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



This pan, inclosed by brickwork and heated by the flames from a 

 fire-box, has a capacity of about 325 gallons. 



After the pan has been filled with crude resin the heating is con- 

 ducted very slowly to prevent " burning. " A workman stirs the 

 mass constantly with a wooden paddle to render the heating uniform. 

 When boiling begins the heating is discontinued, as the temperature 

 should never be allowed to exceed 90 to 100 C. To clarify the 

 mass the temperature is suddenly reduced by drawing the fire. 

 Sometimes a small amount of water is thrown into the fire box and 

 upon the bottom of the pan. If this delicate operation is successful, 

 the mass will settle into several layers after standing for four or five 

 hours. A layer of chips, bark, etc., will be found on the surface; 

 then a layer of resin; and below this a layer of colored water with a 

 deposit of sand, etc., on the bottom. The floating chips and bark 

 are removed by skimming. The resin may then be run out through 

 pipes arranged at different levels, but usually is dipped out. The 

 heaviest material is filtered through a screen to remove the sand, 

 the filtrate separating into a layer of colored water surmounted by a 

 small amount of inferior resin. By this procedure a resin is obtained 

 which on distillation will yield a rosin several grades higher than the 

 original resin would give if distilled with all its impurities. 



Purification in an open pan results in the loss of from 2 to 3 per 

 cent of turpentine, and there is considerable danger of fire. Several 

 pans provided with covers have been designed to overcome the objec- 

 tions cited. 



Closed pans. The pan designed by Dromart (fig. 6) illustrates 

 the closed type. It is provided with a horizontal cover whose edge 

 fits into the groove (R), the latter being fed by a stream of cold 

 water so that the cover is hermetically sealed. The pan is charged 

 without loss of turpentine by means of a box (B) with a trap in the 

 bottom worked by a lever. By manipulating this lever the resin 

 contained in the box falls into the pan. To obtain uniform heating 

 the resin is stirred by means of an agitator (G). At the end of 4 

 to 5 hours the melted resin shows a temperature of from 85 to 

 90 C., and a jet of steam issues from a test hole in the cover. The 

 heat is then reduced, and the liquid mass cooled by dumping in one 

 or two boxes of resin through the trap. After stirring vigorously 

 the mass is allowed to rest for 12 hours. The resin is then decanted 

 through a pipe (V) situated above the bottom so as to keep the layer 

 of water and dirt below its orifice. 



It is sometimes difficult to separate the water and solid impurities 

 from the resin, owing to the fact that the density of the resin and 

 that of the water are so nearly the same. The density of a gum 

 containing 80 per cent rosin and 20 per cent turpentine, at 20 C., is 

 about 1.023, while at the same temperature distilled water has a 

 density of 0.998. Since the water in the resin contains certain amounts 



