This recipe is a canning recipe (as it says to pack into jars and seal immediately). I am not a scientist, so please proceed with caution on any old canning recipes. Canned foods need a certain pH level to prevent botulism, which is why canned foods generally have some sort of acid added to them. This particular recipe does call for lemon pulp and juice so it's possible it could be totally safe. But consider this your friendly warning/disclaimer.
For more information on canning "old time" recipes, look here; http://www.clemson.edu/extension/food_nutrition/canning/tips/04old_time_recipes.html