MAYOR— DETECTING OCEAN CURRENTS. 157 



and found that the colors of the tubes, which had been carefully 

 guarded from light when not in use, had not change in the interval. 



As is well known the unit of hydrogen-ion concentration is i 

 normal hydrogen-ion per liter of water, or about i gram of hydrogen- 

 ion per liter. The purest distilled water contains only about i gram 

 of hydrogen-ion in 10,000,000 liters of water at about 22° C, and 

 thus its hydrogen-ion concentration is about lO"". Sea water, how- 

 ever, is alkaline and contains only about one tenth this concentra- 

 tion of hydrogen-ions, or as we say its hydrogen-ion concentration 

 is about lO"^. 



In order to avoid writing negative exponents Sorensen, 1909, p. 

 28, devised the symbol " PH " to indicate the negative logarithm of 

 the hydrogen-ion concentration. Thus according to Sorensen's sys- 

 tem a normal hydrogen-ion concentration, or iO"° of H-ions per 

 liter, is written PH o; a decinormal H-ion concentration, or lO"^, 

 is PH I ; while sea water with somewhat less than 0.000,000,01 

 normal hydrogen-ion concentration is about lO"^ normal and is des- 

 ignated 8 PH. 



H for example a specimen of sea water had a hydrogen-ion con- 

 centration of 



— - — — — - = o.6I6XIO-^ 

 1.622 X 10'' 



we would call its PH 8.21 because 0.21 is the logarithm of 1.622, 

 and 8 is the logarithm of 10^ and 0.21 -|- 8. =8.21. 



McClendon's borax-boracic colorimetric tubes indicate the true 

 PH of sea water containing 32 to 33 grams of total salts per 1,000 

 grams of sea water (salinity .32 per cent, to .33 per cent.), and the 

 following table gives the correction which McClendon found must 

 be applied in order to find the true PH of sea water of any other 

 salinity : 



Salinity of Sea Water in Correction to be Applied to the 



Grams of Total Salts Reading of the Colorimetric 



per 1,000 Grams of Tube to Find the True PH of 



Water. the Sea Water. 



30 -}- 0.02 



31 4-0.01 



32-33 +0. 



34 — o.oi 



35 — 0.02 



36 — 0.03 



37 — 0.04 



