Re: pH of water

Bas van Velzen (eland@knoware.nl)
Mon, 14 Oct 1996 08:50:24 +0100

>My point was that any reading below 7.0 is acidic; i.e. a reading of 1
>through 6 is acid - the lower the number, the more acid. What Sam said was
>that his reading of 3.5 pH was very alkaline, which can't be true as only
>readings higher than 7 are alkaline (10 being the most alkaline). Water
>having a pH of 4 to 5.5 is mildly acidic, and thus would not be normally
>harmful to the skin, though you would need to add more alkali to any
>sensitive photographic solution to neutralize the acidity. That's why I use
>distilled water for all photo solutions except wash water (our water here,
>running through limestone, has a pH running from 7.5 to 8, which is slightly
>alkaline, but I don't trust it because the pH can vary).

It may have been a typo but the pH range goes from 0 to 14 and not to 10, 0
being most acidic and 14 most alkaline, 7 being neutral. The numbers come
from the exponent of the H+ concentration in a given aquaous solution. pH 7
is a concentration of H+ of 10 to the exponent -7 thus at a pH of say 10 to
-3 there are more H+ ions (better H3O+), this makes the solution more acid,
in the alkaline range there are less and less H+ ions up to 10 exp -14. For
paper safe solutions will be between pH 6 and 8,5. Below 6 the paper will
become too acidic: the cellulose chains will be attacked, above 8,5 the
alkalinity will swell the fibers to a damaging extent. (in simple terms of
course)

Bas

Jonge Eland papierrestauratie
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