volatile materials since his data cover a temperature range (119°to 152°C.) at which the vapor pressure of terephthalic acid should be essentially zero. After the completion of the work reported in this paper, it was learned that a value of 33.3 ± 0.4 was obtained by other workers by means of a thermal gradient strip technique (9). A value of AH. = 33.1 kcal. per mole can be calculated from data obtained for benzoic acid and benzene (3). The contribution to the heat of sublimation per six benzenoid carbons is taken as 10.5 kcal. per mole, and the contribution of each carboxyl group is taken as 11.3 kcal. per mole. LITERATURE CITED(1) "Beilstein's Handbook," supplement 9, p. 841; Handbook of Chemistry and Physics, 47th ed., Chemical Rubber Publishing Co.. 1967.

4-azahomoadamantane, and Mr. A. Gasiecki for some of the microanalyses. We express our appreciation to one of the referees for bringing ref 23a to our attention. 247 O . Recrystallization from ethanol gave the analytical sample: mp 246-247"; ir (CHC18) 3450-2380,

emphasisis being placed on the development of processeswhich produce a maximumamount lhis paper presentsthe resultsof of the in place energy. The followingmisapplyingparticletrackingtechniquesto the cussiondescribesa simple approachto predictionof areal sweep for the in-situ determiningthe areal sweep efficiencyfor recoveryof subbituminous coal. Comparison UCG and comparesthe resultswith field of field data with calculatedvalues indicate experimentalresults. that these techniquesare applicableand support the theory that the in-siturecoveky BACKGROUND of subbituminous coal as encounteredat Hanna, Wyoming,is a permeationprocess. TheThe processbeing utilizedby LERC model predictsbreakthroughof the flame front in the ongoingexperimentation near Hanna, at the productionwell and intermediatepoints Wyoming,is known as the linkedvertical with sufficientaccuracyfor preliminary well process. This processuses reverse design purposes.combustionto modify the naturalpermeability such that gasificationin the forwardmode

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