What are the ingredients in cucumber ketchup?

Answer 1

A recipe from 1886:

Cucumber Catsup

Grate three dozen large cucumbers and twelve white onions; put thee handfuls of salt over them. They must be prepared the day beforehand, and in the morning lay them to drain; soak a cup and a half of Mustard Seed, drain it and add to the cucumbers, with two spoonfuls of whole pepper; put them in a jar, cover with vinegar and cork tight; keep in a dry place.

*This seems to be what we today call pickle relish.

Answer 2

To list the ingredients would be pointless. You need to know the quantities, the order in which to add them, and how long to process the finished product. Suggest you invest a few canning books (Ball Complete Book of Home Preserving is a good one) and use only tested canning recipes. 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.