"2. Iron or copper; and then it has an astringent and disagreeable taste, like ink. "3. Sulphur, or sulphurous vapours; and then it has a very nauseous taste, like a stale and rotten egg. "4. Vitriolic, or marine, or alkaline salt. "5. Earth," _Fixed Air._ "To ascertain the fixed air, the taste is partly sufficient; but pour into the water some tincture of turnsol, and the water will become more or less red, in proportion to the quantity of fixed air it contains." _Iron._ "The iron may be known by means of the galnut and phlogisticated alkali; the galnut put into feruginous water, will change its colour to purple, or violet, or black; and the phlogisticated alkali will produce immediately Prussian blue." _Copper._ "Copper may be ascertained by means of the phlogisticated alkali or volatile alkali; the first turns the water to a brown red, and the second to a blue. The last mode is the surest, because the volatile alkali precipitates copper only, and not iron." _Sulphur._ "Sulphur and sulphurous vapours may be known by pouring, 1. nitrous acid into the water; if a yellowish or whitish sediment be formed by it, there is sulphur, and at the same time a sulphurous odour will be exhaled and evaporate. 2. By pouring some drops of a solution of corrosive sublimate; if it occasion a white sediment, the water contains only vapours of liver of sulphur; and if the sediment be black, the water contains sulphur only." _Vitriolic Salt._ "Water may contain vitriolic salts; that is salts resulting from the combination of the vitriolic acid with calcareous earth, iron, copper, or with an alkali. The vitriolic acid may be ascertained by pouring some drops of a solution of heavy earth; for then a sandy sediment will be formed, which will settle slowly at the bottom of the vessel." _Marine Salt._ "Water may contain marine salt, which may be ascertained by pouring into it some drops of a solution of silver; a white sediment will immediately be formed of the consistency of curdled milk, which will at last turn to a dark violet colour." _Fixed Alkali._ "Water may contain fixed alkali, which may be ascertained by pouring into it some drops of a solution of corrosive sublimate; when a reddish sediment will be formed." _Calcareous Earth._ "Water may contain calcareous earth and magnesia. Some drops of acid of sugar poured into the water, will precipitate the calcareous earth in whitish clouds, which will at length subside and afford a white sediment. A few drops of a solution of corrosive sublimate, will produce a reddish sediment, but very gradually, if the water contain magnesia. "Note. To make these experiments with readiness and certainty, the water to be analysed should be reduced one half by boiling it, except in the case of the fixed air, which would evaporate in the boiling."