Precautions: Do your mixing in a well-ventilated room and wear a mask while mixing. Combine the citric acid with the baking soda and stir well. Add the essential oil to a spray bottle and spray into the mix and stir well. If the mixture is too dry add a little water to the spray bottle and spray into the mixture until it is damp enough to pack together. Pack into the molds (or ice cube tray). Let it dry for several hours or overnight. Store in a airtight container.