THE NAVAL STOKES INDUSTRY. 39 



still by a pipe C attached to the steam dome. The still is constructed 

 entirely of steel made to stand a pressure of 10 atmospheres, although 

 6 atmospheres is never exceeded in actual practice. The still con- 

 sists of a gate valve P for introducing the crude resin and another 

 gate valve Q for discharging the rosin; the body of still D, shaped like 

 a prism; a steel jacket E, circular in shape; 32 tubes H, arranged 

 crosswise in four series of eight tubes each, running through the si ill 

 from one side to the other, through which passes steam from the 

 jacket E; a hood F; a still-head G; and a pipe N, which leads back 

 to the boiler the water produced by condensation of steam in the still. 

 Since the pressure in the boiler and in the steam jacket is the same, 

 this condensed water readily returns to the boiler by its own gravity. 



The crude resin, divided into thin layers by the pipes H, distills 

 rapidly. To carry the turpentine over, water is supplied through a 

 funnel in the top of the hood F. 



The condensing apparatus consists of a tubular condenser J and an 

 ordinary worm K. The condenser is made up of a series of tubes 

 from 10 to 12 feet long, riveted to two steel plates, and is fed with cold 

 water through LL'. The tubular condenser is so efficient that the 

 worm becomes almost useless. 



A still having a capacity of 92 gallons (about 2 barrels) has a heat- 

 ing surface amounting to about 120 square feet, and permits the dis- 

 tillation of one charge in about 40 minutes. 



When the turpentine is completely removed the introduction of 

 waler ceases. The heating is continued by means of the steam 

 jacket until the rosin is free from water. 



COMPARISON BETWEEN DIRECT AND STEAM HEATED STILLS. 



The disadvantages of distilling with directly heated stills may be 

 summarized as follows: 



1 . During the distillation of the crude resin the ligneous impurities may undergo a 

 partial carbonization which colors the rosin. 



2. The rosin becomes exceedingly dark at high temperatures. 



3. The rosin may undergo incipient decomposition and color the turpentine more 

 or less yellow. 



4. Distillation by direct heat is a delicate operation, difficult to regulate, and requir- 

 ing an experienced man. It can be applied only to a comparatively small quantity 

 of material, if good results are to be obtained. 



5. Increased fire risk. 



By using stills heated by steam the above disadvantages are 

 removed, but others are introduced. The reasons why the use of 

 steam stills has not become general are: 



1. Complicated apparatus. 



2. Greatly increased cost of apparatus and expense of operation. 



3. Necessity for a large stock of crude resin, if the still is to be operated economically. 



4. With the majority of apparatus the crude resin must be given a preliminary 

 treatment to remove chips, bark, sand, and other trash. 



