The next flammable liquid hydrocarbon-derivative family is ester. In addition to being flammable, esters may polymerize. They have moderate boiling and flash points narrow flammable ranges, and high ignition temperatures. Esters are made through a process referred to as esterification. An ester is formed when an alcohol is combined with an organic acid, with water as a by-product. This process is illustrated in Figure 5.64 by combining acrylic acid and methyl alcohol; the resulting ester compound is methyl acrylate.