of the Fishery Board for Scotland. 463 



contributed by the fresh water be supposed to be due to the presence of 

 carbonate of lime, then there would be approximately 47*5 mg. per litre of 

 carbonate of lime mixed with the salts contributed by the sea water. 



Now, besides carbonates there are present in river water other salts, 

 notably sulphates, which all tend to alter the relation between chlorine and 

 density in the same direction, that is, to increase the value for D. If 

 for the purpose of illustration the amount of these other salts be 

 assumed to be equal in amount to the carbonates as measured by the 

 alkalinity, 95 mg. per litre would be the amount of salts contributed by 

 the fresh water. If also for the purpose of illustration merely, the excess 

 of density ( 0 S 0 ) of this brackish water over that of distilled water under 

 the same conditions, namely 6*706, be taken as representing the number 

 of grammes of total salts present in it per litre a rough approximation to 

 the quantity of sea salts proper present in one litre of this brackish water 

 will be obtained by subtracting the 95 mg., from 6 "706, and if the remainder, 

 namely 6*611 grammes, be divided by the number of grammes of chlorine 

 actually found in this water, namely 4*55 the value for D corresponding 

 to the sea water as it was before dilation with fresh water of the Baltic 

 becomes 1*4529, while the observed value for D corresponding to the 

 water found at the botton off the Naze was 1*4567. 



Considering the very rough and ready method which I have adopted 

 for the purpose of illustration, this is a very close approximation, and goes 

 far to prove that the sea water entering the Baltic at the time was surface 

 Atlantic water similar to that actually found off the Naze. 



Were this brackish water from the Baltic concentrated by evaporation 

 until it had a density equal to the cold water flowing into the North Sea 

 from the north, the mere determination of the density and the chlorine 

 might not be sufficient to detect any difference between the two, as the 

 value for D would be very much the same in both cases. But the deter- 

 mination of the alkalinity would at once show the difference, for the water 

 obtained by concentrating the brackish water of the Baltic would have 

 an alkalinity about three times greater than that of the North Sea water. 



This would seem to show that the high value for D characterising the 

 cold North Sea water cannot be solely due to the influence of land water. 

 The only other cause which I can suggest as possibly sufficient to pro- 

 duce such a water from water having the composition of the surface 

 Atlantic water as it flows into the North Sea is the formation and subse- 

 quent melting of sea water ice. According to Petterson's observations, 

 the water obtained by melting sea water ice from the Arctic regions and 

 also from the Baltic contains a much higher proportion of sulphates to 

 chlorides than that characterising the sea water from which the ice was 

 produced. That is to say, that the value of D would be greater in the 

 water obtained by melting the sea water ice than in the original sea 

 water. 



On the other hand, the action of the various forms of life, vegetable and 

 animal, existing in such enormous profusion in the warmer waters of the 

 south must tend to lower the value for D, inasmuch as they abstract 

 substances other than common salt and thus tend to increase the chlorine 

 relatively to density. 



The whole subject is one of great difficulty and complexity, and I offer 

 these suggestions as to the origin of these two different watsrs and as to 

 the causes which may have brought about their difference in chemical 

 composition, not because I attach much importance to them in the present 

 state of our knowledge, but simply as a basis for discussion. The problem 

 cannot be satisfactorily solved until a clearer insight has been attained into 

 the distribution of such differences in the chemical composition of ocean 



