972 
THE VOYAGE OF H.M.S. CHALLENGER. 
which will be quoted liberally. With reference to the composition of the salt mixture 
dissolved in sea water, Professor Dittmar says : — 
“A priori , , we should say that this composition cannot be subject to any great 
variation; because, if there were no chemical changes going on in the ocean, and no 
gain or loss of dissolved individual salts, this composition would now, after thousands of 
years’ constant intermixture, be absolutely the same everywhere ; and what is going on 
in the shape of reactions and importation or exportation of individual salts, really 
amounts only to an extremely minute fraction of the whole, even in the course of a 
century. This conclusion is confirmed by the analyses of several hundred samples 
of surface waters, which were carried out by Forchhammer in connection with a 
great research which he published in 1864. 1 According to his results, if we 
confine ourselves to the open ocean, we find that everywhere the ratios to one 
another of the quantities of chlorine, sulphuric acid, lime, magnesia, and total salts 
exhibit practically constant values. With the view chiefly of supplementing Forch- 
hammer’s work, I have made exact determinations of the chlorine, sulphuric acid, lime, 
magnesia, potash, and soda in 77 samples of water collected by the Challenger from very 
different parts of the ocean : — 
12 from the surface. 
10 from depths of 25 to 100 fathoms. 
21 from depths of over 100 to 1000 fathoms. 
34 from greater depths. 
“ The results, while fairly agreeing with Forchhammer’s, were in still closer accordance 
with one another, and thus showed that Forchhammer’s proposition may be extended 
from surface waters to ocean waters obtained from all depths. 
“ The solid matter dissolved in sea water, though strictly speaking, and we may add 
necessarily, of a very complex composition, consists substantially of the muriates and 
sulphates of soda, magnesia, lime, and potash. Forchhammer, after having satisfied 
himself that all the other constituents taken conjointly amount to only a small fraction 
of one per cent, of the total solids, in his individual analyses limited himself to exact 
determinations of the chlorine, sulphuric acid, lime, and magnesia. The potash he deter- 
mined only in a. comparatively small number of samples ; and where he reports the soda 
this component is calculated by difference, on the assumption that the acids and bases 
present exactly neutralise each other. But this assumption had never been proved to 
be correct, and a priori is improbable, because it leaves out of reckoning the carbonate 
of lime which many animals need for forming their shells. I therefore in my analyses 
made it a special point, in addition to the other bases, to determine also the soda by a 
method independent of the assumption quoted ; and on calculating my first set of (21) 
1 Phil. Trans., vol. civ. p. 203, 1865, 
