In a large saucepan, stir together the sugar, corn syrup, water, salt, and glycerin with a wooden spoon. Cook over medium heat, stirring now and then until a candy thermometer reads 255 degrees F. Stir in the butter. Pour the mixture onto a greased flat pan and fold over the edges with a spatula to keep them from hardening.
When the candy is cool enough to handle, brush with lemon juice. Kids grease their hands with butter, take a lump of taffy, and pull and stretch it until it is light and slightly firm. The longer they stretch, pull, and twist the candy, the more air it will have and the closer to beach taffy it will get. The lump can then be cut with scissors into bite-size pieces. When cool, wrap in waxed paper.