After we moved to Chicago, immediately, in April of 1942 — April 19th, by the way. I arrived there on my 30th birthday, April 19th, 1942 — I got the idea that we could probably produce weighable amounts of plutonium by bombarding huge amounts of uranium, hundreds of pounds, for long periods of time, weeks or even months. Then, knowing the chemical properties, we could extract it so that we would have enough to measure its — what we call macroscopic properties. Up until now we were just working on the radioactive properties — unweighable amounts. I had this idea that we could produce it in large enough amounts that we could have it in actual ponderable amounts, weighable amounts. There were a lot of people that thought that this would not be possible but I thought it would. I hired a couple of ultra-micro chemists, Burris Cunningham and Louis Werner here from Berkeley, and Michael Cefola from New York University, and brought them to Chicago. They took these microgram amounts — a microgram is about a 30 millionth of an ounce. They could do chemical investigations with the actual element itself — weighable amounts, ponderable amounts, macroscopic quantities — and that was the key to working out the separation process for the plutonium that would be produced in the chain reacting piles, as they call them, at Hanford, Washington.