Amulet of chemistry

An amulet of chemistry is a jade amulet enchanted via the Lvl-2 Enchant spell.

When equipped, there is a 5% chance to give you an extra dose when brewing potions. The amulet will provide five charges before disappearing.

As of an update on 27 July 2017, players can right-click Options on the amulet to toggle whether they would like to stop making potions when the amulet breaks.

The amulet of chemistry provides no benefit when making potions that output 4 doses such as Super Combat, Anti-venom, Extended antifire etc.

Profit
When using the amulet for solely profit, it should only be used when a single dose of the potion you make has a value of more than 1/5th of the amulet's worth. 

You can see current single dose values for comparison here: