sea-fisheries laboratory 137 



6 — Alealinity. 



The determination of this character gave me a great 

 deal of difficulty. 



Two methods were adopted : — One, by titrating in the 

 cold with standard acid in the presence of an indicator 

 unaffected by carbonic acid ; the other, by adding a known 

 volume of acid, boiling off the carboDic acid, and estimating 

 the excess of acid by titration with standard alkali. 



By neither method could really accurate results be 

 obtained, owing to the difficulty of rinding an indicator 

 which would give a sharp end point in such a dilute 

 solution as sea water. 



Various indicators were employed — methyl orange 

 phenolphthalein, and aurine — but constant end points could 

 not be obtained. 



Each method will now be considered separately. 



(a.) — Direct Titration. 



100 cc. of the water was mixed with just enough 1 

 per cent, solution of methyl orange to have a percep- 

 tible colour, and standard sulphuric acid (about T ~) was 

 run in till a distinct pink colour was produced. This 

 was then titrated back with standard alkali (KOH), 

 and so by a series of zigzag titrations a number of 

 end points were obtained. Unfortunately these were 

 by no means uniform, as each was a trifle higher than 

 the last, so that at the end of about ten end point 

 determinations by this method the amount of sulphuric 

 acid required was found to have increased about 1*0 cc. 

 I did not continue after this point as the value was be- 

 coming absurdly high ; indeed, I think the first end 

 point must be more nearly correct than any sub- 

 sequent one. 



