CHEMICAL CHANGES IN THE COMPOSITION OF SEA-WATER. 



491 



Combining acids and bases 





Average Sea- 

 Water. 



Mud-Water. 



Sodium Chloride, NaCl, 

 Magnesium „ MgCl 2 , 

 Magnesium Bromide, MgBr 2 , 

 Magnesium Sulphate, MgS0 4 , 

 Potassium „ K 2 S0 4 , 

 Ammonium „ (NH 4 ) 2 S0 4 , 

 Magnesium Carbonate, MgC0 3 , . 

 Calcium „ CaC0 3 , 

 Calcium Sulphate, CaS0 4 , . 



77-758 



10-878 



0-217 



4-737 



2-465 



0-345 

 3-600 



79-019 

 11-222 

 0-220 

 3-232 

 2-506 

 0-206 

 0-909 

 2-686 



100-000 



100-000 



The difference between the chlorine calculated from the total salts as sulphates found 

 by analysis, and the chlorine calculated from the density, is in the case of the mud-water 

 (6th portion, Table IV.) 0*326.* When we apply the correction for lime lost by pre- 

 cipitation in the mud shown in Table B, and raise the chlorine calculated from total 

 salts to 19*944, there is a difference of 0*562 between the values of chlorine calculated 

 from total salts and the chlorine calculated from the density in the 6th portion. Again, 

 the difference between the chlorine found by analysis and that calculated from the density 

 is 0*509 in the 6 th portion. In a normal sea- water there would be no such difference, 

 or it would be inappreciable. 



On page 488 the values for D in the various portions of the mud- water are seen to 

 range from 1*4600 to 1*4230. The normal value for D in sea- water is nearly 1*4600. 

 This variation is to be accounted for by a difference in composition between the mud- 

 water and normal sea-water. We find that there has been a precipitation of carbonate 

 of lime from the mud- water, and this is presumably due to a loss of carbonic acid which 

 held the lime in solution as bicarbonate. This loss would lower the density, and raise 

 the chlorine relatively to the other constituents ; decrease of salinity will also be propor- 

 tionate to the weight of carbonate of lime so precipitated. The converse would take 

 place in sea-water containing excess of sulphate or bicarbonate of lime, or even carbonic 

 acid or other gases, as the following experiment shows. Sea- water was allowed to stand 

 in contact with mussel-flesh and sufficient ferric oxide to combine with all the sulphur as 

 FeS. After a time the carbon and hydrogen of the organic matter had completely 

 reduced the sulphates, and the whole of the sulphur was found in combination with the 

 iron as sulphide of iron (FeS), and the carbonic acid and ammonia formed by decay and 

 deoxidation had increased the alkalinity, which over all was equivalent to 4 grammes of 

 carbonate of Lime per litre, normal sea- water having an alkalinity of only 0*12 gramme. 

 The chlorine had in this case fallen 0*9 gramme in relative value, calculated from the 

 density, the difference being wholly accounted for by the increase of akalinity. 



* See top of page 489. 



