arsenious acid, , by mixing it with its own weight of charcoal, placing the mixture in a well-covered crucible, and subjecting the whole to heat, when the metal set free by the charcoal rises, and condenses in the upper part or cover of the crucible. Metallic arsenic is very brittle, can easily be reduced to powder by hammering, or even pounding in a mortar; and when a freshly cut surface is examined, it presents a brilliant dark steel-gray lustre, which, however, readily tarnishes on exposure to the air. The metal, as such, is not considered poisonous, but when introduced into the animal system, it is there faintly acted upon by the juices, and in part dissolved, at the same time, exhibiting poisonous properties. When heated in the open air, it burns with a peculiar bluish flame, and emits a characteristic alliaceous odour. The only use to which the metal arsenic is applied in the arts is in the manufacture of leaden shot of the various sizes, when its presence in small quantity in the lead renders the latter much more brittle than it ordinarily is. Of all the compounds of arsenic the most important is the one already alluded to—namely, arsenious acid, which is an oxide of arsenic. With sulphur, arsenic forms two important compounds: Realgar, , a red, transparent, and brittle substance, which is employed in the manufacture of the signal-light called White Indian Fire; and Orpiment, , or King's Yellow, a cheap pigment of a yellow colour. With hydrogen, arsenic forms arseniuretted hydrogen, , a very poisonous gas, and one which has been fatal to several chemists.
ARSENIOUS ACID is the arsenical compound most familiarly known. It is obtained principally during the roasting of the arsenical nickel ores in Germany in furnaces communicating with flues. When the arsenic of the ore burns, it passes into the condition of arsenious acid, , and rising as vapour into the somewhat cool flue, is there deposited as a grayish powder, known by the names of Smelting-house Smoke, Flowers of Arsenic, Poison-flour, or Rough Arsenious Acid. In this condition, the arsenious acid is contaminated with some impurities, from which it may be separated by introducing the gray powder into an egg-shaped vessel, and applying heat at the lower end, when the arsenious acid rises in vapour, and condenses in the cool end as a transparent glassy or vitreous substance. Ordinary arsenious acid of the shops (which is what is popularly known as arsenic) is a white crystalline powder, which feels decidedly gritty, like fine sand, when placed between the teeth, and has no well-marked taste. It is very heavy, so much so as at once to be noticeable when a paper or bottle containing it is lifted by the hand. It is soluble in about 10 parts of boiling water, or 100 parts of cold water. As ordinarily sold in quantities under 10 lb. in weight, the arsenious acid is required by law to be coloured with of its weight of indigo, or of its weight of soot; the object of the admixture being to render any liquid to which the arsenious acid might be added, with a murderous intent, of a black or bluish-black hue, and thus indicate the presence of something unusual. In packages of 10 lb. and upwards, arsenious acid is allowed to be sold in the pure white crystalline form without coloration. When placed in a spoon, or other vessel, and heated, the arsenious acid volatilises, and condenses in crystals on any cool vessel held above. Again, when arsenious acid is placed on a red-hot cinder, the strong alliaceous odour characteristic of arsenic is given off. When thrown upon water, instead of at once descending through the water like sand, arsenious acid, notwithstanding its great density (specific gravity 3.70), partially floats on the surface, as wheat-flour does; and that portion which sinks in the water rolls itself into little round pellets, which are wetted only on the outside, and contain much dry arsenious acid within. The solution of arsenious acid in water is recognised by three tests:
(1) Hydrosulphuric acid and hydrochloric acid produce a yellow precipitate of sulphide of arsenic, , soluble in ammonia.
(2) Ammonio-sulphate of copper, an apple-green precipitate of arsenite of copper, .
(3) Ammonio-nitrate of silver, a yellow precipitate of arsenite of silver, .
In many cases, arsenious acid is used as a means of destroying animal life, but, happily, the processes for the detection of the poison in organic mixtures and in the animal tissues are unerring and trustworthy.
