This section is from the book "Canning, Preserving Pickling and Fruit Desserts", by Jeanette C. Van Duyn. Also available from Amazon: Canning, Preserving, Pickling And Fruit Desserts.
Select young spinach, wash thoroughly, and steam or boil in a small amount of water. When cooked enough, put into sterilised jars (see Sterilisation), press down with a sterilised spoon until the liquid covers the top, adjust sterilised rubber rings and lids, screw down tightly or fasten down the wire clamp or spring-top jars, and put away out of a draught. When cold and the glass has contracted, again tighten the lids.
Prepare a syrup by boiling together one cupful of sugar in four cupfuls of water for five minutes. Peel and slice sweet potatoes, then boil them in slightly salted boiling water until tender, drain, and cook for five minutes in syrup. Fill into hot sterilised jars (see Sterilisation), letting the syrup overflow the tops of the jars, adjust sterilised rubber rings and lids, screw down tightly, or fasten down the wire clamps of spring-top jars, and put away out of a draught. When cold and the glass has contracted, again tighten the lids.
 
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