UTAH ACADEMY OF SCIENCES 215 
525°C., about 200°C above the temperature of first oil 
production. 
EFFECT OF TEMPERATURE LAG. 
Commercial considerations require that the heating 
of the shale be fairly rapid and that the heat be supplied 
increasingly. Given these requirements, the tempera- 
ture difference between the hot surfaces of the 
shale pieces and the inside temperatures where distilla- 
tion is in its early stages, will become increasingly greater 
until a state of equilibrium is reached, whereby the tem- 
perature difference between the inside and outside sur- 
face of a lump becomes constant. Now this temperature 
difference for unit depth of heat penetration will depend, 
to a large degree, on the amount of heat supplied, the 
thermal conductivity and specific heat of the shale, the 
heat consuming reactions, and the heat carried out by 
convection in the escaping oils and gases. As experimen- 
tal evidence of the amount of the temperature lag, the 
writer has performed retorting tests on shales where the 
temperature was taken at the hot surface and at a point 
within the charge’ two inches from, the hot surface. 
Data taken showed that there was a lag of 250°C between 
the remote shale particles and those next to the heating 
surface. Had lumps of shale four inches in diameter 
been heated similarly, there would have been oil vapors 
liberated in the center, which on working to the surface, 
would have passed through a layer of partially spent 
shale two inches thick, and up to 250°C hotter than that 
at which the vapors were produced. Obviously it is 
probable that the superheat received by the vapors in 
penetrating the hotter exterior, will alone greatly decom- 
pose the oil vapors, but there are present factors work- 
ing simultaneously to augment the cracking. Some of 
these factors are, the finely divided or capillary condi- 
tion of the vapor streams, the pressure which the vapors 
must be under before being released from the shale 
pieces, and the catalytic influence of the carbon deposi- 
tion in the pores of the shales. 
Economic considerations prevent the employment 
of extremely long retorting periods, which would largely 
