Simply take it to your local coin shop or sell it online.
An 1870 US Half Dollar weighs 12.44grams and is 90% silver, giving it an ASW (Actual Silver Weight) of 11.196 grams or 0.36 troy ounces.
Take it to a US currency collector.
Coin dealer, pawn shop, eBay.
There is 24 grams of silver in a 1891 US silver dollar.
As of 01/2010, these coins sell for about $15.00
You can take them to a local coin, collectible, or pawn shop and sell them to them. You can also sell the on an online auction site such as eBay.
1922 is such a common date for silver dollars that the value is only for the silver content. With current silver prices, a '22 Peace dollar is worth about $21. To sell one, either take it to a coin dealer, or post it on eBay.
1922 is one of the most common dates for US silver dollars. They currently sell for around $20-$25 each.
An 1870 US Dollar would be a Seated Liberty Dollar. The Walking Liberty design was used only on half dollars from 1916 to 1947 and on 1-oz silver bullion coins issued since 1986.There's more information at the Related Question.
In 1870, the primary currency used in the United States was the U.S. dollar, which was divided into 100 cents. At that time, the dollar was backed by gold and silver, adhering to the bimetallic standard. The Coinage Act of 1873 later discontinued the minting of certain silver coins, which significantly impacted the monetary system in the years that followed.
Try a coin dealer or take it to a coin show.
Any coin dealer or buyer of scrap gold & silver.