Reaching critical point in a fluid I have carbon dioxide in a pressure reactor. I can control both temperature and pressure inside the container (or, equivalently, temperature and amount of fluid). I need to reach the critical point in an experiment. 
What is the best experimental procedure to reach the critical point? Is this explained in any book or paper?
I know the critical point is at 31.10 °C and 72.9 atm, but I cannot simply rely on these values because the experimental uncertainty of my pressure and temperature measurements is somewhat large (about 0.5 ºC and 1 bar)
I can initially perform the experiment in a reactor with a window (if this helps), but later on I would need to repeat it in a reactor without window.
Surprisingly, I haven't managed to found proper reliable references on this. 
 A: Finally we performed the experiment and we could nicely reach the critical point. We relied on the temperature - specific volume phase diagram (the plot is extracted from these lecture notes):

The region under the curve is the vapor dome, where liquid and vapor coexist. At lower specific volumes there is only (compressed) liquid, and at higher specific volumes there is only gas. The critical point is the tip at the point of the vapor dome. At temperatures higher than the critical temperatures there is supercritical fluid. 
The experimental procedure was to fill up the pressure container with fluid at room temperature until the boundary between the liquid and the vapor was more or less at the mid point of the container. Then we closed the valve and slowly increased the temperature, making sure that the boundary between the liquid and the gas was kept approximately at mid point, injecting or ejecting fluid if needed. This way it was easy to pass though the critical point, point at which the boundary between liquid and gas disappeared. By keeping the specific volume constant, we could pass many times though the critical point by only increasing and decreasing temperature. Critical opalescence was nicely observed at the critical point.
One comment though was that the critical point and the critical opalescence was more easily observed when decreasing temperature. When increasing temperature the fluid remains in some kind of metastable with the two phases even at temperaatures higher than the critical point. If fluid was agitated, then immediately the two phases disappeared and opalescence appeared. 
