Combine the sugar, water, and vinegar in a heavy 3-quart saucepan.
Cook over low heat, stirring constantly, only until the sugar is dissolved.
Cook without stirring over low heat to 240°, or until the syrup forms a firm ball in cold water.
Remove from the heat.
Begin beating the egg whites, using an electric mixer, when the syrup is almost cooked.
Beat until very stiff peaks are formed, but whites are still moist.
When the syrup stops bubbling, slowly pour it into the egg whites (in a steady stream), while beating.
Add the vanilla and salt, and continue beating until the candy is thick enough to hold a shape and loses its gloss.
Drop by teaspoonfuls onto a cookie sheet that has been covered with waxed paper.