Put the treacle, sugar, butter and vinegar into a pan and boil until a few drops harden at once when dropped into cold water. Dissolve the bicarbonate of soda in a very little boiling water, and stir into the candy. Pour into a greased tin. As the edges begin to cool, turn them in with a knife. As soon as the candy is cool enough to be handled, put it on to a marble slab and pull it out until it hardens. Twist it into sticks and cut it into short lengths.