SEA -FISHERIES LABORATORY. 139 



When the boiling was finished, a drop of the 

 phenolphthalein, aurine, or methyl orange solution 

 was added, and the excess of acid was titrated with 

 standard alkali (KOH). Several end points were deter- 

 mined by zigzag titrations with standard sulphuric 

 acid and alkali, and the mean of the values obtained 

 was considered to be correct. 



The values differed from those obtained by the first 

 method, but as by using aurine as indicator very ac- 

 curate and close results were obtained, these were taken 

 as representing the true value of the alkalinity. This 

 was confirmed by a test case performed in an exactly 

 similar manner, only using standard sodium carbonate 

 solution instead of sea water. 



The values obtained by this method always coincided 

 with one of the many end points determined by direct 

 titration, but as this was not always the first, that 

 method may be considered as nearly valueless for 

 accurate determinations. 



As to choice of indicators it was found that aurine 

 gave far more accurate results than any of the others, 

 but phenolphthalein was nearly as good. Methyl 

 orange was on the whole unsatisfactory. 



Of course no estimation of the alkalinity by any of 

 these methods is really accurate, as the amount in the 

 water is perpetually changing owing to the following 

 causes : — (i) action of the sea water on the glass of the 

 bottles in which it was stored ; (ii) difference in tem- 

 perature between the water when used in the laboratory 

 and when first collected, causing loss of carbonic acid ; 

 (Hi) action of microscopic animals in the water till 

 their death. 



