In an immiscible mixture, the partial pressure of a component is equal to the vapor pressure of the pure component. The technique used to separate mixtures of immiscible liquids is referred to as steam distillation and can be an effective method for isolating organic materials from complex mixtures. The earliest isolations of organic substances from natural materials were done using steam distillation. One distinct advantage of steam distillation is the lower temperature required to isolate the organic substance.
The setup shown is a modified simple distillation apparatus wherein a claisen head is added in between the boiling flask and the distilling adapter. The purpose of this is to provide a second opening into the system to accomodate a source of steam or the addition of water.
In actual practice, considerably more water is usually distilled to ensure that all of the organic material has distilled over. One way of determining when all of the organic material has distilled is to check the condensate. If it is clear and is only one phase, the steam distillation is complete.