1,3′-Bipyridinium, 5′-[[4-[[7-[(1′,2′-dihydro-6′-hydroxy-3,4′-dimethyl-2′-oxo[1,3′-bipyridinium]-5′-yl)azo]-1-hydroxy-3-sulfo-2-naphthalenyl]azo]phenyl]azo]-1′-[3-(dimethylamino)propyl]-1′,2′-dihydro-6′-hydroxy-4′-methyl-2′-oxo-, salt with 2-hydroxypropanoic acid (1:2)