Since Ziegler was working at the Max Planck Institute for Coal Research, ethylene was readily available as a byproduct from coal gas. Because of this cheap feedstock of ethylene and the relevance to the coal industry, Ziegler began experimenting with ethylene, and made it a goal to synthesize polyethylene of high molecular weight. His attempts were thwarted because a competing elimination reaction kept occurring causing an anomalous result: instead of ethylene being converted into a mixture of higher aluminum alkyls, its dimer, 1-butene, was almost the only product. It was reasoned that a contaminant must have been present to cause this unexpected elimination reaction, and the cause was eventually determined to be traces of nickel salts. Ziegler realized the significance of this finding; if a nickel salt could have such a dramatic influence on the course of an ethylene-aluminum alkyl reaction, then perhaps another metal might delay the elimination reaction. Ziegler and his student H. Breil found that salts of chromium, zirconium, and especially titanium did not promote the R2AlH-elimination but, instead, enormously accelerated the "growth" reaction. Simply passing ethylene, at atmospheric pressure, into a catalytic amount of TiCl3 and Et2AlCl dissolved in a higher alkane led to the prompt deposition of polyethylene. Ziegler was able to obtain high molecular weight polyethylene (MW > 30,000) and, most importantly, to do so at low ethylene pressures. The Ziegler group suddenly had a polymerization procedure for ethylene superior to all existing processes.