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January 9

pH measurement

For a 20% citrate solution, does direct pH measurement with a pH meter give accurate results, or does such a solution require some other means of pH measurement? 2601:646:8A00:A0B3:940E:B215:E6AD:437C (talk) 03:59, 9 January 2019 (UTC)[reply]

I am tempted to answer "no" for this one, but honestly, it is frustrating but said to be possible. Accurate compared to what is something of an issue. pH is something that is extremely simple in many contexts but gets as complicated as you want it to be. Nonetheless, there are many guides to trying to get the best result [1][2][3] Note that "use whatever equipment you have on hand" is missing from these instructions... that said, the second source does make the suggestion of taking standard calibration buffers and adding large amounts of NaCl to calibrate at high ionic strength, which at first glance sounds reasonable. The first source suggests giving the electrode plenty of time to equilibrate. Just to be sure we're on the same page, understand that just because the 20% citrate solution has a certain pH doesn't mean that the same pH will be read after it is diluted. Wnt (talk) 23:46, 10 January 2019 (UTC)[reply]

Thanks! I am actually trying to make a super-high-strength citrate buffer, so accurate pH measurement is crucial. 2601:646:8A00:A0B3:940E:B215:E6AD:437C (talk) 03:53, 11 January 2019 (UTC)[reply]

Hutchinson Dictionary of Scientific Biography

Does anyone have access to a print copy of the 2004 edition of the Hutchinson Dictionary of Scientific Biography, OCLC 56115168? When it's cited in Pappus of Alexandria, it refers to him living c. AD 200-350, while the online edition to which I have access puts him c. AD 300-350. This could have any of the following explanations:

Print edition says 300, and a Wikipedia editor made a typo.
Print edition says 200, and it was a typo; when the ebook was produced, the typo was fixed.
Print edition says 200, and the long lifespan indicates that there's absolutely no certainty regarding his dates; when the ebook was produced, the editors chose to tweak it.

Given the possibility of #3, I don't want to change it without consulting the printed source: thus this request. Thank you. Nyttend (talk) 04:32, 9 January 2019 (UTC)[reply]

Have you asked the editor who inserted this in 2007? ----jpgordon^{𝄢𝄆 𝄐𝄇} 05:27, 9 January 2019 (UTC)[reply]

No, as Selfworm's not made a single edit in over six months. Nyttend (talk) 05:30, 9 January 2019 (UTC)[reply]

~~I think I can find a hard-copy locally in the next day or so... DMacks (talk) 05:31, 9 January 2019 (UTC)~~ Nevermind...looking at the detailed holdings within reasonable distance, "book" all resolved to "e-book electronic-access". DMacks (talk) 05:35, 9 January 2019 (UTC)[reply]