Place the lemon juice in a saucepan. Sprinkle the unflavored gelatin over the juice and heat to boiling to dissolve the gelatin. Remove from the heat, stir in the sugar, and lemon. Stir well then add the 8 cups of plain yogurt. Mix well and pour into jars or containers. Refrigerate several hours or until set. Makes about 4 quarts of lemon yogurt.