the product is pure nitrate of silver. Dissolve by heating with a small quantity of water; on the solution cooling, or on evaporation, crystals of nitrate of silver are obtained. The solution of pure or refined silver (Argentum Purificatum, B. P.) in nitric acid, evaporation, &c., is the process of the British Pharmacopoeia for the preparation of the nitrate (Argenti Nitras, B. P.). The salt fused and poured into proper moulds, yields the sticks or rods commonly termed lunar caustic. (The alchemists called silver Diana or Luna, from its supposed mysterious connexion with the moon.) The specimen of nitrate of silver obtained in the above reaction, dissolved in water, will be found useful as an analytical reagent. Silver salts are decomposed when in contact with organic matter, especially in the presence of light or heat, a black insoluble compound being formed. Hence the use of the nitrate in the manufacture of indelible ink for marking linen, &c. Fifth Synthetical Reaction.-To a few drops of solution of nitrate of silver add solution of potash or soda or lime-water; a black precipitate of oxide of silver (Ag2O) occurs. The Argenti Oxidum, B. P., is thus made, lime-water being the precipitant employed. (b) Reactions having Analytical Interest. First Analytical Reaction.—To a solution of a silver salt add hydrochloric acid or other soluble chloride; a white curdy pre cipitate of chloride of silver falls. the precipitate does not dissolve. Add nitric acid and boil; Pour off the acid and add solution of ammonia; the precipitate dissolves. Neutralize the ammoniacal solution by an acid; the chloride of silver is reprecipitated. This is the most characteristic test for silver. The precipitated chloride is also soluble in solutions of hyposulphite of sodium or cyanide of potassium-facts of considerable importance in photographic operations. Other analytical reagents than the above are occasionally useful.--Sulphuretted hydrogen, or sulphydrate of ammonium, give a black precipitate, sulphide of silver (Ag,S), insoluble in alkalies. Solutions of potash or soda give a brown precipitate, oxide of silver (Ag2O), converted into a fulminating compound by prolonged contact with ammonia.-Phosphate of sodium gives a pale yellow precipitate, phosphate of silver (Ag,PO1), soluble in nitric acid and in ammonia.- -Arseniate of ammonium gives a chocolate-coloured precipitate, arseniate of silver (Ag ̧AsO1), already noticed in connexion with arsenic acid.-Iodide or bromide of potassium gives a yellowish-white precipitate, iodide or bromide of silver (AgI or AgBr), insoluble in acids and only slightly soluble in ammonia.- -Cyanide of potassium gives a white precipitate, cyanide of silver (AgCy), soluble in excess, sparingly soluble in ammonia, insoluble in dilute nitric acid, soluble in boiling concentrated nitric acid.Yellow chromate of potassium (K,CrO4) gives a red precipitate, chromate of silver (Ag, Cro) -Red chromate of potassium also gives a red precipitate, acid chromate of silver (Ag,Cro,,CrO,).—Many organic acids also yield insoluble salts of silver. Several metals displace silver from solution, mercury forming in this way a crystalline compound known as the silver tree, or Arbor Dianæ.In the blowpipe flame, silver salts, placed on charcoal with a little carbonate of sodium, yield bright globules of metal, accompanied by no incrustation as in the corresponding reaction with lead salts. Antidotes.-Solution of common salt, sal-ammoniac, or any other inert chloride should obviously be administered where large doses of nitrate of silver have been swallowed. A quantity of sea-water or brine would convert the silver into insoluble chloride, and at the same time produce vomiting. APPLICATION OF THE FOREGOING REACTIONS TO THE ANALYSIS OF AN AQUEOUS SOLUTION OF SALTS OF ONE OF THE METALS COPPER, Add hydrochloric acid: Silver is indicated by a white curdy precipitate, soluble in ammonia. Mercurous salts also by a white precipitate, turned black by ammonia. Lead by a white precipitate, insoluble in ammonia. Confirm by boiling another portion of the hydrochloric precipitate in water; it dissolves. If hydrochloric acid gives no precipitate, silver and mercurous salts are absent. Lead can only be present in very small quantity. Mercuric salts may be present. Copper may be present. Divide the liquid into three portions, and apply a direct test for each metal. Lead is best detected by the sulphuric test; the tube being set aside for a time if the precipitate does not appear at once. Mercury is best detected by the copper test. If present, it occurs as mercuric salt. Copper betrays itself by the blue colour of the liquid under examination. Confirm by the ammonia test. If the above reactions are not thoroughly conclusive, confirmatory evidence should be obtained by the application of some of the other reagents for copper, mercury, lead, or silver. APPLICATION OF THE FOREGOING REACTIONS TO THE ANALYSIS OF AN COPPER, MERCURY (EITHER MERCUROUS OR MERCURIC SALT, OR Add hydrochloric acid, filter, and wash the precipitate with a small quantity of cold water. The student should now be able to analyze aqueous solutions containing any common metal. If his operations have hitherto only included One metal of the first group (p. 51), One metal of the second group (p. 63), he should proceed to examine solutions containing a salt of one metal of any of the groups (see next page). If more time has enabled the student to analyze solutions containing One or more metals of the first group (p. 51), One or more metals of the second group (p. 63), One or more metals of the first four groups (p. 106), he should complete this division of study by examining aqueous solutions containing salts of one or more of the metals of any or all of the groups (see next page but one). APPLICATION OF THE FOREGOING ANALYTICAL REACTIONS TO THE ANALYSIS OF AN AQUEOUS SOLUTION OF Add hydrochloric acid. Ppt. If HCl gave no pre- Hg obtained here Sb is also precipi- adding more HCl; the Hg, Pb, If HCl gave no precipitate the metal is still in the liquid; pass H2S through it. If HS gave no precipitate the metal is still in the |