27 



each portion as it distils or passes over being received separately from 

 the other portions and called a fraction. Figure 14 shows graphically 

 what products are derived from the destructive distillation of wood, 

 and the subsequent separation of these products by fractional dis- 

 tillation. In the distillation of tar, iron stills are employed and the 

 first fraction or portion obtained consists of acetic acid and alcohol 

 mixed with some of the light oils. The light oils distil below 150 C. 

 and have a specific gravity of from 0.966 to 1.000; the heavy oils 

 distil above 150 C., have a specific gravity of from 1.014 to 1.021, 

 and contain creosote, toluene, and paraffin bodies. The pitch, which 

 constitutes from 50 to 65 per cent of the material, remains in the 

 retort when the distillation is complete. 



These several fractions, or portions, may be further purified, acetate 

 of lime and alcohol being recovered from the first fraction, while the 

 oily distillates are neutralized with milk of lime and redistilled. The 

 light oils distilling below 150 C. are used as solvents and for varnish 

 making, while those distilling at 150 to 250 C. are treated several 

 times with alkali (boiling the alkaline solution in the air to oxidize 

 impurities) and acid alternately and redistilled. The distillate 

 obtained at from 200 to 250 C. is commercial wood creosote, which 

 has a yellow or brownish color and a smoky aromatic persistent odor 

 different from that of carbolic acid. This is agitated with strong soda, 

 the aqueous layer drawn off is rejected, the remaining oil is mixed 

 with sulphuric acid and allowed to stand until creosote oil separates, 

 when this is driven off with steam and redistilled finally from glass 

 retorts. The creosote obtained boils between 205 and 220 C. and 

 has a specific gravity of from 1.030 to 1.080. It contains from 50 to 

 60 per cent of guaiacol (C 7 H 7 O.OH) and creosote (C 8 H 9 O.OH), and 

 small quantities of other higher phenols. This product is a powerful 

 antiseptic and is used as a disinfectant and preservative. The oils 

 distilling above 250 C. are used for burning. 



Stockholm tar and pine tar or pitch, made by distilling pitch pine 

 or other coniferous woods in heaps covered with earth (see fig. 2), 

 differ in composition from hard-wood and from pine-wood tar made 

 in retorts and are regarded as more valuable. They are used for 

 tarring ropes, calking ships, making soaps, for timber preservation, 

 pitching barrels, and in preparing medicine. 



WOOD OIL. 



When a crude aqueous distillate (see p. 32) is first distilled in order 

 to separate acids, alcohol, and acetone from the tar, some of the 

 lighter oils which are present distil with the acid and alcohol, and 

 finally remain in the alcohol still, or, if distillation is carried further, 

 they pass over in the last stages and separate as an oily layer. This 



[Cir. 36] 



