ABSTRACT
Methods are presented for the estimation of sodium, potassium, calcium, magnesium, chloride and sulphate in sea water and in other solutions, such as the blood and body fluids of marine animals, whose inorganic composition is similar to that of sea water.
The estimations may be performed on 1 ml. samples, and the limit of error is about 2 %.
Sodium is precipitated and weighed as sodium zinc uranyl acetate ; potassium is precipitated as potassium silver cobaltinitrite which is titrated with ceric sulphate ; calcium is titrated with ceric sulphate after two precipitations as oxalate ; magnesium is precipitated with hydroxyquinoline and the precipitate brominated and estimated iodometrically; chloride is treated with silver iodate and the released iodate estimated iodometrically; sulphate is titrated with barium chloride using sodium rhodizonate as indicator.
This formula is preferable to that given by Allen (1914) in that sodium sulphate may be weighed out with greater accuracy than magnesium sulphate.
In any case the traces of calcium found in even the purest sodium chloride and sulphate are sufficient to cause a significant error.
Glazed silica crucibles are best, but good quality porcelain ones with the glaze intact may also be used, except for potassium. For potassium estimations only silica crucibles are safe, since some qualities of porcelain liberate appreciable amounts of potassium when ignited in the presence of sulphuric add. As soon as any part of the inner surface of a crucible becomes in the slightest degree rough to the touch it should be rejected.
Unless the rod is perfectly clean there is a tendency for the precipitate to adhere to it. It may of course be weighed along with the crucible throughout.
4 hr. is sufficient, but the time schedule given here will usually be found the most convenient.
