30 BULLETIN" 229, U. S. DEPARTMENT OF AGRICULTURE. 
gum returns to a normal state of distillation. The heat is increased 
because at the temperature at which the water is vaporized, the gum 
is still in a viscous condition, and is so tenacious as to form a mass of 
bubbles whose shells are not ruptured by the inclosed steam; hence 
the gum swells enormously. In order to remove this water, it is 
necessary to heat the gum to so fluid a state that the bubbles will 
burst readily and allow the steam to escape. After this inclosed 
water has been driven off the distillation usually runs along smoothly, 
since the water that is added merely comes in contact with the sur- 
face of the gum. If excessive foaming takes place after the stream 
of water has been started, the fire is urged as usual, but the flow 
of water is not diminished. If the gum should boil over the distil- 
lation is spoiled, and must be repeated. 
The end of the distillation is reached when a portion of the distillate 
collected in the test glass shows only a very small proportion of 
turpentine. All the turpentine is seldom removed, if the distiller 
wishes to obtain a high-grade rosin. The stream of water is now cut 
off, and the fire extinguished with water to prevent the rosin from 
igniting when it is run out, and to prevent scorching the small 
amount of rosin that always adheres to the bottom of the still. 
Skimming. — The gum always contains more or less trash, such as 
sand, chips, needles, pieces of bark, etc. This all goes into the still 
along with the gum, and is removed at various stages during the dis- 
tillation. The chips are removed with a slammer, 16 inches long by 
14 inches wide, made of wire netting and attached to a long handle. 
Except in the case of dip collected at the end of the season, slam- 
ming is done as soon as the charge is fluid. In o-ther cases skimming 
is done either at the point when the water originally present in the 
gum has passed over, or at the end of the distillation when the rosin 
is ready to be run off. When the gum contains a considerable amount 
of trash, especially bark and needles, a lighter resin will be obtained 
by skimming before distillation. However, in the case of "old 
stuff," there is considerable difficulty in getting the charge fluid 
enough for skimming without excessive loss of turpentine and the 
danger of foaming. 
TREATMENT OF THE ROSIN. 
After the distillation is ended, the rosin, at a temperature of 302° 
to 392° F., is run out by means of a pipe extending flush from the 
bottom of the still and closed by a gate valve. Usually the rosin 
flows through a set of four screens into a vat sunk into the ground. 
One, two, or three screens may be used, however, instead of four. 
The vat is about 4 by 15 feet at the bottom, 4J by 15 feet at the top, 
and 2 J feet deep. The screens are sufficiently large to cover it, with 
the exception of the top one, which is only half the length of the still, 
and is intended to catch only the coarsest chips. The top screen is 
