The USDA no longer approves of the use or alum of picking lime in the preparation of pickles. Refer to the National Center for Home Food Preservation (NCHFP) website, it is an excellent source for current research-based recommendations for most methods of home food preservation and includes many tested recipes.
Pickling lime used to be an accepted method of adding crispness to pickled cucumbers. The USDA no longer recommends use of pickling lime. Pickling lime is alkaline and must all be washed off of the cucumbers or it can result in a less acidic pickling solution. It the pickling solution is not acidic enough it can allow botulism an environment in which to grow. Botulism cases have been linked to this situation and this is the reason it is no longer recommended.
Baking Soda
Alum can be purchased in a one pound package. It is a granulated powder that is used in pickling recipes, papermaking, dying and coloration.
Alum is used as a drying agent in tanning and paper making and is basically a salt compound. It is also used in food products for pickling and baking.
protamine sulfate
No. Alum is an acid and crisping agent, baking soda is an alkaline salt.
A substitute that I have seen for in making crystals is alum. It seems to be a great way to grow them.
I'd check out the spice section of a grocery store (alum is used for some pickling brines), or you could try a drug store. If you can get non-finely powdered alum, you can pulverize it to a fine powder yourself using a mortal and pestle.
One must squeeze a lime.
Yes. Baking soda will work as a substitute in this case.
Yes. Lime juice is more acidic, so it's safe. But you cannot substitute vinegar for lime juice safely.
Lime water is calcium hydroxide diluted in water while lime juice is the juice from lime fruit which contains different chemicals like vitamin c, citric acid, and sugars.