Saltpetre, or Nitre, a concrete saline matter, the nature and properties of which have al-y been stated, vol. iii. p. 268. - Without entering into the particulars relative to the most economical method of manufacturing this Useful salt, we shall briefly point out the requisites to its generation : 1. Animal and vegetable matters intimately blended and exposed to a moderate temperature ; 2. Such a degree of moisture, especially with urine in which nettles, thistles, artichokes, and similar plants, have been boiled, as will promote corruption, without inducing actual putrefaction ; 3. The earth employed ought to be of a loose and porous texture ; for instance, the clay of old mud-walls, or a due admixture of chalk, quick-lime, etc.; 4. A sufficient length of time, namely, from six to twelve months, and upwards ; as, otherwise, a very small quantity of nitre will be obtained by crystallizing the ley made of the saltpetre-rot, or the earth after it has been exposed to the influence of the atmosphere in triangular beds, under proper sheds. - The manner of extracting such earth is exceedingly simple and easy, by means of tubs with numerous holes at the bottom, lined with straw, over which the mould is placed in alternate strata ; with a little pot-ash either strewed between them, or dissolved in the boiling water, which is gradually poured over the solid materials : there is nothing farther required, than proper wooden pails with transverse sticks, in which the liquor, after evaporating it to a proper consistence, is poured and suffered to stand for several days, slightly covered, till the crystals are formed. The remaining fluid, or mother-ley, is again to be boiled, and poured over a new portion of the earth taken from an old nitre-bed, so that none of it may be wasted. - Such is the process that is generally followed in the most profitable saltpetre-works of Germany.
Though nitre affords one of the most extensively useful articles in the arts and manufactures (see Aqua-Fortis), as well as in medicine, yet this powerful salt, when inadvertently taken in too large quantities, is one of the most fatal poisons. There are several attested cases on record, in which from half to a whole ounce of saltpetre has occasioned violent vomiting, convulsions, swelling, and other painful symptoms in persons who, by mistake, had swallowed it in a dissolved state, instead of Glauber's, or similar salts. - The most proper antidotes, in such distressing situations, will be a scruple or half a drain of ipecacuanha with a tea-cupful of sweet-oil, and a large quantity of warm water to be drunk after it, to promote its operation as an emetic. Where this remedy cannot be procured on the spur of the occasion, it will be necessary to make use of copious and frequent draughts of mucilaginous decoctions of marsh-mallows, pearl-barley, salep, or arrow-root powder, sago, tapioca, etc. after which a gentle opiate will afford the desired relief. In all instances of this nature, however, it will be advisable immediately to resort to medical advice.