| In the Frith of Forth, - - - 312 " I At Ritzebuttle, - - - 312 " At Apemalle, in Sleswick, - 216 " At Kiel, in Holstein, - - - 200 " Baltic Sea At Doberan, in Mecklenbergh, - - 168 " At Travemunse, .... 167 " At Zoppot, in Mecklenbergh, - - 76 " At Carshamm, - - - - - 66 " The average quantity of saline matter in sea-water is 3| per cent., and its specific gravity about 1.0274. The composition of sea-water differs also in different locali- ties. Iodine has been found in the Mediterranean sea. Action of Water on Lead. When lead is exposed to atmospheric air, the oxygen of the air combining with it, forms an oxide, while, at the same time the carbonic acid of the air, unites with it forming a thin white crust, which is the carbonate of lead. This formation is accelerated by moisture, and by the presence of an unusual quantity of carbonic acid in the atmosphere. The same process goes on with still * It is now well ascertained, that carbonate of lime has only a slight action on soap, and cannot in the proportions in which it exists in potable waters decompose it, by giving rise to the formation of a clotty precipitate, as we observe with sulphate and nitrate of lime, and chloride of calcium — and this is probably owing to the excess of carbonic acid which prevents the re-action of the calcareous carbonate on the oleate and stearate of soda of the soap. 143 greater rapidity in pure running water. But if water be deprived of all its gases by ebullition, and excluded from contact with the air, the lead will not be acted upon If water, however, be exposed to the air, although all the gases have been expelled, a white powder will soon form around the lead, till, in the course of a few days, there is formed a large quantity of white, pearly scales, which partly float in the water, but are chiefly deposited on the bottom of the vessel. In 12 ounces of distilled water, contained in a shallow glass basin, loosely covered to exclude the dust, twelve brightly polished lead rods weighing 340 grains, will lose 2J grains in 8 days, and the lead will show evident marks of corrosion ; and this action will go on as long as the water is exposed to the air. While these changes are going on, a small quantity of lead will be dissolved, as may be shown by carefully filtering the water acidulating with a drop or two of nitric acid, and evaporating to dryness. Sulphuretted hydro- gen is also a good test, occasioning, where lead is present, first a brown color, and subsequently a black precipitate. Christison has proved that the lead which is dis- solved, is in the form of the carbonate, and hydrate of the oxide, or, oxide of lead, carbonic acid and water. The fact is then sufficiently established, that distilled water has the property of dissolving lead — Does the same hold true in relation to waters in ordinary use 1 In the year 1809, it was first announced by Guyton Morveau, that the salts which are held in solution by some natural waters, destroy their property of acting on lead, and that of these modifying circumstances none are more remarkable in their action than the neutral salts. Dr. Christison has pursued this investigation with great suc- cess, and has proved that this preservative power exists in the case of sulphates, muriates, carbonates, hydriodates, phosphates, nitrates, acetates, tartrates, arsen- ates, &c. These salts, however, do not possess an equally protective influence, the carbonates and sulphates being most, the chlorides the least energetic of those saline substances commonly met with in waters. As a general rule, it appears that those whose acid forms with the lead a soluble salt of lead, are the least energetic ; while those whose acid forms an insoluble salt of lead, are most energetic. The variable quantity of salts necessary to prevent the action of water on lead, may be seen from the following results obtained by actual experiment. Of acetate of soda a 100th part of the water is a prese: Of arseniate of soda 12,000th " Of phosphate of soda 30,000th " Of hydriodate of potash 30,000th " Of muriate of soda 2,000th Of sulphate of lime 4,000th " Of nitrate of potash 100th rvative. 144 The sulphates of soda, magnesia, lime, and the triple sulphate of alumina and potash, possess about the same preservative power ; which appears to depend on the acid, not on the base of the salt. The general results of Dr. Christison's inves- tigations, appear to be, that neutral salts in various,