This letter presents data of the electrical conductivity of KDP solution in the region of 1070 and 2040g KDP/100g water. It was found that there is a point where the slope of the temperature characteristic of the electrical conductivity change and it corresponds to the saturation point of the solution.

Relationships between temperature and specific gravity of methanol solution of urea were measured under various concentration. Solubility and supersolubility curves to methanol were obtained. It was found that methanol is relatively suitable as solvent to the growth of urea crystal.

In the KDP solution Fe3 and Cr3 have a higher content in the crystal separated early. Therefore, it is possible to purify the KDP solution by removal of the crystal separated early as a method contrary to the usual recrystallization method.

High quality KDP crystals can be grown even in growth rate of 3 mm/day by electrodialysis method with pH control. This method has auxiliary electrodes set in the growth chamber.

Relationship between temperature and specific gravity of ethanol solution of urea were measured under various concentrations. Solubility and supersolubility curves of urea to ethanol were obtained. Ethanol was found to be suitable as solvent to the growth of single crystal of urea.

This letter reports the optical Waveguide of KDP-DKDP mixed crystal grown on the {101} plane of DKDP crystal by the LPE technique. The propagation loss of the waveguide is 0.5 dB/cm for the TM modes.