214 DISCOVERY REPORTS 



determinations of hydrogen-ion concentration were regularly made, and during a con- 

 siderable part of the commission all samples were titrated on board for salinity. On 

 certain occasions when the vessels were at Cape Town titrations for salinity were made 

 in the physical and chemical laboratories of Cape Town University, while oxygen 

 samples were worked up in the Government Chemical Laboratory. Thanks are due to 

 Prof. E. Newbery and Dr Marchand for these facilities. 



Salinity was determined by the method described in detail by Oxner and Knudsen,^ 

 in which the samples are titrated against a solution of silver nitrate of known 

 strength, a solution of potassium chromate being used as an indicator. The strength 

 of the silver nitrate is determined previously by titration against standard sea-water 

 of a definite chlorine value supplied by the Laboratoire Hydrographique at Copenhagen. 

 The special burette used in the work is graduated to give the chlorine value as a direct 

 reading, and tables have been drawn up by Knudsen^ from which the salinity can be 

 quickly calculated from the titration. A special pipette for drawing off the required 

 amount of water from the sample is also used, both burettes and pipettes being supplied 

 by the Laboratoire Hydrographique. 



Analysis of samples for dissolved oxygen was carried out by Winkler's method. The 

 samples are fixed on board by the addition of small quantities of each of two solutions, 

 manganous chloride and a mixture of sodium hydroxide and potassium iodide. Man- 

 ganous hydroxide is immediately formed, and on absorbing the oxygen becomes 

 manganic hydroxide. In order to prevent air from entering the sample bottle, it is 

 placed in a flask filled with water from the same depth and corked until required for 

 analysis. The fixed sample will keep for some considerable time. In the analysis the 

 sample is well shaken after the addition of concentrated hydrochloric acid. The manganic 

 hydroxide is broken up and manganic chloride formed, the latter immediately reacting 

 with the potassium iodide present and setting free iodine. Titration against a standard 

 solution of sodium thiosulphate, using starch as an indicator, will give the amount of 

 iodine liberated, and hence, by a simple calculation, the percentage of oxygen in the 

 sample. 



Phosphate content was estimated by Atkins' application of Deniges' method,^ in 

 which the amount of phosphorus pentoxide is found by comparing the blue colour 

 formed on the addition of two solutions to tubes containing (a) the sample of sea water 

 and (b) a solution of potassium dihydrogen phosphate of known strength. By adjust- 

 ment of the heights of the columns, which is easily done in Hehner tubes fitted with 

 stopcocks, the intensity of colour in the lengths of the columns can be matched with 

 accuracy. The solutions used are ammonium molybdate in 50 per cent sulphuric acid 

 and tin dissolved in hydrochloric acid with the addition of a drop of copper sulphate. 



1 Oxner and Knudsen, Bull. Comm. hilertiat. pour I'Explor. sci. de la Mer Mediterraneenne, no. 3, pp. 1-36, 

 1920. 



2 Knudsen, Hydrographische Tabellen, Copenhagen, 1901, and Puh. Circ, Cons. Explor. Mer, 11, 1904. 

 ^ Atkins, Journ. Marine Biol. Assoc, n.s., xiii, pp. 119-50, 1923, and Harvey, Biol. Chem. and Physics of 



Sea Water, p. 42, Cambridge, 1928. 



