UTAH ACADEMY OF SCIENCES 217 
vapors were it not for the fact that a great quantity of 
steam is used in the retort as a scavenging medium and 
also for its chemical benefit to the oil. If the shale is 
retorted very rapidly the destructive results which char- 
acterize the high temperature coking of coals are ap- 
_ proached, wherein all the oil vapors are decomposed to 
gas, tars, and carbon. 
Any oil-shale retort that exposes a large heating 
surface to the vapors, whether it be a horizontal, inclined, 
_or vertical type, and though the shale be rabbled, rotated 
or stirred, unless it uses an efficient scavenging medium, 
will probably produce much gas, much carbon deposition, 
and inferior oil in relatively smaller quantities. 
