[Lucretius]

Hello! I am a technician testing for acid-soluble chloride ion content in concrete cores--see: AASHTO T260--and I do not understand the meaning of the word "persist" as relates to the color change that should occur at the step in the process after the introduction of several drops of 0.1% Methyl Orange indicator solution...specifically: although I routinely see a rather bright red color generated after  the process, the color will fade away in, say, 5 or ten seconds, and will not reappear even after the introduction of several additional mL of concentrated HNO3...so: although I sense that my test sample has been sufficiently acidified by the AASHTO called-for initial 3 mL HNO3, there is some question from other Lab personnel that the red color goes away too rapidly...what, then, would a proper Chemist make of the word "persist" in this context? Thanks for your kind considerations! Sincerly, Michael Maddan. Maine, USA telephone: 207-941-4500

[JGK]

I would say that in this context you should be seeing a colour change which does not fade away after 5 - 10  seconds

[Lucretius]

Thank you for the kind information...I rather expected such a time-frame ( having done the test in question several times ), but thought it a good idea to request another opinion...thanks! Sincerely, Michael Maddan.