Thank you all for the extremely useful information. Yet, I have two further 
queries:

1. when did the expression "deadweight loss" first appear in Samuelson's 
Econonomics? [I would read this as a sign of consolidation in its use: 
indeed, JSTOR shows that Samuelson seemed to be (almost) the only one to use 
the expression until the 1960s!]

2. apart from JSTOR journals, did Hotelling (whom I confused with Haberler 
in my previous message!) ever use the term in his 1930s works on taxation?

Nicola Giocoli