II. CHEMISTRY 



463 



60rxl02 



50 



40 



■5 30 



20 



2400 



1 28 



3.20 

 3 40 



2700 



2500 2600 



Wavelength A 

 Fig. 1. Absorption spectra of nicotinic acid at different pH values. (From Hughes 



2.0 r 



1.605 3.21 4.82 ■ lO--* 



Concentration in moles per litre 

 Fio. 2. Demonstration of Beer's law in buffer at 4.25. (From Hughes et al.^*) 



