remember petroleum ether is not really an ether in the chemical sense. ether being an oxygen atom between two or more carbons. petroleum ether is really light distallites of petroluem (they called it ether back in the day because it was this magical stuff that came from heating crude petroleum) and the light distillates are things like hexane heptane could even be octane pentane etc (the composition probaly varies a bit depending on who made it and how it was purified). so when you have a petroluem ether it is a mix of hexane and other smaller straight chain hydrocarbons, in other words its a good solvent to work with because it evaps easier and has many of the properties as other straight chain hydrocarbon solvents its just a mix of them.