10 



ACETIC ACID 



and Liverpool ; but, on the other hand, where light wood is used, such as that gone- 

 rally carbonised in the Welsh factories, the square ovens answer better. 



An ingenious improvement in the manufacture of pyroligneous acid was patented 

 some years ago by the late Mr. A. G. Halliday, of Manchester, and adopted by 

 several large manufacturers. The process consists in effecting the destructive 

 distillation of waste materials, such as sawdust and spent dyewoods, by causing 

 them to pass in continuous motion through heated retorts. For this purpose tho 

 materials, which are almost in a state of powder, are introduced into a hopper. H 

 (fiff. 6), whence they descend into the retort, B, being kept all the while in constant 

 agitation, and at the same time moved forward to the other end of the retort by 

 means of an endless screw, s. By the time they arrive there the charge has been 

 completely carbonised, and all the pyroligneous acid evolved at tho exit tube, t. Tho 

 residuary charcoal falls through the pipe D into a vessel of water, K, whilst tho vola- 

 tile products escape at F, and are condensed in the usual way. 



Several of these retorts are generally sot in a furnace side by side ; the retorts are 

 only 14 inches in diameter, and eight of these retorts produce in 24 hours as much 

 acid as 16 retorts 3 feet in diameter upon the old system. In the manufacturing 

 districts of Lancashire and Yorkshire, where such immense quantities of spent dye- 

 woods accumulate, and have proved a source of annoyance and expense for their 

 removal, this process has afforded a most important means of economically converting 

 them into valuable products charcoal and acetic acid. 



Mention should also be made of Messrs. Solomons and Azulay's patent for em- 

 ploying superheated steam to effect the carbonisation of the wood, which is passed 

 directly into the mass of materials. Since the steam accompanies the volatile pro- 

 ducts, it necessarily dilutes the acid ; but this is in a great degree compensated for 

 by employing these vapours to concentrate the distilled products, by causing them to 

 traverse a coil of tubing placed in a pan of the distillates. 



As regards the yield of acetic acid from the different kinds of wood, some valuable 

 facts have been collected and tabulated by Stolze, in his work on Pyroligneous 

 Acid : 



Properties of the crude Pyroligneous Acid, 



Tho crude pyroligneous acid possesses the properties of acetic acid, combined with 

 those of the pyrogenous bodies with which it is associated. As first obtained, it is 

 black, from tho large quantity of tar which it holds in solution ; and although certain 

 resins are removed by redistillation, yet it is impossible to remove some of the empy- 

 reumatic oils by this process, and a special purification is necessary. 



In consequence of the presence of creosote, and other antiseptic hydrocarbons, in 

 tho crude pyroligneous acid, it possesses, in a very eminent degree, anti-putrescent 



