CHAPTER III. PRODUCTION OF CREOSOTE FROM TARS. 
In commercial practice creosote is to a considerable extent a by- 
product of the manufacture of other materials. The details of the 
process, therefore, vary somewhat with the end product obtained. 
The process of manufacturing creosote consists, essentially, of the 
distillation of the tar and is in general the same, no matter what 
the end products may be. 
The size and shape of the stills used for the purpose of commercial 
distillation vary somewhat according to the needs of the producer. 
In England and Germany, according to Lunge (10) and Warnes (11), 
the vertical still with a concave-upward bottom is preferred. Figure 
9, taken from Lunge's Coal Tar and Ammonia, shows a cross-section 
of a 25-ton vertical still. Many stills of this general design are used 
in this country, but the horizontal still is more common. Figure 10 
shows a battery of horizontal stills in use in this country. 
The stills are filled to the proper level with crude or settled tar, 
preferably already heated by means of a preheater, and a slow fire is 
started under the still. In the early stages of the distillation extreme 
caution must be exercised, because most coal tar contains water, which 
can not readily be separated by standing. Too rapid heating will 
cause foaming or priming, with a loss of nearly the entire contents, 
unless the priming can be controlled. 
In the United States it seems to be considered good practice to 
stir the contents of the still by using either air or steam, the former 
being preferred. This stirring aids in the prevention of foaming 
over during the early part of the distillation and results in a more 
rapid distillation when it is produced during the latter part of the 
process. A slight chemical reaction is also probably obtained. In 
Europe it is customary to inject steam into the still during the dis- 
tillation of the anthracene oil. The number and graduation of 
fractions taken from coal tar depend largely on the markets for the 
various products. Warnes (11), an English writer, states that by far 
the greatest amount of tar distilled is divided into the following 
fractions: Crude naphtha, light oil, carbolic oil, creosote oil, anthra- 
cene or " green oil," and pitch. Lunge (10), in general, makes the 
same separation and gives the following temperatures as the cutting 
points of the various fractions: 
Crude naphtha Up to 105° or 110° C. 
Light oils From crude naphtha up to 165° or 210° C. 
Carbolic oils From light oil to 230° or 240° C. 
Creosote oil From carbolic oil to 270° C. 
Anthracene oil Above 270° C. 
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