THE NAVAL STORES INDUSTRY. 27 



will not make high-grade lumber, the proportion of high-grade material 

 that can be cut from " turpentined" timber is somewhat less than in 

 the case of similar " round" timber. However, in many cases the 

 process of squaring up the log by sawing off slabs will remove the 

 resinous parts, and the grade of the boards finally cut will not be 

 affected. Tests have shown that the strength of the wood is not 

 altered by turpentining. 



QUALITY OF GUM FROM BOXED AND CUPPED TIMBER. 



As the height of the face increases, the distance the resin must flow 

 to reach the box increases correspondingly. During its journey the 

 gum is constantly losing turpentine by evaporation. Thus, the 

 percentage of turpentine in the dip decreases each year boxed timber 

 is tapped, while the amount of scrape increases. Cups are designed 

 to be raised each season, and thus the gum has to flow a comparatively 

 fhort distance. 



The resin acids in the crude gum readily absorb oxygen, which 

 darkens the rosin. The higher the face the longer the gum is sub- 

 jected to atmospheric oxygen, so that, with boxed timber, light 

 rosins can be obtained only during the first two years. Another 

 sactor which produces dark-colored rosin is the gum that remains 

 attached to the face after the period of collection has passed. This 

 gum becomes yellow to dark brown, and as the following year's gum 

 flows over it to the box, a certain amount of this highly colored 

 product is always dissolved, so that when ordinary methods are used 

 only the lower grades of rosin are produced from gum coming from 

 five-year boxes. In raised cups the gum flows only over the face 

 made during a single season. In practice, however, the cups are 

 seldom raised after the third year, since this greatly increases the 

 cost of collecting the gum. 



COMMERCIAL DISTILLATION OF CRUDE GUM. 



The apparatus commonly used in the United States for distilling 

 gum consists of the simplest type of still, with a " worm" for condens- 

 ing the vapors (PL VIII and fig. 5). A shed, generally open on all 

 sides, covers the still proper, and another and smaller building, 

 placed a short distance away as a precaution against fire, is used for 

 storing the turpentine. It also contains the kettle for heating glue 

 to coat the inside of the turpentine barrels. In many cases the 

 still and warehouse are under one roof. A charging platform is 

 built flush with the collar of the still, the barrels of gum being rolled 

 upon it by means of skids. 



The capacity of stills varies from 10 to 40 barrels. Fifteen and 

 twenty barrel stills are the most common. The term "20-barrel 

 still" refers to the total capacity of the still and not to the number 

 of barrels of gum in a charge. The size of the latter is determined by 



