5. Electrical Resistance 



The approximate electrical resistance range of seawater is 15 

 to Uo ohm-cm compared to 300 to 20,000 ohm-cm for fresh water. Ohm-cm 

 refers to the resistance of matter 1 square centimeter in cross-section 

 and 1 centimeter long (U. S. Army Corps of Engineers, 1962). This dif- 

 ference in electrical resistance between fresh water and seawater is one 

 of the more significant factors which causes corrosion in seawater to 

 proceed faster than in fresh water. 



6. pH Value 



Aqueous solutions will always contain positive^ly charged hydro- 

 gen ions (H ) and negatively charged hydroxyl ions (OH ) as a result of 

 the dissociation of water. It is the relative amounts of these ions that 

 determine whether a solution is alkaline, neutral or acid. If hydrogen 

 ions_ (H ) are in excess, the solution acts as an acid; if hydroxyl ions 

 (oh ) are in excess, the solution acts as an alkali. The pH value of a 

 solution is the means of denoting its degree of alkalinity, acidity or 

 whether it is neutral. The pH value is calculated from the hydrogen ion 

 concentration. The total amount of hydrogen and hydroxyl ions contained 

 in a solution is nearly constant, therefore, it is known that, if the 

 hydrogen ion concentration is increasing, the hydroxyl ion concentration 

 is decreasing. The hydrogen and hydroxyl ion constant for pure water 

 has been determined to he 10"-^^ or 10~ ' hydrogen gram ions per liter and 

 10"' hydroxyl gram ions per liter. The pH value of an electrolyte is 

 determined by use of the formula: 



pH = Log — + 

 H 



Using this formula, neutral solutions have a pH value of 7.0. Acidity 

 increases from neutral as the pH value decreases from 7.0. Acidity 

 approaches a maximum in a solution as pH approaches 0. The alkalinity 

 of a solution increases from neutral as the pH value increases from 7-0 

 to a maximum of approximately 1^.0. Seawater pH values normally range 

 from 8.1 to 8.3 but may approach 7-0 in stagnant basins where hydrogen 

 sulfide is present (Redfield, in Uhlig, 19^8). 



7. Fouling Organisms 



Seawater is inhabited by many species of marine plants and 

 animals. Some of these organisms are likely to become attached to 

 marine structures and are known as fouling organisms. 



Fouling organisms which are considered to have possibilities of 

 affecting metals in seawater have been divided by Clapp (Uhlig, 19^8) 

 into three groups: Sessile organisms, semimotile fouling organisms and 

 motile organisms. 



Shell-building sessile organisms include annelids, barnacles, 

 encrusting Bryozoa, mollusks and corals. Non-shell-building sessile 



