_Tests._—The presence of a salt of lead in solution may be thus ascertained:—1. On passing sulphuretted hydrogen through it, or on adding a few drops of sulphide of ammonium, a black precipitate is given. 2. A white precipitate results from the use of liquor potassæ or liquor ammoniæ. 3. Dilute sulphuric acid gives a similar precipitate, which is insoluble in nitric acid. 4. Iodide of potassium affords a bright yellow deposit (iodide of lead). CHRONIC LEAD POISONING.—The chronic and insidious effects produced by lead upon the constitution are deserving of careful attention. Water impregnated with this metal in its passage through lead pipes or cisterns, acquires poisonous properties. Lead-pigments are sometimes improperly used to color cheese, lozenges, snuff, &c. The endemic colic of Devonshire was due to the absorption of lead contained in cider, which had been made in leaden vessels; and in the wine district of Poictou attacks of colic were so common, from the impregnation of wine with this metal, that we still speak of “colica Pictonum.” The pernicious influence of lead is manifested among those engaged in the manufacture or use of lead compounds, especially painters, lead smelters, plumbers, color grinders, shot manufacturers, workers in sugar of lead, potters, compositors, enamellers of cards, &c. These artisans should be advised to prevent disease by great cleanliness, by avoiding intoxicating liquors, and by drinking freely of sulphuric acid lemonade. The substitution of moist for dry grinding has proved useful. The most prominent _symptoms_ of chronic poisoning by lead are as follows: A blue line around the gums, and the liability of the latter to bleed from any slight cause; emaciation, a pallid tint of the complexion, poorness of blood, and a feeble quick pulse; obstinate constipation, with attacks of colic relieved by pressure; diminution of the renal secretion and rheumatic pains; afterwards comes weakness of the hands, wrists, and arms, ending in paralysis of the extensors, or “dropped wrists,” creeping up the arms. The _treatment_ of these cases must consist in the first instance in the use of purgatives; none being better than sulphate of magnesia with the dilute sulphuric acid. But the remedy of all others is the iodide of potassium, in five or ten grain doses thrice daily; this agent acting most beneficially when employed in conjunction with galvanism to the paralysed limbs. CHAPTER XIX. SALTS OF COPPER.