The phase diagram for the water-triethylamine liquid system has been redetermined for mole fractions of triethylamine ranging from 0.02 to 0.40, with results in general agreement with previous investigators. We have further determined the effects of small quantities of a variety of third components on the temperature of phase separation in this system. Timmermans' generalization that third components which are appreciably soluble in only water or triethylamine will lower the temperature of phase separation is supported by all of our relevant data. His other generalization that third components that are quite soluble in both water and triethylamine will raise the temperature of phase separation is supported by only some of our relevant data. We have found some alcohols (quite soluble in both water and triethylamine) that raise the temperature of phase separation for some water-triethylamine compositions, lower it for other compositions, and necessarily have no effect on the temperatures of phase separation at some intermediate composition.