“41” or “Forty-one” (orangeade)

 
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10 June 1929, Pittsburgh (PA) Post-Gazette, “Pittsburghesque” by Charles F. Danver, pg. 8, col. 6:
The Soda Jerkers’ Code.
The young bartenders in one of those big soda emporiums downtown have a secret code. They use it in relaying orders behind the bar.
(...)
“Forty-one!” (Orangeade.)
 
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29 March 1936, Helena (MT) Daily Independent, “National Youth Administration Compiles Lexicon of the Soda Jerker After Five Months Work” by Helen Dallas, pg. 2, col. 7:
“Eighty-one” for water, “forty-one” for orangeade and “thirteen” to indicate that one of the “big bosses” was drifting around were taken as examples.
 
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10 July 1985, The Times-Mail (Bedford, IN), “Soda jerk unique on American scene” by Ink Mendelsohn, pg. 5, col. 4:
FORTY-ONE—lemonade
 
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29 November 1997, Pueblo (CO) Chieftain, “Word Mysteries” by Chris Woodka, pg. 5A, col. 4:
41—Lemonade, or in some cases orangeade or even milk. Flexner notes cryptically that this is derived from 31 and, earlier, 21. Inflation at work?