I know this topic have been on this site few months ago. I have some questions and suggestion on the topic, how to make 100 % phosphoric acid. I have been following the same procedure Pier described on this site, that is following Bowen's (1966) and Coplen et al. (1983). (i.e., adding P2O5 to 85% orthophosphoric acid and heating at 200 oC) But, the On-line lab manual for Stanford by Mucciarone uses very simple method for his Kiel device. Just heat the ACS grade 85% commercial Phosphoric acid to get ride of the 15% water out of it. Does anyone see any problem with this method? The specific gravity he is using is 1.89 to 1.90 which is similar to the method most are using. WHY do we need to add P2O5 to the 85 % orthophosphoric acid?? Thanks --------------------------------- Get your own web address for just $1.99/1st yr. We'll help. Yahoo! Small Business.