12 BULLETIN 229, U. S. DEPARTMENT OF AGRICULTURE. 



Frequency of chipping. — Table 8 shows the rate with which the 



gum flows. 



Table 8.— Rate of exudation of gum from "chipped' ' longleaf pine. 



Day. 



Grams of 

 gum. 



Total ex- 

 udation. 



Day. Grams of 

 J gum. 



Total ex- 

 udation. 



First 



113.0 

 22.5 

 13.5 

 9.0 



(?) 



Per cent. 

 67.26 

 13. 39 

 8.04 

 5.36 



Fifth and sLxth j 9.0 



Per cent. 

 5.36 



Second 



Seventh i 1.0 



0.59 



Fourth 



Total | 2 168.0 



100.00 



Fifth 











1 No weighing. 



2 168 grams equal 0.37 pound. 



It is seen that 88 per cent of the total flow occurs during the first 

 three days. As the resin ducts become plugged with coagulated or 

 crystallized gum the flow gradually ceases, and the gum thereafter 

 produced is stored in the resin ducts until the ends are again opened. 

 When the ducts immediately above the wound become full, the resin 

 tends to diffuse or soak into the wood further removed from the bark 

 This diffused resin does not drain out when the tree is wounded, and 

 for this reason chipping should be done often enough to insure that 

 the active ducts immediately beneath the bark and above the wound 

 will not remain full of gum. On the other hand time should be al- 

 lowed between chippings for a new supply of gum to form. In prac- 

 tice, trees are chipped once a week. It is possible that more frequent 

 chipping would give a greater yield of gum for a short period (one or 

 two years), but at the same time it might further reduce the vitality 

 of the tree and so result in a smaller total yield over a longer period. 

 The increased yield, moreover, must be enough to justify the addi- 

 tional expense. Experiments are needed to show how the rate of 

 flow is affected by frequency of chipping in operations extending over 

 different periods of years. 



Size and number of faces. — The scar on the tree caused by successive 

 chippings is usually about 14 inches wide, and is known as the "face." 

 Wounding the tree, of course, diminishes its vitality by interfering 

 with the transmission of water from the roots to the leaves and of 

 nutritive matter from the leaves to the roots. When a small tree, 

 8 or 10 inches in diameter, is chipped, it usually either dies outright 

 or its further growth is greatly retarded, even though the width of 

 the face is kept at the minimum. 



PRINCIPLES UNDERLYING THE DISTILLATION OF CRUDE GUM. 



The crude gum was formerly distilled without the addition of 

 water; in consequence the quality of the resulting turpentine and 

 rosin was poor. The yield of turpentine was very low, but it was 

 impossible to increase it without coloring the liquid yellow with the 



