THE EFFECTS OF HEAT. 



2-i3 



Fig. 203. 



rises in the form of vapor^ and is received and condensed 

 in a separate vessel. 



By this means very volatile bodies can be easily separated from less vola- 

 tile ones; as brandy and alcohol from the less volatile water which may be 

 mixed with them. Water of extreme purity can also be obtained by distil- 

 lation, because the non-volatile and earthy substances contained in all spring 

 •waters do not ascend with the vapor, but remain behind in the vessel 



Distillation upon a small 

 scale is effected by means 

 ol a peculiar-shaped vessel, 

 called a retort. Fig. 208, 

 which is half filled with a 

 volatile liquid and heated ; 

 the steam, as it forms, 

 passes through the neck of 

 the retort into a glass re- 

 ceiver set into a vessel filled 

 with cold water, and is then 

 condensed. 



When the operation of distillation is conducted on an extensive scale, a large 



vessel called a " stiW^ is used, and, for con- 

 densing the vapor, vats are constructed, 

 holding serpentine pipes, or "worms," 

 which present a greater condensing sur- 

 face than if the pipe had passed directly 

 through the vat. To keep the coil of pipe 

 cool, the vats are kept filled with cold 

 water. In Fig. 209, a is a furnace, in which 

 is fixed a copper vessel, or still, to contain 

 the liquid. Heat being applied, the steam 

 rises in the head, b, and passes through 

 the worm, d, which is placed in a vessel 

 of water, the refrigerator. The vapor 

 thus generated is condensed in its passage, and passes out as a liquid by the 

 external pipe into a receiver. 



What is th ^^® difference between drying by heat and distillation is, 



difference be- that in one case, the substance vaporized, being of no use, is 

 bT'^heat "^^and allowed to escape or become dissipated in the atmosphere ; 

 distillation ? while in the other, being the valuable part, it is caught and 



condensed into the liquid form. The vapor arising from damp linen, if caught 

 and condensed would be distilled water; the vapor given out by bread while 

 baking, would, if collected, be a spirit like that obtained in the distillation of 

 grain. 



.^~ j^j . ^ . J. 5G2. As some substances, by the application of heat, pass 



matiwi ? directly from the solid condition to the state of vapor, so some 



substances, as camphor, sulphur, arsenic, etc, when vaporized 



