when did they stop putting silver in nickles
Between 1942 to 1945.
Jefferson nickel
As nickel was a strategic war material during World War II, nickels coined from 1942 to 1945 were struck in a copper-silver-manganese alloy which would not require adjustment to vending machines.
wiki:21760646
Jefferson nickel [SEP] Introduction
The Mint conducted a design competition, in early 1938, requiring that Jefferson be depicted on the obverse and Jefferson's house Monticello on the reverse. Schlag won the competition, but was required to submit an entirely new reverse and make other changes before the new piece went into production in October 1938. As nickel was a strategic war material during World War II, nickels coined from 1942 to 1945 were struck in a copper-silver-manganese alloy which would not require adjustment to vending machines. They bear a large mint mark above the depiction of Monticello on the reverse. In 2004 and 2005, the nickel saw new designs as part of the Westward Journey nickel series, and since 2006 has borne Schlag's reverse and Franki's obverse.