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 Unite'd 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 
