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	Ferric nitrate is a paramagnetic compound (One unpared electron),
ferrous nitrate is diamagnetic. The NMR experiment described in 
"Scientific American" could only detect proton resonances. Proton have the
highest resonance frequency in a given field (except for tritium). You
could never see iron-57 at the field used in the experiment, its
gyromagnetic ratio is too low and its natural abundance is too low. 
For example, when protons resonate at 360MHz (8.5T), iron-57 resonates at
ca. 15MHz. Adding paramagnets to a solution while change the magnetic
susceptibility of the solution, which will broaden the line considerably.
Some paramagnetic ions will cause a shift in the resonance rather than a 
broadening, which is usefull for determining the structure of a compound.
Paramagnetic ions can also cause the spin system to relax faster, which
can be very useful. This discusion would be better in sci.chem than
sci.electronics.


		Jeff Forbes
		University of Illinois
		Chemistry Dept.