The Venus Equilateral stories (well, most of them) were written between 1942 and 1945. I think the "ultra-high-dielectric-constant liquid" made its appearance in the story "Firing Line" (1944) but it might have occurred earlier than that... it's been a few years since I last read through the stories.
The stories are collected in "The Complete Venus Equilateral", and are well worth reading... they portray a bunch of RF/EE types, managing a "communications relay satellite station" full of high-power vacuum tube transmitters (this was pre-transistor stuff... "Now we're cooking with glass!"), orbiting the sun at Venus's L4 point. Fun stuff, with a good dash of humor.
I don't think it's in print at the moment, but used copies are available.