CHEMICAL CHANGES IN THE COMPOSITION OF SEA- WATER. 485 



on examination to contain albuminoid or fixed nitrogen ranging from 590 to 800 parts 

 per million expressed or calculated as ammonia (present evidently in proportion to the 

 quantity of undecomposed organic structures). 



Alkalinity of Mud- Waters. — The alkalinity of the mud- waters (evidently due to the 

 presence of carbonates) was increased in a most striking manner when compared with 

 the water immediately overlying the mud, and depended directly upon the chemical 

 changes that had taken place in the sea- water salts in the water associated with the Blue 

 Mud. # The highest alkalinities (calculated as carbonate of lime) obtained from the mud- 

 waters were : — 



Queensferry mud-water .... =03395 gramme per kilogramme. 



Granton Harbour mud- water . . . = 0'6804 „ „ 



Granton Quarry mud-water (winter time) . =0 - 6880 „ „ 



Granton Quarry mud-water (summer time) =1*3737 „ „ 



The alkalinity of the water overlying these muds varied from 0*1072 to 0*1200 

 gramme per kilogramme. The difference between the summer and winter values for the 

 quarry mud-water leads one to suspect that there may be a deposition of carbonate of 

 lime in these muds during summer. Dr Gibson divides the density of sea-water, minus 

 1000, at zero, by the amount of carbonic acid present, and obtains a constant which he 

 designates D A , the usual value of which is 0*54.t By following the same rule we get 

 a very low value for D A with the mud-waters, viz., 0*05. 



At first we were inclined to refer the great increase of alkalinity to the excess of 

 carbonate of lime derived from the solution of the dead shells of calcareous organisms by 

 carbonic acid, the latter being much increased in sea-water through the deoxidation of 

 the sulphates by organic matter, but the total lime present in the water filtered from the 

 muds was found on determination not to have been increased in any notable degree 

 above that present in normal sea- water ; J indeed, the later filtrates show a slight 

 decrease of lime, which points, it may be, to the precipitation of carbonate of lime in the 

 mud. This is most noticeable in the case of the Granton Quarry mud-water, where the 

 alkalinity is very high (see Tables II. and IV.). It was also observed that the increase of 

 alkalinity was approximately proportionate to the diminution of the sulphuric acid (S0 3 ). 



From these results it is evident that the principal increase of alkalinity is due to 

 the deoxidation of sulphates by the organic matters in the mud, and the subsequent 

 decomposition of alkaline or earthy sulphides by the carbonic acid thus produced, and 



* We have seen that the accidental mixture with the overlying water, and also the increased amount of sulphates 

 produced by oxidation of sulphide of iron (FeS) in the mud, caused variations which tended to conceal the true nature 

 of the mud-water, and to alter the density of the various portions. If the mud had been thoroughly mixed up and 

 filtered in an atmosphere free from oxygen {e.g., nitrogen), the water in all the portions obtained by dripping would 

 probably have been alike in composition. 



t See Scottish Fishery Board Report, 1887. 



X In the 1st, and perhaps also in the 2nd, portions of the filtrates, where, as we have seen, the oxidation of the 

 sulphide of iron had increased both the sulphuric acid and the lime, the lime was evidently derived from the carbonate 

 of lime shells, or precipitated carbonate of lime, present in the deposit. 



