 However, this is a less satisfactory system if one desires to collect fractions under a reduced pressure.To do this, a "pig" adapter can be added to the end of the condenser, or for better results or for very air-sensitive compounds, a Perkin triangle apparatus can be used.The Perkin triangle uses a series of glass or Teflon taps to allow fractions to be isolated from the rest of the still, without the main body of the distillation being removed from either the vacuum or heat source, so that the reflux may continue.