21. "I'm not so sure about the refining process ." 22. The chemical _ a suspected carcinogen _ is a byproduct of the petroleum refining process . 23. Pattinson patented his silver refining process in 1833. 24. The filter presses used in the refining process consisted of mats of woven wire and canvas. 25. Uranium was a by-product of the refining process , and the company had little use for it. 26. The copper refining process requires large quantities of sulfuric acid, which is produced on-site at Potrerillos. 27. This ratio depends upon the type of bauxite used in the refining process and extraction conditions. 28. "MTBE is blended into the gasoline at the end of the refining process , " she said. 29. Around 2 per cent of LP gas is obtained as by-product in the petroleum refining process . 30. And although this can be a refined process much has been learned from studies of simple behaviors.
