42 
BULLETIN 1036, U. S. DEPARTMENT OF AGRICULTURE. 
high physical properties and having no sulphonation residues; but 
that those subjected to lower temperatures yielded coal-tar creosotes 
having lower index of refraction values and higher sulphonation 
residues. The inclined-retort tar creosotes were higher in sulphona- 
tion residues, and it seems to be almost universally true that, when 
this type of retort is discharged, there is a small amount of uncoked 
coal in the charge. In the vertical retort there is less chance for the 
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220 240 260 280 
300 320 220 240 
TEMPERATURE °C 
260 
280 300 320 
Fig. 22.— Physical and chemical constants of 
creosotes obtained from tar produced from 
the same mixture of coal at the same tem- 
perature but in different types of retort. 
1. Horizontal-retort tar creosote. 
2. Inclined-retort tar creosote. 
Fig. 23.— Physical and chemical constants 
of creosotes obtained from tar produced 
from the samemixture of coal at thesame 
tc mperature but in difteren 1 1 ypes of oven . 
1. Semet-Solvay tar creosote. 
2. Otto-Holfman tar creosote. 
gases to come in contact with the heated walls of the chamber unless 
a fixing chamber is left above the charge. In the by-product ovens 
the vertically heated ovens usually have a hotter roof than those 
heated horizontally. Of the six vertically heated by-product ovens 
only two produced coal-tar creosotes having a measurable amount of 
sulphonation residue. Of five coal-tar creosotes from horizontally 
heated ovens all but one had a measurable sulphonation residue. Of 
the four that had sulphonation residue the oldest plant produced the 
coal-tar creosotes having the highest sulphonation residue and the 
