Quick thought - Maybe try bubbling mixed gas through limewater? First measure gas mixture. CO2 forms compound in solution and then measure just the N2? HTH YMMV, Mark ********************************************************************** psci-com how-to: Once subscribed, send emails for the list to [log in to unmask] If not subscribed, either subscribe here https://www.jiscmail.ac.uk/cgi-bin/webadmin?A0=psci-com or send requests for items to be posted on your behalf to [log in to unmask] To unsubscribe (or silence messages while away) send an email (any subject) to [log in to unmask] with one of the following messages (ignoring text in brackets) • signoff psci-com (to leave the list) • set psci-com nomail (to stop receiving messages while on holiday) • set psci-com mail (to resume getting messages) Contact list owner at [log in to unmask] Small print and JISCMail acceptable use policy https://sites.google.com/site/pscicomjiscmail/the-small-print **********************************************************************