After you contain a High Energy Pellet to start an Unstationary Scaffold, you reach Test Chamber 08.

Avoid the Poison

There is a pit of toxic liquid in this room. Don't fall in, or you will die.

Contain a Pellet

There is a high energy pellet here. Make a blue portal on the wall where the pellet has made a dark mark. Then, after it goes through the orange portal, make a second blue portal on the part of the wall where the containment machine is shining a light. The pellet will bounce from the wall and go back through the orange portal, flying through the blue portal that you just made, to enter the containment machine. This will make the Unstationary Scaffold start moving.

After that, make a blue portal on a wall that you can reach from where you are. Go through it to reach the platform where there is an orange portal. Now, you need to make a blue portal on the ceiling above the unstationary scaffold, and go through the orange portal when the scaffold is under the blue portal. This is dangerous, because if you don't put the blue portal in the right place, you will fall to your death. My advice is to create the blue portal, then look through the orange one to check that the scaffold is under it when it stops.

After you land on the scaffold, you can reach the elevator that leads to Test Chamber 09.