For the isolation and recognition of arsenious acid in organic mixtures, such as the contents of a stomach, the method generally pursued is called Reinsch's process, from the name of its discoverer. The manner of its application is to treat the organic mixture with water sufficient to render it thin, then add hydrochloric acid to the extent of one-eighth of the volume of the liquid; apply heat, and when the whole has been raised to near the boiling-point, introduce clean, newly burnished pieces of copper in the form of wire, gauze, or foil. If arsenious acid be present in the mixture, a steel-gray coating of metallic arsenic will form on the surface of the copper. This apparent tarnishing of the copper may take place when no arsenious acid is in the mixture, and may be produced by salts of mercury, antimony, &c., as well as by sulphur compounds, and even occasionally by fatty matters. To distinguish between the coating formed by arsenious acid and that produced by other substances, the copper is taken out of the mixture, washed with water, to remove acid; immersed in ether, to dissolve off any adherent fatty matter; dried between folds of blotting-paper; introduced into the lower end of a dry glass test-tube, and there cautiously heated. The metallic arsenic, As, is driven off by the heat from the surface of the copper, rises in vapour into the upper portions of the test-tube; there meets the oxygen of the air, with which it combines, forming arsenious acid, , and thereafter deposits itself on the inner surface of the cool part of the tube in little glistening crystals. On allowing the tube to cool, adding water thereto, and applying heat, the water dissolves the crystals of arsenious acid, yielding a solution, to separate portions of which the liquid tests mentioned above may be successfully applied.
Arsenious acid forms compounds (salts) with alkalis and other bases, which are called arsenites. Some of these are employed in commerce and medicine. Arsenious acid, boiled with a solution of potash, or carbonate of potash, forms an arsenite of potash, used in medicine, and known as Fowler's Solution or liquor arsenicalis. Many sheep-dipping mixtures are composed of arsenious acid, soda, sulphur, and soap, which, when used, are dissolved in a large quantity of water, and thus constitute essentially dilute solutions of arsenite of soda. A compound of arsenious acid and the oxide of copper, called the arsenite of copper, or Scheele's Green, is a pigment largely used by painters as a pretty and cheap green paint. The same substance is, or was formerly, extensively employed in the manufacture of common green paper-hangings for the walls of rooms; and it seems certain that rooms covered with paper coated with this green arsenite of copper are detrimental to the health of human beings residing therein, from the readiness with which minute particles of the poisonous pigment are detached from the walls by the slightest friction, are diffused through the room, and ultimately pass into the animal system. Another green pigment is named Schweinfurth Green, and contains arsenious acid, oxide of copper, and acetic acid, being a double arsenite and acetate of copper; it is also called Paris Green, and used as an insecticide.
When taken into the stomach, it is soon absorbed into the blood, acting powerfully in such skin diseases as Psoriasis, Lepra, Eczema (q.v.), &c. As a tonic alterative it holds a high place, and it is much used in ague, remittent fever, and St Vitus's dance. The usual method of administering arsenic is in small doses (from three to five drops) of the liquor arsenicalis, largely diluted with water, twice or thrice in the day.
When given in the doses above mentioned, for eight or ten days, symptoms of poisoning begin to appear, the skin becoming hot, the pulse quick, the eyelids hot and itchy; the tongue has a silvery appearance; the throat is dry and sore, the gums swollen and tender; and if the treatment is persisted in, salivation ensues, and then come nausea, vomiting, diarrhea, nervous depression, and faintness. The quantity necessary to destroy life, of course, varies, but under circumstances favourable for its operation the fatal dose for an adult is from two to three grains. Death from a poisonous dose of arsenic may occur in a few hours, or after the lapse of days. Arsenic has been used frequently as a slow poison, the symptoms being attributed to inflammation of the bowels from natural causes. Fortunately, in most cases its detection is easy.
In some countries, especially in Austria (though the practice is not unknown in England), arsenic is given to cattle and horses to render the skin bright and glossy. In Styria, arsenic is taken by the peasant girls to increase their personal attractions; and it has been definitely ascertained that over a considerable area in the south-west of Austria, including Styria, Carinthia, Salzburg, Tyrol, Lower Austria, and the Erzgebirge, arsenic eating is largely practised by men, who nevertheless attain a healthy old age. Arsenic eaters, who generally begin the use of the drug secretly, say that it improves the complexion, increases the digestive powers, and so strengthens the respiratory organs as to enable the bearers of heavy burdens to climb mountains with ease. At first a dose may be taken once a week, afterwards daily; and there are authenticated cases of men who consume six grains—enough to poison three men—at one dose without inconvenience. Once the habit is established, it is impossible to give up arsenic eating. Terrible heart-gnawings following any attempt gradually to stop the practice; and sudden cessation causes death. That arsenic can be taken habitually for any length of time with impunity was formerly regarded as a physiological impossibility; and yet the fact is established on unquestionable evidence.
No effective chemical antidote for arsenic has yet been discovered. In case of an overdose, or of intentional poisoning, the following treatment is recommended: Evacuate the stomach by the stomach-pump, using lime-water; administer large draughts of tepid sugar and water, chalk and water, or lime-water; avoid the use of alkalies, but administer charcoal and hydrated sesquioxide of iron; bleed freely; take a tepid bath, and use narcotics. If the fatal symptoms be averted, let the patient for a long time subsist wholly on farinaceous food, milk, and demulcents.