31 
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 phenolphthalem 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 :—(7) action of the sea water on the glass of the 
bottles in which it was stored ; (v7) difference in tem- 
perature between the water when used in the laboratory 
and when first collected, causing loss of carbonic acid ; 
(itt) action of microscopic animals in the water till 
their death. 
