2. Hacia una comprensión de la doctrina de la justificación en San Pablo
2.1 La perspectiva de la justificación en la “Carta a los Gálatas”
C HAPTE� 5 . RESUL'r S
Aqueou s solu t i ons of vari ou s a c i d s were t i t r a t ed
i n th e ab s en c e and in the pre s ence of v ari ou s c ompl ex forming m e t al i ons . C i tri c aci d and i t s magne s ium and
cal cium comp l exe s were th e comp ound s of chi ef i n t er e s t
i n the p re sent wor k becau s e o f the i r i mpor t an c e i n milk.
The methods d evel op ed for th e s e d e t erminati ons were t e s t ed u sing acids wi th reli ab ly known a c i d i t y con st an t s. A
numb er of a c id s b earing a stru ctu ral relat i onship t o c i t r i c a c i d were al s o s tudi ed a s a knowl edge of the c on s t ant s o :f the s e aci d s i s helpful i n eluc i dat i ng and under s t anding
the fa c t ors affe c t i ng the acidi ty of c i tri c acid and the s t ab i li ty of ci trat e complexes. S t ab i li ty c on s t ant s of c i t rat e wi th other cat i ons of the alkaline earth s e ri e s
(
b arium , s t ront i um)
w e r e al s o m easured.A study of the homologou s s er i e s of aliphat i c
ex w di c arb oxyl i c a c id s was made. Su c c ini c a c i d wa s cho s en a s a polyb a s i c a c i d wi th reli ab ly known a c i di ty con s t ant s and glut ari c acid a s b eing s t ructurally rel at ed t o c i t ri c a c i d
(
s e e S e c t i on2 .4) .
Hi gher memb er s o:f the homologou s s eri e s(
all avai lab l e c ommerci ally i n high puri ty)
were i ncluded for s tudy , alt hough not d i r e c t ly rel at ed to mi lk salt sys t em s , b ec au se of the importan c e of t h e s eri es i n s tudi e s of t h e effect of el e c tri cally charged sub st i tuent son acidi ty . At the t ime of mea surement there was only one known s t udy of thi s s eri e s of a c i d s i n aqu eou s solu t i on
(
G ane and I ngold , 1 931 ) . R e c ently a second s t udy ha s b ee nr ep ort ed ( Ninomiya and Toei , 1 969 ) i n whi ch the aci dity c on s t ant s of th e a ci ds h av e b eGn d e t ermined i n 0 . 1 M KNo3 solu t i on at 25°C by pH t i t rati on u si ng a gla s s ele ctrode .
S ome of the r e s ul t s cal culat ed from pH ti tra t i on dat a u s i ng the method s given i n Chap t e r 3 ar e taoula t ed i n thi s
chap t er . R e sul t s report ed by other worker s t ogether wi t h
reference s ar e included for comparison.
5 . 1 THE a w DICARBOXYLIC AC ID S
T able 5.1 gi ve s re sult s for th e homologou s s eri es of al iphat i c aw di c arb oxyl i c a c i d s of general formula
The fi r s t two member s of the s eri e s , oxa l i c acid ( n= o ) , and maloni c acid ( n= 1 ) hav e be en exclud ed b e c au s e
thei r acid s t rength i s t oo great t o allow ac curat e d e t e rm i n- at i on of the fi r s t a c i d i t y con s t ants fr om gla s s ele ctrode t i t ra t i ons and fur ther they are not typ i cal memb e r s of the s e ri e s .
The s olub i l i ty of the a c i d s i n wat er decrea s e s with i ncrea sing n . T hu s a s aturated aqu eous solu t i on of
s ebaci c acid ( n=8 ) at 2 5°C i s app ron mately 0.0 0 13M and i s
the l a s t memo e r of the s eri e s whi ch can b e s tudi ed read i l y i n aqueou s s olut i on .
The clo s e agr eement b e tween the r e sul t s of thi s work and the re sul t s of Pinching and B at e s ( 1 950 ) for
suc c ini c a c i d allows s om e confidenc e i n the r e sul t s for the r emaining a c i d s.
The not e s at the foot of T abl e 5 . 1 conc erning m ethod s and media a l s o appl y t o sub s equent t ao l es i n thi s Chap t e r .