BUFFER ACTION. A buffer in chemistry is any material which lessens the activity of acid or alkali, added to a solution containing that material. Buffer action may be described as the resistance offered by a solution to change of acidity or alkalinity through the addition or loss of acid or alkali. Common buffer sub stances include alkali salts (sodium acetate or phosphate), proteins (gelatin), the phosphates in raw sugars, carbonates in raw water, carbonates and silicates in clay, alum and rosin in paper sizing. Buffers play a very important role in the blood, permitting large amounts of acid to be transported and eliminated without appre ciably changing the slight alkaline reaction of the blood.
The acidity or alkalinity of a solution is measured in terms of the concentration of hydrogen ions (H+) or hydroxyl ions (OW) present. Since there is a definite relation between (W) and concentrations, due to their relationship in the water mole cule, the acidity or alkalinity of a solution can be conveniently expressed, when the quantities are small, in terms of grams of hydrogen ion per litre, and, for the sake of convenience, as the reciprocal logarithmic exponent of this concentration, called the "pH." For example, 0.001 gram of hydrogen ion per litre of solution may be expressed as I X I gram per litre, or simply as pH3. At pH 7, hydrogen ions and hydroxyl ions are present in equal quantities and the solution is neutral. The buffer action of certain substances is made possible by the circumstance that they maintain an equilibrium between their ionized and non-ionized forms, according to the older theory of ionization; and that the ionized form has a definite pH value. As acid or alkali is added, the equilibrium shifts so that the pH is held as nearly constant as possible. Thus, although acid or alkali is added (within reasonable limits), the pH of a buffer solution will change only very slightly. Dilution changes the pH of buffer solutions only slightly; for example, sodium acetate of pH 4-615 on fivefold dilution shows a pH of 4.665. (See HYDROGEN ION CONCENTRATION; SOLUTIONS.) See Trans. Am. Electrochem. Soc. (1927) ; W. Clark, The Determina tion of Hydrogen Ions. (A. NE.)