1. The problem statement, all variables and given/known data I'm trying to revive an old project a previous grad student had been toying with. Essentially, the reaction requires a sealed quartz tube (with a dilute acid) to be placed ("free-floating") inside a thick walled-autoclave capable of well over 40,000 PSI. The reaction is run at 500C. I'm trying to figure out how to appropriately equate the two pressures such that the pressure around the free floating quartz tube is the same that is inside the tube, so the tube will not burst. What is the best way to go about this, assuming I know the temperature and pressure I wish to run the reaction? 2. Relevant equations Previously, I thought the ideal gas law would work. Obviously, this was not a good approximate since we're dealing with water, which isn't an ideal gas even in gas form... I then used steam tables to find the density of water, which I then multiplied the amount of volume I was wanting to fill at that pressure, and used that mass as the basis of water I needed to add. This did not work. 3. The attempt at a solution Above.