Formula for De Vries' Extract

Formula for De Vries' Extract is a scroll in that is used to make De Vries' Extract, a potion which makes it possible to spot invisible enemies.
It can be automatically given by Triss after placing the sensors during the quest The Source, or purchased from the following merchants:
*Hermit at his hut in the Fields
*Kalkstein at his laboratory in Old Vizima 
== Contents ==
:Formula for De Vries' Extract
:De Vries' Extract: makes it possible to spot invisible opponents.
== Journal entry ==
* Formula: De Vries' Extract
cs:Recept na odvar de Vries
de:De Vries' Extrakt (Schriftrolle)
fr:Recette de l'infusion de Vries
it:Ricetta dell'estratto di de Vries
pl:Recepta na Wywar de Vries
ru:Рецепт экстракта Де Врие
Category:The Witcher scrolls