From electro motive-force measurements of the cell wit hou t liquid junction :Pt; H 2, HCI (m), AgCI; Ag thro~l gh the range 0° to 95° C, calculations have been made of (1) t he standard potential of t he s Ilver-silver-chloride electrode, (2) the activity coefficient of hydrochloric acid in aqueous solutIOns from m (molality) = 0 t.o m~O .l and from 0° to 90° C, (3) the relative partial mo lal hcat conte nt of hydrochIol'lc aCId , and (4) the relatIve partial molal heat capacity of hydrochlo ric acid.The extrapolati?ns were made by the method of least s quares with the a id of punch-card techl1lqu es . Data from at least 24 cells were analyzed at eae h temperature and 81 cells we re s tudied at 25° C. The valu e of the standard potential was [ound to be 0.22234 absol ute volt at 25° C, a nd t he standard deviation was 0.02 millivolt at 0° C 0.01 mi lli volt at 25° C and 0.09 millivolt at 95° C. The resul ts from 0° to 60° C a re compared with earlier d eterll1ina~ t lOns of t he sta ndard potential and other quantities derived from the electromotive fo r ce.

Isopiestic vapor pressure measurements have been made on this system at 25°; the activity coefficients of urea in sodium chloride solution and of sodium chloride in urea solution have been evaluated and the extent to which solubilities of one solute in a solution of the other can be calculated is discussed.

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J -' A b uff er sol ution containing p otassiu m dihydrogen p hosphate (0.008695 m olal) an d d isodiu m h ydrogen phosphate (0.03043 molal) is p roposed as a pH standard for t he p hysiologically important r a nge, pH 7 to 8. The proposed stand ard solut ion is prepared by dissol ving 1.179 g (air weight ) of po tassium dihyd rogen phosp hate and '1.3 03 g (a ir weight) j of disodium h ydrogen phosphate i n a mmonia-free water a nd di lut in g to 1 liter at 25°C . The ionic strength is 0.1.Standa rd pH val ues (pH .) were assign ed t o t his r eference solution at tem peratures from 0 to 50 °C by mea ns of emf m easuremen ts of h ydrogen-sil ve r chlorid e cells wit hou t liquid jun ction. Th e acti vity coeffi cient of chl ori de ion, upon whi ch t he assignment of pH. d epends, was eval uated by means of a r ece nt ly proposed convention. By t his m eans, '-standard values precise to ± 0.001 u ni t co uld be deri ved from t he emf data. At 25°C pH .is 7.4 14 , a nd at 38 °C it is 7.382. The operatio na l consistency of t hese standard values wit h t hose for t he 0.025-m equ imo lal p hosp hate bu ff er (one of t he KBS p ri mar y s ta ndards) was d em o nst rated . I . IntroductionThe acid-ba se beh avior of blood and o ther physiological fluids h as b een widely s Ludied in recen t year s in m edical and biological la boratories in an a t temp t to discover t be relationships that exist among physiological fun ctions, pathological condi tions, and pH.Many of these fluids are well buffered, and t he detection of any sys tem atic variation of pH with physiological condi tion would therefo re b e exp ected to r equire precise measuring equipmen t. Such equipmen t is readily available commer cially in t he form of the n ewer highly-sensitive pH mcter s with a gl ass electrode.Experience has shown that, wi th the exer cise of care, the inves tiga tor or clinician can ob tain glasselectrode pH valu es, for reduced blood and other body fluids, th at agr ee wi thin ± 0.01 uni t wi th pH numbers obtained by m eans of the hydrogen electrode [1]. J Th e high degr ee of sta bili ty in these biological systems and in the m easuring appara tus sugges ts that blood pH m easurem en ts with a precision of 0.00 5 unit (or even 0.001 unit) could profitably b e m ade. M eaningful comparisons of highly precise resul ts of different laboratories could th en b e m ade, provided that a sui table referen ce standard wer e available.Unfortunately, useful comparisons of pH data , quo ted to 0.001 uni t, from differen t sources h ave in general b een impossible. The difficulty can be a t tributed to the fact t ha t in all of the m a.jor conventions definin g pH [2], a 110n thermod yn amic conven tion concerning single-ion s,ctivi ty coeffi cien ts is by n ecessity adop ted . A t th e present time no single convention fo1' definin g a n ionic activity is widely accepted . Al th ough the conven tions used her etofore to estimat e single-ion activity coeffi cien ts are " reasonable" and yield pH numbers consisten t 1 :Figures in brackets...

The question is di sc u~se d whether, a nd to what extent, the vapor press ure lowering of an aqueous solutlOn contallllllg t wo salts A and B can be co mpou nded a dditively from t he vapor press ure lowerings of a solution con tain ing the salt A a lone a nd another solution containin& t l~e salt B alone. In sorn.e insta nces the a dditivity of vapor press ure lowering is t rue wlthm less than 0.5 p ercent ; S IX systems have been examined a nd the greatest deviation from a dditivity a mounts to 2.0 percent.