Aqueous solutions of Nal containing CCl 4 and MgCl 2 at various concentrations were irradiated under air with 1 MHz ultrasound and the yield of I - 3 was determined. The yield was not affected by MgCl 2 at concentrations up to 0.1 M. This contrasts with the finding of Lepoint and co-workers, who reported a sharp minimum in the yield at a MgCl 2 concentration of 2.5 10 - 3 M. Above 0.1 M, the yield decreased to 60% at 1 M MgCl 2 , the reason being the lower solubility of CCl 4 at high MgCl 2 concentrations. In the absence of CCl 4 , another dependence on the MgCl 2 concentration was observed: the yield was not affected up to 1 M, and at higher MgCl 2 concentrations the yield rapidly decreased owing to the increased viscosity of the solution. On the basis of these observations, there is no strong reason to postulate an electrical mechanism for the initiation of chemical reactions in the cavitation bubbles.