“For the benefit of many readers perhaps a brief and nontechnical description of the preparation of acetic acid would not be amiss, and would explain the necessity for the essentials indicated above. In brief, the process is as follows:
“(a) A suitable timber is heated in a closed retort. This is termed ’dry distillation,’ and results eventually in the carbonisation of the wood—i.e., charcoal is obtained in the retort.
“(b) Tar, vapours and gases are distilled over during the carbonisation of the wood. These liquors and gases pass through condensers. The gases pass away, while the condensed liquors separate out into (1) wood tar, (2) a watery liquor called pyroligneous acid or crude wood vinegar.
“(c) The pyroligneous acid is separated from the tar, and again distilled to obtain the acetic acid present.
“(d) This crude acid is steam-heated with milk of lime, which fixes the acid, forming calcium acetate (or acetate of lime).
“(e) Eventually the calcium acetate is taken out in the form of a thick paste, which is spread to dry. When dry this ’grey acetate’ is the main source of all glacial acetic acid now made.
“(f) The acetic acid is released from the ’acetate of lime’ by the action of sulphuric acid. It is then distilled several times, and under various conditions, in order to increase its strength. In the past copper tubes were used for this purpose, but owing to the fact that traces of copper were found to be injurious to rubber, some works instal tubes of glazed earthenware for the distillation.
“Such is the process in outline, and it will be seen that no proposal to manufacture glacial acetic acid on an estate could be considered feasible, although it would not present any great difficulty on a large scale and under skilled direction. Furthermore, the cost of the plant would be far too great for any estate.”
Although it is clear that pure acetic acid is beyond the scope of an estate, crude pyroligneous acid has been produced on a varying scale in this country and in Ceylon. In the latter country some success was obtained by the distillation of coconut shells with comparatively inexpensive plant. In this country, wood-distillation was practised on a few estates, but improved facilities for obtaining pure acetic led to a termination of the experiments, although sufficient crude acid could then be made at a reasonable cost.
The pyroligneous acid obtained, is generally clear, after nitration, and of a dark brown colour. It has a peculiar odour reminiscent of smoked sheet-rubber, or of creosotic substances in general.