You must be an Alchemist Artificer to use the Alchemist's Potencifier Gasket and you created this wee gadget automatically (and may add it to your possessions) when you took on the Alchemist (Artificer) sub-class. 

Once built or otherwise received, it may be incorporated (one time only, 1 Action or Bonus Action to do so) into your Alchemist's Supplies, Manifold Tool, or All-Purpose Tool, +1 (or similar). Ie, whichever tool is used by the Alchemist to cast their alchemy related spells. 

When using said tool with the Alchemist's Potencifier Gasket attached, the Alchemist may cause one additional effect whenever they use their level 3 Alchemical Savant  feature. The gasket causes any target who takes (ie is not immune to) the Alchemical Savant hp damage to make a new CON Saving Throw against the Alchemist's Save DC. 

On a failure the Artificer may impose one of either, the Poisoned condition, the Blinded condition, or 'silence' the target (ie they cannot cast spells with a Verbal component or otherwise communicate verbally for all their coughing). No extra penalty to the target on a successful save. 

This condition lasts until the end of the target's (or targets') next turn. 

NB: 'Deafened' is in the tag list as a stand-in because there is no condition for 'silenced' - although it is described in the Silence spell.

Notes: Poisoned, Blinded, Deafened, Artificer