WATER OF THE IRISH SEA. 299 



doubtless produced by the decomposition of nitrogenous 

 organic matter. Now, since this process of decomposition 

 is continually going on to an enormous extent on the sur- 

 face of the earth, we should naturally expect to find far 

 more ammonia and nitric acid in sea-water than analysis 

 shows to be actually present. The amount of the substances 

 thus formed on the earth must be very large ; but the 

 quantity carried down to the sea by the rivers is exceed- 

 ingly minute : we are acquainted with at least fifty ana- 

 lyses of rivers flowing" dii'ectly into the sea ; but in none 

 does the proportion of nitrate exceed i part in 100,000 of 

 water, even when the river receives the sewage matter of 

 large towns. This remarkable disappearance of nitrate 

 and ammoniacal salts is undoubtedly to be traced to the 

 peculiar absorptive power of soils for salts containing ni- 

 trogen in a form available for the nourishment of plants. 

 Way has shown that nitrates and ammoniacal salts are 

 completely removed from solution on filtration through a 

 layer of soil. 



XII. Estimation of the Iron. 



The precipitate formed in the retort on adding the caustic 

 soda to the sea-water was assumed to contain the whole of 

 the iron as ferric oxide. This precipitate was dissolved in 

 dilute sulphuric acid, the iron reduced by means of zinc, 

 and its amount estimated by a permanganate solution, of 

 which one cubic centimetre was equivalent to 0*001 06 

 of oxygen. Amount of re^Oj found in 1000 grms. 

 = 0-00465. 



The following synoptical Table shows the mean results 

 of the foregoing determination : the numbers express the 

 amount of the various ingredients in 1000 grms. of the 

 sea- water : — 



