THE NAVAL STORES INDUSTRY. 



37 



of dissolved matter, its density may be greater than the figure given, 

 while the density of resin richer in turpentine will be less than 1.023. 

 To separate the two it is necessary to lower the density of the resin or 

 increase the density of the water. The former is accomplished by 

 adding certain amounts of "heads" and "tails" from a previous dis- 



tillation, and the latter by adding a cheap salt, such as common salt 

 or soda. 



DISTILLATION BY DIRECT HEAT. 



Direct heating is the method of distillation generally employed in 

 France. The type of still and its method of operation are exactly 

 the same as in the United States. 



