Mushrooms (Agaricus campestris). Salt.
Wipe or wash the mushrooms one by one. Remove the stems and pack the caps into sterilized jars. Ad just new rubbers, put one teaspoonful of salt into each jar, put the lids on loosely, and stand the jars on a rack in a washboiler.
Pour in sufficient cold water to come nearly to the top of the jars. Be careful not to have too much, or in boiling the water will overflow the jars. Cover and boil for one and one-half hours.
Fill two jars from a third; put on the lids, return the jars to the boiler and cover and cook for thirty minutes longer.
Lift out the jars onto a towel wrung out of tepid water and see that the tops are as tight as possible.
Keep in a cool dark place.