Ah, the 40 second test.
I’ll let the April 29, 1911 edition of the Carroll County Citizen-Times from Delphi, Indiana explain:
Should you want to use a thermometer, a 60-second test means the oil is about 320 deg. F. and a 40-second test would be about 360 deg. F.
From the box of C.N. from De Soto, Kansas.
Sweet Potato Croquettes
3 c. mashed sweet potatoes
salt and pepper to season
2 eggs (allow 1 tsp. water to each egg)
Bread or cracker crumbs
- Wash, pare, and cook sweet potatoes in boiling water.
- Drain, dry, and mash.
- Allow potatoes to cool.
- Make into flour and roll in crumbs, eggs, and crumbs again.
- Dry in deep fat, using 40 second test.
- Drain on brown paper; serve hot.