Origin

Nitre is at present obtained almost exclusively from the East indies, where it is extracted from the soil occasionally overflowed by the Ganges, and enriched by the animal and vegetable matters washed down by that stream from the vast region which it drains. This earth is impregnated with the nitrates of potassa and lime, and, on being lixiviated in connection with wood ashes, yields a solution chiefly of the former salt; the lime of the nitrate of lime being replaced, in the process, by the potassa of the ashes. The nitre is then obtained from the solution by evaporation and crystallization. As imported, however, it is very impure, containing, with other foreign substances, a considerable proportion of common salt, from which it must be freed by a carefully conducted process of solution and crystallization before it is fit for use.

The salt may also be artificially prepared by exposing to the air, for a long time, a mixture of animal and vegetable matters, with more or less lime in the shape of refuse mortar, etc., and treating the mass, which now contains nitrates of potassa and lime, by a process analogous to that employed with the earth of the Ganges. (See U. S. Dispensatory.)

Properties

Nitre crystallizes in long, white, semitransparent, striated, six-sided prisms, with dihedral summits. it is inodorous, of a sharp, saline, somewhat cooling taste, very soluble in water hot or cold, but more so in the former, and insoluble in pure alcohol. it contains no water of crystallization, and is permanent in the air. Thrown into the fire, it decrepitates, in consequence of the rapid evaporation of water contained mechanically between the laminae of its crystals. At a high temperature it melts; and, at a still higher, gives out oxygen, and is resolved into hyponitrite of potassa, which, with a further increase of the heat, is in its turn decomposed, with the escape of a mixture of oxygen, nitric oxide, etc. Nitre may be known to contain potassa by affording a yellow precipitate with chloride of platinum, and nitric acid, by causing live coals to burn more briskly when thrown upon them, and by yielding whitish or reddish fumes when decomposed by sulphuric acid.

1. Effects On The System

In small doses, repeated at short intervals, as ten grains, for example, every two hours, nitre diminishes the frequency and force of the pulse, and the temperature of the body, and at the same time very often acts as a diuretic or diaphoretic, evincing generally a preferable direction to the kidneys, but sometimes acting on the skin, especially when administered with warm drinks, or in conjunction with other diaphoretic medicines. When taken in powder, it sometimes occasions a feeling of coolness in the stomach, and a general chilliness, probably through the absorption of free heat during its solution. in larger doses it produces these effects more decidedly. Mr. Alexander found a drachm of it, on several occasions, to reduce the frequency of the pulse, within a few minutes, from 70 to 60. (Essays, p. 105.) in quantities increasing gradually from one to five drachms daily, in divided doses, continued for somewhat more than a week, it was observed by F. Loftier, several times, towards the close of the period, to diminish the pulse to 20 beats in the minute. Along with this reduction of the circulation, there were feelings of general weakness, mental depression, and drowsiness. (Am. Journ. of Med. Sci., xviii. 204.) From quantities varying from two scruples to one or two drachms, given three times a day, dissolved in a large proportion of barley-water, and continued for a week or longer, Dr. John Cargill generally observed no inconvenience; but occasionally, in persons of nervous temperament, noticed as the result of its influence, general tremblings, difficulty of speech, giddiness, abnormal sounds in the ears, partial forgetfulness, and an extraordinary debility of the limbs, especially the lower, which sometimes seemed to the patient as though paralyzed. (Lond. Med. Gaz., Oct. 1851, p. 640.) in still larger doses than those mentioned, if given dissolved in a very large quantity of water, nitre seems to act mainly as a purgative. M Devilliers states, as the result of his own experience, that from half an ounce to an ounce of it may be given as a purgative, not only without inconvenience, but often with advantage (Dict. des Sci. Med., xxxvi. 138); and the same fact is asserted by many other writers, among whom are Merat and De Lens, who declare that their own experience is confirmatory of that of M. Devilliers. (Dict. de Mat. Med., v. 479.) When long continued, even in moderate doses, nitre is said to produce chronic irritation of the stomach, impair digestion, and debilitate the system generally; and by some it is thought to deprave the blood, and favour the generation of a typhoid condition. Nitre escapes rapidly from the circulation, and chiefly, though not exlusively, by the urine. in a case in which 270 grains of the salt were taken daily, not more than 158.7 grains were passed during the same time by the kidneys. (Guy's Hosp. Rep., 1863, p. 177)

Poisonous Effects

Numerous instances of death from large quantities of nitre, taken by mistake for some other saline substance, are on record; and until recently it has generally been considered as essentially poisonous in excessive doses. But experience has, within a few years, abundantly shown, that its noxious effects are ascribable to the manner in which it is taken, rather than to any necessarily poisonous quality. it is when swallowed in powder, or concentrated solution, that it acts thus injuriously. From the doses of two scruples up to two drachms, previously mentioned as having been given by Dr. Cargill with entire safety, when dissolved in not less than half a pint of barley-water for each dose, the same writer observed, if they were exhibited in concentrated solution, very unpleasant effects, such as intense griping pain, great thirst, anxiety, pallor of the face, cold perspiration, and a reduced pulse. The symptoms, however, disappeared under free dilution. (Lond. Med. Gaz., ut supra.) One ounce has often acted as a violent poison, and in several instances has caused death. Any quantity above three or four drachms may be considered poisonous, if taken in powder, or dissolved in only a small quantity of water. The symptoms usually produced, though not all ordinarily in the same case, are heat and severe pain in the stomach, vomiting and purging, bloody discharges, griping pains in the bowels, feeble pulse, cold extremities, great muscular debility, faintness, insensibility, and sometimes convulsive movements before death. Vomiting does not always occur, and, when it happens early, is rather favourable than otherwise; as it may evacuate the poison. Dr. Christison knew a case, in which an ounce was taken without any other unpleasant symptom than vomiting, which took place in fifteen minutes. Sometimes death happens with little other obvious effect than great prostration. A case was recorded by Dr. John W. Snowden, of N. Jersey, in which a man, having taken three ounces and a half of nitre at one dose, at the end of five hours suddenly fell from his chair and died, with no other preceding phenomena than a slight sense of heat in the epigastrium, thirst, and three operations on his bowels. (N. Jersey Med. Reporter viii. 117) in the fatal cases, death has generally occurred within a period varying from two to five hours. Signs of inflammation of the mucous membrane of the stomach, sometimes attended with gangrene, have generally been noticed upon postmortem examination. in a case which came under the notice of Dr. Geoghegan, of Dublin, in which death resulted in two hours from an ounce or an ounce and a half of the salt, the membrane was found much inflamed, but none of the salt could be detected in the stomach. (Taylor on Poisons.) The rapidity with which the fatal effect is produced is much greater than is generally the case from the most violent corrosive poisons, as arsenic, corrosive sublimate, or even sulphuric acid. inflammation of the stomach, therefore, is probably not the main cause of death. Besides, in the case of Dr. Snowden, already referred to, there were no symptoms of gastric inflammation. in that of Dr. Geoghegan, in which death occurred in two hours, and none of the salt was found in the stomach, the poison must have been rapidly absorbed. Hence it may be inferred, that death occurs in consequence of the entrance of the poison into the circulation. Of its mode of operating when there I shall treat immediately.