39 



province of the chemist; but the chemical phase of the latter cont- 

 sists .sorely of routine analyses, and so may concern the theoretic 

 chemist only in sent secondary stage. As an example of the first 

 category we might cite the problems of lime chemistry (Page IC ). 

 Examination of variations in the nitrate content of the sea water 

 per se might illustrate the second category; it is promoted to the 

 truly chem cal category Y;hen the cause and the effect of the varia- 

 tions in the nitrate-concentration come into account. 



As the whole cycle of matter in the sea depends upon the fact 

 that the latter is filled with salt water (a solution not a mere 

 mechanical mixture), it follows that chemical problems are more or 

 less inherent in every phase of sea science. Consequently thG_ 

 reader T/ill find repeated references to various chemical questions 

 in the sections on oceanic biology and on submarine Geology. In the 

 present chapter we wish simply to outline the sorts of chemical 

 problems that center around the nature of sea water, and around the 

 reactions taking place between its various constituents. 



The ?v.ost basic of these, as a part of Oceanography, concerns 

 the processes which cause the extraordinary uniformity in comoosi- 

 tion of the waters in all parts of the sea. The oceans cover .lore 

 than t.YO thirds of the surface of the globe; in depth, temperature, 

 light intensity, and pressure thsy run the whole gamut from v/armth, 

 bright illuminatiov;_ c,'id freedom from any pressure save that of the 

 overlying atmosphere, to icy cold, permanent darkness and the sub- 

 jection to pressures of 400 atmospheres and upwards per square inch. 

 Furthermore the rivers that empty into the sea contribute solutes 

 that only vary from river to river in their composition, but that as 

 a whole differ v;idely from sea water in kind, while organic communi- 

 ties of different sorts withdraw different salts from the solution 

 in different parts of the sea. Nevertheless the relative proportions 

 of the different substances in the solution we name "sea water" are 

 regionally so uniform all over the oceans that it is customary not 

 only to regard sea water as a substance practically constant in its 

 composition, but in practice to employ the concentration of one group 

 of its salts OS a dependable index to the total saltness. 



This conception is not actually correct, for it has long been 

 known that differences, both regional and seasonal, do exist in the 

 proportionate amounts of different substances (especially among the 

 rarer of these) dissolved in the water. Nevertheless sea v/ator is 

 certainly the most uniform in composition of any of the substances 

 comm.on upon our planet. And most geologists, ar.guing from the com- 

 position of the skeletons of marine animals that have lived in the 

 past, together with that of sedimentary rocks that were laid dovm at 

 different periods under the sea, believe that comioaratively little 

 change has taken place in the sea v/ator itself (except in its total 

 salinity), except that during the earlier geologic periods the pro- 

 portion of lime salts in solution seems to have been much smaller 

 than has been the case in more recent times. To unravel the inter- 

 play of factors (evaluating each) which maintains this uniformity 

 at present, and has maintained it in the past, is one of the most 

 attractive problems in geochemistry, for while various explanations 

 have been proposed, we believe no one would seriously maintain that 

 any of them is adequate. 



