Combine tomatoes, cabbage, peppers and onion in a large bowl. Sprinkle the canning salt over the vegetables and mix together.

Let stand for 4 hours. 

Drain, rinse vegetables and then drain thoroughly. 

In a large pot add the brown sugar, mustard seed, celery seed, horseradish and vinegar. Bring to a boil and then reduce heat to a simmer. Simmer for 15 minutes. 

Add the vegetables and then bring the mixture to a boil. 

Ladle the hot mixture immediately into prepared jars, filling to within 1/4 inch of tops. Remove any air bubbles. 

Wipe the jar rims and threads clean if needed. If using traditional canning jars, cover with 2-piece lids. Screw bands on.

If using Weck jars, carefully place the Weck rubber gasket on the lid of the jars. Place the lid on the jar and secure the lid with 2 evenly spaced Weck clamps. 

Place jars on an elevated rack in a hot water bath canner. Lower rack into canner. {Water must cover jars by  2 inches. Add boiling water, if necessary.}

Cover; bring water to a boil. Process 10 min. Remove jars and place upright on a towel to cool completely. Cool jars for 12-24 hours. 

After the jars have cooled, check the seals by pressing the middle of the lids with your finger. If lids spring back, lids are not sealed and refrigeration is necessary. {Traditional canning jars}. 

For Weck jars, check to make sure your seal is pointing downwards. 

Remove rings or clamps and store jars in a cool dark place. 

Yields about {8} pints