The SISAK (i.e. Short-lived Isotope Studied by the AKufve -technique) system was used for investigation of the reaction between osmium tetroxide and NaOH as a model for chemical study of hassium. The result was a two- stage extraction procedure. In the first extraction stage, OsO4 was extracted from NaOH solutions of different concentrations into toluene and the following equilibrium constants for the reaction of OsO4 and NaOH were obtained: K´= (2.35 ± 0.04) 104 for formation of Na[OsO4(OH)] and K″= 6 ±4 for formation of Na2[OsO4(OH)2] out of Na[OsO4(OH)]. The purpose of the second extraction stage was to transfer the activity from the aqueous phase into the organic phase in an efficient way. In order to fulfill this purpose the basic aqueous phase from the first extraction stage was acidified with HCl, HClO4 or H2SO4 and the activity was extracted into toluene either with or without tri-n-octylamine (TOA) as an extracting agent. The extraction efficiency in this stage was around 90% in both cases although there were indications that extraction with TOA had a somewhat higher distribution ratio. An attempt was also made to use Aliquat 336 as an extracting agent to transfer activity into the organic phase. This experiment showed that Aliquat 336 can extract the activity very efficiently. There was, however, a problem with the purity of the liquid phases.