EN
The results of positron lifetime and ultrasonic velocity measurements in dilute aqueous pyridine (PYR) solutions show unusual changes in ultrasonic, annihilation data in function of pyridine concentration. The results obtained suggest that strong structural changes occur in the system, in the region of low pyridine concentrations. Liquid clathrate hydrates forming in the system are supposed with unusual stoichiometry and untypical geometry. They are supposed to be very short-living and/or unstable.