WHAT IS pH AND HOW IS IT MEASURED? A Technical Handbook for Industry   (click on the title to view the complete handbook)

Almost all processes containing water have a need for pH measurement. Most living things depend on a proper pH level to sustain life. All human beings and animals rely on internal mechanisms to maintain the pH level of their blood. The blood flowing through our veins must have a pH between 7.35 and 7.45. Exceeding this range by as little as oneā€tenth of a pH unit could prove fatal.
Commodities such as wheat and corn, along with other plants and food products, will grow best if the soil they are planted in is maintained at an optimal pH. To attain high crop yields, farmers must condition their fields to the correct pH value. Different crops need different pH levels. In this case, one size does not fit all.

Proper pH control keeps milk from turning sour, makes strawberry jelly gel, and prevents shampoo from stinging your eyes. In plating plants, pH control is used to ensure the luster of chrome on various products from nuts and bolts to toasters and automobile bumpers. The pH of wastewater leaving manufacturing plants and wastewater purification plants, as well as potable water from municipal drinking water plants, must be within a specific pH "window" as set forth by local, state or federal regulatory agencies. This value is typically between 5 and 9 pH, but can vary from area to area.
Other pH applications include:
• Neutralization of effluent in steel, pulp and paper, chemical, and pharmaceutical manufacturing
• Hexavalent chromium destruction
• Cyanide destruction
• Reverse osmosis
• Odor scrubbers
• Pharmaceutical manufacturing
• Chemical and

Definition of pH
Just as the kilometer is a measure of distance and the hour is a measure of time, the pH unit measures the degree of acidity or basicity of a solution. To be more exact, pH is the measurement of the hydrogen ion concentration, [H+]. Every aqueous solution can be measured to determine its pH value. This value ranges from 0 to 14 pH. Values below 7 pH exhibit acidic properties. Values above 7 pH exhibit basic (also known as caustic or alkaline) properties. Since 7 pH is the center of the measurement scale, it is neither acidic nor basic, it is called "neutral." pH is defined as the negative logarithm of the hydrogen ion concentration. This definition of pH was introduced in 1909 by the Danish biochemist, Soren Peter Lauritz Sorensen.