THE NAVAL STORES INDUSTRY. 47 



longleaf, and the amount of timber available for turpentine opera- 

 tions in the Southeast is constantly diminishing. These two facts 

 make it reasonable to suppose that turpentine operations in the large 

 tracts of virgin pine timber of the West will in time be justified. 



SPECIAL PROBLEMS INVESTIGATED ARIZONA AND CALIFORNIA 

 WESTERN YELLOW PINE. 



EVAPORATION FROM CUPS. 



The rate of evaporation from the cups in Arizona was determined 

 by exposing cups half full of fresh gum to the action of the air and 

 weighing them at regular intervals. The samples of gum were secured 

 by taking small amounts from as many of the cups as necessary on 

 the first or second day after a fresh streak had been put on. Two 

 samples were taken from each area after each dipping. Since dip is 

 collected every three or four weeks in commercial operations the loss 

 in weight during the first four weeks is the significant figure in the 

 evaporation tests. Forty-eight evaporation samples were used. Of 

 these 14 showed no loss at all in weight for the first four weeks; the 

 remaining 34 samples showed losses ranging from 1.5 to 10.5 per cent. 

 The average loss in weight for all the samples was 3 per cent. The 

 gum as exposed contained turpentine, rosin, water, and chips. The 

 loss by evaporation was of course made up of turpentine and water. 

 The average loss of turpentine by evaporation from the cups in the 

 Arizona experiments was therefore less than 3 per cent. The average 

 loss in six similar evaporation tests in California was 2.5 per cent. 

 No evaporation figures are available for southeastern operations. 



COMPARISON OF YIELDS FROM NORTH AND SOUTH FACES ARIZONA. 



The total yield for 50 cups on the north side of 50 trees from the 

 first dipping on June 3 to the last dipping on November 3 was 242.6 

 pounds and for 50 cups on the south side of the same trees 266.2 

 pounds. These weights show a 9 per cent greater flow on the south 

 side of the trees than on the north. Figure 10 shows the average 

 yield per week for both the north and south faces of each of the 50 

 trees, arranged in order of the yields from the south faces. Twenty- 

 seven south cups yielded more than the corresponding north cups, 

 while 17 north cups showed an excess over the corresponding south 

 cups. The remaining six trees had about the same flow for both cups. 

 The diagram shows the tendency of faces on the same tree to give 

 the same yields. Trees having an exceptionally good or exceptionally 

 poor flow generally show it in both faces. 



EFFECT OF TEMPERATURE ON WEEKLY YIELD OF GUM. 



Figure 1 1 shows the average flow per cup for 50 trees for each week 

 and the corresponding average temperature. With but few excep- 



