<Ray West> wrote in message
...
> Can anyone tell me how much citric acid is needed to lower the Ph of a
> given ammount of water from Ph7 to Ph4 or 5. A search of the web has
> revealed nothing.

Unfortunately cannot answer your (un)specific question, but have some
remarks. First, what are you preserving or preparing or brewing? Or
planting? and what country are you working from? We might be able to point
you in the right direction.
In our FAQ http://rfpfaq.jaclu.com/rfpFAQ.htm are some discussions on pH
and how it works in food preservation, and iirc, we had a discussion last
year on where to buy pH testing supplies on this newsgroup. The brewing
newsgroup may have some answers for you. If this is a gardening question,
many of us have gardens, and there are a number of gardening groups. BTW, I
found that the garden test probes are not very accurate in my limited
investigation. If it is important to your work, it's best to buy the goodest
tools you can afford that will do the job. Some test equipment is not too
terribly expensive, but you pay for what you get. A brewer's store or
scientific supply shop are good places to start.
All that said, I believe that 1 tablespoon of citric acid (sour salt) [not
vitamin c (ascorbic acid)] in one pint of ordinary tomatoes will bring the
pH down far enough to be healthfully kept after boiling water bath, i.e.,
4.6 or below. These things are so varied as fruits, juices, and veggies have
different pH according to time of year, watering schedule, place of origin,
variety, and believe it or not - site in the field/garden. Our FAQ has some
tables of substitution and the exact measurements, which I disremember as I
have not had my coffee yet.
hth, Edrena