_Tests._—Solutions of the sulphate and nitrate of copper are blue; the chloride is green. The salts of copper may be thus identified: 1. A polished knife or needle introduced into the solution is soon covered with a coating of copper. 2. Ammonia produces with a salt of copper a bluish precipitate, readily soluble in excess of ammonia, and forming a splendid blue solution. 3. Ferrocyanide of potassium gives a claret-colored gelatinous precipitate, if the copper be abundant; otherwise the deposit is of a light brown. 4. Sulphuretted hydrogen gas yields a deep-brown precipitate. 5. A few drops of the copper solution are to be placed on platinum foil, and slightly acidulated; on touching the foil, through the solution, with a strip of zinc, metallic copper is deposited on the patinum. CHAPTER XX. SPECIFIC VEGETABLE IRRITANTS. LABURNUM (_Cytisus laburnum_).—Every portion of this plant is poisonous. The seeds are frequently eaten by children, and give rise to vomiting and purging, with dilatation of the pupils, rigors, rigid limbs, &c. _Œnanthe crocata_, _Phellandrinum aquaticum_, _Æthusa Cynapium_, _&c._, strictly speaking, belong to this group. BLACK HELLEBORE (_Helleborus niger_) or _Christmas Rose_, grows in shady woods, and bears a large flower in January. The leaves and root when eaten give rise to abdominal pain, vomiting and purging, vertigo, cold sweats, and collapse, resembling that of malignant cholera. An infusion of this plant is sometimes administered by quacks to destroy intestinal worms. It has proved fatal to children under these circumstances. Several other substances variously grouped for the sake of convenience should come under this heading. CHAPTER XXI. SPECIFIC ANIMAL IRRITANTS. CANTHARIDES (_Spanish Flies_). This poison is well known, and is usually administered in the form of powder or tincture. Of the former, twenty-four grains have destroyed life; of the latter, one ounce. This poison has been employed as an aphrodisiac and to induce abortion, by persons ignorant of its dangerous effects. This is, perhaps, the most frequent cause of poisoning by cantharides. Applied externally it has proved fatal, as in the case of a girl affected with scabies, who anointed the whole of her body with cantharides ointment in mistake for that of sulphur. She died in five days, after suffering from the symptoms of poisoning by cantharides. It produces an acrid taste, vomiting, purging, burning heat in the stomach, pain in the loins, severe strangury, bloody urine, and priapism. Then there is faintness with giddiness, the limbs become rigid, and delirium with convulsions precede death. Sometimes the matters ejected from the stomach or passed in the stools contain shining golden or green particles, the remains of the wing cases of the beetles, which constitute the drug, readily seen with a lens, or even with the naked eye.