Jean,

Go to the USDA Nutrient Data Laboratory

http://www.nal.usda.gov/fnic/foodcomp/srch/search.htm

You can search the nutrient composition of almost any food.

If you type in chicken bullion you'll get: "Soup, chicken broth cubes,
dehydrated, prepared with water" and the nutrient composition.

For example, chicken bullion cubes prepared with 6 fl oz contains 2 mg
Magnesium/9 kcal.

s/d contains 13 mg magnesium/100 kcals - so the magnesium content of the
bullion cubes is too high - although you could mix the cube in a pint of
water to get  .125 mg/oz or better still, a quart to get 0.0625 mg/oz. At
that dilution, he couldn't drink enough to take in enough magnesium to
cause a problem.

Magnesium isn't really the problem - its the urine pH.  At urine pH less
than 6.1, struvite doesn't form regardless of the magnesium content of the
food.  The tendency of struvite to form is determined by urine pH.  The
magnesium content of the diet only becomes important when urine pH is
greater than 6.1.  s/d produces an acidic urine that dissolves struvite.
You really need to get him on a struvite-dissolving diet.

Phil.