64 Hydrogen-ion Concentration and Electrical Conductivity 



8.398. It is, however, difficult to think in terms of negative loga- 

 rithms, and so the tables at the end of this paper give the Ph and also 

 the hydrogen-ion concentration of the sea-water expressed arith- 

 metically. Despite its artificiality, however, one soon finds that the 

 Ph system gives a clearer idea of the alkalinity or acidity of a solution 

 than does a direct expression of the hydrogen-ion concentration. 

 Thus, in testing water, Ph 7 would indicate practical neutrality; Ph 

 above 7, alkalinity; and below 7, acidity. 



The carbon-dioxide tension of the sea-water was calculated from 

 the Ph and the temperature by the method devised by McClendon, 

 Gault, and Mulholland (1917, Carnegie Inst. Wash. Pub. No. 251, 

 p. 36). McClendon found that the Ph of sea- water falls 0.01 for 

 1° C. decUne in temperature. Thus if the Ph be 8.25 at 27° C, it 

 may be expected to be 8.24 at 26° C. While this is true under normal 

 conditions, if the sea-water be diluted with river-water, or if there 

 be upwelling of cold currents carrying water rich in CO2 to the sur- 

 face, the Ph may rise while the temperature declines. Thus, near the 

 equator in the Pacific, I have observed a rise of 0.13 in the Ph while 

 the temperature sank 0.45° C, due to the upwelling of water from the 

 depths. 



The salinity of the sea is expressed in grams of total salts per 1,000 

 grams of sea-water, and was determined by the well-known method 

 of using a standard AgNOa solution with K2Cr04 as an indicator, and 

 testing against a sample of standard sea-water obtained from Pro- 

 fessor Martin Knudsen. 



The thermometers used read to 0.1° C. and were compared with 

 a thermometer which had been standardized by the U. S. Bureau of 

 Standards. 



Tests made on the yacht Anton Dohrn in Florida showed that one 

 might take samples of sea-water from the stern of the vessel while 

 in motion without any detectable error in the Ph, the result being 

 the same as if one dipped the sample up from the bow or stopped the 

 ship and went out in a small boat for it. 



Of course the only certain way for determining a current while 

 at sea is to anchor and use current meters, but in default of this 

 possibility we were obliged to rely upon the difference between the 

 position the ship expected to make and what she did make — the dif- 

 ference being ascribed to ''currents." This is, of course, a crude and 

 inaccurate method, for it makes no allowance for leeway due to wind 

 or for errors in steering, but it was the only method available. 



The thymolsulphonephthalein colorimetric tubes gave correct 

 readings when used for testing the Ph of sea- water of salinity 0.32 

 or 0.33 per cent, but for higher salinities a correction of —0.01 is to 

 be applied to the Ph as read on the tube for every unit in rise of 

 saUnity. Thus, for salinity 34, if the tubes read 8.22 the correct 



