It would depend on who you mean by "they", but up until the mid 20th century, silver had been used to make coins for over two thousand years.
Sorry. No U.S. one dollar silver coins were struck in 1834. Look at the coin again and post new question.
The U.S. did not make any silver dollars from 1804 to 1835 inclusive. There has been a flood of counterfeit dollar coins on the market over the last couple of decades, some good, but many with significant goofs in date and/or design. If you have an "1834 dollar" it is one of the latter, I'm afraid.
All coins come from a mint. Casino coins are sometimes solid silver.
There were proof sets made in 1974 and 1975 where all 8 of the coins were silver, and proof sets made during those years when none of them were silver. Assuming that your coins are in a set, check the 1 Cent coin - if it looks silver, then all the coins in the set are silver; if it looks bronze, then none of the coins in the set are silver.
Just recently with the advent of bullion coins such as the American Silver Eagle. Coins intended for circulation were never 100% silver because silver is simply too soft of a metal for coinage. They were 90% silver in American coins until 1964 for dimes, quarters and half dollars, but other than bullion coins, no coins are made of 100% silver.
No British circulating coin has contained any silver since 1946. From 1919/1920 to 1946, all British silver coins contained 50% silver. Prior to 1919/1920, all British silver coins were made from sterling silver or, 92.5% silver.
Yes they are silver
The only U.S. coins currently made that are silver are American Silver Eagles and other special collectors coins sold by the U.S. Mint. These coins are NOT released for circulation.
Nothing is 100% PURE silver but like most silver coins it is 99.999% silver
You can sell silver coins to a coin collector, jewelry shop ect.
"Pure" silver coins were never minted in Britain. The closest to pure silver used in coins is sterling silver which is 92.5% silver usually alloyed with copper. Sterling silver coins were last issued for general circulation in 1919 and 1920, beyond 1919/1920 the coins were debased to 50% silver. The Royal Mint still produces Proof and bullion coins (not for general circulation) which are made from sterling silver, but this is reflected in the price you pay for them.
With those dates, the coins are Silver Eagle bullion coins that are made from one ounce of silver and value is whatever the spot price of silver is at time of sale.