Re: ammonium citrate recipe?
A while back (in the archives) there was a reference to making your own amm citrate using household ammonia and citric acid. However, the reference to the original recipe is no longer available on the internet...Is "household ammonia" available that is nothing but ammonium hydroxide (no surfactants or other additives)? I'm not sure it is in the US.
In any case, you can never be certain of the concentration of your ammonia without testing, so no formula will do. You will have to measure either the concentration of the ammonium hydroxide or some indicative parameter of the resulting ammonium citrate solution. The proportion to prepare a neutral solution is 5.365:1 by weight of citric acid (crystals) to ammonia (NH3), but it is up to you to determine how much ammonia by weight is in each volume of your ammonia water.
Adding citric acid to the ammonia water "until the ammonia smell disappears" would be a crude first approximation.
In 1911, the ACS published an article on preparing neutral ammonium citrate solution by measuring conductivity:
Here are some instructions from 1888, from "A Treatise On Beverages" by Charles Herman Sulz:
Solution Of Citrate Of Ammonia: Prepare by neutralizing 12 ozs. of citric acid with ammonia 11 fl. ozs., or sufficient, and add distilled water to yield 20 fl. ozs. of product. Store in bottles free from lead. Spec. grav. 1209 [this should probably be "1.209"]. Citric acid combines with ammonia, forming ammonium citrate and water. The solution is clear and colorless, has a saline taste, and should not change either litmus or turmeric-paper.
Note that author Sulz does not specify the concentration of ammonia, hence the caveat "or sufficient" and the instructions to test the resulting solution with indicators (note that the specified indicator papers would give at best a somewhat better approximation than doing it by nose).