I shot these with my Yashica t3, which I have on me at all times.
Carbonic acid is not to be recommended on account of the comparatively high value of t3.
From a practical point of view the value of t3 may be regarded as the limit to which the temperature falls.
The values of t3 and p3 are accurately known only for a few substances.
The highest pressure will therefore be found at Tc and the lowest at t3.