Introduction: "Because of the importance of the value of the transport mean free path of thermal neutrons in deuterium oxide, Kash and Woods proposed to redetermine this value in deuterium oxide (99.4 atom-percent deuterium, by an extrapolation method. Kash and Woods thought that the low value of the transport mean free path might be a source of error. This paper relates studies of procedures by which (1) boron material would be dissolved in high content deuterium oxide without adding foreign atoms, particularly hydrogen atoms which might adversely affect the test, (2) the boron content of the deuterium oxide solvent may be determined, (3) ion exchangers may be deuterized and de-deuterized, and (4) ion exchange may remove specific ions from solution."