24 



BULLETIN 1003, U. S. DEPARTMENT OF AGRICULTURE. 



thermometer 1 until the turpentine has been recovered. The tem- 

 perature is then raised to 343° C, and the bottom coil (d) made to 

 join in the circulation of the oil by opening valve o until destructive 

 distillation of the charge has been effected. Valves ?n, n, and o are 

 adjusted (ordinarily unnecessary) so that thermometers 2, 3, and 4, 

 registering the temperature of the return oil from coils &, C, and d, 

 respectively, read essentially alike, indicating thereby that the oil 

 flows equally through the three coils. 



PROCEDURE. 



Turpentine is present in resinous wood, along with rosin, as an 

 oleoresin. Subjected to the designated retort temperature this oleo- 

 resin is partially sweated out and escapes from the pores of the wood, 

 losing the turpentine by vaporization, while the resin accumulates 



Fig. 3. — Plan of retort used for distillation of samples. 



with certain decomposition products, as pitch, in the bottom of the 

 retort. The distillation is therefore conducted in two stages. 



During the first stage the turpentine is recovered, and the result- 

 ing rosin liberated from the wood is collected in the bottom of the 

 retort. The oil-bath temperatures during this stage are between ap- 

 proximately 220° and 265° C. The valve to the bottom coil (d) that 

 lies embedded in the molten rosin is then opened, and the tempera- 

 ture of the circulating oil raised to 343° C. This brings about de- 

 structive distillation of the wood and the rosin, with the production 

 of pyroligneous acid and the formation of rosin oils containing also 

 creosote and other constituents derived from the wood, which distil 

 from the retort in two stages as light oil and heavy oil. 



The light and heavy oils come over with the aqueous distillate 

 (pyroligneous acid) resulting from the chemical transformation of 

 the wood and rosin during the destructive stage of the distillation, 



