Dabberraven said:

 When using a silver caduceus to extract a level  8 elixir,  I know the elixir is then destroyed. [...]

Good evening Dabberraven:

Assuming that by exctracting you mean removing from a slot, you do not need a caduceus to extract a potion, the caduceus enables you to extract a potion without destroying it.

Also, remember that "extracting" does not mean "applying" but rather the opposite. You can add any potion to one of the three slots, it is only when you wish to replace a potion in a slot with another one, you will need a caduceus if you do not want the potion destroyed after extraction.

Example:

All slots are full and one of these contains a level 6 Resistance potion. You have managed to mix a further level 6 Resistance poton and would now like to mix these two, so you extract the one in the slot using a caduceus (otherwise it will be destroyed), mix the two level 6 Resistance potions to make a level 7 potion and put it back in the free slot.

Hope that helps.
P.

PS: You may use 3 of the 8 potion types at one time (in the three slots provided) but they must all be different ones. You could not, for example, activate 2 or more Resistance potions regardless of level.

thank you