This section is from the book "Progressive Cookery", by E. M. Hinckley. Also available from Amazon: Progressive Cookery.
To one peck green tomatoes, sliced, add a pint of salt; cover with water, and let them stand twelve hours ; squeeze them out, and let them remain in fresh water a few hours. Take ten or twelve green peppers and seven large onions, put them with the tomatoes and chop all fine ; put them in a porcelain kettle with weak vinegar, and let them boil or scald awhile ; draw off the vinegar and take some good old cider vinegar, a pint of white mustard seed, and some grated horseradish, add two tablespoons of brown sugar, mace, cinnamon, cloves, to your taste. Boil up and pour over all and put away in jars.