Daly's Bartenders' Encyclopedia by Tim Daly (1903, p.82)

Scotch whisky — Scotch whiskeybase
1 lumpsugar — loaf sugarbase
0.5 glasshot water — Half fill the glass with hot water to dissolve the sugar.dilution
  1. Dissolve the loaf sugar in hot water in a hot whiskey glass.
  2. Fill the glass with Scotch whiskey and serve.

This is a straightforward checkpoint for the sling branch surviving alongside fuller punch variants.

Its stripped-down hot build is the defining point.

The Hoffman House Bartender's Guide by Charles S. Mahoney (1905, p.199) — Hot

1 piecelemon peel acid
1 wine-glassScotch whiskey base
boiling water — Fill glass three-quarters full.dilution
nutmeg — Grate on top.other
1 lumpsugar sweetener
  1. Fill the glass three-quarters full with boiling water over the Scotch whiskey, sugar, and lemon peel.
  2. Grate nutmeg on top and serve.

Garnish: Lemon peel and grated nutmeg

Jack's Manual by J. A. Grohusko (1910, p.56)

1 piecelemon peel acid
1 portionScotch whiskey — Source gives 100% Scotch whiskey.base
0.5 lumpsugar base
1 glasshot water dilution
nutmeg — Grate a little nutmeg and serve.other
  1. Build the sugar, hot water, lemon peel, and Scotch whiskey in a glass.
  2. Grate a little nutmeg on top and serve.

Garnish: Lemon peel and grated nutmeg

Ice: None

The Up-to-Date Bartender's Guide by Harry Montague (1913, p.41)

1 piecelemon peel acid
1 jiggerScotch whisky — Scotch whiskeybase
0.75 glasshot water — Fill glass three-quarters full.dilution
nutmeg — Grated on top.other
1 lumpsugar sweetener
  1. Put the Scotch whiskey, lump sugar, and lemon peel in a whiskey glass.
  2. Fill the glass three-quarters full with hot water, grate nutmeg on top, and serve.

Garnish: Lemon peel and nutmeg

See also: Hot Whiskey Sling, Hot Rum Sling