| 释义 |
pH|piːˈeɪtʃ|
Formerly pH, Ph.
[Introduced (in Ger.) as pH· by S. P. L. Sörensen 1909, in Biochem. Zeitschr. XXI. 134, the p repr. G. potenz power and H· the hydrogen ion.]
1. A measure of the acidity or alkalinity of a solution, equal to the logarithm to the base 10 of the reciprocal of the effective concentration (activity) of hydrogen ions (in moles per litre).
A pH of 7 corresponds to a neutral solution, one less than 7 to an acidic solution, and one greater than 7 to an alkaline solution.
1909Jrnl. Chem. Soc. XCVI 861 The optimal concentration was pH = 4·4 to 4·6. 1920W. M. Clark Determination Hydrogen Ions i. 26 As a matter of typographical convenience we shall adopt pH in place of PH+. 1921Jrnl. Nat. Dental Assoc. VIII. 653/1 He uses agar with a Ph value of 8·1 as a basis for blood agar. 1935W. A. Koehler Princ. & Applic. Electro-Chem. II. xiv. 359 The bulb dips into the solution of unknown PH. 1937Pierce & Haenisch Quantitative Analysis viii. 121 Acid-base indicators are highly colored organic dyes which exhibit a change in color when the pH of a solution is changed. 1952C. E. L. Phillips Small Garden iii. 25 For general garden purposes in this country best results come from a neutral or slightly acid pH reading. 1970Pure & Appl. Chem. XXI. 33 In all existing national standards the definition of pH is an operational one. Ibid., The difference between the pH of two solutions having been defined as above, the definition of pH can be completed by assigning a value of pH at each temperature to one or more chosen solutions designated as standards. 1974P. Svendsen Introd. Animal Physiol. xiii. 143 The maximum acidity of the wine is about pH 4·5.
2. attrib. and Comb., as pH meter, pH scale, pH value; pH-dependent adj.; pH-stat, a device for automatically maintaining a solution at constant pH.
1960Jrnl. Bacteriol. LXXIX. 734 (heading) Temperature and pH-dependent changes of electrophoretic mobility of Pasteurella pestis. 1972Brit. Jrnl. Nutrition XXVIII. 389 The pH-dependent rearrangements have also to be borne in mind when performing administration experiments with formylfolates in metabolic studies.
1940Reilly & Rae Physico-Chem. Methods (ed. 3) xii. 493 The Beckman pH meter..uses the principle of the potentiometer system in which the voltage of the electrode system is balanced against that of a standard cell. 1968Passmore & Robson Compan. Med. Stud. I. vi. 3/1 The pH measured electrometrically by a glass electrode and a pH meter is not in fact a precise measure of actual hydrogen ion concentration.
1920W. M. Clark Determination Hydrogen Ions ii. 41 It is advantageous to show the position of the several indicators on the pH scale. 1973F. G. Shinskey pH & pIon Control in Process & Waste Streams iii. 57 The pH scale is not bound to the limits of 0 to 14.
1957Methods Biochem. Anal. IV. 174 A pH-stat consists of an appropriate cell..connected with a suitable pH-meter which in turn is connected with an adjustable controlling device. 1974Sawyer & Roberts Exper. Electrochem. for Chemists ix. 417 In general autotitrators that work with a preset endpoint lend themselves to application as pH-stats.
1920W. M. Clark Determination Hydrogen Ions ii. 38 To a series of test tubes are added, seriatim, 10 cc. of each of a series of standard solutions whose pH values are known. 1932T. P. Francis Mod. Sewage Treatm. 252 The pH values for filter effluents should not differ by more than ·6. 1946J. W. Day Harvest Adventure iii. 44 Every acre of arable land has had a dressing of chalk. In all..some 30,000 tons have been put down, the idea being to maintain a pH-value of 5. 1974Encycl. Brit. Macropædia X. 606/1 Some volcanic lakes are extremely acid, however, with pH values below 4, and some lakes with very high pH values, such as Lake Nakuru, Kenya, also occur in nature. |