



21 



From these figures it appears that distillation is, for 1m practical 

 purposes, complete at 430 C., as the additional volatilization above 

 this temperature is only about 1.5 per cent. The chief products are 

 formed continuously throughout the entire process, which proceeds 

 in three characteristic periods: (1) At a temperature from 150 to 

 280 C., acetic acid, methyl alcohol, and wood creosote are the chief 

 products; (2) from 280 to 350 C., large volumes of gases are also 

 given off; (3) and from 350 to 430 C., solid hydrocarbons are dis- 

 tilled. Chorley and Ramsay a have found that the yields of both 

 methyl alcohol and acetic acid continue up to about 500 C., or at 

 least above 380 C. The quantity of methyl alcohol formed increases 

 with rise of temperature to a maximum at about 300 C. and gradually 

 falls above that temperature, while the quantity of acetic acid formed 

 under the same conditions increases to 350, with a slight fall in 

 quantity between 350 and 450. Barillot, 6 on the other hand, found 

 that on a large scale acetic acid ceased to be formed above 300 C. at 

 the end of thirteen hours. On the whole, therefore, it appears that, 

 while the yields of both alcohol and acid have reached the maximum 

 at 300 to 350 C., the formation of both continues up to 450, beyond 

 which point it is useless to raise the temperature. 



Experiments and experience have both shown a lower yield of acid 

 and alcohol when the wood was rapidly heated than when slowly 

 heated, but the experiments of Chorley and Ramsay just cited show 

 that maximum yields of both products may be obtained even when 

 distillation is completed in two or three hours. It appears, therefore, 

 from the data that the low yields obtained from fast heating in practice 

 are due to overheating rather than to rapicl heating. In the case of 

 overheating, secondary reactions are set up by the high heat, resulting 

 in the destruction of some of the alcohol and acid. This is particu- 

 larly liable to occur where no provision has been made to remove the 

 products of distillation from the influence of high heat. Further, 

 when the vapors are evolved rapidly without provision for their 

 prompt removal there is apt to be considerable loss from " bio wing of 

 the retorts/' that is, the escape of gases around the door due to pres- 

 sure within the retort. On the other hand, slow distilling allows the 

 vapors to pass out with less loss from blowing or secondary reactions. 

 It is of the greatest importance, therefore, that provisions be made for 

 the rapid removal of the vapors from the retort and for their com- 

 plete condensation subsequently. 



J. Soc. Chem. Ind., 1892, 2: 395. 

 &Compt. rend., 1896, 122: 735. 

 [Cir. 36] 



