To All Listmembers, At Reading we use Louwers-Hapert HV stopcocks and Vacutaps in a wide variety of applications on our stable isotope extraction lines and associated glassware to provide vacuum seals down to 1 E-7 mbar. Their HV stopcocks have performed very well over several years constant use but we have found serious corrosion problems with the more expensive Vacutaps in one specific application - when used to seal glass reaction vessels containing 100% Orthophosphoric acid during the preparation of CO2 gas from carbonates for subsequent analysis of 13-C and 18-O. After about 40-50 such preparations, the white plastic part of the Vacutap starts to corrode, first by patchy discolouration which gets progressively worse until the material begins to flake off, eventually rendering the Vacutap unusable. Once started, the corrosion apparently continues even during off- line storage. When the HV stopcocks are used in the same glassware, no such corrosion problems have been encountered. I would be interested to hear if anyone else on the list has experienced similar problems with these Vacutap valves and if so, what solutions may have been adopted to overcome it. Many thanks. Michael Isaacs +++++++++++++++++++++++++ Dept. P.R.I.S, University of Reading, Whiteknights, Reading RG6 6AB, U.K. Tel: +44-118-9875123x7974 Fax: +44-118-9310279 Email: [log in to unmask] +++++++++++++++++++++++++