PH temperature increases. Pure water is neutral, pH 7 at (25 °C), being neither an acid nor a base. Contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and bases respectively. Measurements of pH are important in agronomy, medicine, chemistry, water treatment, and many other applications. The pH scale is traceable to a set of standard solutions whose pH is established by international agreement. Primary pH standard values are determined using a concentration cell with transference, by measuring the potential difference between a hydrogen electrode and a standard electrode such
Esophageal pH monitoring hydrochloric acid in the distal esophagus. Formal measurement of acid in the esophagus was first described in 1960 by Tuttle. He used a glass pH probe to map the gastroesophageal pH gradient, and demonstrated a sharp gradient in normal subjects and a gradual sloping gradient in patients with esophagitis. Four years later, Miller used an indwelling esophageal pH electrode to continuously measure esophageal and gastric pH for a period up to 12 hours. This technique required that the patient keep their hands immersed in saline to serve as a reference. Prolonged monitoring became feasible in 1974 when Johnson and DeMeester