Dissolve the gelatin in the boiling water in a large saucepan. In a separate saucepan boil together the sugar and 4 cups water. Add the pineapple juice, orange juice and lemon juice. Cool. Combine the gelatin and juice mixtures. Pour into plastic containers and freeze. Set out about 3 hours before serving. Add the ginger ale just before serving. The punch will be slushy.