12 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



C. Steam Distillation. 



Very frequently a separation of a liquid or a solid from a mixture 

 can be effected by the process of steam distillation. The liquid, or 

 solid, has usually a higher boiling-point than water, but the vapours 

 of the liquid and of the water do not interfere with each other. The 

 effect of the steam is to reinforce the vapour pressure of the liquid, so 

 that the liquid distils with water under atmospheric pressure at a lower 

 temperature. 



Steam is generated in a large flask, or tin can, which is provided 

 with a cork carrying a long safety tube about 80 cm. long, reaching 

 almost to the bottom, and with a delivery tube. The flask is half- 

 filled with water. The delivery tube when the steam is ready is con- 

 nected to the flask containing the mixture. This flask is placed in a 



FIG. 8. 



sloping position so as to prevent splashing of its contents and mechanical 

 carrying over of substance into the condenser. The steam is passed 

 into the bottom of the vessel by a tube which is bent so that its end 

 lies in a vertical position, and to prevent condensation of the steam 

 the flask is also heated. The steam and other vapour reach a long 

 condenser by which water and substance are condensed and are col- 

 lected in a receiver (Fig. 8). 



The separation of substance and water is effected by filtration if 

 solid, by simple separation if liquid, or by extraction with a solvent 

 such as ether, chloroform, etc. The solvent is then dried, removed by 

 distillation, and the substance or substances obtained by distillation 

 or fractional distillation. 



