238 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



gasoline production. He had discovered the thermal "cracking" 

 process with which, by the use of heat and pressure, he could convert a 

 large portion of the fraction of crude oil between the kerosene and the 

 lubricating oil cuts into gasoline. But this "cracked" gasoline fell 

 into ill repute, largely because the refiner had not learned to finish it 

 in such a fashion that it would not gum in the engine, resulting in 

 sticking valves with attendant poor operation. 



A comparison of notes by the refiner and the automobile designer 

 brought out fundamental information which initiated the series of de- 

 velopments with which we are presently concerned. This information 

 was that the knocking tendency of the higher compression automobile 

 engine could be materially reduced or in some cases entirely eliminated 

 by the use of the heretofore disfavored cracked gasoline in preference 

 to the previously used straight-run gasoline, even though this straight- 

 run material be cut to the extremely light old-time so-called high-test 

 grade. Here was chemical synthesis of hydrocarbons appearing for 

 the first time because very rough test methods, as then developed, 

 showed that the cracked gasolines contained substantial quantities of 

 olefins and aromatics, whereas the original crude oil contains few if 

 any of these types of hydrocarbons. As a matter of interest, the 

 earliest method of estimating the antiknock characteristics of motor 

 gasoline came into being at this time. It matched the antiknock 

 tendency of the fuel against known mixtures of benzol and Pennsyl- 

 vania straight-run gasoline in a small single-cylinder laboratory engine 

 and gave the results in terms of "benzol equivalent." 



Two parallel series of developments were thus started in the refinery 

 as a result of the move by the engine designers to higher compression 

 motors. One series was aimed at removing or otherwise taking care 

 of the then prevalent deficiencies of cracked gasoline with respect to 

 gum-forming tendencies, chemical instability, and offensive odor. 

 Processes to remove the gummy materials, soon identified principally 

 as diolefins, from the cracked gasoline took the form of treatment with 

 sulfuric acid and vapor phase treatment over activated fuller's earth. 

 Further, various processes were developed to convert the malodorous 

 mercaptans, which appeared in the gasoline as a result of an analogous 

 cracking of sulfur compounds in the heavier cracking stock, into 

 sweet-smelling alkyl disulphides, acceptable both to the public and 

 to the motors. The result of these developments was the assumption 

 by cracked gasoline of its rightful place as a desirable and important 

 component of motor gasoline. 



The other series of developments which raced ahead at this time 

 had to do with the production of cracked gasoline itself. Literally 

 scores of thermal cracking processes and variations thereof were 

 invented and many of them were patented. As special methods of 

 fabrication were developed and new steel alloys able to stand high 



