[_Inks formed of solutions _and washed with solutions of the following salts_, of_ _become_ Muriate of antimony, tincture of galls, yellow. Green vitriol, tincture of galls, black. Nitrate of cobalt, oxalic acid, blue. Subacetate of lead, hydriodic acid, yellow. Arseniate of potash, nitrate of copper, green. Nitrate of copper, prussiate of potash, brown. Solution of gold, muriate of tin, purple. Perchloride of mercury, hydrochlorate of tin, black.] DIVING-BELL. The first divers learned their art by early and adventurous experience, in trying to continue under water as long as possible without breathing; and, indeed, it must be allowed that some of them carried it to very great perfection. This art, however, excites little surprise; for, like running, throwing, and other bodily dexterities, it requires only practice; but it is certain that those nations called by us uncultivated and savage excel in it the Europeans[274], who, through refinement and luxury, have become more delicate, and less fit for such laborious exercises. In remote ages, divers were kept in ships to assist in raising anchors[275], and goods thrown overboard in times of danger[276]; and, by the laws of the Rhodians, they were allowed a share of the wreck, proportioned to the depth to which they had gone in search of it[277]. In war, they were often employed to destroy the works and ships of the enemy. When Alexander was besieging Tyre, divers swam off from the city, under water, to a great distance, and with long hooks tore to pieces the mole with which the besiegers were endeavouring to block up the harbour[278]. The pearls of the Greek and Roman ladies were fished up by divers at the great hazard of their lives; and by the like means are procured at present those which are purchased as ornaments by our fair. I do not know whether observations have ever been collected respecting the time that divers can continue under water. Anatomists once believed that persons in whom the oval opening of the heart (_foramen ovale_) was not closed up, could live longer than others without breathing, and could therefore be expert divers. Haller[279], however, and others, have controverted this opinion; as people who had that opening have been soon suffocated, and as animals which have it not can live a long time under water: besides, when that opening is perceptible in grown persons, it is so small as not to be sufficient for that purpose, especially as the _ductus arteriosus_ is scarcely ever found open.