In 1891, James Dewar invented a method of producing liquid oxygen and
nitrogen in bulk quantities.  Where can I get a detailed description
of his process, including diagrams and photos of the apparatus?

I understand how liquid gasses are produced in this modern era with
huge compressors and industrial equipment, but I'm specifically
looking for detailed plans that would allow me to reproduce his
original apparatus (or something very much like it).

Dear iammrjvo-ga, 

The best source is the papers of Sir James Dewar which are kept at the
Royal Institution of Great Britain. They include photographs, lecture
notes, experiment notes, laboratory apparatus notebooks, and
correspondence.
A full list appears here:
http://www.aim25.ac.uk/cgi-bin/search2?coll_id=2955&inst_id=17

Contact details for the Royal Institution of Great Britain are:

The Royal Institution of Great Britain
21 Albemarle Street
London
W1S 4BS
Telephone: (+44) 0 20 7409 2992
Fax: (+44) 0 20 7629 3569
Email
For general enquiries: 
ri@ri.ac.uk

Access Information

Open : M-F 9-4.30 
Letter of introduction required 
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http://www.rigb.org/rimain/heritage/index.jsp


I could find no other sources for you, but I did find reference to
this book which may assist if you can obtain it through your library.
James Dewar, Collected Papers of Sir James Dewar, ed. Lady Dewar
(Cambridge: University Press, 1927)

I hope this answers your question. If it does not, or the answer is
unclear, then please ask for clarification of this research before
rating the answer. I shall respond to the clarification request as
soon as I receive it.
Thank you
answerfinder

Search strategy included
"James Dewar" archives
://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=%22James+Dewar%22+archives
"James Dewar" experiments "liquid oxygen"
://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=%22James+Dewar%22+experiments+%22liquid+oxygen%22

Good news.  Although a trip to the Royal Institute is out of the
question, I stopped by a university and picked up a copy of Dewar's
Collected Papers.  Sure enough, here is what I'm looking for.

I was a bit disappointed with this answer at first, but I have come to
believe that this is the best answer possible.  This information
doesn't seem to be available online.

I need a reminder of the fact that details of 100+ year old
experiments are only to be found in print.  I could have arrived at
this answer myself if I were willing to think in more traditional
terms.

Thank you and good work.