On the specific gravity and temperatures of sea-waters, in different parts of the ocean, and in particular seas; with some account of their saline contents

Abstract

After some preliminary remarks upon the labours of others in this department of inquiry, Dr. Marcet proceeds to the immediate objects of his own investigation, which were to ascertain the specific gravity of many specimens of sea-water from different parts, and afterwards to examine their saline contents. The results relating to the first of these objects are prefaced by an account of the mode of taking the specific gravities, and of the instrument by which the water was raised, and of which two plates are annexed. The author then proceeds to the inferences deducible from his experiments, which, for the sake of conciseness, are given in the form of tables; whence it appears that the ocean in the Southern hemisphere is rather more salt than in the Northern, in the proportion of 1029.19 to 1027.57. The mean specific gravity of specimens from various parts of the equator, is 1027.77, and therefore a little exceeds that prevalent in the Northern hemisphere, while it is decidedly less than that of the Southern Ocean. There is no material difference between different east and west longitudes at the equator, nor in the same hemisphere. In general, the salt seems most abundant in the deepest water, and in that furthest from land; the vicinity of ice also diminishes the saltness: if therefore this quality should increase in approaching the pole, it may be considered as militating against the probability of the ocean being extensively frozen in those regions. In general, small inland seas, communicating with the ocean, are less salt than the ocean itself. The waters of the Mediterranean, however, are more saline, and in attempting to account for this circumstance, the author’s attention is directed to the relative densities of water from different depths of the ocean; and though in some cases it appeared lightest at the surface, such a result was generally referable to the vicinity of thawing ice, for, in ordinary circumstances, the density at great depths in no instance exceeded the mean density of the waters of the ocean. In regard, however, to different seas or arms of the ocean, the case is often different, in consequence of local circumstances. At the entrance of the Dardanelles, for instance, the difference between the upper and lower strata is as 1020 to 1028. Dr. Marcet next details some researches upon the congelation of sea-water which takes place at 28°, and when slowly effected, is always attended by the total separation of the salt, which forms a strong brine that is washed away by the neighbouring water. The different specimens of water obtained from the ice in the late Northern Expedition, varied very little in specific gravity; the water was sweet, and in many instances its specific gravity did not exceed that of distilled water.