noes 
Ane 

34 | GEOGNOSY. [Book IL 
certain circumstances, be held in solution in water. Moreover, unless. 
there be some counteracting process to remove these mineral 
ingredients, the ocean water ought to be growing, insensibly perhaps, 
salter, for the supply of saline matter from the land is incessant. ° 
Tt has been ascertained indeed, with some approach to certainty, that 
the salinity of the Baltic and Mediterranean 1s gradually increasing.’ 
The average proportion of saline constituents in the water of the 
ereat oceans far from land is about three and a half parts in every 
hundred of water. But in enclosed seas, receiving much fresh water, 
it is greatly reduced, while in those where evaporation predominates 
it is correspondingly augmented. Thus the Baltic water contains 
from one-seventh to nearly a half of the ordinary proportion in 
ocean water, while the Mediterranean contains sometimes one-sixth 
more than that proportion. Forchhammer has shown the presence 
of the following twenty-seven elements in sea-water: oxygen, 
hydrogen, chlorine, bromine, iodine, fluorine, sulphur, phosphorus, 
nitrogen, carbon, silicon, boron, silver, copper, lead, zine, cobalt, 
nickel, iron, manganese, aluminium, magnesium, calcium, strontium, 
barium, sodium, and potassium.” To these may be added arsenic, 
lithium, caesium, rubidium, gold, and probably still other elements. 
A variable proportion of organic matter is always present. The 
chief mineral constituents occur in the following average ratios :— 
Percentage, 
Sodium chloride (common salt) . . . . . 7%5°786 
Magnesium ‘chloride’.* 2° vo Se 
Potassium chloride . . oi S= Ge. SUE, Sees 
Calcium sulphate (gypsum) gi 2. ote ery 
Magnesium sulphate (Epsom salts) . . . . 5°597 
Sodium ‘bromide 47/0 07.9" .P es, el 

100-000 
Total percentage of salts in sea-water . . 3°527 
In addition to its salts sea-water always contains dissolved atmo- 
spheric gases. From the researches conducted during the voyage of — 
the Bonité in the Atlantic and Indian Oceans it was estimated — 
that the gases in 100 volumes of sea-water ranged from 1°85 to 3:04, 
or from two to three per cent. From observations made during 
the Porcupme cruise of 1868 it was inferred that the proportion of — 
oxygen was greatest (25°1 per cent.) in the surface water, and least 
(19°5) in the bottom water, while that of carbonic acid was least at 
the top (20°7) and greatest (27:9) at the bottom, and that the action 
of the waves was partially to eliminate the latter gas and to increase 
the amount of oxygen. More recently, however, during the voyage 
of the Challenger, Mr. J. Y. Buchanan ascertained that’ the 
proportion of carbonic acid was always nearly the same for similar 
* Paul, in Watis’s Dictionary of Chemistry, v. p. 1020. 
* Forchhammer, Phil. Trans. ely. p. 205. According to Thorpe and Morton (Chem. — 
Soc, Journ. xxiv, p. 506), the water of the Irish Sea contains in winter rather more salts — 
than in summer, owing to diminished evaporation and a less supply of fresh water. — 
These authors state that in 1000 grammes of the summer water of the Irish Sea they — 
found 0°04754 gramme of carbonate of lime, 0:00503 of ferrous carbonate and traces of 
silicic acid. 
