While they had demonstrated that the fission of uranium produced more neutrons than it consumed, this was still not a chain reaction. Szilard persuaded Fermi and Herbert L. Anderson to try a larger experiment using of uranium. To maximize the chance of fission, they needed a neutron moderator to slow the neutrons down. Hydrogen was a known moderator, so they used water. The results were disappointing. It became apparent that hydrogen slowed neutrons down, but also absorbed them, leaving fewer for the chain reaction. Szilard then suggested Fermi use carbon, in the form of graphite. He felt he would need about (50.8 metric ton) of graphite and of uranium. As a back-up plan, Szilard also considered where he might find a few tons of heavy water; deuterium would not absorb neutrons like ordinary hydrogen, but would have the similar value as a moderator. Such quantities of material would require a lot of money.