Distilling a plant means you drive steam through the flower to carry off its essential oil.
You pile lavender flowers in a vessel, through which steam rises, and this steam carries off the essence of the flower. The steam-essence mixture rises through the goose-neck condensation tube, called in French the “col-de-cygne” (which means “swan neck) where it cools off and becomes liquid. The liquid mixture goes into a separator (in French – a “vase florentin”, or Florentine flask) where it settles. The essential oil rises to the top, for it is lighter than water. The essence-infused water remains at the bottom for it is heavier than the oil. The separator has two taps – the one at the top to draw off the essential oil, and the lower tap to draw off the distilled water, also known as hydrosol, a therapeutic by-product of distillation. This floral water can be used in cosmetics and for certain therapeutic treatments.