214 TRANSACTIONS OF THE 
largely by some of the causes mentioned above, but such 
changes may also be due to properties inherent in the 
retort design. 
The first action of heat upon the shale begins to 
take place at a very low temperature and results in the 
removal of some of the occluded gases which exist in 
very small quantities. Next the actual distillation of the 
kerogen or change of state takes place, wherein a heavy 
fluid apparently is produced which is soluble in organic 
solvents. The decomposition temperature range of this 
substance may be influenced to some extent, as has been 
attributed, to the influence of pressures developed within 
the shale pieces so that the evolved vapors are produced 
at excessively high temperatures. Finally as the vapors 
are produced within the shale pieces they immediately 
become subject to the destructive or damaging effects 
caused by their passing through zones of higher tempera- 
tures before they escape from the retort. The vapors are 
certain to become superheated somewhat, since they will 
readily absorb heat from the hotter shale surrounding, 
due to their low specific heats. The vapors on passing 
outwardly from a lump of shale will move in a direction 
opposite to the flow of heat, and will obviously become 
hotter as they pass outwardly through the lump, since 
the lump is transmitting the heat inwardly. Consider, for 
instance, that a piece of oil-shale the size and shape of a 
brick, is being heated and that the heat is being supplied 
equally to all portions of one of the larger faces. When 
the temperature of oil production is reached, neglecting 
side radiation, the entire surface starts distilling simul- 
taneously, it being the first part to reach distillation tem- 
perature. If the temperature of the heat supply does not 
increase, the distillation on the heated surface will soon 
become negligible although only a portion of the total 
possible oil has been produced from the kerogen, which 
was first subjected to the distilling temperature. How- 
ever, the distilling zone will work on through the shale 
until the entire mass has reached the same initial degree 
of decomposition. An increase of temperature will re- 
new the evolution of oil vapors, but the final oil will not 
be produced until the temperature reaches approximately 
