How can i manipulate the pressure of a controlled environment like a flask?

Im doing an electrolysis experiment and I want to test whether pressure has any effect on the amount of hydrogen produced by electolysis. I just don't know how to get my electrolysis experiment into a controlled environment where I can raise or lower the pressure of the environment.How can i manipulate the pressure of a controlled environment like a flask?
The obvious easy answer is simply control the temperature of the flask.How can i manipulate the pressure of a controlled environment like a flask?
Pressure can be regulated by:





Changing the size of the container





Adding or removing reactant





Raising and lowering the temperature





Good Luck! :)
Because a flask can't take a great deal of positive pressure, the range you'll have to work with is limited. It can take a fair amount of reduced pressure, (i.e. vacuum) however, so that could potentially widen your range.





In any case, if you are content with working within a range of less than + or - one atmosphere, you can use a mercury manometer to monitor the pressure. If you used a large enough U-tube and a separate reservoir of mercury (such as a separatory funnel connected by a flexible tube) you could even adjust the pressure by varying the height of the reservoir.





Whether this is a feasible approach for you depends on your situation and resources. If you're doing this at home or in a high-school setting, I doubt that you'll have access to the equipment or the needed amount of mercury (a good thing, actually, unless you're set up to do it safely). However, if you're prepared to handle the stuff and are in an industrial or university setting this might be a viable approach. Professional lab equipment such as the nitrometer used for nitrogen determination in organic compounds makes use of this very principle, so it is one option.





There are others, of course, and also other ways to monitor and adjust the pressure.





Good luck with your experiment. I'd attach a drawing of the possible setup if I could, but haven't figured out how to paste graphics into these answers yet ;-)